Solar Systeman introduction

THE NEW

SOLAR SYSTEM

The Sun

Eight Planets

In short anything that goes about Sun is solar system !!

Dwarf Planets

Many many satellites of the planets

Comets, asteroids, small objects

Indus civilisation (c 2000 BCE) is said have had rudimentary astronomical thoughts. Many illustrations found in Indus seals have been interpreted as perhaps having astronomical significance. This seal is said to represent – seven stars – Ezhu meen (Tamil) – Saptha Rishi/ Ursa major.

Planets, nav graha, in Indian Puran were conceived as nine deities. Sun, moon and two phantom planets (Rahu and Ketu) were included along with five visible planets in the list.

In Puranic traditions the stars were considered to be gods. Puran talks of 27 nakshatras –guardian of night- as 27 deities or smaller gods of Hindu pantheon.

That does not mean that all that was in Indian tradition was mere myths. Rather tall personalities like Aryabhata formulated that Earth and moon were spears, Earth revolved resulting in day and night and natural causes for eclipses.

As a bridge between Ptolemy’s geocentric epicycle cosmos to Copernicus’s heliocentric theory, Kerala mathematician and astronomer, Neelakanta Somayaji (1444-1550) proposed a partial heliocentric theory. Inner planets like Mercury and Venus go around Sun. While other planets and Sun along with inner planets go around Earth.

Anticipating Kepler, the Kollam calendar made by the Kerala mathematicians around 825 AD, devised a calendar wherein the time spend by Sun in each Rasi is not fixed uniform time, but varies. In the Rasis like Vrichika, Danush and Maragam Sun was spend about 29 days but Sun will stay for 32 days in Rishabam, Mitunam and Karkadagam. That is when Earth is far away in its elliptical path, (~ July) it’s angular movement is slow. Whereas when it is nearer to sun (~ January) it will appear to move faster. This was taken into account by the Kerala mathematicians.

Sun is about 500 crore years old. It is about 15 crore kilometre away. It takes about 8 mts for sun light to reach Earth from Sun. It is so massive that it is equal to about 3,33,000 times Earth mass. It has more than 28 times gravity as earth at its surface. However its density is only about 1.41 gm/cm3. It has about 73% hydrogen, 25% helium and 2% oxygen,

nitrogen, iron, carbon and other elements.

Sun SpotsExtreme UV image

The size of Earth as compared to solar fare. Every square meter of Sun emits about 62,00,00,000 watt per second. Nevertheless only one in

billion part reach Earth.

Earth in comparison

Every second about 60 crore tonne of hydrogen undergo nuclear fusion and converted into 58 crore tonne helium. The difference in the mass results into energy according to Einstein’s formula E=mc2. 3.8 x 1023 kilowatt energy is produced every second. This energy is adequate to meet the energy need of whole Earth for next 500 years! Sun is expected to shine in the same manner for another 500 crore years.

Mercury is the smallest of the eight planets. It’s diameter is just 4880 km, just bigger than our moon. It takes just 88 days to go around sun. It takes 59 days to revolve around itself. It does not have any stable atmosphere. However due to solar wind the surface evaporates and

light atmosphere is formed.

One of the mystery of Mercury is why while some areas are heavily cratered, some regions lack them. Concentration of Iron in Mercury is rather high, and how more iron got accumulated into Mercury is

yet to be satisfactorily answered.

Mercury and Venus being an inner planets would be seen to rise or

set along with Sun.

Mercury will be seen about 1 hr before sunrise or 1 hr after sun set. Therefore observing Mercury is rather a rare event.

While day time temperature is as high as 350 degree, the night time temperature is as low as –180 degree. Largest crater on Mercury is named after Kuiper, an astronomer. Many features on the surface of Mercury is named after writers and creative personalities.

After moon brightest celestial object in the night sky is

Venus.

Galileo Galilee used telescope to observe Venus. On seeing the waxing and waning phases of Venus, just like that of Moon, Galileo concluded heliocentric solar system.

Ptolemy's system Copernicus’s system

It is by using radar and other imaging technology that we can see the surface features of Venus. It is always covered by a thick layer of atmosphere.

Venus’s atmosphere is ever covered by thick clouds of sulphuric acid. The atmospheric pressure is about 100 times more than that of Earth. Due to resultant green-house effect the surface temperature of

Venus is about 482 degree.

First spacecraft to reach the surface of Venus was Soviet spacecraft Venera-4 in 1967. First photographs of Venus surface was obtained by Venera-9 in 1975

Surface of Venus

Maat Mons on the surface of Venus: 5 km above the surface.

Venus is women’s only planet. Most of the surface features on Venus is named after women.

Usha mountain

Kali Mountain

Gauri mountain

Madavi Crater

Indira Crater

Moon is the 6th largest satellite in solar system.

Light will take about 1.25 seconds to reach Earth from moon. It takes about 27 ½ days to go around Earth, but the period between each full moon is about 30 days.

Moon goes around in elliptical orbit, tilted at about 5 degree. Apogee is at 357200 km and perigee is 407100 km.

The relative position of Earth, Moon and Sun results in the phases.

Though every new moon day moon is in line with Sun, due to the tilt of its orbit, it will not cause eclipse every new moon

day.

It’s axis is tilted at 6.5 degree and hence at times the north pole is towards Earth and at times south pole. Time taken for moon to revolve around itself and around Earth is about the same time. Hence only one face ~ 59% of surface is seen from Earth. Remaining 41% cannot be seen from Earth.

The far side of moon was first seen by Soviet spacecraft Luna 3.Subsequent examination inform that the far side has much more dense pockmark –craters- than the nearside. Moon’s far side, has attracted the space rocks on itself and thus has been a proactive cover for Earth.

While the first spacecraft to land on moon was Luna 2 (1959) crash landed on moon, Luna 9 (1969) made a soft landing. Apollo –11 with Neil Armstrong, Edwin Aldrin and Michelle Collins landed on moon in 20 July 1969. It returned with about 21.7 kg of moon rock.

Moon’s surface is covered with pockmark like craters. Most of them are impact craters caused by bombardment of space rocks

Aristarchus crater

Accidentally the angular size of moon and sun from Earth is about same ~ 0.5 degree. And hence once in a while moon could completely block Sun when it comes in between making total solar eclipse. Eclipse is a wonderful celestial phenomenon.

How Moon formed? One theory claimed that Moon broke away from young earth, while another claimed that moon was formed elsewhere and captured by Earth. The third the left over material from early earth accreted into moon

Recent studies indicate that a mars sized object crashed onto earth about 4.6 billion years ago. The debris that were thrown away accreted into Moon.

Geological study of the surface and composition of Moon give more credence to this theory.

Mars takes about 23 hrs to revolve in its axis. Its atmosphere is only about 1% of Earth’s atmosphere. 95.3% is carbon dioxide and

rest nitrogen and other gases.

Olympus mons

Tharsis Volcanoes mons

Marineris Valley

Viking -1 landed here

Lomonosove crater

Viking -2 landed here

Utopia plains

Amazonis Sinai platea

u

Moon plateau Argyre

crater

Hellas crater

Prometheus terra

Ganges chasma

Pathfinder

Mars surface has very large canyon structure and big craters. Occasionally plant wide dust storms rage.

The first to land on Mars was Soviet craft Mars-2 (1971). More than 37 spacecrafts have been sent on Mars mission. However only 18 of them have been successful in reaching Mars. There have been 11 attempts to land on Mars, of this only 6 have landed safely and functional.

The northern hemisphere of Mars is younger and the Southern part is older. Southern hemisphere appears to be lowlands while the northern side is highlands. How such a arrangement came into being is an

enigma.

Two moons of Mars were found in 1877. Phobos and

Deimos.

Phobos

Deimos

Mars has solid ice, including water ice in its poles.

Mars has no plate tectonic movements and hence unlike Earth all the volcanoes are concentrated in one place. Tallest mountain in the Solar system and volcano is Olympus. Its crater is itself is about 6 km high.

Micro-organic fossil-like structure seen from a Mars rock fuelled interest about Mars and potential life in Mars

There has been evidence of flow of liquid water on the surface of Mars long, long ago. How Mars lost its water; how global scale climatic change occurred, are questions that haunt scientists.

Eclipse seen from another planet!. Two moons of Mars occasionally cause partial eclipse and Pathfinder mission captured the eclipse

that took place in 2004.

Between the orbit of Mars and Jupiter there are numerous space rocks of varying sizes. These together are called asteroids or minor planets.

The first object in asteroid belt was discovered on Jan 1, 1801. The object is now classified as dwarf planet- Ceres.

Today more than a lakh of the asteroids are identified and classified. Many of these asteroids have ‘Indian’ names- 2211-Hanuman; 2987-Sarabhai, 7855-Tagorr, 4130-Ramanujan and so on.

3753 Cruithene is a asteroid that is locked into Earth’s orbit. It oscillates on Earth’s orbit, and some claim that it is Earth’s second moon!. Even at its nearest position it will be at 150 lakhs km away from Earth. It’s size is just 30-40 km only!

Some of the asteroids are locked into Jupiter’s. They are called Trojan asteroids. They are concentrated at about 60 degree on both side of Jupiter.

Asteroids are composed of rocks and boulders bound together due to gravity and the surface is covered with fine dust

Asteroids are usually irregular in shape

Jupiter’s diameter is 11 times bigger than Earth. Its mass is 318 times that of Earth. It is so big that one can comfortably place 1300 earths inside it. It takes about 12 years to go around Sun.

Galileo discovered the four largest Moons of Jupiter. In his telescope the moons appeared as tiny dots. The position of the dots changed over days and he found that they

were orbiting Jupiter.

Galilean moons- Io, Europa Callisto and Ganymede. In fact Jupiter has more than 63 satellites.

Ganymede is the largest moon in the solar system. It is even larger than Pluto. The surface of Ganymede has two distinct parts- one older rocks with many craters, the other new terrain with very little craters. It is believed to have plate tectonics just like Earth.

Callisto is full of craters, while it has no plate

movements.

Europa has hardly any craters and has a surface like marble floor. But it has many crakes. Scientist estimate that the surface is frozen ocean underneath one may find water filled ocean.

Io being pushed and pulled by the gravity of Jupiter has many many hot geysers on its surface.

On the surface of Jupiter one sees stripes like Zebra. Each stripe is a layer of wind movement. Each layer moves in opposite direction.

Eye of Jupiter is famous. The ‘eye’ is actually a storm on its atmosphere. The size of eye is about 20,000 km. It is known to have existed since at

least Galileo; that is at least for about 400 years.

During July 1994 a comet named Shoemaker Levy was captured by

Jupiter and crashed on its surface.

SATURN or Shani has been much maligned planet in Hindu tradition.

Actually it is one of the most beautiful planets

with its majestic rings.

It was Cassini who in 1676 distinguish it to be

number of rings

When Galilio looked at Saturn in 1610 through telescope for the first time he was stunned. He perceived Saturn to have two structures on both side.

With improved telescope in 1616 he perceived it to structure like ears to a face.

1655 Huygens could discern it to be a ring

like structure.

The rings of Saturn is actually consist of rocks of size from few meters to millimetre. It is a plate like structure that goes around the Saturn not like a solid plate but like

many rings.

Ring System of Saturn

Saturn takes about 30 years to go around Sun and about 10 hrs to rotate in its own axis. It has more than 56 moons.

Titan is the largest of the Saturn’s Moons. It is looked up by scientist with keen interest because its atmosphere is almost like the early Earth. Study of Titan may provide clues about how life evolved in Earth.

Some of the tiny moons of Saturn confine the rings into its place by their gravity. Janus and Epinetheus coorbit around each other even while orbiting Saturn.

Saturn is so big that about 764 Earth could be packed in Saturn. It is 95 times massive than Earth. Nevertheless its density is only 0.69. That is if one can have a big enough bath tub, Saturn will float on it like a rubber ball!

Mimas

Dione

Tethys

As Saturn goes around the Sun, it would turn its various faces towards Earth; hence the plane of ring would appear to change over period of time

The upper layer of Saturn is also turbulent; with high speed storms and wind jets.

Uranus also has rings, but not so grand as Saturn.

13 March 1781 Uranus was discovered by William Hershel and his sister Carolina. It was the first planet that found no place in the Bible, any Puranas or any religious texts.

Miranda

Uranus is composed of 83% hydrogen, 15 % helium, 2% methane and other trace

gases.

Uranus has five big moons and 22 small moons. Most of the moons of Uranus are named after the character from Shakespeare- Miranda, Titania and so on.

Axis of Uranus is tilted along the ecliptic and hence Uranus appears to roll rather than revolve around Sun. Why the axis is tilted so much is a riddle yet to be solved.

As it goes around Sun, at times its southern pole is towards sun, and it is summer as well as day time in South pole. Whereas northern pole is freezing cold and dark night. This process flip-flops every 42 years.

Neptune is 30 times more massive than Earth. It takes about 16 hrs to revolve around its axis. It takes 164.8 years to go around once.

Neptune was discovered by Adams and Levarrier by mathematically calculating where it should be from the gravitational perturbation it caused on

the path of Uranus.

It was discovered in 1846. Thus it has not even completed one round about sun since its discovery.

Great dark spot on the face of Neptune is about half the size of Earth. It is NOT a storm in its atmosphere. Rather it is a hole in its methane cloud cover. The dark spots on its surface is not a fixed at one location. It migrates from one location to another.

Neptune has 13 moons. Largest of it is Triton. It is the coldest object in the solar system.

Neptune is composed of 74% hydrogen, 25% helium 1 % methane and rest trace gases. As the methane gas absorbs red spectrum blue/ violate spectrum is prominent. Thus it looks dark shining blue planet.

In olden days the sudden appearance of Comets was considered bad omen.

Comet was called Dum-ketu and in various civilisations it was imagined to be various scary objects.

Norman king William considered the appearance of comet in 1066 as good omen. A new star a new king was his slogan. He fought his enemies and became the king of England.

Comet has essentially two parts. Head or core which is largely rocks and ice, tail which is vaporised materials.

Edmund Halley was the first scientist to study the comets and its paths using the then novel Newton’s theory of gravitation. He discovered that the comet subsequently named after him will return after 76 years. The comet appeared in 1682 and he predicted it to

appear again in 1759.

Recently a spacecraft impacted into a comet – Temple- 1 to study its features. It is said that at least half of the water on Earth’s surface could have come from comet impacts on Earth.

As the sun rays evaporate ice, the tail of the comet shows up. The tail is prominent when it is nearer to sun and it always points away from the Sun.

Comets have their origin in a region beyond Pluto called Oort cloud. It is estimated that thee may be more than 100,000 comets. The period of comets may be as low as a few years and as high as a thousand years or more. They are the material left over from the original solar cloud after sun and the planets were formed.

The tails of comets may look very different - some with hardly any tail; some with a long one and a few with more than one tail!

Dwarf planets

Ceres discovered in 1801 is a dwarf planet. It is only 950 km in diameter. It takes 4.6 year to go around sun once. It is estimated to contain a solid core with a frozen water ice over coat.

Pluto and charon are twin dwarf planets. It was discovered in January 1930 by Clyde Tombaugh. It is by comparing more than 10000 photographs that he was able to discover Pluto.

Charon was discovered only in 1978. Before the discovery of Charon, pluto’s mass and size was estimated higher.

Pluto-Charon has two moons Nix and Hydra orbiting them.

Charon and Pluto are binary planets, they rotate about a common centre of gravity that is about 1000 km above Pluto. One face of Charon and Pluto face each other, as there revolution is locked into this state due to mutual gravitational pull.

Eris is the third dwarf planet in the solar system. In fact it is bigger than Pluto with a diameter of 2600 km. This dwarf planet was discovered in 2005. It takes about 556.7 years to rotate Sun and is inclined in a orbit of 44 degree. It has a small moon named Dysnomiya. It rotates Eris once in 14 days. Discovery of Eris was the reason Pluto was reclassified as a dwarf planet.

While many comets have a long period ~ 1000 years, some have very short period 50 –100 years. These comets are said to belong to a Kuiper belt a region beyond Pluto a about 30-50 astronomical unit region from Sun.

Many Kuiper belt objects have been discovered. Sedna, Varuna are some of them. More than 10 objects which are larger than 1000 km in diameter has been discovered till now.

While Oort cloud is the original primordial material, Kuiper belt objects are the first stage of the planet formation – proto planets.

The Solar SystemHow did it evolve?

About 460 crore years ago there was a very big and colossal gas cloud- primordial solar cloud. The cloud rotated about itself due to self gravity and began to shrink. In the center the mass accreted and became dense. Most of the mass in the cloud concentrated at the center resulting in the birth of sun. As the core of this sun became more massive and denser the temperature rose to an extent that thermonuclear reaction – fusion could take place. Sun started to shine.

While the rest of the material went around and around the central mass.

Small dust particles were attracted initially by electrostatic attraction.

Once the small rocks became sufficiently bigger gravity also played a part.

Slowly the proto planets were

formed.

Proto planets fused to gather to form planets like Mercury, Earth and so on.

Gas giants like Jupiter and Saturn were formed by the accretion of the light elements.

The icy materials and gases like methane became

Uranus and Neptune.

The leftover proto planets became the Kuiper cloud while the left over original material became the Oorth cloud. The materials that failed to accrete into a planet due to the gravitational perturbation of Jupiter became asteroid

belt.

Initial phase of solar evolution was full of bombardments. One result is pockmark like craters on Moon, Mercury and so on. As most of the space rocks in the inner region got exhausted the bombardment tapered off around 3 billion years ago.

On such bombardment resulted in the formation of moon. Once it was postulated that moon could have formed due to accretion of materials

around Earth, could have been captured or could have split from Earth

Planets beyond solar system orbiting other stars.

They are called as exoplanets

More than 350 of them have been

discovered.

The formation of solar system is not pure guess work. Looking at the night sky one can clearly see evidence of gas cloud accreting, star

formation, accreting disk, planet formation.

Stars like this which are young and having a gas cloud indicate the stages of evolution of solar system.

Bruno was burned alive for speculating that the stars are similar to Sun, perhaps having planets and some of them may even harbour life. Today it is no longer a mere speculation. In fact till now more than 350 exoplanets - plants revolving other stars have been discovered. Many of them are massive like Jupiter. What an irony!

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