Issue 2 - Physical Research Laboratoryacsi/pdf/acsi-issue-2.pdf · Spectroscopic study of Comet...

M A Y 2 0 1 6

( U p d a t e d )

I s s u e 2

P e r i h e l i o n a p p r o a c h o f c o m e t 6 7 p / c g c a r r y i n g p h i l a e

Image Description: Post-perihelion image of comet 67P/C-G taken by PACA member and Director of The Virtual Telescope, Dr. Gianluca Masi on 13th August 2015, at 02:44:13 UT.

CONTENTS

Letters

Claudia J. Alexander (1959 - 2015) 1

Dr. Padma A. Yanamandra-Fisher

On the difficulty in finding new and complex molecules in Comets 3

Dr. Michael J. Mumma

Rosetta: Perihelion approach and Beyond 9

Dr. Matt Taylor

Rosetta Lander Philae: First Data from the surface of a Comet 10

Dr. Stephan Ulamec

PACA Rosetta67P 12

Dr. Padma A. Yanamandra-Fisher

Spectroscopic study of Comet Lovejoy 16

Vikrant kumar Agnihotri

Study of Cometary Atmospheres 17

Smitha V. Thampi

The science of sungrazers 19

Karl Battams

Electron Irradiation of Cometary Ice Analogs - N2O - CS2 ice

mixtures 24

Sarath Raman, Pavithraa Sundararajan

Proposal

Concept for a comet chaser/flyby mission 28

Dr. Shashikiran Ganesh

Thesis

Spectroscopy, Chemical Synthesis of Interstellar Ice Analogues 29

Binukumar G Nair

Events

NCAMP @ ISAMP

Opportunities

Recent Books on Comets

Astroproject

Invitation for Submitting Letters

Claudia J. Alexander (1959 - 2015)Dr. Padma A. Yanamandra-Fisher, Space Science Institute, Boulder, Colorado, USA.(padmayf at gmail.com)

Comet 67P/Churyumov-Gerasimenko(CG), the final target of ESA mis-sion Rosetta, was also the pinnacle

of Dr. Claudia Alexanders extraordinaryprofessional achievements. She lost herbattle with breast cancer on 11 July 2015and left behind a wonderful and multi-faceted legacy from students to scientists.Although journalism was first choice forstudy, Claudia chose science as a compro-mise with her parents to attend schoolin California. With impressive creden-tials such as undergraduate degree fromUniversity of California, Berkeley; mas-ters from University of California, LosAngeles (UCLA), Ph.D. from Universityof Michigan, Claudia was employed atNASA/Jet Propulsion Laboratory (JPL),as an engineer for NASA/Galileo missionto Jupiter. As she rose in her career atJPL, Claudia served as the last ProjectScientist for Galileo mission, as the space-craft was allowed to crash into the planet,Jupiter; served on NASA/ESA/Cassinimission to Saturn; and finally the USNASA Project Scientist for ESA/Rosettamission to comet 67P/CG via several as-teroid fly-bys. Claudia was always seek-ing to improve various procedures to en-hance performance of the mission. Clau-dia was interested in the application anduse of both social media and amateur as-tronomers in support of ESA/Rosetta mis-sion to comet 67P/CG and instrumen-tal for my role as US Rosetta Collabora-tor for Global Amateur Observations of

Comet 67P since 2014. Thanks to hersupport and confidence (and supported byESA/Rosetta Project Scientist, Dr. MattTaylor), a global community of amateurobservers was created on several social me-dia, including Facebook, Flickr, Twitter,etc., with a joint JPL call for participa-tion. At last count, nearly 250 amateurobservers have signed up to participate inthe 67P observing campaign!

On a personal level, Claudia was aremarkable, multi-faceted person; deter-mined to achieve success, as a blackwoman in a field where there were fewand a strong advocate for many importantcauses: from STEM-related causes to theinclusion of indigenous peoples (such asNative American and Hawaiian) to helpbroaden their languages to include astron-omy in a balance with their cultural her-itage. Claudia was a great writer, withseveral successful childrens books, withthe latest book released recently. Clau-dia also was a strong advocate to ensure,as Project Scientist, there were properand adequate resources for the US Teamsfor ESA/Rosetta mission to allow the USTeams to provide the required work prod-ucts for the ESA/Rosetta mission. Shehad a vision of how to integrate and en-hance the various components of such alarge and ambitious mission and empowerpeople to produce their best.

Astrochemistry Letters 1

ESA/Rosetta Project Scientist, Matt Taylor(left), US Project Scientist for Rosetta, ClaudiaAlexander (center) and the authour, Padma A.

Yanamandra-Fisher (right) at the 2014American Geophysical Union (AGU) meeting in

San Francisco, CA, USA.

Besides science, Claudia enjoyed lifewith her devotion to her family she wasunmarried, but her family of parents, sib-lings, nieces and nephews was her solidfoundation. With interests from dancing,writing, horse riding, tennis (she enjoyedwatching Roger Federer) and journalism,Claudia had multi-circles of friends in allthese fields. She impacted and left alegacy of knowledge, role models, and var-ious activities to promote STEM-literacyamongst young girls.

Claudia Alexander was a true trailblazerfor many generations to come. I hopeshe is watching from the heavens as comet67P/CG goes through perihelion on 13 Au-gust 2015, with ESA/Rosetta spacecraft inorbit around the comet.


On the Difficulty of Finding Newand Complex Molecules in CometsDr. Michael J. Mumma, NASA Gaddard Space Flight Center,USA (Michael.J.Mumma at nasa.gov)

Almost from the moment in 1970when I first was exposed to discus-sions on the chemistry of comets,

talk turned to methods for detecting theexpected parent volatiles that could ex-plain the observed free radical species seenin cometary comae (OH, CN, C2, C3, CO+,etc.), and to the possible astrochemical im-plications of the native ices in cometarynuclei from which they derived. Duringthe decadal 70s, I was strongly influencedby extended and continuing discussionswith Armand Delsemme, Bertram Donn,William M. Jackson, and Fred Whippleduring our attempts to define and achievein situ exploration of comets, and throughlaboratory investigations to understandthe molecular processes that might controltheir properties.

Fred Whipple envisioned the cometarynucleus as an icy conglomerate composedof refractory (meteoritic) dust and na-tive (primary) ices, whose sublimationupon warming created the visible comaand tails so familiar to ground-based ob-servers (Whipple 1950). In so doing, headopted and extended Pol Swings sugges-tion that the nucleus of comet Encke con-tained polyatomic molecular ices, whoserelease and dissociation produced the freeradical species observed at optical wave-lengths (Swings 1948a, 1948b). Whippleand Swings suggested that the polyatomicmolecules stored in the nucleus were of in-

terstellar origin, and thus of primary im-portance for understanding planetary ori-gins. Whipple further proposed that wa-ter ice was dominant, with ices of methane,ammonia, and other species present insmaller amounts.

Whipples proposal triggered a decades-long effort to detect the proposed pri-mary (parent) volatiles through astrophys-ical spectroscopy that in 1985 producedthe first definite detections of primaryvolatiles in a cometary coma: hydrogencyanide and water vapor were detectedin comet 1P/Halley using ground-basedradio and airborne infrared observatories(HCN: Despois et al. 1986, Schloerb et al.1986; H2O: Mumma et al. 1986, Weaveret al. 1986). In 1986, in situ spacecraftmeasurements confirmed these discoveries,added ten more species to the suite ofknown primary volatiles, and acquired im-ages of a cometary nucleus for the firsttime (Praderie Grewing 1987, Eberhardt1999). The combined results decisivelyconfirmed the Whipple-Swings model ofthe icy conglomerate nucleus.

Today, we recognize that the composi-tion of cometary ices can sometimes re-flect changes induced by thermal and ra-diation processing, so their identities andabundances can provide central clues tothose aspects of planetary heritage. Yet,extending the ground-based detections ofcometary H2O and HCN to more com-


plex species has proven difficult and was/isstrongly dependent on advances in boththeoretical and observational capabilities.I will use my own experience as an exam-ple, keeping in mind that my experiencesare certainly not unique in struggling toachieve new ends.

My initial foray was an attempt to de-tect infrared emission from NH3 (2, 10 mi-crons band) in comet C/1973x Kohoutek,using a laser heterodyne spectrometerthat utilized a then-developmental lead-salt laser as a local oscillator. Workingday and night for 3 months, my team builtthe spectrometer, mated it to a telescope,and acquired astronomical data but thecomet fizzled and ammonia could not bedetected (Mumma et al. 1975). We nextdecided to use CO2 lasers as local oscilla-tors, building our own since commercialdevices were not well suited to astrophys-ical needs. After perfecting the spectrom-eter, in 1976 we emplaced it at the Mc-Math Telescope at Kitt Peak National Ob-servatory, and then in 1981 moved it tothe NASA IRTF on Mauna Kea. Duringthis period, we studied CO2 non-thermalemission on Mars and Venus, trace gasesin Earths atmosphere, and NH3 in stellaratmospheres and in Jupiter.

We searched for NH3 whenever a suit-able target comet appeared, but repeatedfailures showed that our approach wasfundamentally flawed. Our stellar workrevealed that the gases there were rota-tionally relaxed but vibrationally hot, ow-ing to the collisionally impoverished low-density atmosphere. The eureka momentcame when I realized that the cometaryatmosphere was both very cold and colli-sionally impoverished, suggesting that ra-diative decay from solar-pumped excitedstates would compete favorably againstcollisional quenching, thereby permittingintense ro-vibrational emission lines char-acterized by low rotational temperatures.The optimum wavelength domain for de-tections would also depend on the specificsof the process and the molecule in ques-

tion. I immediately embarked on intenseconsideration of the physics involved, andpresented first thoughts at a conference in1981 (Mumma 1982). Hal Weaver joinedme as a post-doctoral fellow that year, andour greatly expanded version of this ideawas submitted for publication on 8 Marchand accepted on 28 June 1983 (Weaverand Mumma 1984). Our models assumedfluorescence equilibrium. Unknown to us,Crovisier and Encrenaz were developingthe idea in parallel, but they emphasizedLTE rotational populations at 300K sothen-available molecular databases couldbe used for simulations; their paper wassubmitted on 12 March and accepted on26 April 1983 (Crovisier and Encrenaz1983). These two papers form the basisfor the now-widely accepted observationalapproach of solar-pumped infrared fluores-cence, for detection of primary volatilesin comets. Many subsequent papers es-tablished the methodology for vibrationalband systems of molecules having up to 8atoms (C2H6).

This work demonstrated that the primewavelength region for ground-based detec-tions was in the near infrared (3-5 micron),not the mid-infrared as first conceived.It further showed that high spectral res-olution was needed, and that a Dopplershift (to avoid extinction) was needed forvolatiles that had terrestrial counterparts.Moreover, only low rotational tempera-tures were expected. Together, these con-straints drove the initial search strate-gies, leading to detection of water (the2.7 micron fundamental band, 3) in comet1P/Halley using the University of Ari-zonas infrared Fourier Transform Spec-trometer (FTS) on NASA's Kuiper Air-borne Observatory, on 22 and 24 De-cember 1985. Water detections followedin comets C/1987 P1 (Wilson) (in 1987)and 23P/Brorsen-Metcalf (in 1989), buta new approach was mandated by sensi-tivity needs. The team attempted detec-tions of methane in comets Halley and Wil-son, without success, and the large opti-


cal bandwidth of the FTS presented largestochastic noise to the detection system.However, the airborne detections of wa-ter vapor in three comets confirmed thetheoretical predictions of solar-pumped in-frared fluorescence from primary volatiles,and the importance of high resolutionspectroscopy for detecting them.

Even before 1986, it was clear that grat-ing spectroscopy with array detectors of-fered a possible solution to the sensitivityquestion. In 1987, these instruments werebarely emerging, and the first was com-missioned at the NASA IRTF on MaunaKea, Hawaii. CGAS featured a simple 32element linear array behind a cryogenicgrating that narrowed the optical band-width per pixel, thereby reducing shotnoise from the optical background dramat-ically. The first proposed use for cometarydetections was proposed independently bytwo teams that then merged for a Target-of-Opportunity campaign on C/1987 P1(Bradfield) (Brooke et al. 1990). By 1989,2-D array-based (58x62 and 128x128) cryo-genic grating spectrometers were availableat KPNO and UKIRT, and my Team ex-tended the CGAS findings to other cometswith these more powerful instruments.We also teamed with John Lacys team tosearch for OCS and CO near 4.7 and 5.0m in comets C/1990 Levy (DiSanti et al.1992).

After 1992, ground-based capabilities ex-panded rapidly. CSHELL at IRTF en-abled a major breakthrough by couplinghigh resolving power with a 256x256 ar-ray detector. With CSHELL, my teamdetected an emission line of H2O near 2micron in C/1991 T2 (Shoemaker-Levy).CSHELLs upgrade to an InSb detector ar-ray in 1995 permitted detection of H2O incomet 6P/dArrest (Mumma et al. 1995).These detections of H2O emission in twocomets were the first definite detectionsof cometary water from ground-based ob-servatories.

The planned de-commissioning of the

KAO in 1995 emphasized the critical needto develop a new method for detectingcometary water from ground-based obser-vatories. The problem can be stated suc-cinctly: how can we make Earths atmo-spheric water disappear, so as not to ab-sorb the water lines emitted by an ex-traterrestrial source. The successful strat-egy seems obvious once explained and soit is but it was not so obvious before thestrategy was conceived, and then demon-strated!

The breakthrough was dependent on rec-ognizing that fluorescent emission fromsolar-pumped excited quantum statescould penetrate to the ground if thetransition terminated on an excited ro-vibrational level that was not populated atatmospheric temperatures. It was rootedin the discovery of hot-band emission in1P/Halley that was identified in spectraacquired on the KAO; 3 unidentified emis-sion lines were seen in March 1986. I hadbrought a copy of the H2O spectral atlasof Flaud Camy-Peyret to New Zealandfor the March flights, and searched the at-las for these lines. Comparison of the newlines revealed that they belonged to the 3011-010 hot band that emitted in the 2.7micron region. Several years later whenconsidering ways to make terrestrial wa-ter vapor disappear, I realized that fluores-cent transitions that terminated on morehighly excited states would be transmit-ted to the ground, permitting detection ofH2O from ground-based observatories.

In 1990, Michael DiSanti (then my post-doctoral associate) and I considered possi-ble band systems and identified the 111-100 hot-band near 2.0 micron as a fa-vorable candidate. In 1992, we targetedits detection in C/1991 A1 (Shoemaker-Levy) with CSHELL/IRTF and in 1995targeted it in 6P/d'Arrest - detecting wa-ter in these two comets confirmed thestrategy. In 1996, we targeted water innewly discovered C/1996 B2 Hyakutake,detecting many lines of this band and us-ing the resulting water production rate


as the comparator for trace gases CO,CH4, HCN and C2H6 detected in thiscomet (Mumma et al. 1996; Dello Russoet al 2002). Since then this approachhas been extended to more than 10 wa-ter hot bands that span the 1-5 m region,providing a means to quantify the dom-inant volatile in comets simultaneouslywith individual trace species. CSHELLalso cleared the path for detections ofmany primary volatiles in comets Hyaku-take and C/1995 O1 (Hale-Bopp) at 3-5micron (L- and M-bands). In 1999, we ex-tended the strategy to prompt emission ofhighly excited OH produced by water pho-tolysis (an outgrowth of my Ph.D. disser-tation on dissociative excitation of smallmolecules) and later comets providing asecond approach for direct measurementsof water in comets.

CSHELL reigned supreme until 1999,when NIRSPEC at Keck-2 was commis-sioned - the first cryogenic cross-dispersedhigh resolution grating spectrometer ata high altitude site. During the com-missioning run, 7 primary volatiles andOH* (prompt emission) were detected inC/1999 H1 (Lee) (Mumma et al. 2001).Up to 12 primary volatiles have beendetected in a given comet with NIR-SPEC, and all simultaneously with wa-ter. Subsequent instrumental advancesincluded higher resolving power (80,000)and the use of four 1K x 1K InSb ar-rays (CRIRES/VLT) (but single spectralorder) and the imminent commissioning ofiSHELL/IRTF, equipped with a Hawaii-2RG HgCdTe 2K x 2K detector array,cross-dispersion, and ultra high spectralresolution (approx 80,000). An upgradefor CRIRES is now in progress that willprovide similar capability for VLT, withcross-dispersion and with three 2K x 2KHawaii-2RG detector arrays. These facili-ties will provide higher sensitivity, greaterspectral grasp, and improved specificity(higher spectral resolving power), and willenable detections of new and more com-plex volatile species, along woth isotopo-

logues of the more abundant species.

The ever higher spectral resolving power(now approaching resolution of 3 km/s)required similar expansion of laboratorydata on molecular band systems, alongwith advanced quantum mechanical bandmodels hundreds of papers have reportedthese new findings and their application tofluorescence models for comets and otherastrophysical sources.

Today, many primary volatile are mea-sured routinely in a moderately activecomet (cf. Mumma and Charnley 2011).Improvements in sensitivity now permitmeasurement of primary volatiles at abun-dances as small as 100 ppm (relative toH2O). To date, more than 20 cometshave been characterized in this way, andwe now can build an emerging taxon-omy based on cosmogonic parameterssuch as composition, isotopic fractiona-tion, and nuclear spin temperatures ofprimary volatiles, along with dust signa-tures such as crystallinity and mineralogy.The number of detected species has ad-vanced as the observational capabilities ex-panded (Figure 1), and is even now under-going a revolution with the emergence ofIRAM-EMIR and ALMA at radio wave-lengths, and of next-generation powerfulhigh resolution cryogenic spectrometers atinfrared wavelengths (iSHELL/IRTF andCRIRES+/VLT). This trend will expandwith the commissioning of iSHELL/IRTF,CRIRES+/VLT, and the near IR high res-olution and massively parallel spectrom-eters at 30-m class telescopes (E-ELT,TMT, GMT).

While local processing can affect theabundance ratio of bulk species in comets,the abundance ratios of isotopologues aremore robust because few mechanisms ex-ist to modify one isotopologue more effi-ciently than another within the nucleus.For this reason, D/H in water and HCN,14N/15N in nitriles (CN and HCN), and12C/13C in organics (CN and C2) haveassumed high importance. Compared


with terrestrial values, cometary values for12C/13C are consistent in CN and C2, but14N/15N is much lower in CN (15N is en-riched), and D/H varies strongly in wa-ter and hydrogen cyanide. Most cometsshow water more enriched in deuteriumcompared with Earths oceans, but the en-richment in 103P/Hartley 2 was exactlyconsistent with that in ocean water (VS-MOW), showing that comets of this typecould have contributed water to Earth.mHowever, care must be taken when in-

terpreting such limited measurements, es-pecially when the context is unknown.For example, ROSINA reported the D/Hratio in coma water to be enrichedto 3 VSMOW while 67P/Churyumov-Gerasimenko was still far from the Sun(3.7 AU), where water is not yet fullyactivated (Altwegg et al. 2015). Thesurface layer was likely enriched in HDOby fractionation of water emplaced duringthe last retreat from perihelion (the va-por pressure of HDO is lower than thatof H2O), and so an enriched value shouldbe seen as the comet becomes active againon its next return to perihelion. The testwill come when water is fully activatedand both isotopologues are subliming fully,perhaps during the near-perihelion pas-sage. The emerging compositional and iso-topic taxonomies are crucial for extrapo-lating in-depth analytical information ob-tained from the few comets sampled di-rectly, such as 67P, to the many that aresampled only remotely.

The composition and structure ofcometary nuclei hold vital clues to under-standing the formation and evolution ofmatter in the early Solar System (Mumma,Weissman Stern 1993; Irvine et al. 2000;Bockele-Morvan et al. 2004; Mummaand Charnley 2011). Relating the sam-pled comets to the diverse populations oficy planetesimals is a critical step whentesting models of the evolution of ma-terial from the natal interstellar cloudcore through entry into the protoplanetary

disk, possible processing in the disk, for-mation of the nal icy bodies, and injec-tion into their cosmic reservoirs. Withthe aid of dynamical models, the emerg-ing taxonomies will also help to assess thesignicance of each cometary class for ex-ogenous delivery of organics and water toterrestrial planets.

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Rosetta: Perihelion approach and Beyond

Dr. Matt Taylor, Scientific Support Office, Rosetta Mission (mtaylor at cosmos.esa.int)

Alot has happened in the world of

Rosetta in the last months. Wehave been orbiting the Sun along

side Comet Churyumov Gerasimenko fora year and on 13th August we will reachperihelion.

In the last year we have become moreand more familiar with out target, a duallobed comet, which we affectionately referto as duck-shaped. This frozen body ofdust and ices is around 4 km across andits outer atmosphere or coma currentlystretches well over 100, 000 km into a tail,based on estimations from ground basedobservations. Ground based observationsare very important to Rosetta, and ontop of professional observations, we havea very active amateur connection, coordi-nated by Padma A. Yanamandra-Fisher aSenior Research Scientist at the Space Sci-ence Institute, USA.

On 11 July Rosetta lost a dear colleague,Dr Claudia Alexander, the US project sci-entist who passed away suddenly. Claudiaworked for NASA at JPL. She was an em-inent planetary scientist and was deeplyinvolved with the Rosetta Mission as USRosetta project scientist. She was passion-ate about outreach, including engagingamateur astronomers through the ground-based observing campaign of Rosettas tar-get comet, 67P/ChuryumovGerasimenko.Claudia was also very well known forher role in NASAs Galileo and Cassiniprojects. She will be greatly missed. Last

month you heard from Alan Stern andNew Horizons. We have some connectionthere, as Alan is Rosetta colleague also asPI of the Alice instrument. In fact, we ac-tually pointed Rosetta at Pluto when NewHorizons was doing its fly by!

In July, we released the first results ofPhilae, from the surface of the comet. Theresults indicated the surface of the cometto by covered by a thin dust layer with avery hard subsurface. We detected a num-ber of organics molecules, some of whichare key in playing a role in pre-biotic syn-thesis of amino acids, sugars and nucle-bases: the ingredients of life. It is impor-tant to stress that we do not see life itselfthough. Only the building blocks. Theexistence of such complex molecules in acomet, a relic of the early Solar System,imply that chemical processes at work dur-ing that time could have played a key rolein fostering the formation of prebiotic ma-terial. We found little evidence of an in-trinsic magnetic field indicating that mag-netic field would have had little role toplay in the aggregation processes as thecomet was formed. We are beginning tosee significant activity at the comet, soPerihelion is going to be an exciting time.,as one can see from recent images.

Following this month, the mission willcontinue through to September 2016,where we will de-orbit the Rosetta space-craft into the comet, landing for a 4th time!


Rosetta Lander Philae: First Datafrom the surface of a CometDr. Stephan Ulamec, German Aerospace Center, DLR, 51147 Cologne. (Stephan.Ulamec at dlr.de)

November 12th, 2014, when Philaelanded on comet 67P/Churyumov-Gerasimenko, this was the first time

in history, when in-situ investigation of acometary nucleus became possible.

Comets are believed to be 'left overs'from the time of the formation of the solarsystem, about 4,6 billion years ago. In ad-dition they are believed to contain organicmaterial, possibly triggering the formationof life on Earth.

CAD model of the Philae Lander, withinstruments deployed

Philae is part of the ESA (EuropeanSpace Agency) Rosetta mission, and wasprovided by an international consortium,led by the German Aerospace Center,DLR, with large contributions from MPS,

CNES, ASI and other partners. It was at-tached to the mother spacecraft during itsten years of cruise. Only, when Rosetta ar-rived at the target comet, in August 2014,it became possible to characterize the nu-cleus with orbiter instruments and to se-lect an appropriate landing site.

The Lander was separated from Rosettaat an altitude of about 22 km and touchedground after seven hours of ballistic de-scent. It was intended to be anchoredby two harpoons, but, unfortunately thosefailed to fire, so Philae was bouncing offand landed after several ground contactsabout 1km from the original site in an areanow called 'Abydos'

Scientific data were gained during de-scent, the bounces and at Abydos. All ofthe ten scientific instruments aboard theLander could be operated at least once,until the batteries depleted after about64 hours after separation. Unfortunately,Philae is now at a spot which is poorlyilluminated and after the first scientific se-quence in November, it took eight monthstill 67P (and Philae) were close enough tothe sun, and the Lander could again estab-lish radio contact with the mother space-craft.

The terrain is characterized by roughrock-like structures. (Note that the ma-terial is not expected to be rock, but sin-tered, porous ice-dust agglomerate with


high organic content.) The instrumentMUPUS, attempting to hammer a pene-trator into ground indicated a surprisinglyhigh crushing strength of at least 4MPa!

Two mass spectrometers on board theLander, COSAC and Ptolemy, deliv-ered spectra immediately after the firsttouch-down. While COSAC identified16 molecule species, including amines,amides and alcohols (some of which are ofprebiotic relevance), Ptolemy found clearindication for organic polymers in thecometary material.

CONSERT, a radar tomographerallowed insight into the global inter-nal structure of the comet nucleus,indicating a rather homogeneous in-terior, with a permittivity of ∈=1.27 corresponding to a porosity of 75 to85 percent.

ROMAP, a fluxgate magnetometer iden-tified a lack of remnant magnetization ofthe comet surface, which is interpretedthat there was no significant magnetic fieldin the planetary disc, when 67P formed.

The camera ROLIS, looking 'downward'provided fascinating images of the firsttouch-down site with a resolution op to1cm. The terrain is characterized bycoarse regolith and embedded boulder-likefeatures.

The teams will continue to work on pos-sibilities to command Philae, so that morescientific data can be obtained until the he-liocentric distance will become too largeagain to power the Lander (probably endOctober 2015).

Philae provided unique science on struc-ture and composition of a cometary nu-cleus. Part of these results will enhancethe planning for future missions to comets,

particularly those foreseeing landing orsampling.

References

J. Biele et al., The landing(s) of Phi-lae and inferences on comet surface me-chanical properties. Science 349, aaa9816

(2015).

S. Ulamec, et al., Rosetta LanderPhilae: landing preparations, Acta

Astron. 107, (2015).

J.-P. Bibring et al.,

67P/Churyumov-Gerasimenko sur-face properties as derived from CIVApanoramic images. Science, 349,aab0671 (2015).

T. Spohn et al., Thermal and mechan-ical properties of the near-surface layersof comet 67P/Churyumov-Gerasimenko.Science 349, aab0464 (2015).

F. Goesmann et al., Organic com-pounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC massspectrometry. Science 349, aab0689

(2015).

P. Wright et al., CHO-bearing or-ganic compounds at the surface of67PChuryumov-Gerasimenko revealed byPtolemy.Science 349, aab0673 (2015).

W. Kofman et al., Properties of the67P/Churyumov-Gerasimenko interiorrevealed by CONSERT radar. Science,

349, aab0639 (2015)

H.-U. Auster et al., The nonmagneticnucleus of comet 67P/Churyumov-Gerasimenko. Science 349, aaa5102

(2015).

S. Mottola et al., The structureof the regolith on 67P/Churyumov-Gerasimenko from ROLIS descentimaging. Science 349, aab0232 (2015).


PACA Rosetta67P: Leveraging Amateur Astronomers andSocial Media in Support of ESA/Rosetta Mission to Comet67P/Churyumov-Gerasimenko (CG)

Dr. Padma A. Yanamandra-Fisher, Space Science Institute, California, USA.(padmayf at gmail.com)

Rosetta Mission to Comet67P/CG and Need for Ground-based Observational Support:

The European Space Agency (ESA)Rosetta mission (with 18 European part-ners and NASA), launched in 2004, isan ambitious engineering and science mis-sion. The spacecraft consists of an or-biter (Rosetta) and lander (Philae), witha combined suite of 21 instruments torendezvous with a comet, drop a landeron the comet to study it in situ, orbitthe comet and escort it into the inner so-lar system to its perihelion, all the whilelearning about the composition, the ini-tiation and sustaining of activity of thecomet. After encountering two asteroids,an earth swing-by, the Rosetta spacecraftexit from a near-3 year hibernation on 20January 2014 to resume its journey to itsfinal destination, comet 67P/Churyumov-Gerasimenko (67P). The key milestonesfor the mission are: (a) encounter withits final target, comet 67P/Churyumov-Gerasimenko (or 67P), in May 2014; (b)orbit insertion in August 2014 and map-ping of 67P; (c) release of lander, Phi-lae, in November 2014; and (d) escort67P on its journey to perihelion in August2015. The target for the Rosetta mission,67P/Churyumov-Gerasimenko (67P), dis-covered by Klim Churyumov and SvetlanaGerasimenko in 1969, is a short-periodcomet, low orbital inclination, and influ-

enced by Jupiters gravity field. Suchcomets are know as Jupiter Family comets(JFC) and considered to originate in theKuiper Belt, just outside the orbit of Nep-tune. Since its discovery in 1969, thecomet has been observed on six appari-tions, with an orbit of 6.45 years. Frompast apparitions, it is known that thecomet becomes active about a month be-fore perihelion, with at least three activejets and a long tail that persists months af-ter its perihelion passage seasonal changesof the comet. Rosettas close-up views ofthe comet nucleus and the observationsof the initiation of the comets activity in-dicate the nucleus is bi-lobed or rubberducky shaped, very dark and has an or-bital period of 12 hours; with the nar-row/neck part of the nucleus exhibitingthe first jet activity was observed. Globalobservations from Earth are still neces-sary, to compare with previous appari-tions and relate observed changes withthe varying activity level. Therefore, theRosetta mission sought ground-based ob-servational support from both professionaland amateur astronomers worldwide. Theadvantages of professional facilities allowsthe use of large telescopes to be able to ac-quire data of the comet; however, since thecomet is expected to be faint (around mag-nitude 12) even at closest approach, a ded-icated global international network of am-ateur astronomers is necessary to be ableto observe the comet whenever it is avail-


able at their particular location and builda temporal and spatial data base of obser-vations. The ground-based observationsconsist of two networks: (i) professionalobservers and (ii) amateur astronomers,each with a coordinator, to ensure thebest observations are acquired in supportof the mission and to liase with the mis-sion science teams. As part of the sup-port for ESA/Rosetta mission, a comple-mentary two-pronged ground-based obser-vational program was initiated late 2013:a professional observer component, over-seen by Dr. Colin Snodgrass, Open Uni-versity, England and an amateur observercomponent, overseen by Dr. Padma A.Yanamandra-Fisher, Space Science Insti-tute, USA. As Global coordinator foramateur observations, Dr. Yanamandra-Fisher initiated a core network of ama-teur observers, based on the legacy of herwork with the NASA/CIOC and the equiv-alent social, amateur observer networksfor Comets C/2012 S1 (ISON) and C/2013R1 (Siding Spring). The resulting networkof observers is the basis of the Facebookgroup, PACA Rosetta67P, including mem-bers of the media, educators, Rosetta mis-sion managers and team members in addi-tion to the observer network. Formed inJanuary 2014, the observer network hasimaged comet 67P/CG from March 2014,when the comet was just detectable byamateurs, at a magnitude of 19-20 andavailable in the southern latitudes, withPeter Lake, of iTelescope.net in SidingSpring, Australia, being one of the firstobservers. Since then, regular contribu-tions by other PACA observers such asEfrain Morales (Puerto Rico, USA), An-dres Chapman (Argentina, South Amer-ica), Rolando Ligustri (Italy), have formedthe basic timeline of the comets chang-ing magnitude with time or its light curve.As the comet became available at otherlatitudes, other PACA members/imagershave joined the campaign, with observersas far north as Essex, England (Dave Ea-gle, Peter Carson, Nick James) contribut-ing data.

Leveraging Amateurs and SocialMedia:

The availability and access to variousforms of social media with the immedi-ate dissemination of observations and re-sults, while being able to engage withother professional and amateur colleaguesglobally. Perceiving a need for an orga-nized connection between the Pro-Am ob-server communities, I created The PACAProject from my earlier Pro-Am effortsin support of NASA Comet Observingcampaigns (CIOC) for comets C/2012 S1(ISON) in 2013, which dramatically dis-integrated on its perihelion day of 28November 2013 and C/2014 A1 (Sid-ing Spring), which flew by very closeto Mars on 19 October 2014. Cur-rently, The PACA Project is involvedin the Ground-based Amateur campaignto observer ESA/Rosetta missions target,67P/Churyumov-Gerasimenko (CG) thatis en route to its perihelion on 13 Au-gust 2015. Since the formation of its Face-book group, PACA Rosetta67P, in Jan-uary 2014, the group consists of a coregroup of amateur astronomers, (their lo-cations shown as red dots in Figure 1),professional observers and members of themission teams, including the two projectscientists (Drs. Matt Taylor/ESA andClaudia Alexander/NASA/JPL).

The various social media, creative lo-gos, bookmarks illustrating the Egyptiantheme used by Rosetta to name the vari-ous regions of the comet nucleus and thelanding site for Philae lander; and ap-propriate QR codes relating to the so-cial media are shown, created by variousmembers of the Facebook group, PACARosetta67P.

JPL/PACA Call for Participa-tion:

Since November 2014, the comet was be-hind the sun or conjunction, and there-fore not visible to observers on ground.Following the first recovery detection


of the comet of magnitude 16.9, post-conjunction by three French amateur ob-servers (Maury, Bosch and Soulier) usinga remote observatory in Chile on 12/13April 2015, JPL issued a call for participa-tion to the amateur community (link canbe found at:http://rosetta.jpl.nasa.gov/

rosetta-science-blog/be-part-excitement

with mirror coverage at ESA Rosettablog site found at:http://blogs.esa.int/rosetta/2015/04/

16/

to announce the recovery of the cometand to encourage both professionals andamateurs to observe and characterize thecomet through perihelion and severalmonths post-perihelion, when the cometssouthern hemisphere (currently dark dueto lack of insolation) will become verybright for a short time, even as the Rosettaspacecraft continues it high resolution spa-tial images of the comet exhibiting increas-ing jet activity over its surface, simultane-ously providing two unique views : closein to the nucleus and the far-field globalimage of the comets coma and tail.

The amateur observers data will be col-lected and crowd sourced by both profes-sionals and amateurs to characterize thecomet and model it activity. The datawill also be archived in ESA/Planetary Sci-ence Archive (PSA) for its legacy valuetoo. While the spacecraft, Rosetta, in or-bit around 67P/CG nucleus since August

2014, provides high resolution and multi-spectral images of the comet and its ac-tivity; maps the location and detection ofvarious chemical species, etc., the ground-based observations (both professional andamateur) provide a complementary per-spective of the evolution of the cometscoma and tail. Figures below indicate theevolution of the comet and its tail, frommagnitude of 16 to 13, as expected by theobservations of its previous apparitions.

Latest image from 12 August2015, a day before perihelion:

As we await eagerly the perihelion pas-sage of the comet and images/data fromRosetta spacecraft, here is one of thelatest images of comet 67P/CG, sent inby the amateur astronomer, Jean-GabrielBosch, imaged from the Space Observa-tory (Chile), showing a bright nucleus anda faint dust tail.

This historic moment in cometaryobservations will be upon us in afew hours on 13 August 2015, ascomet 67P/CG goes through itsperihelion passage:

with a spacecraft in orbit around thecometary nucleus and characterize the ac-tivity with several different instrumentsto determine the nature of activity, abun-dance of chemical species through perihe-lion passage while ground-based profes-


sional and amateur observations will pro-vide a timeline/reference for the Rosettaobservations. The ground-based observa-tions will provide another important re-source: a bridge between legacy data setsof previous apparitions and future appari-tions as the comet returns next in approx-imately 2021/22. A new chapter in thecometary physics is being written withESA/Rosetta mission. Congratulations tothe ESA and NASA teams for a great en-gineering marvel that has provided bothnew perspectives on cometary activity andengaged several generations of audiences

globally.

Finally, this article is a tribute to thededicated work of the late Dr. Clau-dia Alexander, the US NASA ProjectScientist, who passed away on 11 July2015, on the eve of the pinnacle of bothESA/Rosetta mission and her professionalcareer.

For more images of comet 67P/CG fromPACA network:https://www.flickr.com/photos/

pro-amastronomy/sets/72157641578093805


Spectroscopic study of Comet Lovejoy

Vikrant kumar Agnihotri, Cepheid’s Astronomy Club, Kota, Rajasthan (agnihotri80.vk at gmail.com)

We carried out the imag-ing/spectroscopy of cometC2014Q2 Lovejoy as on

24.12.2014, UT: 18:47:06. The cometimaged at sloan g’2 band (400nm-550nm)wavelength, also the spectrum capturedusing star analyzer grating (SA-100)within filter wheel fixed with 0.2m SCTtelescope mounted on sky-watcher NEQ6mount.

The spectral image captured oversensor KAF8300 (Atik383L+ cooledmonochrome CCD) coupled with filterwheel assembly The comet image man-ually guided over the field of view ofCCD using double cross view applicationof APT- Astro Photography Tool. Thetelescope mount was commanded usingEQ-direct (ASCOM platform supported)+ Starrynight (SN7). The 50 imagedare stacked in maximDL and false colorimaged created in DS9. The spectral im-age files processed in RSpec spectroscopysoftware.

We examined the dia-atomic carbon(C2) and NH2 predominantly in comet.


Study of Cometary Atmospheres

Smitha V. Thampi, Space Physics Laboratory (smitha vt at vssc.gov.in)

Comets are regarded as the most pris-tine objects of the solar system,which preserve the information on

the primitive solar nebula because theyhave not undergone much thermal evolu-tion (except for the outer irradiation man-tle). Comets are usually inert at large he-liocentric distances, but develop a comaand tail when they come close to the Sunas the gas sublimes and evolves off the sur-face and dust is also dragged along. Ini-tially, the solar wind permeates the thincomet atmosphere formed from sublima-tion, until the size and plasma pressure ofthe ionized atmosphere define its bound-aries. Water (H2O) ice is the most domi-nant volatile in most comets. In additionto this, cometary ices also consist of CO2

and CO molecules and modest amountsof molecules like CH4, NH3, H2CO andCH3OH, probably contained within com-plex organic compounds.

The chemical composition of the cometsis mostly assessed by remote sensing -spectroscopic observations. In the caseof H2O, the infrared emissions are diffi-cult to observe from ground because ofstrong attenuation by the terrestrial atmo-sphere. Water does not have any spectro-scopic transitions in UV or visible regionsof solar spectrum. Hence, the emissions ofthe dissociative products of H2O (OH, Oand H) is studied to understand the pro-duction and spatial distribution of H2O incomets (e.g. Furusho et al. 2006). Theprimary products of dissociation of H2O

molecule are H and OH. A small fractionis O and H2. The [OI] lines (green (5577Ao) and red-doublet (6300, 6364 o) lines)are prompt emissions of metastable oxy-gen atoms that have been observed in sev-eral comets, and the value of the inten-sity ratio of green to red-doublet (G/R ra-tio) has been used to identify the whetherthe parent source of these lines is H2O orCO2/CO in the coma of comets (Bhard-waj and Raghuram, 2012). The H2O pro-duction rates in comets are also derivedby observing the emissions from its dis-sociative products, like OH (18-cm, 3080Ao), O (6300 Ao) and H (Lyman-alpha).Recently, Decock et al (2015) studied theG/R ratio in four comets and found thatthe ratio varies as a function of nucleo-centric projected distance due to the colli-sional quenching of O(1S) and O(1D) bywater molecules in the inner coma. Itwas also found that that the main parentspecies producing O(1S) and O(1D) in theinner coma is not always the same. Theyalso discovered that the [OI] line emissionsmay be used to estimate the CO2 relativeabundance in comets (Decock et al., 2015).Similarly, the CO2 production rate incomets has been derived using Cameron-band emission of CO molecules, assumingthat photodissociative excitation of CO2 isthe main production mechanism of CO inthe metastable state (Weaver et al., 1997).However, model calculations by Bhardwajand Raghuram (2011) showed that photo-electron impact excitation of CO is alsosignificant for the Cameron band emis-


sion, together with dissociative excitationof CO2.

Apart from remote-sensing, informationon the composition of comets is obtainedfrom in situ mass spectrometry, for in-stance comet Halley was observed withthe mass spectrometers of VEGA andGiotto. The more recent Rosetta space-craft had three mass spectrometers, capa-ble of studying the atmospheric composi-tion: ROSINA (on the orbiter), Ptolemyand COSAC (both on the Philae Lan-der) and a suite of plasma analysers. Us-ing the Rosetta Plasma Consortium ioncomposition analyzer, Nilsson et al (2015)studied the evolution of water ions onthe Jupiter family comet 67P/Churyumov-Gerasimenko. The first in situ measure-ment of N2 on comet 67P/Churyumov-Gerasimenko was made by the ROSINAmass spectrometer aboard the Rosettaspacecraft. Actually, though molecular ni-trogen (N2) is considered to be the mostabundant form of nitrogen in the proto-solar nebula, N2 was not detected previ-ously in comets (Rubin et al., 2015). TheROSINA, being a Double Focusing MassSpectrometer (DFMS) has a high massresolution of m/m about 3000 at 1 per-cent at atomic mass per unit charge 28m/q, allowing the separation of N2 fromCO (Rubin et al., 2015). Very recently,Goesmann et al (2015) reported the pres-ence of a suite of 16 organic compounds,including many nitrogen bearing speciesand four compounds methyl isocyanate,acetone, propionaldehyde and acetamydeon comet 67P/Churyumov-Gerasimenko,that had not been previously reported incomets. The measurements were from

COSAC (COmetary Sampling And Com-position) mass spectrometer, and the spec-trum was obtained 25 minutes after Phi-laes initial touchdown. These new ob-servations would definitely lead to newinsights regarding the chemical composi-tion of comets, the production of volatilesin comets and about the formation ofcometary grains from protosolar nebula.

References

Bhardwaj and Raghuram, The

Astrophysical Journal, 745:1 (18pp),

doi:,:10.1088/0004-637X/745/1/1 (2012)

Bhardwaj and Raghuram, Mon. Not. R.

Astron. Soc. 412, L25L29 (2011)

Decock et al., Mon. Not. R. Astron.

Soc. 412, L25L29 (2011)

Furusho, R., Kawakitab,

H., Fusec, T., Watanabe, J.,

Adv. Space Res. 9, 19831986.

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(2006)

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J. B., ApJ, 422, 374, (1994)


The Diverse Science of Sungrazing Comets

Karl Battams, US Naval Research Laboratory, Washington DC (karl.battams at nrl.navy.mil)

October 2015 marked the 50th an-niversary of the spectacular peri-helion passage of one of the most

celebrated comets in modern astronomy.Discovered September 18, 1965, cometC/1965 S1 (Ikeya-Seki) passed a mere468,000 km from the solar surface on Oc-tober 21, 1965, attaining a peak estimatedbrightness of magnitude -10, and being vis-ible to the naked eye in broad daylight.Comet Ikeya-Seki was a Sungrazing cometand a member of an extended populationof comets known as the Kreutz group,whose origin dates back to an unidenti-fied parent object that fragmented millen-nia ago. Ikeya-Seki was the seventh ob-served member of the Kreutz group, withan added eighth being observed in 1970,yet despite these observations, little wasknown of the Kreutz population. Kre-sak (1966) hypothesized a dense meteorstream in the Kreutz orbit, but the na-ture of the objects rendered ground-basedimaging of all but the brightest mem-bers an impossibility. In 1979, the SOL-WIND coronagraph on the USAF P78-1 satellite made the first space-based de-tection of a Kreutz-group comet (Mars-den, 1981, Michels et al. 1982). Sev-eral more detections followed from SOL-WIND and the later Solar Maximum Miss-sion (SMM), leaving a known populationof around twenty Kreutz objects by thelate 1980s.

In 1995, the launch of the jointESA/NASA Solar and Heliospheric Obser-vatory (SOHO) heralded the dawn of a

new era of comet observations. The coro-nagraph telescopes aboard the spacecraft- designed to block direct sunlight and ob-serve the Suns corona in visible in light- yielded not only unprecedented viewsof solar phenomena such as coronal massejections, but also a wealth of detections ofsmall, previously unknown sungrazing andsunskirting comets. Since routine opera-tions began in 1996, SOHO has discoveredover 3,000 comets.

Approximately 85 percent of these ob-jects are Kreutz sungrazers, with the re-maining 15 percent belonging primarilyto one of four new families of cometsidentified solely by SOHO. The launchof the twin NASA Solar Terrestrial Re-lations Observatory (STEREO) in 2006added two additional coronagraphs andtheir unique Heliospheric Imagers (HI) toimage the near-Sun environment with un-precedented sensitivity and viewing cir-cumstances very different from SOHO.These instruments have yielded extraordi-nary views of comet tails interacting withthe solar wind, as well as discovering overfifty new comets.

The wealth of observations and discover-ies of near-Sun and sungrazing comets nowoffered to us by the SOHO and STEREOheliospheric observatories present myr-iad opportunities for studying the manyunique aspects of these objects. We canbroadly separate these focus areas intothree categories - evolution, dynamics,


and physical properties - though overlapclearly exists between all three.

Regarding evolution, we can perhapsfundamentally look back to the progeni-tor of the Kreutz-group, which at someunknown time, and for unknown reasons,fragmented into some unknown number ofchild objects. The objects subsequentlyfragmented and, via a process referredto as cascading fragmentation (SekaninaChodas, 2007), led to the present day sce-nario in which around two-hundred smallKreutz objects are discovered each year.This fragmentation process is not uniqueto the Kreutz group, or sungrazing comets.The so-called Marsden and Kracht popu-lations of near-Sun object, first identifiedby SOHO, are related families with orbitalperiods of around five years. This shortorbital period has enabled SOHO to ob-serve repeat passages of certain individ-ual objects, including one object observedto return as a pair of objects at the nextapparition (Marsden et al., 2005), givingus indirect observation of an ongoing cas-cading fragmentation process. The Mars-den and Kracht populations follow differ-ent orbital paths, but it has been welldemonstrated (Ohtsuka et al, 2003, Sekan-ina Chodas, 2005) that they once werepart of the same system, which itself hasdirect ties to comet 96P/Machholz, theQuadrantid and Daytime Arietid meteorstreams, and perhaps asteroid 2003 EH1(Jenniskens, 2004). Thus through discov-ery and observation of near-Sun and sun-grazing populations, including other newlyrecognized families such as the Meyer andKracht II groups (Marsden, 2005), andnumerous individual pairs of objects ob-served by SOHO and STEREO, we canbegin to describe and understand the com-plex evolution of inner solar system ob-jects.

Such studies of comet family evolutionnaturally lead us to the question of dy-namics. What is happening to these ob-jects as they fragment? How do seem-

ingly diverse bodies and populations relateto one-another, and over what time-scaleshave the apparent changes occurred? Inmany cases we can look to gravitationalinteractions - specifically and most obvi-ously with Jupiter - as a primary driverof the dynamic evolution of cometary or-bits. However, comets also experiencenon-gravitational forces - a result of thephysical activity of the comet leading toa jet effect whereby sublimation of waterice from the comets surface creates a mo-mentum transfer that gradually alters anobjects orbit over time. These effects aredescribed by empirical laws first derivedby Marsden et al (1973), and remain rou-tinely adopted to describe cometary or-bits. Recent studies of sungrazing comets,however, are beginning to question the ex-tent to which these laws can be applied tocomets undergoing the extreme sublima-tion we expect in the near-Sun environ-ment. In the case of C/2012 S1 (ISON),for example, numerous observers reportedsignificant deviations of the comet from itsnominal and well-described orbit in thedays preceding perihelion (e.g., Cordineret al. 2014). Similar effects were observedin C/2011 W3 (Lovejoy), and have beentheorized for most of SOHOs small Kreutz-group comets. Regarding comet ISON, itis firmly established that by the last fewdays of its existence, the comet had un-dergone at least one major fragmentationevent, and was likely experiencing ongoingand catastrophic events until it finally va-porized (Knight Battams, 2014, SekaninaKracht, 2014, Combi et al. 2014). Sekan-ina Kracht (2014) demonstrated that thedeviations in comet ISONs orbit couldbest be explained by extreme momentumtransfer driven by sublimation of sodiumand not water, as typically assumed in thestandard model of non-gravitational forces(Sekanina Kracht, 2015).

When we consider the concept of ex-treme sublimation we must also considerthe physical (and chemical) properties.Comets have been remotely observed spec-


troscopically for decades, and we now havethe ESA Rosetta mission, for example,performing very detailed in situ studiesof the physical and chemical properties ofcomet 67P/Churyumov-Gerasimenko. Itis reasonable to assume that many of theproperties of comets like 67P transfer tosungrazing comets, but particularly in thedays and hours surrounding perihelion wecan argue that sungrazers become theirown distinct class of comet, complete withproperties we may not ordinarily assignto classical comets. Cometary activity isdriven by solar radiation, with various icessublimating at different distances from theSun. However, when we consider sungraz-ing comets, we can no longer assume anobject that sublimates typical cometaryvolatiles. Studies looking at the sublima-tion distances of inner solar system dust(Mann et al. 2004) show that once insideapproximately 14 solar radii (approx. 0.07AU), non-volatiles such as olivines and py-roxenes begin sublimating, and are ulti-mately followed by much harder materi-als such as quartz. For sungrazing comets,there comes a point at which the entiresurface of a comet is unstable, regardlessof composition. The physical and chemi-cal processes at this stage are both com-plex and poorly understood, but collec-tively lead to the ultimate destruction ofmost sungrazing comets. Mechanisms forthis destruction mostly center on contin-ual breakup of the object into small pieces,but the physical mechanism for that ini-tial breakup itself is not well understood.Tidal (gravitational) forces only becomerelevant within approximately 2 solar radiifrom the Sun (Knight Walsh, 2013), how-ever, the overwhelming majority of Sun-grazing comets are vaporized or entirelyfragmented before they reach this close tothe Sun (Biesecker et al. 2002, Knightet al. 2010). Processes such as sublima-tion pressure (Steckloff et al. 2015) havebeen proposed as an alternative to simplesublimation-driven mass loss models, butthese remain theoretical with little to nodirect observational support.

The wealth of observations, and theunique nature of sungrazing comets, offerrare insight beyond just studies of comets.The solar physics community has, in re-cent years in particular, embraced cometsas unique and valuable probes of the solarwind and the near-Sun environment.

The solar wind was first theorized due tothe presence and direction of comet tails.Today, with instruments such as the Helio-spheric Imager (HI) on the STEREO mis-sion, we are able to observe comet tailsin extreme proximity to the Sun, and seetheir interaction with both the solar windand coronal mass ejections (CMEs). In2007, STEREO-HI witnessed a CME com-pletely rip the tail from comet 2P/Encke(Vourlidas et al. 2007). The STEREO-HI instrument has subsequently observedseveral comet tails strongly interactingwith the solar wind, enabling unique mea-surements of the speed (Ramanjooloo etal. 2014) and turbulence (DeForest etal. 2015) of the solar wind, and address-ing critical questions in solar and spaceweather studies. Data returned by theUltraviolet Coronal Spectrometer (UVCS)instrument on SOHO has similarly yieldedunique insights into the solar wind proper-ties near the Sun (Giordano et al. 2015).

Sungrazing comets that survive to nearor beyond perihelion enable detailed stud-ies of the solar corona and its complexmagnetic fields. In July 2011, the NASASolar Dynamics Observatory (SDO) wit-ness the complete destruction of cometC/2011 N3 (SOHO) in extreme ultravio-let (EUV) observations of the solar corona.(Schrijver et al. 2012). Later that sameyear, comet C/2011 W3 (Lovejoy) madea spectacular passage through the corona,with observations from SDO and both ofthe EUV imagers on STEREO showing acomplex striated tail pattern behind thecomet. It was found that sublimated ma-terial released from the comet was beingrapidly ionized to a state strongly pre-


ferred by EUV imagers, and was seen toilluminate the solar magnetic field lines inthe inner corona (Bryans Pesnell, 2012).These one-of-a-kind observations enabledunique studies of the Suns field lines, andtemperatures and electron densities of thesolar corona, and allowed models of the en-vironment to be validated against directobservation of a well-defined probe in thatregion (Raymond et al. 2014).

Thus near-Sun and sungrazing cometsact as wind-socks and probes of a largelyunexplored environment, and offer in-sights that go far beyond studies of comets.Advances in both cometary and solarphysics have been enabled directly by thepast and ongoing detections and observa-tions of comets by heliospheric observa-tories. The planned ESA Solar Orbiterand NASA Solar Probe Plus missions holdfuture promise with their high-resolutionheliospheric imager instruments that willstudy the near-Sun region as the space-craft evolve on orbits that will ultimatelytake them to within 12 solar radii of theSun and operate in the same domain asthe comets we have been studying. TheSDO and SOHO spacecraft, and one ofthe STEREO spacecraft, currently con-tinue routine operations, with the authoracting as liaison to the operation teamsto inform them of potential comets of in-terest, perhaps requiring special observingsequences. The NASA-funded SungrazerProject, led by the author, continues toenable citizen science discoveries of sun-grazing comets on a daily basis.

References

Biesecker, D. A.; Lamy, P.; St. Cyr,

O. C.; Llebaria, A.; Howard, R. A.m

2002, Sungrazing Comets Discovered with

the SOHO/LASCO Coronagraphs 1996-1998,

Icarus, 157, Issue 2, p. 323-348

Bryans, P.; Pesnell, W. D., 2012,

The Extreme-ultraviolet Emission from

Sun-grazing Comets, ApJ 760:18

Combi, M. R.; Fougere, N.; Mkinen,

J. T. T.; Bertaux, J.-L.; Qumerais,

E.; Ferron, S., 2014, Unusual Water

Production Activity of Comet C/2012

S1 (ISON): Outbursts and Continuous

Fragmentation, ApJ 788:7

Cordiner, M. et al, 2014, Mapping

the Release of Volatiles in the Inner

Comae of Comets C/2012 F6 (Lemmon) and

C/2012 S1 (ISON) Using the Atacama

Large Millimeter/Submillimeter Array,

ApJL, 792:L2

DeForest C.E., Matthaeus, W.H.,

Howard, T.A., Rice, D.R, 2015,

Turbulence in the Solar Wind Measured

with Comet Tail Test Particles, ApJ

812:108

Giordano, S.; Raymond, J. C.; Lamy,

P.; Uzzo, M.; Dobrzycka, D., 2015,

Probing the Solar Wind Acceleration

Region with the Sun-grazing Comet

C/2002 S2, ApJ 798:47

Jenniskens, 2004, 2003 EH1 is the

Quadrantid Shower Parent Comet, ApJ

127:3018-3022

Knight, M. M.; A’Hearn, M. F.;

Biesecker, D. A.; Faury, G.; Hamilton,

D. P.; Lamy, P.; Llebaria, A., 2010,

Photometric Study of the Kreutz Comets

Observed by SOHO from 1996 to 2005,

Astr. Journal, 139, Issue 3, pp.

926-949

Knight, M. M., Battams, K., 2014,

Preliminary Analysis of SOHO/STEREO

Observations of Sungrazing Comet ISON

(C/2012 S1) around Perihelion, ApJ,

782L, 37

Sungrazing Comet ISON (C/2012 S1)

around Perihelion, ApJ, 782L, 37 Knight,

M.M., Walsh, K.J., 2013, Will Comet

ISON (C/2012 S1) Survive Perihelion?,

ApJ, 776:L5


Kresak, L., 1966, A Meteor Mission

into the Orbit of Sun-grazing Comets,

Bulletin of the Astronomical Institute

of Czechoslovakia, vol. 17, p.188

Mann, I. Kimura, H., et al, 2004,

Dust Near the Sun, Space Science Rev.,

110:269-305

Marsden, B.G, Sekanina, Z., Yeomans,

D.K, 1973, Comets and nongravitational

forces. V., Astronomical Journal, Vol.

78, p. 211

Marsden, B.G., 1981, Probable

Sungrazing Comet, IAU Circular 3640

Marsden, B.G, Battams, K. Kracht,

R., Oates, M., 2005, Comets C/2005 E3,

2005 E4 (SOHO), Minor Planet Electronic

CIrcular 2005-E87

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Comets, Ann. Rev. Astronomy

Astrophysics, vol. 43, Issue 1,

pp.75-102

Michels, D. J.; Sheeley, N. R.;

Howard, R. A.; Koomen, M. J., 1982,

Observations of a Comet on Collision

Course with the Sun, Science, Volume

215, Issue 4536, pp. 1097-1102

Ohtsuka, Katsuhito; Nakano, Syuichi;

Yoshikawa, Makoto, 2003, On the

Association among Periodic Comet

96P/Machholz, Arietids, the Marsden

Comet Group, and the Kracht Comet Group,

Pub. Ast. Soc. of Japan, Vol.55,

No.1, pp.321-324

Ramanjooloo, Y., Jones, G.H., Coates,

A.J., Owens, M.J., Battams, K., 2014,

Solar Wind Velocity Measurements from

near-Sun comets: C/2011 W3 (Lovejoy),

C/2011 L4 (Pan-STARRS), and C/2012 S1

(ISON), Poster session, ACM, Helsinki,

Finland, 2014

Raymond, J. C.; McCauley, P. I.;

Cranmer, S. R.; Downs, C., 2014, TheSolar Corona as Probed by Comet Lovejoy

(C/2011 W3), ApJ 788:152

Schrijver, C. J.; Brown, J. C.;

Battams, K.; Saint-Hilaire, P.; Liu,

W.; Hudson, H.; Pesnell, W. D., 2012,

Destruction of Sun-Grazing Comet C/2011

N3 (SOHO) Within the Low Solar Corona,

Science, vol. 335, issue 6066, pp.

324-328

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of the Marsden and Kracht Groups of

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System. II. The Case for Cascading

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(ISION) SHortly Before Perihelion:

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Effects in Orbital Motions of the

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Tail Disconnection, ApJ 668:79-82


Electron Irradiation of Cometary Ice Analogs -N2O - CS2 ice mixtures

Sarath Raman, Pavithraa Sundararajan, Physical Research Laboratory, India(pavi.nctu at gmail.com)

Figure1: Schematic of the Experimental setuphoused at PRL, Ahmedabad used to record theInfrared spectra of Astrochemical ices containinga Zinc Selenide (ZnSe) substrate cooled to 85 Kin an Ultrahigh Vacuum chamber with a pressure

less than 10-9 torr.

Introduction

The first identification of Carbon mono-sulfide (CS) in the InterStellar Medium(ISM) in 1971 with column density1014 molecules cm-2 in Orion A, W51,IRC+10216 and DR21 (Penzias 1971) andin the NGC 2264 cluster in 1972 (Zucker-man 1972) and on Comet West in 1980(Smith 1980) started the quest to traceits parent molecule CS2 in the ISM andcomets. CS2 was first detected on Comet122P/de Vico in 1995 by comparing theunidentified spectral lines of the comet

in the visible and ultraviolet region withthe experimental spectra of supersonicallycooled CS2 (Jackson, Scodinu et al. 2004).Recently (Sivaraman 2016) has confirmedthe presence of CS2 in the cold traps ofLunar South Pole. Extensive experimen-tal studies have been made on this sim-ple molecule CS2 but its reaction withother ice mixtures in interstellar conditionis still least explored.

Nitrous oxide (N2O) was also detectedin the Interstellar medium (ISM) inSgrB2(M) in the year 1994 which was thethird molecule found in space to have N-Obond (Ziurys 1994). N2O is yet to be dis-covered on comets. CO2 has been detectedon comets (Combes, Moroz et al. 1986)and the recent results from ESAs Rosettamission revealed the presence of molecu-lar Nitrogen in the coma of comet 67P/ChuryumovGerasimenko. Rich nitrogenand carbon dioxide in planetary environ-ment produces N2O. N2O can be formedon extraterrestrial ices when molecular ni-trogen and carbon dioxide ice mixturesare irradiated with 5 KeV and 10 KeVelectrons (Corey, Chris et al. 2005). Ex-periments show that solid nitrogen oxideswhen bombarded by Argon atoms and ionsat 4 KeV produce ozone which is not possi-ble in gas phase (Jim Liang 1984). Ozoneis a biomarker to trace the existence ofextraterrestrial life. N2O also plays an im-portant role in the catalytic destruction ofozone in Earths stratosphere (Portmann,


Figure 2: Infrared spectra of CS2 N2O icemixture after deposition at 85 K (black) andspectra after irradiating the ice mixture for 30

minutes (red).

Figure 3: Infrared spectra of the ice mixturebefore and after irradiation (a) C3S2 observedafter irradiation at 2055 cm-1 and (b) SO2 after

irradiation at 1150 and 1154 cm-1

Daniel et al. 2012). Chemical processingof solid N2O at 25 K by 1 KeV electronsproduced ozone and oxides of nitrogen likeN2O2, N2O3, N2O4 and N2O5 with NO,NO2 and O2 as intermediates (Sivaraman,Ptasinska et al. 2008). Therefore study-ing the reaction of N2O with CS2 in theISM and on planetary bodies will refineour knowledge towards the formation ofsimple to complex molecules bearing car-bon, sulphur and nitrogen.

Experiment

Experiments were carried out in the ex-perimental chamber housed in the labora-tory for low temperature Astrochemistryat Physical Research Laboratory (PRL),India. An UltraHigh Vacuum (UHV)chamber, that can reach base pressures upto 10-10 mbar, containing a cold head withZinc Selenide (ZnSe) substrate cooled to85 K. An all metal leak valve was used tointroduce gases to form molecular ices onto the cooled ZnSe substrate at 85 K.

Pure CS2 molecules were let into the gasline after two freeze-pump-thaw cycles atliquid nitrogen temperature. The gaseousN2O molecules were also let into the gasline to mix with CS2 molecules and thenthe gas mixture was let into the chamberand was made to condense on the ZnSesubstrate kept at 85 K, and monitored us-ing the Fourier Transform Infrared Spec-trometer operating in the Mid-IR region(4000 500 cm-1) with a resolution of 2cm-1. After recording a spectrum at 85K, the ice mixtures were irradiated with 1keV electrons at 10 microA to initiate thechemical reaction.

Results and Discussion

The N2O and CS2 molecules were mixedin the gasline and deposited on the ZnSe


substrate at 85 K. An IR spectrum wasrecorded at 85 K. The IR band assign-ments of N2O and CS2 obtained are pre-sented in Table 1. The ice mixtures wereirradiated with 1 KeV electrons for 30minutes and another IR spectrum wasrecorded as shown in Figure 2. The mainproducts found to appear after irradiationwere C3S2 at 2055 cm-1 and SO2 at 1150and 1154 cm-1 as shown in Figure 3.

SO2 can be formed by the following reac-tion (a), (b) and (c); C3S2 can be formedby reaction (d):

CS2 −→ CS + S (Maity, Kim et al. 2013)

S + O −→ SO (+O) −→ SO2

S + O2 −→ SO2

3 CS2 −→ C3S2 + 4 S (Sivaraman 2015)

Conclusion

The N2O and CS2 ice mixture, kept at85 K, upon electron irradiation was foundto synthesis C3S2 and SO2. From the ex-periments carried out we could clearly seethat carbon and sulphur bearing moleculeswere synthesized in larger amounts. The

available S atoms from the CS2 and Oatoms from N2O were found to react read-ily in synthesizing SO2. Therefore, we pro-pose SO2 to be one of the largely availablemolecules on cometary nucleus rich in CS2

and oxygen bearing simple molecules.

References

Combes, M., V. I. Moroz, et al.

(1986). "Infrared sounding of comet

Halley from Vega 1." Nature 321(6067s):

266-268.

Corey, S. J., J. B. Chris, et al.

(2005). "Investigating the Mechanism

for the Formation of Nitrous Oxide

[N2O(X 1+)] in Extraterrestrial Ices."

The Astrophysical Journal 624(1): 436.

Jackson, W. M., A. Scodinu, et al.

(2004). "Using the Ultraviolet and

Visible spectrum of Comet 122P/de

Vico to Identify the Parent Molecule

CS2." The Astrophysical Journal Letters

607(2): L139.

Jim Liang, J. M. (1984). "Fast Atom

and Fast Ion Bombardment of Solid

Nitrogen Oxides: An FT-IR Study."

Journal of American Chemical Society

106: 5039-5040.

apiski, A., J. Spanget-Larsen, et al.

(2001). "Vibrations of nitrous oxide:

Matrix isolation Fourier transform

infrared spectroscopy of twelve N2O

isotopomers." The Journal of Chemical

Physics 115(4): 1757-1764.

Maity, S., Y. S. Kim, et al. (2013).

"On the detection of higher order

carbon sulfides (CSx; x = 46) in low

temperature carbon disulfide ices."

Chemical Physics Letters 577: 42-47.

Penzias, A. A., Solomon, P. M.,

Wilson, R. W., Jefferts, K. B (1971).

"Interstellar Carbon Monosulfide."

Astrophysical Journal 168: L53.


Portmann, R. W., J. S. Daniel, et al.

(2012). "Stratospheric ozone depletion

due to nitrous oxide: influences

of other gases." Philosophical

Transactions of the Royal Society

B: Biological Sciences 367(1593):

1256-1264.

Sivaraman, B. (2016). "Electron

irradiation of carbon dioxide-carbon

disulphide ice analog and its

implication on the identification of

carbon disulphide on Moon." Journal of

Chemical Sciences 128(1): 159-164.

Sivaraman, B., S. Ptasinska, et al.

(2008). "Electron irradiation of

solid nitrous oxide." Chemical Physics

Letters 460(13): 108-111.

Smith, A. M., Stecher, T. P.,

Casswell, L. (1980). "Production of

carbon, sulfur, and CS in Comet West."

Astrophysical Journal 242: 402-410.

Ziurys, L. M., Apponi, A. J.,

Hollis, J. M., Snyder, L. E. (1994).

"Detection of interstellar N2O: A

new molecule containing an N-O

bond." Astrophysical Journal 436(2):

L181-L184.

Zuckerman, B., Morris, M., Palmer, P.,

Turner, B. E. (1972). "Observations of

cs, HCN, U89.2, and U90.7 in NGC 2264."

Astrophysical Journal 173: L125.


Concept for a comet chaser/flyby mission

Dr. Shashikiran Ganesh, Physical Research Laboratory, India (shashi at prl.res.in)

Mars Orbiter Mission (MOM) show-cased ISRO’s potential in deepspace navigation with a great suc-

cess in the maiden venture. The technol-ogy has been demonstrated and now is thetime for Indian scientists to take advan-tage of the capabilities. One of the keyareas that need to be addressed with a ded-icated space mission is that of long periodcomets. Long period comets are supposedto be relatively less affected by weatheringdue to lesser number of close perihelionpasses. Hence their study would allow usbetter understanding of the pristine build-ing blocks at the early stages of Solar Sys-tem evolution.

So far, all the missions to comets, start-ing with International Cometary Explorer(ICE) to the current Rosetta/Philae, havetargeted short period comets where the or-bits are relatively well known, understoodand predictable with reasonable accuracy.The recent encounter of Comet C/2013 A1(Siding Spring) with Mars is a unique casewhere spacecraft meant for Mars observa-tions (including MOM) were able to con-tribute to study of the comet.

Thus a comprehensive mission with asuite of instruments must be designed,built and kept on standby for launch toa long period comet that would make asuitable pass through the inner Solar sys-tem. Long period comets such as the mas-sive Comet C/1995 O1 (Hale-Bopp) arediscovered when they are sufficiently farenough away. Hence they provide for a suf-ficient lead time for computing and settinga deep space course for a suitable flyby ofthe comet. Again taking the case of Hale-Bopp, the comet was discovered on 23rdJuly 1995 at a distance of over 7AU andapproached perihelion (distance of 0.9AU)on 1st April 1997. Generally long periodcomets are in orbits with very different in-clination angles with the ecliptic and get-ting spacecraft to follow those orbits wouldbe quite demanding in terms of power fortrajectory mapping and corrections. Itwould be a very rare orbit that would al-low us to accompany the comet as beingdone by the Rosetta spacecraft. Hence aprecisely timed flyby would be most ap-propriate to sample the comet. It is herethat ISRO’s recently demonstrated poten-tial for cheap, low gestation missions canmake a unique mark in planetary explo-ration on an international scale.


Spectroscopy and Chemical Synthesis ofInterstellar Ice Analogues (Thesis Abstract)

Binukumar G Nair, The Open University, UK.(binukumarg at gmail.com)

Absorption spectra of pure NO ice, CH3OH+NO[1:1] ice mixture and, pure CH3OH ice at

deposited at 28 K.

Molecular synthesis and chemical evo-lution in the interstellar mediumhas been studied under laboratory

conditions. The method of preparationand energetic processing of interstellar iceanalogues on surfaces, spectroscopic prin-ciples for monitoring chemistry and mor-phology of these ice analogues and analysismethodologies are discussed in detail.

The modification of a portable, ultra-high vacuum (UHV) system for electron ir-radiation, vacuum ultraviolet (VUV) spec-troscopy and temperature programmeddesorption (TPD) of interstellar ice ana-logues are described in this thesis. Ex-perimental procedures to grow interstel-

lar ice analogues of pure molecules andmixtures are described. The results fromthe various experiments discussed in thisthesis are classified into four main parts:VUV spectroscopy, electron irradiation ofinterstellar (IS) ice analogues, simultane-ous irradiation and generation of IS iceanalogues and temperature programmeddesorption of interstellar ice analogues.

Temperature dependent vacuum ultravi-olet (VUV) photo-absorption spectra ofpure molecular ices such as HCONH2,HCOOH, HCOOCH3, CH2CHCH2OHCH3COOCH3, CH3CH2COOH, C6H6 andO3 have been measured on the UV1 beam-line of the ASTRID Synchrotron at theUniversity of Aarhus in Denmark andUV A1 beamline at NSRRC, Taiwan.These spectra and photo-absorption cross-sections in the condensed phase are alsopresented. In particular, temperature de-pendent VUV photo-absorption character-istics of condensed ice films of O3 aremeasured for the first time. Electroninduced molecular synthesis in pure or-ganic ice films of HCONH2, HCOOCH3,CH3COOH, NO and binary ice mixturesof CH3OH+NO (1:1) are also reported.Newly identified pathways of molecularsynthesis and results of electron destruc-tion cross-sections are discussed. Molec-ular synthesis during simultaneous elec-tron irradiation and physisorption of abinary mixture of CH3OH+NH3 (1:1)


is studied for the first time. Simul-taneous irradiation-deposition has shownvery interesting behaviour in terms of ef-ficiency of formation of radical speciessuch as OCN-, NH4

+ etc and biologicallyimportant complex organic species suchas HCONH2, HCOOCH3, CH3COOH,CH3OCH3, CH2CHCHO etc. Simulta-neous irradiation-deposition closely simu-late the effect of cosmic ray irradiation in

a dense molecular cloud and reveal newpathways of formation with higher efficien-cies even at lower column densities of reac-tants. Finally preliminary results of a tem-perature programmed desorption study ofpure NO ice films are also presented alongwith the future challenges and strategies.

For full thesis please write to:[email protected]


Events

National Conference on Atomicand Molecular Physics

NCAMP @ ISAMP

3-6 January 2017

At

Physical Research Laboratory,India

For more updates: http://www.prl.res.in

Opportunities

• Indian Centre for Space Physics invites applicationfrom the candidates for the post of Project Scientistsand Post Doctoral Fellows in Astrophysics, Earth andSpace Science.

Contact Dr. Ankan Das: [email protected]

• PDF Position - Recovering geochemical evolution ofMars from the study of Martian meteorities.

Contact Dr. Amit Basu: [email protected].

• PDF Position - Simulating astrochemical ices in thelaboratory. Opportunity to build an experimental setupto study chemical synthesis of low temperature molec-ular ices under shock conditions.

Contact Dr. Bhalamurugan Sivaraman: [email protected]

• PDF Position - Linking Comets with cold ISM clouds.

Contact Dr. Shashikiran Ganesh: [email protected]

For more information:http://www.prl.res.in/∼ acsi/

Recent Books on Comets

1. Author: Alan Hale

Title: The Comet Man

Link:http://www.earthriseinstitute.org/thecometman.html

2. Author: Uwe Meierhenrich

Title: Comets and their Origin

Link:http://as.wiley.com/WileyCDA/WileyTitle/productCd-

3527412816,subjectCd-ES12.html

ASTROPROJECT

Captured on 14/12/2013.

Location: Mount Abu Infrared observatory, Mt Abu, Rajasthan,India.

Comet C/2013 R1 (Lovejoy) photographed by Rakesh Rao risingover the light polluted Abu valley. Also seen is a sporadic meteor

burning up in the Earth atmosphere.

The sharp line near the horizon marks the edge of the boundarylayer of the atmosphere frequently seen in winter at Mt Abu.

Invitation for Submitting Letters

We are pleased to invite your articles (in the form of a 2-3paragraphs and an image if possible) for the next issue.

Kindly email your articles to [email protected]

To stay tuned about the updates in Astrochemistry,check our website:

http://www.prl.res.in/∼ acsi/

Facebook:https://www.facebook.com/astrochemistryindia?fref=ts

Twitter:

https://twitter.com/AstrochemPrl

Office Bearers of the Society:

Bhalamurugan Sivaraman and Shashikiran Ganesh

Physical Research Laboratory, India

Email id: [email protected], [email protected]

N A T I O N A L E D I T O R I A L B O A R D

A n k a n D a s

I n d i a n C e n t e r f o r S p a c e P h y s i c s

A m i t P a t h a k

T e z p u r U n i v e r s i t y

B h a l a m u r u g a n S i v a r a m a n

P h y s i c a l R e s e a r c h L a b o r a t o r y

S h a s h i k i r a n G a n e s h

P h y s i c a l R e s e a r c h L a b o r a t o r y

S h y a m a N a r e n d r a n a t h

I n d i a n S p a c e R e s e a r c h O r g a n i s a t i o n

S a t e l l i t e C e n t e r

I N T E R N A T I O N A L E D I T O R I A L B O A R D *

B i n g - M i n g C h e n g

N a t i o n a l S y n c h r o t r o n R a d i a t i o n R e s e a r c h

C e n t e r , T a i w a n

M i c h a e l J . M u m m a

N A S A G o d d a r d S p a c e F l i g h t C e n t e r , U S A

N i g e l M a s o n

T h e O p e n U n i v e r s i t y , U K

* W i t h e f f e c t f r o m A s t r o c h e m i s t r y L e t t e r s I s s u e 3 .

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