Now, why do we call it
Our Solar system? That is because our Sun is one of the huge number of stars in
the Universe which have planets orbiting them. Our Solar system is but one of
them, so we have to categorise it as our solar system.
The centre of our
Solar system on the very basis of which it exists is the Sun, which accounts
for 99.86% of the mass of the solar system.
Our solar system
comprises of planets, their moons, Comets and Asteroids.
The weight of our Sun
is 1.99*10 raised to the power of 27 tons. It has 8 planets orbiting it as you
all know. At one time the number of planets was considered to be 9, but later
Pluto was downgraded as a dwarf planet and has thus gone out of the list of
Planets brining their number down to 8.
Earths average
distance from the Sun is equivalent to about 150 million Km. This distance is
known as the Astronomical Unit or AU.
Apart from the Planets
and their Moons, the solar system also consists of the Asteroid belt between
the orbits of Mars & Jupiter. The Asteroid belt consists of millions of
asteroids which are irregular in diameter. There are 1 million asteroids in the
belt that have a diameter of 1 Km or over along with Ceres the dwarf planet
which has a diameter of about 950 Km. and accounts for 35% of the mass of the
asteroid belt. Ceres weighs app. 9.4* 10 raised to the power of 17 tons which
is large, but nowhere compared to our moon, Ceres only has about 1.5% of the
our moons mass. It is called a dwarf planet because it has enough gravity to
have a round shape unlike the other asteroids whose shape is irregular.
The ASTEROID BELT is a
remnant from the formation of the solar system which got formed 4.6 billion
years ago. The gravity of Jupiter has prevented the belt of asteroids from
forming into a planet. Although there are millions of asteroids in this region,
most of it is empty space and spaceships can easily travel through it without
any harm.
The KUIPER BELT is an
icy region consisting of many millions of icy fragments and stretches from the
end of the orbit of Neptune the last planet about 30 AU from the Sun to 50 AU. It
is more like the Asteroid belt but it is far larger. While most asteroids are
composed of rock and metal, the Kuiper belt objects are highly frozen
containing Methane, Ammonia and Water. The Kuiper belt consists of the dwarf
planets like Orcus, Pluto, Haumea, Quaoar and Makemake.
The OORT CLOUD is a
theoretical vast spherical shell surrounding the solar system containing
billions of icy objects (comets) and is located between 2000 and 200,000 AU
from the Sun. It marks the outermost boundary of the solar system. All the
Comets come in from either the Kuiper Belt or the Oort Cloud. Like the Asteroid
belt and the Kuiper belt, this too originated at the time of formation of the
Solar System 4.6 billion years ago. The Oort cloud is home to long period
comets which have orbits varying from decades to thousands of years.
The 8 planets of the
solar system can be classified into 2 distinct groups: 1. Terrestrial & 2.
Giants (Also known as Jovian)
TERRESTRIAL PLANETS are
much smaller and have rocky hard surfaces, while the Jovian planets have gases
and ices with a low density but with Giant sizes. They lack a solid surface,
have extensive ring systems and have many moons.
TERRESTRIAL
PLANETS
JOVIAN PLANETS are
comprised of Hydrogen and Helium with traces of methane, ammonia, water and
other gases in their atmospheres. Although to us only Saturn appears to have
rings but all the Jovian planets have them but their rings are less brighter
than those of Saturn which is the reason why we don’t see them. All of them
have numerous moons with Jupiter and Saturn have more than 60 moons each,
Uranus more than 20 and Neptune more than 10.
JOVIAN PLANETS
All the 4 Jovian
planets are massive in size but are very low on density. Jupiter is the largest
of them all with a 1,43,000 Km diameter. Neptune is the smallest with a 49.500
Km diameter compared to earth’s 12,750 Km.
MERCURY.
Mercury is the
smallest and the closest planet to the Sun. It is only slightly larger than our
Moon. It has a very minor atmosphere as most of the gases on its surface have
escaped due to its extreme heat as well as Suns gravitation. It has a bare
atmospheric layer and it does not have any moons at all. Its temperature ranges
from 430 degrees Celsius to -180 degrees Celsius and it is a barren and rocky
world like our moon.
Mercury orbits the Sun
in just 88 days, but it is very slow on its rotation and takes 59 days to
complete one rotation.
Mercury’s thin
exosphere consists of Oxygen, Sodium, Hydrogen, Helium and Potassium. It has a
diameter of 4880 km compared to about 3500 km for our moon. It is at a distance
of 58 million Km from the Sun.
Two spacecraft
“Mariner 10” and “Messenger” have gone to Mercury. Messenger mapped Mercury by
taking pictures of its surface.
MERCURY
VENUS.
Venus is the second
planet from the Sun and is almost like a twin to Earth in size. It has a
diameter of about 12100 Km compared to Earth’s 12750 Km. It is at a distance of
about 108 million Km from the Sun.
Surprisingly despite
being the 2nd planet in the solar system and being almost double the
distance of Mercury from the Sun, it is much hotter than Mercury and is the
hottest planet in the Solar system. The heat is because of its thick
atmospheric layer consisting of Carbon Dioxide and clouds of Sulphuric acid.
Venus has an
atmosphere that is far thicker than any other planet in our solar system. It
has an average temperature of 465-470 degrees Centigrade. There is hardly any
variation between its day and night temperatures because of its thick
atmospheric cloud.
Venus is earth’s
closest planetary neighbour and it is only about 40 million Km away from the
earth on average. Apart from the sun and the Moon, Venus is the brightest
object visible to us in the sky.
Venus has a retrograde
spin that is it spins in the opposite direction than most other planets. Venus
is the only planet named after a female God Venus. Venus has valleys and high
mountains filled with volcanoes.
Venus does not have any
Moon, but it has a quasi-satellite known as “Zoozve”. Quasi satellites,
sometimes called Quasi moons are actually asteroids that orbit the Sun while
staying close to a planet. Zoozve ranges in size from 200 to 500 mtrs across.
VENUS
Mars
had fascinated many an astronomer and there had been many science fiction
novels about Martians visiting us. The HG Wells “War of the Worlds” is a
classic work creating a fascinating tale about the Martians despite it not
being a nice one.
I
always fondly remember the Mars series by Edgar Rice Burroughs which I read a
long time ago and found them fascinating. It used the low gravitation of Mars
which is about one third of the earth and gives higher muscle power to a guy
named John Carter from Earth who accidentally gets transferred to Mars.
That
transfer is certainly impossible but that was a fantasy. Edgar Rice Burroughs
really gives rein to his full imagination in that first Mars series novel named
“Princess of Mars”.
Mars is
a desert like planet with a thin layer of atmosphere, that too consisting of
Carbon Dioxide and Nitrogen. This is the only planet in the solar system where
we sent rovers to roam the landscape. We have found strong evidence that Mars
was much wetter and warmer with a thicker atmosphere billions of years ago.
MARS
Mars
was named by the ancient Romans in the name of their God of war as the Planet
appeared red which reminded them of blood. Iron minerals in the Martian dirt
oxidize (rust) to give it its red colour.
MARTIAN LANDSCAPE
Although
Mars is unlikely to have any life forms today, there are strong indications
that life exited once on Mars.
Mars
has a diameter of 3390 km which is about half the size of Earth. Mars is 228
million Km from the Sun (average). The distance of Mars from the earth varies
from just 54 million Km to 225 million Km as both the earth and Mars are
orbiting the Sun.
Mars
rotates on its axis in about 1 day just like the earth, but the year on Mars is
a little over double that of ours. Surprisingly even the axis of rotation of
Mars is tilted somewhat similar to earth giving it seasons.
Mars
has 2 moons: Phobos (20 odd Km across) and Deimos (13 odd Km across), both of
which are too small and were probably captured asteroids unlike our moon. They
are uneven in shape with Deimos being more distorted.
Mars
has a very large canyon which is 4800 Km across and is 320 Km at the widest,
and 7 Km at the deepest.
Mars
has the largest volcano in the solar system named Olympus Mons. It is 3 times
taller than Mount Everest.
There
are a number of evidences that water existed in plenty on Mars at about 1
billion years ago. There is water on Mars today but it is only found as ice
under the surface in the Polar Regions.
Mars
has very thin atmosphere which mostly consist of Carbon Dioxide, Nitrogen and
Argon. It does not offer any protection against the hits of asteroids, comets
and meteorites not to speak of Cosmic rays.
The
Martian temperature varies between 20 degrees Celsius and -153 degrees Celsius
where nothing can survive.
In one
billion years, Earth too would become as uninhabitable as Mars but for
different reasons. The Suns luminosity would increase by 10% by then, causing
global temperature to increase, the oceans would start to evaporate and our
atmosphere would lose Oxygen which would wipe out most complex life forms and
leave a dead desert planet which Mars is today but only much hotter. Anyway 100
crore years are far too many to be worried about, because the human species was
born only 300,000 years ago.
Look at
the terrain of Mars in the following video filmed by one of the Rovers, it is
almost similar to the Earth but the difference is it is barren and is without
water.
https://www.youtube.com/watch?v=Vy_RPd0rblI
JUPITER
THE BIG BROTHER OF PLANETS IN OUR SOLAR SYSTEM.
Jupiter
is the first of the Jovian planets and it is also by far the biggest planet in
our Solar System. Jupiter alone has a mass that is equal to more than 2.5 times
of all the other planets combined. Like all other Jovian planets it is full of
gases and lacks a solid surface. It weighs 318 times the weight of the earth.
Jupiter
has a diameter of about 139,800 Km. If Jupiter is hollow it can take 1000
Earths into it. It is also the oldest planet of all. It rotates the fastest of
all planets and completes a rotation in just 9.9 hours despite its huge frame. So
it has the shortest day in the solar system. Jupiter’s average distance from
the Sun is 778 million Km. Jupiter spins almost upright with very little tilt
in its axis and hence does not have any seasons.
JUPITER
Jupiter
is full of Hydrogen and Helium and it has swirling clouds of Ammonia and water.
It has an extreme climate that cannot support life. But one of its moons
“Europa” is a most likely candidate to have life in the ocean underneath the
ice sheets. The cloud tops of Jupiter have a temperature of -110 degrees
centigrade. However as one descends into Jupiter’s gaseous atmosphere
temperature starts increasing drastically and reaches tens of thousands of
degrees at its core.
Jupiter
has some 95 moons and those include “Io”, “Europa”, “Ganymede” & “Calisto”
all of which were discovered by Galileo with a Telescope made by him in 1610. Ganymede
is the largest moon in the solar system and is bigger than Mercury.
In our
solar system, Europa is the best candidate to have life after the earth. It has
seas of frozen water and beneath the ice sheets life is likely to exist.
Jupiter
too has 4 main rings around it even though we cannot see them from the earth. The
composition of Jupiter is more like the Sun full of Hydrogen and Helium. Deep
down the atmosphere the temperature and pressure increase compressing Hydrogen
into a liquid. This gives Jupiter the largest ocean in the solar system but
made of Hydrogen and not water.
There
is no surface on Jupiter for the landing of any craft. It is filled with
swirling hot gases under tremendous pressure and temperature so no craft can
land on Jupiter. Not only that, it cannot fly through its atmosphere either
because it would be crushed, melted and vaporized.
Jupiter
has colourful stripes and spots on its surface when seen by us through
telescopes. Winds on Jupiter reach over 500 km an hour and the stripes may be
swirling gases of sulphur and phosphorous.
The
famous great red spot of Jupiter, a swirling accretion of clouds is twice as
wide as the Earth and has been seen for the past 300 years.
Jupiter
has a magnetic field is 20,000 times as powerful as that of the Earth.
SATURN.
Saturn
is the 2nd largest planet in the solar system and the special thing
about it is that it is surrounded by beautiful rings which are visible through
small telescopes. Although all Jovian planets have rings, those of Saturn are
much more thicker and more visible. Saturn has a set of 7 main rings with
spaces between them. The ringlets are made of ice and rock.
Like
Jupiter, Saturn too is full of Hydrogen and Helium. Saturn rotates on its axis
in about 11 hours but its year is fairly long and is equal to 29 earth years. Saturn
is the farthest planet that can be discovered with the naked eye.
SATURN
Saturn has a shocking number of 274 moons. 4 Robotic spacecraft visited
Saturn and they are Pioneer 11, Cassini, and Voyager 1 & 2. Saturn’s moons
are very varied and many of them present a different terrain.
Saturn has a diameter of about 120,000 Km. It is at an average distance
of 1.4 billion Km from the Sun.
There are a number of mysteries in Saturn that are yet to be uncovered.
Its moon Enceladus has jets of water that spray from it and its another moon Titan
has lakes of Methane.
The major moons of Saturn are Titan which is the largest, Mimas, Tethys,
Enceladus, Dione, Rhea, Hyperion and Lapetus.
There is absolutely no chance of life on Saturn but there is promise of
life on its moons Enceladus & Titan which have oceans.
Saturn’s ring system extends up to 282,000 Km from it but the vertical
height is just 10 meters.
Saturn is the only planet in the solar system whose density is less than
that of water, so it would float in a gigantic ocean of water if there is one.
Like
Jupiter, there is no surface on Saturn for the landing of any craft. It is
filled with swirling hot gases under tremendous pressure and temperature so no
craft can land on Saturn. Not only that, it cannot fly through its atmosphere
either because it would be crushed, melted and vaporized.
Saturn’s
magnetic field is 578 times as powerful as that of the earth.
URANUS.
Saturn
is a gas giant. Most of the planet is made up of water, ammonia & methane. It
has a thick atmosphere consisting of Hydrogen & Helium with traces of
carbon dioxide and Carbon Monoxide and has a temperature of -224 Degrees
Centigrade. Uranus’s atmosphere winds have a peak wind speed of 900 Kmph. and it remains
unexplained as to why that is so. The planet also has very less internal heat
compared to other planets and why that is so is not clear. The blue green colour
of Uranus comes from methane in its atmosphere.
URANUS
Like all the Jovian
planets Uranus too has a ring system, a magnetosphere and many moons. Uranus has
29 moons of which 5 are major and are known as Miranda, Ariel, Umbriel, Titania
& Oberon. It has 13 faint rings
around it.
Uranus can be barely seen with the naked eye. It
has a sideways 98 degree tilt in its axis that causes extremely long 42
yearlong seasons. Uranus has a Cyan colour (between blue and green) because of the
presence of Methane in its atmosphere.
NEPTUNE.
Neptune
is the last planet of the Solar System now as Pluto has now been classified as
a dwarf planet. It is at a distance of 4.5 billion Km from the Sun and has a
diameter of 49500 km. Neptune orbits the Sun once every 165 earth years.
NEPTUNE
It has
an intense blue colour on account of its atmospheric methane absorbing red
light. It is an ice giant with thick and windy atmosphere of Hydrogen, Helium
and Methane. It has a mantle of water, ammonia and methane ices.
Neptune
has atmospheric winds of extremely high speeds of up to 2000-2100 km per hour.
Neptune
has 16 moons and is surrounded by 5 main rings. Triton is the only major moon
of Neptune. Voyager 2 spacecraft is the only one that visited Neptune. It is
the only planet to be discovered by mathematical prediction rather than by observation.
Neptune
is the only planet in the solar system that cannot be seen with the naked eye.
IMPORTANT
MOONS OF THE PLANETS WHICH HAVE CHANCES OF SOME FORM OF LIFE
Technically none of the far off planets from the Sun
in our Solar system should be able to have any sort of life forms due to their
extremely cold conditions. However, although they themselves do not have any chance
of having any life, they exert tidal forces on account of large gravitational
forces on their moons on account of which some heat is generated and that enables
water to be present on some of the bigger moons which have atmosphere. There is
also a phenomenon called orbital resonance when multiple moons are there for a
planet. In this, when their orbital periods are separated by small round
integers they exert gravitational tidal forces on each other.
1. GANYMEDE.
Jupiter’s
Moon, Ganymede is special because it is the largest and most massive moon in
the Solar System. In fact, it is bigger than the planet Mercury. It has a
diameter of 5270 Km and a mass of 1.48*10 tons.
GANYMEDE.
Ganymede
is composed of silicate rock and water in equal proportions. It has a liquid
metallic core. Its underground ocean contains more water than all the water on
the earth combined. Ganymede has a thin Oxygen atmosphere consisting of Oxygen,
O2 and O3. The Hubble Space Telescope discovered the
presence of a thin oxygen atmosphere on Ganymede.
Several
spacecraft have explored Ganymede. The probe Galileo discovered its underground
ocean and magnetic field. Ganymede is tidally locked to Jupiter with its one
side always facing Jupiter.
Ganymede
is in resonance with Jupiter’s other moons, Io and Europa and for every orbit
of Ganymede Europa orbits the Jupiter 2 times and IO 4 times.
Although
the weather on Ganymede is too cold, its sub surface ocean may be much warmer.
The ocean exists inside 150 Km of icy crust and may be able to sustain some
sort of life just like in the case of Europa.
Another
moon of Jupiter Callisto is also considered to Europa and Ganymede and some
form of life may be present in its oceans which are warm to tidal forces by
Jupiter.
2.
EUROPA
One of
the Moons of Jupiter known as Europa is something special for us because it is
a most probable candidate for finding life in another planet. It can be viewed
from the earth by way of small binoculars.
EUROPA.
Europa
is an icy moon and is the closest Moon orbiting Jupiter. In size Europa is only
slightly smaller than our own Moon. It consists mainly of Silica rock and has a
molten core at its centre. It has a thin atmosphere consisting of Oxygen.
It has
a smooth surface and lacks any sort of substantial craters or mountains which
are rather surprising. Europa is the smoothest object known in the Solar
system. Europa has salty liquid oceans of water on its surface whose extent is
more than the oceans on earth.
Its
closeness to Jupiter gives rise to tidal heating that keeps water from forming
into ice. There is every chance that there is life in those seas if not on its
other surface. However, in March 2024, scientists have reported that Europa has
much less Oxygen than what was previously thought.
The
Hubble space telescope took an image of Europa in 2012 which had a jet of water
erupting near its South pole. The image suggests that the plume may be some 200
km high. In 2018 there was supporting
evidence for these water plumes in the data from the Galileo space probe.
3.
CALLISTO.
Calisto
is the 2nd largest moon of Jupiter next to Ganymede and is as big as
Planet Mercury. It is the outermost moon of the 4 Galilean moons of Jupiter.
CALLISTO
The
surface of Calisto is the most cratered in the Solar System with its surface
mostly covered with impact craters. It
is formed with 50% rock and 50% ice. Compounds detected on the surface of
Calisto include water ice, carbon dioxide, silicates and organic compounds.
Calisto has a small silicate core. The Galileo space mission has indicated that
the moon may have an ocean of sub surface water at a depth greater than 100 km.
It is
not in orbital resonance with Jupiter like the other 3 major moons Io, Europa
and Ganymede and is therefore not tidally heated and therefore has fewer
chances for life to evolve.
4.
TITAN.
Titan
is the largest moon of Saturn and the 2nd largest moon in the solar
system after Ganymede. It is larger than planet Mercury, and is the only moon
that has a dense atmosphere in the solar system. While Mercury has mainly iron
and rock while Titan has mostly ice and water. When viewed from Saturn it would
take up as much as 11 times space than our own moon does from earth. Of course
that is from above its thick atmosphere.
TITAN.
In fact
Titan is the only body in the entire solar system with water on its surface (and
not beneath an ice sheet) excluding our own planet Earth. Titan has a rocky core surrounded by layers of
ice and sub-surface ammonia rich liquid water.
Its
thick atmosphere prevented us from knowing about it till the CASSINI HUYGENS
mission of 2004 provided much information about it. It was discovered that
Titan had lakes of Hydrocarbon at its polar regions. It was also discovered
that Titans atmosphere had Super Rotation i.e. its atmosphere rotated much
faster than the planet. The surface of Titan is generally smooth with only some
impact craters.
The
atmosphere of Titan is mainly Nitrogen & Methane. There are hydrocarbon
clouds and heavy organo-nitrogen haze. Its wind and rain creates surface
features similar to earth like dunes, rivers, lakes, seas (probably of liquid ethane
and methane). Titans Methane cycle resembles Earths water cycle but at a much
lower temperature at -179 Degrees Celsius. Due to these features Titan is
called the most Earth like object in the Solar System albeit with a different
chemical composition of its atmosphere. Its surface pressure is also similar to
earth at 1.45 times that of earth.
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