Planetary sciences and exploration: An Indian perspective · The solar system consists of a central...

Planetary sciences and exploration: An Indian perspective

J N GOSWAMI∗ and S V S MURTY

Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India.∗e-mail: [email protected]

Studies of cosmic ray records in meteorites and lunar samples in the nineteen sixties mark thebeginning of research in planetary sciences in India. These studies led to very significant results thatinclude discovery of ancient solar flare records in meteorites and constancy of solar and galacticcosmic ray fluxes over long (million year) time scales. Several research groups in India studiedfossil records of nuclear track, noble gas, nitrogen, trace element and radioactivity in returnedApollo and Luna samples to understand both the nature of long-term solar wind, solar energeticparticle and galactic cosmic ray fluxes as well as chemistry of lunar rocks and soils and theirevolution on the lunar surface. The identification of meteorites of martian origin has also led tostudies of such meteorites to understand the evolution of martian atmosphere over time. Analysisof diagnostic trace elements in samples of Cretaceous-Tertiary (K/T) boundary and chronology ofDeccan volcanism supported asteroid impact as the cause of extinction of life ∼65 million yearsago. Studies of impact craters records in the Indian shield have also been pursued and led tothe identification of new impact structures. The realization that some primitive meteorites hostrefractory oxides and silicates that are some of the first solids to form in the solar system has openeda new window to study the events and time scales leading to the origin and early evolution of thesolar system. Meticulous studies of isotope records in early solar system solids using secondary ionand noble gas mass spectrometry techniques, primarily done at the Physical Research Laboratory,Ahmedabad led to the identification of fossil records of short-lived nuclides of stellar origin in earlysolar system solids. Studies of these records provided a chronological framework for the origin andearly evolution of the solar system, led to the identification of the short-lived nuclide 26Al as theheat source for early melting of planetesimals and bolstered the proposal for a supernova triggeredorigin of our solar system.

Studies of planetary astronomy carried out in India have also led to significant results thatinclude the discovery of the rings of Uranus and of new asteroids. Observations of cometary dustand emission of X-rays from planets as well as analytical modelling of martian ionosphere andaerosols and cometary atmosphere have also yielded important results.

A new chapter in planetary science research in India was scripted with the successful launch ofChandrayaan-1 on 22 October, 2008. The data obtained by instruments onboard Chandrayaan-1has already yielded significant new results and the Chandrayaan-2 mission is being planned with atargeted launch in 2012. Future planetary exploration plans are being formulated with Mars andcomets/asteroids as plausible targets. This review provides a brief outline of planetary researchactivities in India from the very beginning, a broad outline of important contributions made duringthe last two decades and a future perspective, including those for planetary exploration.

1. Introduction

The solar system consists of a central star, theSun, surrounded by eight planets, a few minor

planets, and a large number of planetary satellites,asteroids and comets populating different regionsof the solar system. Our present understandingof the origin of the solar system is based on our

Keywords. Meteorite; moon; solar activity; solar system; martian atmosphere; planetary exploration; planetary astronomy.

457

458 J N GOSWAMI AND S V S MURTY

Figure 1. Extraterrestrial samples available for laboratory studies are shown in the top and middle panels along withsolar system objects of interest for exploration (bottom panel). From left to right (top panel): a refractory oxide (hibonite)grain, polished surface of a spheroidal refractory (oxide + silicate) inclusion, both from primitive carbonaceous meteorite; acometary grain from Wild-2 collected by Stardust mission; mm-sized chondrules from chondritic meteorite; (middle panel):Representative samples of chondrite, achondrite, stony-iron and iron meteorites and a lunar rock returned by Apollo mission;(Bottom panel): Comet Wild 2; Asteroids Ceres and Vesta; Moon and Mars.

knowledge of star formation processes coupled withastronomical observations and laboratory as wellas remote sensing studies of various solar systemobjects. The formation of the solar system can betraced back to a natural or triggered gravitationalcollapse of a dense interstellar molecular cloudfragment, about 4.6 billion years ago. This led tothe formation of a massive object at its centrethat became self-luminous due to the continuousinput of gravitational potential energy of the in-falling material and the proto-Sun was born. Theresidual gas and dust surrounding the proto-Sun,the so-called solar nebula, continued to feed theproto-Sun until the increased gas density and asso-ciated pressure towards the center of the nebulabrought a halt to the accretion and the nebulamaterial settled down to the central plane underthe influence of the gravitational effect of theSun. Dust grains grew in size during this processof settling through mutual aggregation and theprocess of growth continued in the denser environ-ment of the disk formed in the mid-plane lead-ing to formation of meter-sized objects. Furthergrowth of objects took place due to local gravita-tional perturbation in the disk and ten to hundredkm-sized objects, the so-called planetesimals, wereformed. Analytical studies, assuming certain initialconditions, suggest that this whole process can takeplace in less than a million years, a very short timescale if we consider the age of the solar system.Collisional aggregation between planetesimals canlead to the formation of sufficiently massive objects

that can gravitationally perturb and attract othersmaller objects towards it leading to a run-awaygrowth resulting in the formation of planetary-sized objects. The time scale for the growth of plan-etesimals to planets could be several tens of millionyears or more.

In recent years, our ability to identify solarsystem objects that can provide records of eventsand processes taking place during the very earlyevolutionary stages of the solar system hasconsiderably improved our understanding of theformation of the solar system. Most of the infor-mation in this regard comes from studies of mete-orites and, in particular, carbonaceous chondritesthat closely resemble composition of the solarphotosphere and represent some of the most primi-tive samples of the solar system. Evolution of theMoon and Mars can also be studied by analyzinglunar samples brought back by the Apollo andLuna missions and studies of lunar and martianmeteorites. Extraterrestrial samples, representingdifferent stages of evolution of the solar system,that are currently available for laboratory studiesare depicted in figure 1. The various remote sensingmissions to planets and their satellites over the lastfour decades have also provided us with a wealthof information about the planets, satellites, aster-oids and comets and the space environment aroundthese objects. In the absence of any previous reviewcovering work done in India on different aspects ofthis field, we provide a brief overview of the initialstages of research in the field of planetary sciences

PLANETARY SCIENCES AND EXPLORATION: AN INDIAN PERSPECTIVE 459

Figure 2. Nuclear tracks produced by Fe group (figure a) and heavier (Z ≥ 30) nuclei (figure b) revealed after polishingand suitable chemical etching of mineral grains in meteorites. The high track density near the grain surface and the sharpgradient with depth (figure a) is typical of irradiation by low energy solar flare particles. In figure (b), the more abundantFe-group nuclei tracks have been removed by polishing to reveal the much longer tracks produced by trans-iron (Z ≥ 30)group of nuclei. Scale bar is 10 micron.

carried out in India and a broad perspective ofresearch conducted during the last two decades andpossible future directions.

2. Solar and galactic cosmic ray records inextra-terrestrial samples

Studies of extra-terrestrial samples was initiatedat the Tata Institute of Fundamental Research(TIFR), Bombay, in the mid-sixties to look forfossil records of ancient cosmic ray heavy nucleitracks preserved in meteorite samples. Low energyheavy nuclei (Z > 20) of solar or cosmic originincident on silicate grains in meteorites or lunarsamples can create microscopic solid state damagesthat can be enlarged by suitable chemical etchingand one can use a high magnification optical micro-scope to look at such linear damage trails alongthe path of the cosmic ray heavy ions (see figure 2)that are termed as nuclear tracks (Fleischer et al1975). The great advantage of using lunar samplessor meteorites as probes is the fact that they areexposed to cosmic rays in space for millions of yearsand thus provide tremendous collecting power evenif one looks at a small grain less than a millimeterin size. In fact the first records of cosmic ray iron-group very heavy ions were found in meteorites(Fleischer et al 1967). One of the major discov-eries in the field made during this period by thegroup at TIFR, concurrently with an Europeangroup, is the observation of ancient solar flareheavy ion tracks in silicate grains of certain mete-orites (Lal and Rajan 1969; Pellas et al 1969). Thelow energy (1–100 MeV/n) solar flare heavy ionshave a range less than a millimeter in silicate mate-rial and as atmospheric ablation removes the sur-face layers of any meteorite reaching the earth, one

does not expect to observe solar flare records inmeteorites. The identification of solar flare tracksin grains collected from interior of meteorites isbased on a characteristic gradient in track densi-ties as a function of depth within the grain and alsohigh track density compared to the average back-ground density of tracks produced by high energygalactic cosmic rays (see figure 2). It is obviousthat such grains were exposed either in space oron the surface of the meteorite parent body, anasteroid, where they received solar flare irradiationbefore they became a part of the host meteorite.Meteorites containing solar flare irradiated grainswere also found earlier to contain records of solarwind ion implantation (Gerling and Leveski 1956;Wanke 1965; Eberherdt et al 1965), as inferredfrom studies of noble gas records in them, and weretermed as gas-rich meteorites. These observationsled to the prediction that rock and soils exposed onthe surface of the moon will have abundant recordsof solar energetic particles (SEP) that would havehad unhindered access to the surface of the moonthat is devoid of an atmosphere or an intrinsicmagnetic field. This was indeed confirmed when thereturned lunar samples were analyzed later. Stud-ies of gas-rich meteorites have provided a wealthof data on ancient solar flare records (figure 3)going back to more than 4 billion years (Goswami1991; Goswami et al 1980, 1984). Studies of nucleartracks in lunar samples also led to the first obser-vation of enrichment of very heavy nuclei (Z ≥ 30)relative to the Fe-group in ancient solar flares(Bhandari et al 1973a) compared to their normalsolar abundance. This observation was confirmedin contemporary solar flares (Shirk 1974) basedon data obtained from spacecraft experiment. Thefirst experimental evidence for an active early Sunwith flare activity at least thousand times greater


Figure 3. Sharp track density gradients as a function ofshielding depth measured in lunar and meteorite samplesexposed to solar flare irradiation at various epochs in thepast (from Goswami 1991).

than at present also came from studies of nucleartrack and noble gases in grains from gas-rich mete-orites (Caffee et al 1987; Hohenberg et al 1990;Caffee et al 1991) that have received their solarflare irradiation more than 4.2 billion years back.Noble gas data for the grains having solar flarerecords in gas-rich meteorites show that they havereceived energetic particle irradiation doses thatare orders of magnitude higher than those receivedby the non-solar flare irradiated grains (figure 4).Since orders of magnitude difference in galactic cos-mic ray irradiation for these two groups of grainscan be ruled out, the excess seen in solar flareirradiated grains can be attributed to an intenseshort-term irradiation by solar energetic particlesfrom an active early Sun prior to their compactioninto their host meteorite. A much earlier study ofnuclear track records of galactic cosmic ray heavynuclides in lunar samples and meteorites showedthat the relative abundances of Fe group and heavynuclei (Z ≥ 30) group show little variation withtime or distance in the solar system (1 to 3 astro-nomical units) during the last few billions of years(Bhandari and Padia 1974) indicating a remarkablesimilarity in the elemental composition of sourcesresponsible for these nuclei in the galactic cosmicradiation.

The nuclear track records in the lunar samplesalso allowed delineation of time scales of mixing

and turnover of the loosely consolidated lunar sur-face, the so-called lunar regolith, due to bombard-ment of meteoritic objects over a wide size range.The presence of solar flare track records in lunardrill core soil samples, collected at various Apollosites, suggests that lunar soils currently at differentdepths were once exposed to solar flare radiation onthe lunar surface indicating extensive mixing andturnover of the lunar regolith. Studies of galacticcosmic ray track records in lunar rock samples alsoallowed delineation of their lunar surface exposuredurations that are typically a few million years.The erosion rate due to micrometeorite impacts onexposed rock surfaces on the moon was estimatedto be about a millimeter per million years. For anexhaustive review of the work done during the earlyyears of the Apollo and Luna era reference is madeto Lal (1972).

Studies of nuclear track records in meteoriteswere soon followed by studies of radioactivity inmeteorites and lunar samples resulting from inter-actions of solar and galactic cosmic ray protonand alpha particles with target nuclides such asNa, Mg, Al, Si, Ca and Fe in lunar samples andmeteorites (Reedy and Arnold 1972; Lal 1972;

Figure 4. Histogram of cosmic ray exposure ages deter-mined from studies of 21Ne content in individual grains fromthe carbonaceous chondrite Murchison. The solar flare irra-diated grains, identified from their track records prior tonoble gas studies, shown in the top panel have receivedorders of magnitude higher dose of irradiation compared tothe grains without solar flare irradiation records (bottompanel); from Caffee et al 1991.


Figure 5. Long-term averaged 26Al activity based onstudies of Apollo 16 and 17 rocks samples exposed to solarenergetic particles (SEP) on the lunar surface for 0.5 to∼5 million years. A close match of expected and observedvalues suggests constancy in the SEP flux over the abovetime scale (from Bhandari 1981).

Reedy et al 1983). Records of radioactive andstable noble gas nuclides produced by low energy(1–100 MeV/n) contemporary solar energetic parti-cles can be found easily in surficial layers ofreturned lunar rock samples exposed directly tothe Sun, while those produced by high energygalactic cosmic rays can be found in samples ofboth lunar samples and meteorites. The half-livesof different radionuclides, such as 26Al (0.72 Ma),53Mn (3.7 Ma) allowed estimation of long-termaveraged galactic cosmic ray intensities in 1–3 AUspace. Studies of galactic cosmic ray producedshorter-lived radionuclides (e.g., 24Na; half-life =2.6 y) provide a way to delineate the strength of thesolar modulation effect of galactic cosmic rays overthe 11 year solar cycle, while records of relativelylonger-lived nuclides (e.g., 44Ti; half-life 63 y) allowextending such study over much longer durationsby selecting meteorites that fell at different timesduring the last two centuries. Results obtainedfrom studies of solar flare produced 26Al activity inlunar samples exposed at the surface for differentdurations, shown in figure 5, suggest that the solarflare activity averaged over time scale >100,000years has remained nearly the same during thelast few million years (Bhandari et al 1975, 1976;Bhandari 1981). The possibility of a variation inthe solar activity at smaller time scale cannotbe ruled out when one combines data for othershorter-lived nuclides such as 81Kr (half-life =0.21Ma) and 14C (half-life = 5730 y) (Reedy 1998).A careful study of 44Ti produced during the period1883 to 1992, in suitably selected meteorites thatfell on earth at different epochs of the above period,

showed that during one of the prolonged solarquiet times, the so-called Gleissberg minima, theheliospheric magnetic field was much weaker thanthat estimated from observation of sunspot number(Bonino et al 1995).

Studies of noble gas records in lunar andmeteorite samples were also initiated during theApollo era using indigenously built noble gasmass spectrometer. Studies of cosmic ray producedstable noble gas nuclides in meteorites or lunarsamples provide the integrated exposure ages ofthese samples to cosmic rays in space or on thelunar/asteroidal surface. Similarly, studies of radi-ogenic stable noble gases, such as 4He and 40Ar(products of U, Th and K decays, respectively)provide information on the formation ages of theanalyzed samples (see, e.g., Ozima and Podosek2001).

An important contribution from studies of noblegas records in lunar and gas-rich meteorite samplescarried out in India was the identification ofthe isotopic composition of neon, emitted duringenergetic solar flares. It is generally not possi-ble to partition out the solar flare component ofnoble gases in an extra-terrestrial sample exposedto solar radiation in the presence of the orderof magnitude more abundant low energy solarwind component. This problem was circumventedby sequential mild etching of the samples toremove the trapped low energy (keV/n) solar windcomponent that resides within the top 0.1μ ofthe sample so that the deeper sited high energy(MeV/n) solar flare component, that have muchlonger range than the solar wind particles, can bedeciphered easily. The first results on long-termaveraged solar flare noble gas isotopic composition(see figure 6) was obtained using this approach(Nautiyal et al 1986; Padia and Rao 1989); similarresult was also reported by other groups (Wieleret al 1986).

Several martian meteorites have also been inves-tigated, to decipher their cosmic ray exposureduration in space as small objects followingtheir ejection from Mars and hence their proba-ble delivery mechanism to Earth. Nuclear trackand noble gas studies of the martian meteoriteALH84001 showed that the Mars–Earth transittime for fragment ejected from Mars could be upto 16 Ma and is consistent with model calculationfor the case of a direct ejection from Mars andtransfer to Earth (Goswami et al 1997), ratherthan two (or multi) stage break up events in space,following ejection from Mars, prior to reachingEarth (Gladman et al 1996).

Most of the work discussed above was primarilydone at TIFR until 1973 and then at the PhysicalResearch Laboratory (PRL), Ahmedabad. Duringthis period studies of extraterrestrial samples were


Figure 6. Trapped neon composition in acid-etchedlunar soils, that removes the surface sited solar wind(SW) component, shown in a three isotope neon plot.The 21Ne/22Ne ratio is an indicator of average shieldingduring SEP irradiation. The data when extrapolated to low21Ne/22Ne ratio define a solar flare (SF) neon isotope compo-sition that is distinctly different from SW and demonstratethat SEP Ne is relatively enriched in the heavier isotope(from Nautiyal et al 1986).

also initiated at the Indian Institute of Technology(IIT), Kanpur. The focus of research at IITKanpur, was the study of cosmic ray producedradioactive nuclides in meteorites. 3H activitiesin artificially irradiated silicate targets have beenstudied to simulate meteoroid irradiation andderive production rates (Trivedi and Goel 1973).Expertise gained in these studies was also appliedfor neutron activation analysis of trace elements inlunar and meteorite samples. In particular, radio-chemical methods developed for the assay of 3Hand 14C have been used for the study of Li andN abundances in moon and meteorite samplesthrough their production by reactor irradiation bythe nuclear reactions 6Li(n, α)3H and 14N(n, p)14C,respectively (Shukla et al 1978). Lunar samplesfrom Apollo and Luna missions and all classesof meteorites have been extensively analysed forN and Li (Goel and Kothari 1972; Murty et al1982, 1983). Both radiochemical and instrumentalneutron activation analysis techniques weredeveloped for the study of several trace elementsas well as for the isotopic composition of Os andHg (Goel and Murty 1983; Thakur and Goel 1989).

The return of the Luna 16, 20 and 24 samplesby Russia and providing the same to the IndianNational Science Academy (INSA) for scientificresearch led to participation of Bhabha AtomicResearch Center, in addition to PRL and IIT,Kanpur, in lunar sample studies. The results fromthe multi-disciplinary studies conducted by thesegroups that included analysis of nuclear track,noble gas, nitrogen, major and trace elements,mineralogy and petrography have provided very

useful results that appeared in a special publica-tion Further advances in Lunar Research of INSA,in 1974 and also in an INSA proceeding volumein 1979 in addition to other publications in inter-national journals (Bhandari et al 1973b; Goswami1978; Bhasin and Sunta 1979; Deshpande et al1979; Goswami et al 1979; Murali et al 1979; Murtyet al 1979a, b). During the period from 1965 to1980 more than a hundred publications resultedfrom studies of extraterrestrial samples carried outin India.

3. Origin and early evolution of thesolar system

In the mid-eighties, the focus of planetary researchin India shifted to studies of meteorites to under-stand the early evolution of the solar system,evolutionary history of meteorites and their parentbodies, the asteroids, and continuing studies of pastsolar activity. The important results on studies ofpast solar activity, including that from an activeearly Sun have already been noted earlier. In thefollowing we provide a brief outline of researchactivities carried out primarily at PRL in the fieldof solar system studies.

Astronomical observations of Sun like starsduring its initial stages of evolution, the so calledT-Tauri stars, suggest an extremely active earlyphase for our Sun that could have raised thetemperature of the solar nebula to more than athousand degree centigrade. Analytical studies ofcondensation of solids from a hot gas of solarcomposition at low pressure (∼10−3 Atm) suggestthat the first solids to form in the nebula willbe oxides and silicates composed of refractoryelements Al, Ca, Mg and Ti (Grossman 1980)such as Corundum (Al-oxide), Hibonite (Ca-Al-oxide), Spinel (Mg-Al-oxide), perovskite (Ca-Ti-oxide) and Fe-free silicates (anorthite, fassaite,diopside, fosterite). In fact, carbonaceous chon-drites, that represent some of the most primi-tive and pristine solar system objects availablefor laboratory studies, contain such rare micro-scopic refractory solids (see figure 1), that are nowcollectively termed as Ca-Al-rich Inclusions (CAIs)and are considered to be the first solids to form inthe solar system (Grossman 1980; Macdougall andGoswami 1981). Advances in experimental tech-niques allow us to analyze these microscopic solidsin great detail and the results obtained from suchstudies have led to new ideas and concepts aboutthe formation and early evolution of the solarsystem. Precise estimate of the time of formationof these refractory solids also provide us the age ofthe solar system and the current best estimate is4567±1 million years (see, e.g., Russell et al 2006).


The chemical composition and mineralogicalmake up of the various meteorites suggest thattheir parent bodies, the asteroids, have under-gone very different evolutionary histories. CAIsare mostly present in a group of meteorites calledchondrites, and more abundant in the sub-groupcarbonaceous chondrites, whose chemical compo-sition closely matches that of solar atmosphere,making them some of the most primitive meteoritesthat have suffered very little or no thermal or shockmetamorphic history. The parent bodies of non-carbonaceous or so-called ordinary chondrites havegone through various degrees of thermal evolution(see, e.g., Huss et al 2006). The name chondrite isderived from the fact that these meteorites haveabundant sub-mm to mm-sized silicate spherulescalled ‘chondrules’ that are a product of high tem-perature transient events in the nebula that lead tomelting of nebular solids followed by rapid cooling(see, e.g., Scott and Krot 2005) leading to theirspheroidal shape (see figure 1). Chondrules areconsidered to be the second set of solar systemobjects to form in the solar nebula following theCAIs. The parent bodies of the so called differenti-ated meteorites that include achondrites, irons andstony-irons (see figure 1) have undergone meltingand differentiation leading to metal-silicate frac-tionation (see, e.g., McSween 1999). Understand-ing of the processes leading to formation of theachondrite parent bodies is important for under-standing differentiation processes undergone by allthe terrestrial planets.

4. Time scales of early solar system events

A major breakthrough in our understanding oftime scale of events in the early solar systemcame following the identification of fossil records ofthe now-extinct short-lived nuclide 129I (half-life =15.7Ma) in a meteorite based on the observedexcess of its stable decay product 129Xe (Reynolds1960). This observation provided evidence that thefreshly synthesized short-lived nuclides of stellarorigin were present at the time of formation of thesolar system. Since then the presence of close to adozen such nuclides of different half-lives, rangingfrom 0.1 Ma (41Ca) to 82 Ma (244Pu), at the time offormation of the solar system, has been confirmed.In particular, the discovery of the presence ofthe short-lived nuclide 26Al (Lee et al 1976) hasdramatically changed our view of the time scale ofthe early solar system processes in this field.

Records of now-extinct short-lived nuclides withshort half-life [e.g. 41Ca (0.1 Ma), 26Al (0.72 Ma),60Fe (1.5 Ma), 53Mn (3.7 Ma)] in early solarsystem solids can serve as high precision relativechronometer of events and processes taking place

Figure 7. A schematic illustration of the time scale ofprocesses taking place, starting from the proto solar cloudcollapse to the formation of various solar system objects. Therelative time intervals could be precisely determined from astudy of the fossil records of the stable decay products ofnow extinct short lived radionuclides present in the earlysolar system, as illustrated in the inset.

during the early evolution of the solar system(figure 7). However, this is strictly valid only ifthese nuclides are injected into the protosolar cloudfrom an external source, plausibly a stellar source,and distributed uniformly in the solar nebula sothat they are characterized by canonical solarsystem initial abundances. In such a case, the abun-dance of these radio-nuclides in early solar systemsolids forming at different epochs will be system-atically different from their abundances in the firstsolar system solids (CAIs) and this time differ-ence can be accurately ascertained with precisionof < 0.1Ma. However, the possibility that some ofthese nuclides were in fact produced within thesolar system itself via interaction of solar ener-getic particles (SEP) with nebular gas and dustwas also proposed (see e.g., Shu et al 1997). If true,this will invalidate the role of these nuclides as arelative chronometer of events in the early solarsystem. Research done at PRL for more than adecade has provided very significant results in thisfield. These include identification of fossil recordsof the radionuclide 41Ca, having the shortest half-life amongst such radionuclides detected so far,in first solar system solids (figure 8; Srinivasan


Figure 8. A plot of Ca-K isotope system based on datafrom several Ca-Al-rich refractory inclusions (CAIs) repre-senting some of the first solar system solids. Presence ofthe now-extinct nuclide (41Ca) at the time of formationof the analyzed objects can be inferred from the enhanced(41K/40K) as a function of 40Ca/39K, compared to terres-trial samples that formed much after 41Ca became extinct(from Srinivasan et al 1996).

et al 1994, 1996) and establishing the correlatedpresence of 41Ca and 26Al in CAIs with initialabundances that rule out their co-production bySEP, and confirmed their stellar origin (Sahijpalet al 1998, 2000). Hints for the possible presence ofanother short-lived nuclide 36Cl (half-life = 0.3Ma)were also found (Murty et al 1997) and later con-firmed by more precise analysis (Lin et al 2005).The very presence of 41Ca (half-life of 0.1 Ma) ofstellar origin also constrains the time scale for thecollapse of the proto-solar molecular cloud leadingto the formation of the Sun and the first solar sys-tem solids to less than a million years (Sahijpalet al 2000; Goswami and Vanhala 2000). This timescale is much shorter than the time scale for thenatural gravitational collapse of a molecular cloudfragment to form a sun like star (Mouschovias1989; Shu 1995) and bolstered the proposal fora triggered collapse of the protosolar cloud lead-ing to the formation of the solar system first sug-gested by Cameron and Truran (1977). It is nowbelieved that the injection of the freshly synthe-sized short-lived nuclides from a stellar source itselfact as a trigger leading to the collapse of theprotosolar cloud (see, e.g., Goswami and Vanhala2000; Vanhala and Boss 2002). Analytical modelingof injection of freshly synthesized stellar productsinto the protosolar cloud have indeed showed thatthe same process can also initiate the collapse ofthe cloud if the velocity of the stellar materialimpinging the protosolar cloud is ∼20 km/s and

within the time frame of less than a million years,inferred from the presence of 41Ca in early solarsystem objects (Vanhala and Boss 2002). Vari-ous stellar sources, such as, low mass stars thatend their life as a thermally pulsing asymptoticgiant branch (TP-AGB) star, high mass stars thatend their life as supernova as well as massiveWolf–Rayet stars that have a very short lifetime(several millions of years) and may also have anexplosive end are considered as plausible sourcesof the short-lived nuclides present in the earlysolar system. These nuclides are produced dur-ing nucleosynthesis processes taking place in thesestars towards the end of their life. Model calcula-tions were performed by several groups in USA andEurope to estimate stellar production of the short-lived nuclides and their stable counterparts, mixingof the freshly synthesized stellar material with pre-existing proto-solar cloud devoid of the short-livednuclides, the time interval between production atthe stellar source to the formation of the first solarsystem solids where fossil records of the short-livednuclides are found, to infer the most plausible stel-lar source of the short-lived nuclides present in theearly solar system solids (see figure 9; also Goswamiand Vanhala 2000; Goswami et al 2005 and refer-ences therein). At present there is a general con-sensus that a high mass star that ended its life as asupernova is the most probable source of the short-lived nuclides present in the early solar system (seee.g., Huss et al 2009).

The detection of fossil records of the short-lived nuclide 10Be (half-life = 1.5Ma) in early solarsystem solids (McKeegan et al 2000), which is nota product of stellar nucleosynthesis, and is pro-duced only by energetic particle interaction withtarget nuclides such as C, N and O, have againraised questions on the suggested stellar originof the short-lived nuclides present in the earlysolar system. A combined study of 10Be, 26Al and41Ca records in refractory early solar system solidscarried out at PRL clearly showed that 10Be ispresent in early solar system solids that are devoidof the other short-lived nuclides, such as 41Caand 26Al and thus the source of 10Be is decou-pled from the source of the other two nuclides(Marhas et al 2002). This reaffirmed a stellarorigin of the short-lived nuclides. Analytical cal-culations also suggest that contribution, if any,from energetic particle interactions to the inven-tory of most of the short-lived now-extinct nuclidespresent in the early solar system is small, at <10%level (Goswami et al 2001, 2005; Marhas et al2002).

Our present understanding of the evolution ofthe early solar system suggests the refractory CAIsto be the first solar system solids to form in thesolar nebula. As noted earlier, the next solids to


Figure 9. A schematic illustration of the solar-stellar con-nection inferred from the presence of now-extinct short-livednuclides of stellar origin in CAIs. The stellar source maybe identified by modelling production of the nuclides indifferent stellar sources, their injection and mixing withnuclides present in the protosolar cloud and elapsed timescale between injection and incorporation of the nuclidesinto CAIs and matching the same with data obtained fromlaboratory studies of CAIs (from Goswami and Vanhala2000).

form in the nebula are the sub-mm to mm-sizedchondrules, present in all chondrites (Scott andKrot 2005). Estimation of the time differencebetween formation of the CAIs and chondruleshas been attempted by using 26Al as a relativechronometer. Since the CAIs have a characteris-tic value of solar system initial 26Al/27Al, the laterformed chondrules will have lower initial valuesdepending on the difference in their time of forma-tion relative to the CAIs. The initial studies sug-gested that the chondrule formation took placemore than a million years after the CAIs and con-tinued for ∼1–3 million years (Russell et al 1996;Kita et al 2000; Huss et al 2001). It was soonrealized that the inferred time scales for some chon-drules may not be exact as they may have sufferedthermal metamorphism on their parent bodies thatcan affect the Mg isotope records. A careful sampleselection and an extensive study carried out atPRL has now conclusively established (figure 10)that the effective duration of formation of chon-drules present in the ordinary chondrites is abouta million years (Rudraswami et al 2008).

The early melting of asteroids, representing theparent bodies of the achondrites, requires a viableheat source and several possibilities have beenproposed. In particular, energy released duringthe decay of the short-lived nuclide 26Al, initiallypresent in these objects, has long been consideredas the most plausible source (Urey 1955). Theshort half-life of this nuclide, coupled with rea-sonable abundance of Al in solar system objects,make this an ideal candidate for early melting of

parent bodies of achondrites. Following the iden-tification of 26Al records in some of the first solarsystem solids, several unsuccessful attempts weremade to identify fossil records of residual 26Al insamples of differentiated meteorites (Davis et al1988; Bernius et al 1991; Hsu and Crozaz 1996).A major contribution of the PRL group in thisfield is the first identification of 26Al record in sam-ples of the differentiated meteorite Piplia Kalan,an achondrite, that fell in Rajasthan in 1996. Al-Mg isotope studies of plagioclase and pyroxene inthis meteorite using an ion microprobe revealedexcess 26Mg in them resulting from in situ decayof 26Al (figure 11; Srinivasan et al 1999). Thisresolved one of the long standing issues in plan-etary sciences for more than three decades. Thisfinding also suggested that the process of accre-tion, heating, melting, differentiation and crustformation in asteroids representing parent bodiesof achondrites was complete within 3–5 Ma. Laterstudies of records of 26Al and another now-extinctshort-lived nuclide 182Hf in achondrites confirmedthe results and put a more stringent constraintof <3Ma for this differentiation process and insome cases this time scale could be even ∼1Ma(see, e.g., Halliday and Kleine 2006; Wadhwa et al2006).

Studies of short-lived now extinct nuclides haveprovided a time scale of events leading to theformation of the solar system objects, startingwith the first solar system solids, the CAIs,followed by chondrules, chondrites, achondritesand other differentiated meteorites, the stony-ironsand irons. This is shown schematically in figure 12.A significant change in the evolutionary time scales

Figure 10. Inferred time of formation of chondrules, rel-ative to CAIs, the first solar system solids, based on fossilrecords of the now-extinct radionuclide 26Al in them. Thesechondrules are sampled from meteorites that have experi-enced very little thermal metamorphism during their resi-dence in their parent asteroids and most of them preservedtheir pristine 26Al records (from Rudraswami et al 2008).


Figure 11. Demonstration of the presence of the short lived radionuclide 26Al in the basaltic achondrite Piplia Kalan(photograph on left) based on the observed enhancement in 26Mg/24Mg ratio in Al-rich phases compared to the terrestrialvalue (from Srinivasan et al 1999). The inferred initial 26Al/27Al allows estimation of the time of formation of Piplia Kalanrelative to CAIs characterized by a canonical initial 26Al/27Al of 5 × 10−5.

Figure 12. A schematic of the gradual evolution of the solar system inferred from laboratory studies of early and lateformed solar system objects. Recent results are suggestive of very early differentiation of planetesimals pre-dating theformation of chondrites.

of the early solar system has come about in recentyears, primarily due to the revision in the timeof formation of differentiated achondrites based onhigh precision studies of the fossil records of thenow extinct short-lived nuclide 182Hf that decaysto 182W with a half life of 9Ma. However, there arestill gaps in our knowledge and we are not yet closeto the final answer of the earliest stage of evolutionof the solar system.

5. Nitrogen and noble gas studies ofextra-terrestrial objects

In contrast to the records of short-lived nuclides inearly solar system objects that may be used to infertime scale of various early solar system events, therecords of variations in stable isotope abundances,

such as those of volatile elements N and noble gases(He, Ne, Ar, Kr and Xe) are very useful in under-standing the evolutionary processes.

Studies of noble gas and nitrogen isotope com-position of solar system objects using static massspectrometry is a highly specialized field. Sucha facility has been established at PRL in thelate eighties for investigating early solar systemprocesses and formation and evolution of planetarybodies. A brief outline of some of the importantresults obtained from studies carried out at PRL ispresented here.

A class of differentiated meteorites calledureilites contain about 2 wt.% elemental carbon,mostly in the form of micro-diamonds. The originof the diamonds has been enigmatic. Through asimultaneous study of N and noble gases in bulkureilites and the separated C phases (diamond,


Figure 13. Nitrogen isotope composition in variouscarbon phases (amorphous carbon, graphite and diamond)present in ureilite. The diversity of the values and thedifficulty in relating them through Rayleigh fractionationprocess demonstrates their independent origin as solarnebula products (Rai et al 2003a).

graphite and amorphous carbon) it has beenestablished that while diamond and amorphous Ccontain noble gases, graphite is devoid of them.Further, all three carbon phases host N, but withdifferent isotopic composition and N isotope com-position in diamonds is independent of their respec-tive host ureilites. These results (figure 13; Raiet al 2003a, b) rule out the earlier proposal thatdiamonds in ureilites are product of in situ con-version of graphite or amorphous carbon. Thesedata suggest that ureilite diamonds are nebularproducts which were later incorporated into theparent body of ureilites.

The textural and petrological characteristics ofchondrules suggest their formation by transientheating and melting of chondrule precursor solidsfollowed by rapid cooling (see, e.g., Scott and Krot2005). However, the exact formation mechanismof chondrules is still not completely understood.Studies of trapped and cosmogenic noble gases andnitrogen components have the potential to resolvethis issue. A laser microprobe, capable of analyz-ing very small amounts of gases from sub-milligramsamples has been set up at PRL to analyze indi-vidual chondrules to address these issues (Mahajanand Murty 2003). The results show that nitro-gen isotope composition of chondrules is differentfrom their respective host chondrites, and it alsovaries for chondrules from ordinary and enstatitechondrites. These results suggest that chondruleprecursor solids are not the same as their hostchondrites (Das and Murty 2009), a constraint thathas to be accounted for by any chondrule formingmechanism.

The accretion and formation of planets and theirsubsequent evolution depends on their internal

heat content. The volatiles present in the accret-ing materials will be degassed and get redistributedin the interior of the planet and also get accumu-lated in the atmosphere (if the body is large enoughto retain an atmosphere) or lost to space. Studyof noble gases and nitrogen in the atmosphereand interior reservoirs of a planet allows oneto model the formation and evolution of aplanet.

The presence of martian meteorites in our mete-orite collection is confirmed by matching thetrapped noble gas compositions in such mete-orites with that of contemporary Mars atmosphereobtained by spacecraft that landed on Mars.Ancient martian atmospheric composition inferredfrom the study of the oldest martian meteoriteALH84001, with a formation age >4Ga, pro-vided an important input to model the evolu-tion of Mars atmosphere with time (Murty andMohapatra 1997), in addition to indicating thepresence of an interior (Mars mantle) N com-ponent, as well as aqueous alteration effects inMars. Studies of another set of martian mete-orites Y000593 and MIL03346 suggest the pres-ence of more than one interior N and noble gascomponents. Presence of multiple volatile compo-nents that are pristine, suggests that Mars mantleremained frozen since very early in its history.This interpretation is consistent with the very lowvalue of (40Ar/36Ar) ratio of 42 for Mars mantle,reported so far and suggests a very low degree ofdegassing for planet Mars, as compared to Earth,a consequence of very early heat loss in the case ofMars.

Earlier studies, based on chemical compositionor single element (oxygen) isotopic systematicshave suggested carbonaceous chondrites as thedominant building blocks of Mars. However, thebulk Mars Fe/Si ratio and the moment of iner-tia factor, inferred assuming such precursor com-position, are not consistent with the recent andmore accurate values obtained by Pathfinder spacemission. Based on the two isotopic systems, Nand O, it is proposed that Mars is made ofE and H chondrites in the proportion of 74 : 26.Such a model (figure 14) not only reproduces theexpected bulk Fe/Si ratio and the moment ofinertia factor of Mars, but also consistent withCr isotope systematics (Mohapatra and Murty2003).

6. Impact crater, volcanism andmass extinction

Impact cratering is a very dominant force inshaping the face of all the inner planets, theplanetary satellites and asteroids. Lonar Crater in


Figure 14. Plot of Δ17O (variation in 17O/16O from stan-dard value after fractionation correction) vs δ15N (variationin 15N/14N from standard value), allows identification of theprecursors of differentiated solar system object. For Mars,one can rule out carbonaceous chondrites (C1 and CV) aspossible precursors and suggest a mix of enstatite (E) andordinary (O) chondrites in the ratio of 76 : 24 as the mostplausible precursors (from Mohapatra and Murty 2003).

Maharashtra (figure 15) is a well-known impactcrater. Studies were conducted at IIT Kharagpur,to infer the nature of the impact event and thecomposition of impacting body based on majorand trace element compositions of Lonar samplesthat are products of the impact event (Mishraet al 2009). Based on textural and mineralogicalstudies and shock features present in samples of the‘Dhala structure’ within the Bundelkhand craton,carried out at the Allahabad University, a mete-orite impact origin of this structure is now con-firmed (Pati et al 2008). The ‘Ramgarh structure’in Rajasthan, has also been proposed to be ofimpact origin based on similar studies carried outat the JNV University (Sisodia et al 2006).

Figure 15. Lonar impact crater (presently a lake), in Bhuldhana district, Maharashtra. This km-sized crater formedabout 25,000 years ago.

Asteroid impact has been also linked to large-scale mass-extinction on earth. The presence ofiridium enhancement in the clay layer presentat the Cretaceous-Tertiary (K-T) boundary datedat ∼65 million years ago, led to the suggestionthat the large scale extinction of life at the K-Tboundary was fuelled by the impact of an asteroid∼10 km in size. However, there is a counter viewthat this extinction could be due to the eruptionof the Deccan volcanism at nearly the same time.Detailed studies carried out at PRL on iridiumand other trace element abundances in the K-Tboundary layer (figure 16), coupled with extensivegeochronological studies to constrain the durationof the Deccan volcanism, using Ar-Ar dating tech-nique, showed that the peak of Deccan volcanismis separated by a couple of million years from thetime of K-T extinction giving credence to the aster-oid impact hypothesis as the cause of this extinc-tion (Bhandari et al 1996; Venkatesan et al 1993;Shukla et al 2001; Pande 2002).

7. Analytical modeling of martian andcometary atmosphere

Spacecraft exploration of the Mars has provideda large data base on contemporary martianatmosphere including the electron and ion densi-ties in both day- and night-side ionosphere. Severalresearch groups in India from PRL, NPL (NationalPhysical Laboratory, Delhi), BHU (Benares HinduUniversity) and SPL (Space Science Laboratory,Trivandrum) have carried out analytical studiesto understand the martian atmospheric processesin conjunction with the spacecraft data, particu-larly from Mars 4 & 5, Viking 1 & 2, Mars GlobalSurveyer (MGS) and Mars Express. Analyses of alarge number of electron density profiles obtainedby MGS from regions free from crustal magneticfield effects revealed several features that are at


Figure 16. Ar-Ar dating of samples from various strataof Deccan volcanic layers suggest episodic eruption over anextended period of more than six million years with majoreruptions predating the K/T boundary event at 65 millionyears as indicated by the occurrence of the Ir-enriched layer.These results suggest an asteroid impact rather than Deccanvolcanism as the most plausible cause for both the iridiumanomaly and widespread extinction at the K/T boundary(from Shukla et al 2001).

variance with theoretical expectations (Mahajanet al 2007). Neutral densities of seven differentspecies, such as CO2, N2, O2, have been derivedfrom the MGS data to model expected ion andelectron densities in the 115 to 220 km zone andare compared with electron density data from theradio occultation experiment in the same space-craft to validate the model calculations. Analy-tical modeling of the day time and night timeionospheres of mars, to cover the height intervalup to ∼200 km, and taking into account all therelevant atmospheric species, chemical reactionsamongst them and considering solar EUV, X-raysand galactic cosmic rays as the ionizing sources,have yielded the height of electron density peaksand electron density that are in reasonable agree-ment with spacecraft observations. These estimatesalso allowed the calculation of the approximateheights of the various layers (D, E, F) in mar-tian ionosphere (Haider et al 2006, 2009; Seth et al2006).

The role of aerosols in the martian climatesystem and its impact on electrical conductivityin the lower atmosphere as well in the day andnight-time atmosphere in Mars have been mode-led by a group in IIT Kanpur, by consideringcharging of aerosols via attachment of ions in themartian atmosphere that reduces the atmosphericconductivity. Galactic cosmic rays are the primaryionizing agent in the lower atmosphere and pro-duce molecular ions. Solar photons can also serve

as ionizing agents during day time. The ions andion clusters produced by cosmic rays and solar pho-tons get attached to aerosols during the night time,a feature that gets enhanced during dust storm dueto increased dust opacity and resultant increasein the aerosol-ion attachment process. Analyticalmodeling suggests that a majority of the ions andmost of the electrons get attached to aerosols. Theconductivity can decrease by a factor of five in thelower atmosphere due to ion attachment processesand could be down by two orders of magnitudeduring dust storms with opacity of ∼5 (Michaelet al 2007, 2008).

Effort has also been made to model the abun-dances of the C, H, N, O, and S compoundsdetected in coma of comets using a coupled-chemistry model and considering solar EUVphotons, photoelectrons and solar wind electronsas the ionizing sources. Comparison of the ana-lytical data with those observed for comet Halleyby Giotto spacecraft provided reasonable agree-ment and the model could also reproduce the majorpeaks in the observed spacecraft spectra in themass region 10–40 amu (Haider and Bharadwaj2005).

8. Planetary astronomy

Astronomical observations of solar system objectshave been also pursued sporadically in the country,primarily at the Indian Institute of Astrophysics(IIA), Bangalore and at PRL. One of the verysignificant results obtained from these studies isthe discovery of Saturn-like ring system of Uranusbased on near-infrared observation during a near-grazing occultation of a stellar source by Uranus(Bhattacharya and Bappu 1977). The observationstaken from the Kavalur observatory revealed dim-ming of light, in addition to those expected fromoccultation by the known satellite system, sug-gesting the presence of an occulting body (ies)much closer to the planet. IIA has also initiatedanother project, ‘Kalki’ to survey the sky with aSchmidt telescope to observe comets, asteroids andplanets and discover new asteroids/comets. Severaldozens of asteroids have been detected during thisstudy including six new asteroids (Rajamohan et al1988), the first one of which has since been named‘Ramanujan’. Inferring the precise size of aster-oids using lunar occultation technique has beenpursued at PRL from the Mt. Abu observatoryand sizes of close to half a dozen asteroids havebeen estimated with this approach (Chandrasekhar2007). Studies of optical polarimetry of cometsfrom this observatory have also been conducted toinfer the characteristics of cometary dusts. Obser-vations of cometary coma at different locations in


the direction of the comet tail suggest that bothcomet NEAT C/2001 Q4 and 17P/Holmes have amix of grains of silicates and organic compositionand enhanced abundance of smaller grains as onemoves outward in the coma (Ganesh et al 2009;Joshi et al 2009).

The Sun emits ultraviolet and X-ray photonsfrom the high temperature coronal regions andit also emits both X-rays and energetic parti-cles during solar flares. These energetic photonsand particles can interact with relatively coolplanetary bodies and produce X-rays through awide variety of processes. Space-based observationshave detected planetary X-rays from Venus, Earth,Moon, Mars, Jupiter, Saturn, and also from Io andEuropa (see, e.g., Bhardwaj and Gladstone 2000;Bhardwaj and Lisse 2007). High spatial and spec-tral resolution observations of planetary X-rays areimportant for understanding the processes respon-sible for production of X-rays on planetary bodies.The space-based X-ray observatories, Chandra andXMM-Newton, are providing excellent data onplanetary X-rays and an active programme in thisarea is being pursued at Space Physics Laboratory,Trivandrum.

The terrestrial X-ray aurora is generated byenergetic electron bremsstrahlung, while that inJupiter the dominant mode is charge exchangewith ionized heavy ions and solar wind ions withsome contribution from electron bremsstrahlung.Observations by Chandra observatory led to thediscovery of X-rays from the rings of Saturn(figure 17), revealing that very cold objects inour solar system can also be an X-ray source(Bhardwaj et al 2005). The energy of the X-rayssuggest oxygen in water-icy cold rings is the sourceof the fluorescent X-rays. The X-ray emission

Figure 17. X-ray image at (0.49–0.62) keV of theSaturnian system taken from Chandra Observatory reflect-ing emission of oxygen Kα line (from Bhardwaj et al 2005).

Figure 18. Image of the Jupiter’s radiation belt at610 MHz obtained from the Giant Metrewave Radio Tele-scope at Pune (from Bhardwaj et al 2009).

from low-latitude (non-auroral) disk of the planetsEarth, Jupiter and Saturn are mostly produced byscattering of solar X-rays by atmospheric species.X-ray emission from non-auroral disk of Saturncould be directly related to a flare from an activesunspot region that was clearly visible from bothSaturn and Earth. Thus, planetary X-rays fromthe giant outer planets suggest their direct link toactive processes occurring on the Sun.

Synchrotron radio emissions from Jupiter havebeen observed using the Giant Metrewave RadioTelescope (GMRT) at Poona (Bhardwaj et al2009). These observations provided the first evi-dence of a large (20%) day-to-day variability at610 MHz (figure 18) – a finding that could haveimportant consequences for our understanding ofthe dynamics of Jovian radiation belts as it is gen-erally believed that Jupiter’s synchrotron emissionsare quite stable.

9. Planetary exploration

The solar system can be divided into an innerand an outer region. The inner solar system con-sists of the planets Mercury, Venus, Earth andMars representing (silicate + metal) objects, whilethe outer solar system, consisting of the planetsJupiter, Saturn, Uranus and Neptune representsprimarily gaseous planets with a small rockycore. The asteroids, left over material of innersolar system objects, populate the region betweenMars and Jupiter. All the planetary satellites,both in the inner and outer solar systems areprimarily silicate + metal dominated objects with


some of the outer solar system satellites havingicy crust/mantle. The four terrestrial planets haveseveral distinct characteristics that are an outcomeof their formation and evolutionary differences.

It is generally believed that the planets, as wesee today, have formed close to their present loca-tion via accretion of planetesimals. The accretedplanets evolve due to their internal energy con-tent that is made up of both accretional energyand energy from radioactive decay that will dependon the total mass of the planet and the chemi-cal composition (of radioactive elements), respec-tively. Smaller planets (like Mercury) may quicklyexhaust their heat content either by melting or byloss due to conduction/radiation and their evolu-tion become static. During any large-scale melting,the volatile that are exhaled by the interior of theplanet will form the surface reservoirs (atmosphereand/or hydrosphere). If the gravity of the planet isfeeble these surface reservoirs are quickly lost andthe planet does not have an atmosphere. While forplanets of the size of Earth and Venus the heatloss is slow and they continue to evolve and holdthe surface reservoirs up to the present, the case ofMars is intermediate. Mars might have ceased toevolve a few hundred million years ago and is alsoholding a thin atmosphere. Essentially, the size andchemical differences of the terrestrial planets haveresulted in their different modes of thermal evolu-tion. A closer look at the surface features to gleanthe physical, chemical and mineralogical aspectswill reveal imprints of the evolutionary recordsof the planet. At present we have sample returnmission only from moon and there are reasons tobelieve that some of the meteorites are of martianorigin. It is therefore essential to have planetaryexploration missions to various solar system bodiesto improve our understanding of their formationand evolutionary history.

The current decade has seen a revival in the fieldof lunar exploration, with several new initiativesby various space agencies. These efforts began in2003 with the Smart-1 mission of European SpaceAgency that was followed by the Change-1 mis-sion of China and the Japanese mission Kaguya(SELENE), both in late 2007. These were followedby the Indian Chandrayaan-1 mission in late 2008and the US mission LRO (Lunar ReconnaissanceOrbiter) launched in mid-2009.

The launch of Chandrayaan-1 remote sensingmission (figure 19) to the moon ushered a new erain planetary science research in the Indian con-text. The initial discussion on the possibility ofhaving such a mission with indigenous capabilitiesstarted in 1997 during the annual session of theIndian Academy of Sciences. This was followed bya series of discussions in different forums duringthe next few years leading finally to the formation

Figure 19. The Chandrayaan-1 spacecraft.

of a task team by Indian Space Research Organi-zation (ISRO) early this decade. The task teamproduced a comprehensive report on all the techni-cal and scientific aspects of the mission, includingscience objectives and potential science payloads.This report was discussed extensively and finallysubmitted to the Govt. of India in early 2003 andthe same was approved later that year. ISRO fixeda target launch date of early 2008 and the launchof Chandrayaan-1 took place on 22 October, 2008.

Even though the Apollo and Luna missions andthe returned lunar samples have provided a largevolume of data and plausible evolutionary sce-narios for the Moon have been proposed, thesemissions primarily explored the equatorial regionsof the moon. Mapping of the whole moon wasaccomplished only in the nineties by two US mis-sions, Clementine and Lunar Prospector. The dataobtained by these missions have furthered ourunderstanding of the moon and also raised newquestions regarding the origin and evolution ofthe moon (Bhandari 2002, 2004). The need forlunar data at high spectral and spatial resolu-tion for a better understanding of its origin andevolution was clear and the Chandrayaan-1 mis-sion primarily aimed at achieving this objective.The possibility for the presence of resources such


as water in the permanently shadowed lunar polarsites, suggested by data from Clementine andLunar Prospector missions, and the presence oftrapped 3He in lunar ilmenite, a potential fusionfuel for the future also enhanced the possibilityof using the moon as a potential base for futureplanetary exploration. The science objectives ofthe Chandrayaan-1 mission and details of variouspayloads are described in a series of papers inCurrent Science (25 February, 2009 issue). Thismission has already yielded some important results(presentations in 40th Lunar and Planetary ScienceConference, March, 2009, Abstracts: Lunar andPlanetary Institute, Houston).

10. Indian missions to Moon, Mars,Asteroids/Comets

Any long-term plan for planetary exploration hasto be made in the global context and indigenoustechnical capabilities. The Chandrayaan-1 missionled to the establishment of a 32 m deep-space net-work antenna and coupled with the developmentand induction of new generation geostationarysatellite launch vehicle soon, ISRO possesses thecapability to send planetary exploration missionsto all the inner solar system objects. The currentlyproposed ISRO plan for planetary explorationwithin the coming decade has Moon, Mars andComet/Asteroid as the targets. Chandrayaan-2,officially approved with a targeted launch in 2012,will include a lander and a rover, in addition to theorbiter, for an in depth study of a lunar site of highscientific interest.

The presence of water on Mars during pastepochs has made exploration of Mars high inagenda of most of the space agencies involved inplanetary exploration. Although most of the recentmissions to Mars are concentrating on exploringsurface for signature of water, comprehensive stud-ies of the martian atmosphere, ionosphere andaerosol/dust and atmospheric dynamics are stilllacking. The proposed Indian Mars obiter missionwill focus on the study of Mars upper atmosphere,its interaction with radiation and energetic par-ticles from the Sun, and with galactic cosmicrays, atmospheric dynamics and martian weather.Remote sensing studies of chemical, mineralogicaland morphological features of the martian surfaceas well as magnetic anomalies on the surface (theirorigin and consequences), will be conducted andfocused studies to assess and understand the water-rock interactions on Mars surface and their role onthe possible existence of life on Mars will be impor-tant science objectives of this mission. It is alsoproposed to study Phobos, the captured satelliteof Mars during this mission.

It is now well accepted that asteroids are theparent bodies of most of the meteorites, except fora small number of meteorites that are of lunar andmartian origin. Comparison of the reflectance spec-tra of asteroids with those of meteorites has estab-lished a tentative connection between meteoriteclasses and possible parent asteroids, not with-standing the effects of space weathering and theconsequent alteration of the asteroidal reflectance.The case of comets is more elusive. They arelike deep freezers, faithfully preserving the recordssince the birth of solar system and may containa greater proportion of interstellar grains in theirpristine form. They may also hold clues for the ori-gin of life forming bio-molecules. Although cometsare expected to be pristine solar system mate-rial, we do not have a bulk sample of cometsin our collection. Some of the microscopic extra-terrestrial dust particles collected at stratosphericlevel by high flying aircraft appeared to be ofcometary origin. Our present idea about cometarycomposition is based on remote sensing missionslike Giotto to comet Halley and earth based obser-vation of comets. The recent Stardust mission tocomet Wild-2 has successfully brought back sev-eral thousand particles of microscopic cometarydust. Laboratory analysis of these samples revealedvery interesting results including the unexpectedpresence of a microscopic high temperature refrac-tory object. ESA has launched ‘Rosetta’ missionto conduct both remote sensing and in situ studiesof a cometary surface using a combination of anorbiter and a lander.

A focussed study of asteroids and cometsthrough space missions is very important, as thesebodies have preserved the records of early solarsystem processes intact. The principle objectives ofan asteroid mission are to establish the meteorite-asteroid connection on a firm footing, and under-standing the size, composition and differentiationof asteroids in the context of their thermalevolution. There had been several flyby missionsto asteroids and only the NEAR orbiter missionof NASA studied in detail the asteroid Eros. TheJapanese sample return mission Hayabusa to aster-oid Itokawa in 2003, is on its way back with asmall fragment of the asteroid and the NASA’sDawn mission was launched in 2007 for studyingtwo of the large asteroids, Ceres and Vesta. Keep-ing in view the global scenario, ISRO is proposinga mission to explore comets (flyby) and asteroid(orbiter) during the later part of next decade.The target asteroid will be one of those that areconsidered probable parent bodies of the primi-tive/differentiated meteorites and will be selectedas per the launch schedule and the possibility ofhaving flyby opportunity of comets and other aster-oids. ISRO will have all the infrastructural facilities


needed for launch, command, control, communica-tion and data transfer in place for the proposedmissions.

11. Future perspective

Two of the primary objectives of research in thefield of planetary sciences are to understand theorigin of the solar system and its evolution tothe present state and the origin of life on earth andits possible existence elsewhere. Recent discoveriesof planetary systems around sun-like stars tell usthat planet formation is not unique to our Sun.However, most of these extra-solar planets aremore massive and at greater proximity to the cen-tral star, though a couple of cases of ‘earth-size’planets, with some having atmosphere, have alsobeen detected (Santos et al 2005). Even thoughobservational and laboratory studies as well asmodelling efforts led to a broad understandingof the formation of planets, processes that couldexplain the exo-planets in general and the solarsystem planets (both terrestrial and Jovian), inparticular are not yet well understood. Search forexo-planets will intensify with the recent launchof KEPLER mission by NASA. Efforts are beingmade at PRL to develop high precision instru-ment to carry out planet search using the Mt. Abuobservatory.

Laboratory studies of microscopic early solarsystem objects, including the recently returnedsamples of comet Wild-2, and expected returnof Hayabusa spacecraft bringing back asteroidsample will provide further insight into the earli-est phases of evolution of the solar system. Thepresence of presolar grains in primitive meteoritesand of now-extinct short lived nuclides in thenascent solar system serve as excellent probes toimprove our understanding of solar-stellar rela-tions and the evolution of matter in our galaxy.Recent technical developments have provided uswith tools that are capable of probing micro-scopic samples at a spatial resolution of hundrednanometers and destructive analysis of micro-gramsamples for precision elemental and isotopic com-positions. Some of these instruments are currentlyinstalled in a few research laboratories, universitiesand IITs in the country and encouraging resultshave been obtained from them.

Exploration of Mars, the icy satellites of Jovianplanets, the satellites of Saturn, Titan, with amassive atmosphere like that of Earth, is expectedto provide clues about the possibilities of life formsbeing present in these environs and will possiblybroaden our outlook on the definition of life. Inten-sive exploration of asteroids and comets will helpus understand the evolution of rocky objects in the

solar system and may provide definitive answers tothe question if comets have seeded life on earth andelsewhere.

The recent foray into planetary exploration byIndia brought to focus the need to enlarge thescientific strength in this area that was pursuedin very few places in the country. The PLANetaryScience and EXploration (PLANEX) program,initiated by ISRO with PRL as the nodal center,is putting sustained effort in this direction thathas led to some visible results. More than twentyresearch groups at various research institutes, uni-versities and IITs are working with PLANEXsupport in areas that are within the broad frame-work of planetary sciences. Some of the scientificresults presented in this review on studies of impactcraters and martian ionosphere and aerosols arebased on work done under the PLANEX pro-gramme. The programme also provides access tostate-of-the-art analytical facilities at PRL to allthe participating groups and a forum for discussionon various aspects of planetary sciences and explo-ration. A planetary science data repository alongwith data analysis tools and expertise will soon beprovided under this programme, starting with datafrom the Chandrayaan-1 mission. We can look for-ward to a very productive and modern phase ofearth and planetary research in the country.

Acknowledgement

We thank Drs. A Bhardwaj, S Chandrasekhar,S A Haider and K S Baliyan for providing inputson studies of planetary astronomy and martianatmosphere. We also thank the Editor for patienceand support that made this submission possible.

References

Bernius M, Hutcheon I D and Wasserburg G J 1991 Searchfor evidence of Al-26 in meteorites that are planetarydifferentiates; Lunar Planet. Sci. 22 93–94.

Bhandari N 1981 Records of ancient cosmic radiation inextraterrestrial rocks; Proc. Indian Acad. Sci. (EarthPlanet Sci.) 90 359–382.

Bhandari N 2002 Quest for Moon; Curr. Sci. 83 377–393.Bhandari N 2004 Scientific Challenges of

CHANDRAYAAN-1: The Indian lunar polar orbitermission; Curr. Sci. 86 1489–1498.

Bhandari N and Padia J T 1974 Secular variations in theabundances of heavy nuclei in cosmic rays; Science 1851043–1045.

Bhandari N, Goswami J N, Lal D and Tamhane A S1973a Long-term fluxes of heavy cosmic ray nuclei basedon observations in meteorites and lunar samples; Astro-phys. J. 185 975–983.

Bhandari Narendra, Goswami Jitendra and Lal Devendra1973b Cosmic ray irradiation patterns of Luna 16 and20 soils: Implications to lunar surface dynamic processes;Earth Planet. Sci. Lett. 20 372–380.


Bhandari N, Bhattacharya S K and Padia J T 1975The surface radioactivity of lunar rocks: Implicationsto solar activity in the past; Proc. Lunar Sci. Conf. 61913–1925.

Bhandari N, Bhattacharya S K and Padia J T 1976 Solarproton fluxes during the last million years; Proc. LunarSci. Conf. 7 513–523.

Bhandari N, Shukla P N, Ghevariya Z G and Sundaram S M1996 K/T boundary layer in the Deccan Intertrap-peans in Anjar, Kutch; Geol. Soc. Am. Spec. Paper 307417–424.

Bhardwaj A and Gladstone G R 2000 Auroral emissions ofthe giant planets; Rev. of Geophys. 38 295–353.

Bhardwaj A, Elsner R F, Waite J H Jr., Gladstone G R,Cravens T E and Ford P G 2005 The discovery of oxygenKα X-ray emission from the rings of Saturn; Astrophys.J. Lett. 627 L73-L76.

Bhardwaj A and Carey M Lisse 2007 X-rays in thesolar system; in Encyclopedia of the Solar System (eds)McFadden L A, Weissman P R and Johnson T V,Academic Press, 637–658.

Bhardwaj A, Ishwara-Chandra C H, Udaya Shankar N,Misawa Hiroaki, Imai Kota, Miyoshi Yoshizumi,Tsuchiya Fuminori, Kondo Tetsuro and Morioka Akira2009 GMRT Observation of Jupiter’s Synchrotron RadioEmission; Astron. Soc. of the Pacific Conf. Ser. (inpress).

Bhasin B D and Sunta C M 1979 Thermoluminiscence ofLuna-24 core samples; Adv. Lunar Res., Luna-24 SamplesINSA 39–48.

Bhattacharyya J C and Bappu M K V 1977 Saturn-like ringsystem around Uranus; Nature 270 503–506.

Bonino G, Cini Castagnoli G, Bhandari N and Taricco C1995 Behaviour of the heliosphere over prolonged quietperiods by 44Ti measurements in meteorites; Science 2701648–1650.

Caffee M W, Hohenberg C M, Swindle T D andGoswami J N 1987 Evidence in meteorites for an activeearly Sun; Astrophys. J. 313 L31–L35.

Caffee M W, Hohenberg C M, Nichols R H Jr., Olinger C T,Wieler R, Signer P, Swindle T D and Goswami J N 1991Do meteorite contain irradiation records from exposureto an enhanced activity Sun?; in The Sun in time (ed)Sonnet C P and Giampapa M S, Arizona Univ. Press,413–425.

Cameron A G W and Truran J W 1977 The supernovatrigger for formation of the solar system; Icarus 30447–461.

Chandrasekhar T 2007 Chord lengths across main beltasteroids from stellar occultations in the near infrared;Bull. Astron. Soc. India 155–161.

Das J P and Murty S V S 2009 Trapped nitrogen in indi-vidual chondrules: Nature of chondrule precursors andclues to formation mechanisms; J. Geophys. Res. E 114E01008 doi:10.1029/2008JE003232.

Davis A M, Prinz M and Laughlin J R 1988 anion microprobe study of plagioclase-rich clasts in theNorth Haig polymict Ureilite; Lunar Planet. Sci. 29251–252.

Deshpande V V, Dharwadkar S R and Jakkal V S 1979Thermogravimetric and X-ray diffraction analyses ofLuna-24 regolith samples; Adv. Lunar Res., Luna-24Samples INSA 59–61.

Eberhardt P, Geiss J and Grogler N 1965 Further evidenceon the origin of trapped gases in the meteorite KhorTemiki; J. Geophys. Res. 70 4375–4378.

Fleischer R L, Price P B, Walker R M, Maurette M andMorgan G 1967 Tracks of heavy primary cosmic rays inmeteorites; J. Geophys. Res. 72 355–366.

Fleischer R L, Price P B and Walker R M 1975 Nucleartracks in solids: Principles and applications (Berkeley:Univ. of California Press) pp. 605.

Ganesh S, Joshi U C and Baliyan K S 2009 Optical polari-metry of Comet NEAT C/2001 Q4 Icarus (in press).

Gerling E K and Levisky L K 1956 On the origin of the raregases in stony meteorites; Doklady Akad. Nauk. USSR(Geochemistry) 110 750–755.

Gladman B J, Burns J A, Duncan M, Lee P andLevison H F 1996 The exchange of impact ejecta betweenterrestrial planets; Science 271 1387–1392.

Goel P S and Kothari B K 1972 Total nitrogen content ofsome Apollo-14 samples by neutron activation analysis;Proc. 3rd Lunar Sci. Conf. 2041–2050.

Goel P S and Murty S V S 1983 Presolar grains in micro-inclusions of iron meteorites. Adv. Space Res., PergamonPress 2, No. 12, 13–18.

Goswami J N 1978 Particle track based irradiation andaccretion history of the Luna 24 regolith column; Geo-phys. Res. Lett. 5 147–150.

Goswami J N 1991 Solar flare heavy ion tracks in extraterrestrial objects; in The Sun in time (eds) Sonnet C Pand Giampapa N S, Arizona Univ. Press, 426–444.

Goswami J N and Vanhala H A T 2000 Extinct nuclidesand the formation of the solar system; in Protostars andplanets IV (eds) Mannings V, Boss A and Russell S,Arizona Univ. Press, 965–996.

Goswami J N, Lal D, Rao M N and Venkatesan T R 1979Depositional history of Luna 24 drill core soil samples;Earth Planet. Sci. Lett. 44 325–334.

Goswami J N, Lal D and Macdougall J D 1980 Charge com-position and energy spectra of ancient solar flare heavynuclei; in The ancient Sun: Fossil record in the earth,moon and meteorites; (eds) Pepin R O, Eddy J A andMerrill R B (New York: Pergamon Press), 347–364.

Goswami J N, Lal D and Widening L L 1984 Gas-rich mete-orites: Probes for particle environment and dynamicalprocesses in the inner solar system; Space Sci. Rev. 37111–159.

Goswami J N, Sinha N, Murty S V S, Mohapatra R K andClement C J 1997 Nuclear tracks and light noble gasesin Allan Hills 84001: Preatmospheric size, fall character-istics, cosmic ray exposure duration and formation age;Meteorit. Planet. Sci. 32 91–96.

Goswami J N, Marhas K K and Sahijpal S 2001 Didsolar energetic particles produce the short-lived nuclidespresent in the early solar system?; Astrophys. J. 5491151–1159.

Goswami J N, Marhas K K, Chassidon M, Gounelle M andMeyer B 2005 Origin of the short-lived nuclide present inthe early solar system; in Chondrites and the Protoplan-etary Disk (eds) Krot A N, Scott E R D and Reiputh B,ASP Publ. 341 485–514.

Grossman L 1980 Refractory inclusions in the Allende mete-orite; Ann. Rev. Earth Planet. Sci. 8 559–608.

Haider S A and Bharadwaj Anil 2005 Radial distribution ofproduction rates, loss rates and densities correspondingto ion masses ≤40 amu in the inner coma of comet Halley:Composition and chemistry; Icarus 177 196–216.

Haider S A, Seth S P, Choksi V R and Oyama K I 2006Model of photoelectron impact ionization within the highlatitude ionosphere at Mars: Comparison of calculatedand measured electron density; Icarus 185 102–112.

Haider S A, Abdu M A, Batista I S, Sobral J H, Luan Xiaoli,Kallio Esa, Maguire W C, Verigin M I and Singh V2009 D, E, F layers in the daytime at high latitude ter-minator ionosphere of Mars: Comparison with Earth’sionosphere using COSMIC data; J. Geophys. Res. 114A03311, doi:101029/2008JA013709.


Halliday A N and Kleine T 2006 Meteorites and the timing,mechanism and conditions of terrestrial planet accretionand early differentiation; in Meteorites and the early solarsystem II (eds) Lauretta D S and McSween H Y Jr.(Tucson: University of Arizona Press) 775–801.

Hohenberg C M, Nicholas R H, Olinger C T andGoswami J N 1990 Cosmogenic neon from individualgrains of CM meteorites: Extremely long pre-compactionexposure histories or an enhanced early particle flux;Geochim. Cosmochim. Acta 54 2133–2140.

Hsu W and Crozaz G 1996 Mineral chemistry andthe petrogenesis of eucrites: I. Noncumulate eucrites;Geochim. Cosmochim. Acta 60 4571–4591.

Huss G R, MacPherson G J, Wasserburg G J, Russell S Sand Srinivasan G 2001 Aluminium-26 in calcium-aluminum-rich inclusions and chondrules from unequi-librated ordinary chondrites; Meteorit. Planet. Sci. 36975–997.

Huss G R, Rubin A E and Grossman J N 2006 Thermalmetamorphism in chondrites; in Meteorites in the EarlySolar System II (eds) Lauretta D S and McSween H Y Jr.(Tucson: Univ. of Arizona) 567–586.

Huss G R, Meyer B S, Srinivasan G, Goswami J N andSahijpal S 2009 Stellar sources of the short-lived radionu-clides in the early solar system; Geochim. Cosmochim.Acta (in press).

Joshi U C, Ganesh S and Baliyan K S 2009 Optical polari-metry of comet 17P/Holmes; Mon. Not. R. Astron. Soc.(in press).

Kita N T, Nagahara H, Togashi S and Morishita Y2000 A short duration of chondrule formation in thesolar nebula: Evidence from 26Al in Semarkona ferro-magnesian chondrules; Geochim. Cosmochim. Acta 643913–3922.

Lal D 1972 Hard rock cosmic ray archaeology; Space Sci.Rev. 14 3–102.

Lal D and Rajan R S 1969 Observations on space irradiationof individual crystals of gas-rich meteorites; Nature 233269–271.

Lee T, Papanastassiou D A and Wasserburg G J 1976Demonstration of 26Mg excess in Allende and evidencefor 26Al; Geophys. Res. Lett. 3 109–112.

Lin Y, Guan Y, Leshin L A, Ouyand Z and Wang D 2005Short-lived chlorine-36 in a Ca- and Al-rich inclusion fromthe Ningqiang carbonaceous chondrite; Proc. Natl. Acad.Sci. 102 1306–1311.

Macdougall J D and Goswami J N 1981 Windows to earlysolar system processes: Refractory inclusions in the CVand CM chondrites; Proc. Ind. Acad. Sci. (Earth Planet.Sci.) 90 1–26.

Mahajan K K, Singh S, Kumar A, Raghuvanshi S andHaider S A 2007 Mars Global Surveyor radio scienceelectron density profiles: Some anomalous features inthe Martian ionosphere; J. Geophys. Res. 112 E10006,doi:10.1029/2006JE002876.

Mahajan R R and Murty S V S 2003 Laser micro-probe for the study of noble gases and nitrogen in sin-gle grains: A case study of individual chondrules fromDhajala meteorite; Proc. Ind. Acad. Sci. (EPS) 112113–127.

Marhas K K, Goswami J N and Davis A M 2002 Short-livednuclides in hibonite grains from murchison: Evidence forsolar system evolution; Science 298 2182–2185.

McKeegan K D, Chaussidon M and Robert R 2000 Incor-poration of short-lived Be-10 in a calcium-aluminum-rich inclusion from the Allende meteorite; Science 2891334–1337.

McSween H Y 1999 Meteorites and their parent planets;Cambridge Univ. Press, pp. 324.

Michael M, Barani M and Tripathi S N 2007 Numericalpredictions of aerosol charging and electrical conductivityof the lower atmosphere of Mars; Geophys. Res. Lett. 34L04201, doi:10.1029/2006GL028434.

Michael M, Tripathi S N and Mishra S K 2008 Dust charg-ing and electrical conductivity in the day and night-time atmosphere of Mars; J. Geophys. Res. 113 E07010,doi:10.1029/2007JE003047.

Misra S, Newsom H E, Shyamprasad M, Geissman J W,Dube A and Sengupta D 2009 Geochemical identificationof impactor for Lonar crater, India; Meteorit. Planet. Sci.(in press).

Mohapatra R K and Murty S V S 2003 Precursors of Mars-constraints from nitrogen and oxygen isotopic compo-sition of martian meteorites; Meteorit. Planet. Sci. 38225–241.

Mouschovias T Ch 1989 Magnetic fields in molecular clouds:Regulator of star formation; in The physics and chemistryof interstellar molecular clouds (eds) Winnewessar G andAmstrong J T (Berlin: Springer Verlag) 297–312.

Murali A V, Pawaskar P B and Reddy G R 1979 Chemicalstudies of two Luna-24 regolith samples; Adv. Lunar Res.,Luna-24 Samples INSA 49–58.

Murty S V S and Mohapatra R K 1997 Nitrogen andheavy noble gases in ALH84001: Signatures of ancientmartian atmosphere; Geochim. Cosmochim. Acta 615417–5428.

Murty S V S, Shukla P N and Goel P S 1979a Lithium inLuna-24 samples; Adv. in Lunar Res., Luna-24 SamplesINSA 1–4.

Murty S V S, Shukla P N and Goel P S 1979b Total nitrogenin Luna-24 samples; Adv. in Lunar Res., Luna-24 Sam-ples INSA 29–31.

Murty S V S, Shukla P N and Goel P S 1982 Non-cosmogenic6Li in iron meteorites; Earth Planet. Sci. Lett. 60 1–7.

Murty S V S, Goswami J N and Shukolyukov Yu A 1997Excess 36Ar in the Efremovka meteorite: A strong hintfor the presence of 36Cl in the early solar system; Ap.J. Lett. 457 L65–L68.

Nautiyal C M, Padia J T, Rao M N and Venkatesan T R1986 Solar flare neon composition and solar cosmic rayexposure ages based on lunar mineral separates; Ap. J.301 465–470.

Pande K 2002 Age and duration of the Deccan Traps, India:A review of radiometric and paleomagnetic constraints;Proc. Indian Acad. Sci. (Earth Planet. Sci.) 111 115–123.

Ozima M and Podosek F A 2001 Noble gas geochemistryCambridge Univ. Press.

Padia J T and Rao M N 1989 Neon isotope studiesof Fayettville and Kapoeta meteorites and clues toancient solar activity; Geochim. Cosmochim. Acta 531461–1467.

Pati J K, Reimold W U, Koeberl C and Pati P 2008 TheDhala structure, Bundelkhand craton, Central India –Eroded remnant of a large paleoproterozoic impact struc-ture; Meteorit. Planet. Sci. 43 1383–1398.

Pellas P, Poupeau G, Lorin J C, Reeves H and Audouze J1969 Primitive low-energy particle irradiation of mete-oritic crystals; Nature 223 272–274.

Rai V K, Murty S V S and Ott U 2003a Nitrogencomponents in ureilites; Geochim. Cosmochim. Acta 672213–2237.

Rai V K, Murty S V S and Ott U 2003b Noble gases in ure-ilites: Cosmogenic, radiogenic and trapped components;Geochim. Cosmochim. Acta 67 4435–4456.

Rajmohan R, Shankar P N, Bhattacharyya J C,Kuppuswamy K and Paranjpye A 1988 Project Kalki –a sky survey with the Schmidt telescope: 2; Bull. Astr.Soc. India 16 21–28.


Reedy R C 1998 Studies of modern and ancient solarenegetic particles; Proc. Indian Acad. Sci. (Earth PlanetSci.) 107 433–440.

Reedy R C and Arnold J R 1972 Interaction of solar andgalactic cosmic-ray particles with the Moon; J. Geophys.Res. 77 537–555.

Reedy R C, Arnold J R and Lal D 1983 Cosmic-ray recordin solar system matter; Science 219 127–135.

Reynolds J H 1960 Determination of the age of the elements;Phys. Rev. Lett. 4 8–10.

Rudraswami N G, Goswami J N, Chattopadhyay B,Sengupta S K and Thapliyal A P 2008 26Al recordsin chondrules from unequilibrated ordinary chondrites:II. Duration of chondrule formation and parent bodythermal metamorphism; Earth Planet. Sci. Lett. 27493–102.

Russell S S, Srinivasan G, Huss G R, Wasserburg G J andMacPherson G J 1996 Evidence for widespread 26Al inthe solar nebula and constraints for nebula time scales;Science 273 757–762.

Russell S S, Hartmann L, Cuzzi J, Krot A N, Gounelle Mand Weidenschilling S 2006 Timescales of the solar proto-planetary disk; in Meteorites in the early solar system II(eds) Lauretta D S and McSween H Y Jr. (Tucson: Univ.of Arizona) 233–251.

Santos N C, Benz W and Mayor M 2005 Extrasolar planets:constraints for planet formation models; Science 310251–255.

Sahijpal S, Goswami J N, Davis A M, Grossman L andLewis R R 1998 A stellar origin for the shortlived nuclidesin the early system; Nature 391 559–561.

Sahijpal S, Goswami J N and Davis A M 2000 K, Mg, Ti andCa isotopic compositions and refractory trace elementabundances in hibonites from CM and CV meteorites:Implications for early solar system processes; Geochim.Cosmochim. Acta 64 1989–2005.

Scott E R D and Krot A N 2005 Chondritic meteoritesand high temperature nebular origin of their compo-nents; in Chondrites and the protoplanetary disk (ed)Krot A N, Scott E R D and Reiputh B, ASP Publ. 341485–514.

Seth S P, Jayanthi U B and Haider S A 2006 Estimationof peak electron density in upper ionosphere of Mars athigh latitude (50◦–70◦N) using MGS ACC data; Geophys.Res. Lett. 33 L19204, doi:10.1029/2006GL027064.

Shirk E K 1974 Observation of transiron solar flare nucleiin an Apollo 16 command module window; Astrophys. J.190 695–702.

Shu F H 1995 The birth of sunlike stars; in Molecularclouds and star formation (eds) Chi Yuan and JunhanYou (Singapore: World Scientific) 97–148.

Shu F H, Shang H, Glassgold A E and Lee T 1997 X-raysand fluctuating x-winds from protostars; Science 2771475–1479.

Shukla A D, Bhandari N, Kusumgar S, Shukla P N,Ghevariya Z G, Gopalan K and Balaram V 2001Geochemistry and magnetostratigraphy of Deccan flowsat Anjar Kutch; Proc. Indian Acad. Sci. (Earth Planet.Sci.) 110 111–132.

Shukla P N, Kothari B K and Goel P S 1978 Simultaneousdetermination of nitrogen and lithium by thermal neu-tron activation analysis; Anal. Chim. Acta 96 259–269.

Sisodia M S, Lashkari G and Bhandari N 2006 Impact originof the Ramgarh structure, Rajasthan: Some new evi-dences; J. Geol. Soc. India 67 423–431.

Srinivasan G, Ulyanov A A and Goswami J N 1994 41Ca inthe early solar system; Astrophys. J. 431 L67–70.

Srinivasan G, Sahijpal S, Ulyanov A A and Goswami J N1996 Ion microprobe studies of Efremovka CAIs: II.Potassium isotope composition and 41Ca in the earlysolar system; Geochim. Cosmochim. Acta 60 1823–1835.

Srinivasan G, Goswami J N and Bhandari N 1999 26Al ineucrite Piplia Kalan: Plausible heat source and forma-tion chronology of eucritic parent bodies; Science 2841348–1359.

Thakur A N and Goel P S 1989 Huge variations in theisotopic ratio 196Hg/202Hg in some acid-insoluble residuesof Sikhote Alin and other iron meteorites; Earth Planet.Sci. Lett. 96 235–246.

Trivedi B M P and Goel P S 1973 Nuclide production ratesin stony meteorites and lunar samples by galactic cosmicradiation; J. Geophys. Res. 78 4885–4900.

Urey H 1955 The cosmic abundances of potassium, uranium,and thorium and the heat balances of the earth, the moonand mars; Proc. Natl. Acad. Sci. US 41 127–144.

Vanhala H A T and Boss A P 2002 Injection of radioac-tivities into the forming solar system; Astrophys. J. 5751144–1150.

Venkatesan T R, Pande K and Gopalan K 1993 Did Deccanvolcanism pre-date the cretaceous/tertiary transition?Earth Planet. Sci. Lett. 119 181–189.

Wadhwa M, Srinivasan G and Carlson R W 2006 Timescalesof planetary differentiation in the early solar system; inMeteorites in the early solar system II (eds) LaurettaD S and McSween H Y Jr. (Tucson: Univ. of Arizona)715–731.

Wanke H 1965 Der Sonnenwind als Quelle der Urdelgase inSteinmeteoriten Z Naturf; B20a 946–949.

Wieler R, Baur H and Signer P 1986 Noble gases fromsolar energetic particles revealed by closed system step-wise etching of lunar soil samples; Geochim. Cosmochim.Acta 50 1997–2017.

Planetary sciences and exploration: An Indian perspective · The solar system consists of a central...

Documents

Transcript of Planetary sciences and exploration: An Indian perspective · The solar system consists of a central...