In this vast universe, there exists a galaxy which is known as Milky Way and in that galaxy exists our home, our very own solar system. Once upon a time, there was no sun, planet or moon but only dust and gases, then around 4.6 billion years ago matter in this solar nebula started collapsing under its own gravitation which in the end formed a protostar. Protostar is a young version of a star which slowly becomes a star. After some time, the core started fusing hydrogen and the gravitational collapse was stopped with the formation of our Sun. The left over rocks and dust slowly formed planets, asteroids and moons. Scientists still are not sure about the processes that were responsible for the formation of planets but there are some pretty good theories like core accretion, pebble accretion and disk instability method which tries to explain the creation of our home.
Our Sun is one of the focii of the elliptical path that is traced by a planet. It is the largest source of heat and light in our solar system and occupies about 99.8% mass of the solar system! It majorly consists of Hydrogen and Helium and is a stable mid aged star. When it uses up all it’s Hydrogen, our Sun will turn into a red giant engulfing half of the inner planet and wiping out life on Earth (of there is any left till then). Then it will become a comparatively small white dwarf which will be its life’s last stage.
Surrounding the Sun, our solar system consists of 4 rocky or inner planets, 4 outer or gas giants with moons, asteroids and other debris. The objects in the increasing order of their distance from the Sun are Mercury, Venus, Earth ,Mars, Asteroid Belt, Saturn, Jupiter, Uranus, Neptune and the Kuiper Belt which contains the famous dwarf planet Pluto.
Mercury which is named after Roman messenger of gods is the smallest planet in our solar system with a radius of approximately 2,439.7 kilometres. It is also the closest planet to Sun with a high eccentric elliptical orbit. It has no natural satellite. It takes around 88 days to complete a revolution around the Sun and has almost 0 degree of axial tilt. The first 2 spacecrafts to visit the planet were Mariner 10 and MESSENGER. Mercury’s surface resembles the surface of moon, it is filled with rocky terrains, crates due to asteroid impacts, mountains and valleys. Mercury has no atmosphere but surprisingly has a magnetic field, which tells us that it’s core must be in a molten state.
The next closest planet to Sun is Venus. It is named after the Roman goddess of love and beauty. Venus takes about 225 days to complete one revolution around the Sun and unlike other planets, it rotates from East to West with respect to it’s surface (as there are no directions in space). Just like Mercury, it has no moons or rings. Venus and Earth are often referred as sister planet as Venus is very similar to Earth if we talk about it’s size and mass but, Venus has a really thick atmosphere made up of green house gases like carbon dioxide and sulphur dioxide and because of such strong green house effect Venus is currently the hottest planet on the solar system. It is almost impossible to get a glimpse of Venus’ surface from the space because of the thick clouds that cover it. Venus’ atmosphere exerts around 92 times of pressure than that of Earth’s which is a reason that it is very difficult for rovers and landers to stay intact on its surface. Interestingly more than 40 spacecrafts have explored Venus and it’s hot desert like surface. Venus is often referred to as the morning or the evening star because earthlings can see it during that time.
Next up is our planet Earth. Earth is the only place in our Universe where life is till now known to exist. Earth was formed around 4.5 billion years ago which was discovered by Clair Patterson. It has one moon along with strong magnetic field and Van-Allen Belts. This magnetic field is generated by the rotation of molten core and mantle which also drives the motion of tectonic plates (plate tectonics theory was given by Alfred Wegner). Earth is around 71% water which contributes to it’s name, the blue planet. Earth takes around 366 days to go around the Sun and around 24 hours to go around it’s axis of rotation once which is tilted by an angle and seasons are a result of this tilt. It is the largest inner planet and is around 149,597,871 kilometres (the mean distance, it goes around the Sun in an elliptical orbit just like other planets do), this distance is also called as an AU or 1 Astronomical Unit. Our planet is extremely beautiful and rich in life which is a very unique property as compared to other planets.
Our next stop is Mars which has always been one of our prime suspects of alien life. Mars is the second smallest planet of our solar system with a distinct reddish colour surface and atmosphere which is caused by the presence of rust on the surface. It has got two weirdly/potato shaped moons named Phobos and Deimos. There have been a ton of missions to study Mars with the most recent one being InSight, all of them revealed that the possibility of presence of life on Mars in present conditions is almost 0 but there have been some speculations about aliens living on Mars in the past. Mars is covered by a thin atmosphere and takes about 687 days to go around the Sun once. It has a rocky terrain and is home to some of the highest peaks and deepest valleys of the solar system! InSight is right now digging into the Mars’ surface to provide us with the unknown information about it’s inner composition. Some parts of Mars’ orbit lie in the habitable or the Goldilock zone but liquid water is still absent on Mars. The space missions are really helping us in understanding Mars better and hopefully someday we will walk on this rocky and dusty planet.
Between the inner and outer planets, there exists a separation called a stage asteroid belt. This is a place where tiny countless objects know as asteroids exits. This belt is located between Mars and Jupiter and is about 1 AU wide. The concentration of Asteroids here is comparatively larger than other places in solar system but still is very less. Ceres, a dwarf planet is also one of these billion asteroids moving in this belt, infact it is the largest one. There are some theories that describes the origine of this belt, one of which is that these rocky pieces were actually going to form a planet but couldn’t due to Jupiter’s immense gravitational force. Asteroids can also get out of this belt due to gravitational pull and then they can wander around in the solar system. This belt is also called as the Main Asteroid belt to differentiate it from NEOs( Near Earth Objects) and Trojans.
The planet in the solar system after the asteroid belt is Jupiter. Jupiter is the largest planet in the solar system and is a gas giant. It would take around 1321 Earths to fill a hollow Jupiter! It is majorly composed of Hydrogen and has no solid surface. If you somehow try to land on Jupiter, you will fall into it’s core as it’s surface is made up of gases. Jupiter is suspected to have liquid metallic hydrogen underneath its surface! This might have formed because of the immense pressure and this variant of hydrogen can easily conduct electricity but it doesn’t occur naturally. Jupiter has got a great number of moons, till now Jupiter has 79 known satellites including the 4 famous Galilean moons which were discovered by Galileo( Io, Europa, Ganymede, Callisto). It also has a faint but visible ring system. Jupiter also has a very strong gravitational as well as magnetic field which protects Earth by pulling many asteroids towards Jupiter. It is also very easy to see Jupiter even in the cities with naked eyes and Jupiter is the third brightest object in the night sky, after moon and Venus. Jupiter is also famous for its huge dust storms, the most famous one being the Great Red Spot. This is a storm which is as huge as almost 3 Earths and is going on since a long time.
The next planet is probably the most beautiful one when observed from the space. Saturn which is named after the Roman goddess of agriculture is the second largest planet in the solar system and has got a massive ring system which makes it unique in our solar system. These rings aren’t continuous, rather they are made up of small chunks of ice and space debris. It takes around 11 hours to rotate around it’s axis and almost 29 Earth years to go around the Sun once. Its radius is about 9 times than that of Earth and it has got around 62 moons. Saturn is the least densest planet(even less denser than water!) in our solar system and is mostly made up of hydrogen and helium. It has got a strong gravitational force and fairly strong magnetic field. Just like Jupiter, Saturn lacks the solid surface but most probably has got a solid core. Saturn’s moons are very diverse and different, some of them even have their own atmosphere, Titan which is one of the satellites of Saturn even has hydrocarbon lakes on its surface! Saturn’s moon Enceladus even shows signs of liquid water and ice with salts, this even puts Enceladus in our list for potentially hosting alien microbial life! The recent Cassini spacecraft helped us to explore Saturn more which was intentionally destroyed in 2017.
Uranus which is named after the Greek god of sky Ouranos is called as an ice giant because of its freezing temperature and presence of icy materials like water, methane and ammonia in it’s atmosphere. Uranus and Neptune are extremely similar but definitely different from Saturn and Jupiter and that is why they are referred as ice giants and not gas giants. Uranus is extremely tilted, it is just like a ball rolling around the Sun and taking about 84 years to complete one revolution. It is roughly 20 AU away from the Sun and takes about 17 hours to rotate around it’s axis of rotation. Uranus has got a lot of hydrogen sulphide in it’s atmosphere which makes it small like rotten eggs. It has 27 known moons with a visible ring system. There hasn’t been a dedicated space mission to study about Uranus but there have been some flybys by spacecrafts like voyager 2 and Voyager 1 ( Voyager 1 recently crossed the Heliosphere, becoming second hand made object to do so!). Uranus is probably the most dull planet in the solar system of you see it through visible light but is very interesting once you see in other forms of light. It has got layers of clouds and every layer is composed of something different than the previous layer! Uranus is covered with high speed winds which are actually faster than that at Jupiter bit slower than that at Neptune.
The last, the farthest from Sun and the coldest planet is Neptune. It is named after the Roman god of sea and is the densest outer planet with 14 moons. Just like other gaseous and icy planets, Neptune is also mainly composed of hydrogen, helium, ammonia and methane. It has strong visible weather changes with high speed winds which are actually the fastest in our solar system. These winds often form big storms just like Jupiter’s great red spot! Neptune also has a faint and barely visible ring system and is about 30.1 AU far from the Sun. Neptune, which takes around 165 years to complete one revolution around Sun, is actually the only planet which was predicted in theories before it’s discovery. An eighth planet(Neptune) was predicted to exist by observing the anomalies in Uranus’ orbit. Neptune takes around 16 hours to complete one rotation and it’s axial tilt is very similar to that of Earth’s. As it is composed of gases (with a solid core), it’s surface takes different time to rotate at different latitudes.
Behind Neptune there is a whole new icy world known as Kuiper belt or the Edgeworth-Kuiper belt. This belt contains billions and millions of small rocks floating around in space which includes Pluto. This belt is home to 3 officially recognised dwarf planets which are Haumea, Pluto and Makemake. Many of these bodies have their own moons and thin atmospheres like Pluto has a moon named Charon, Haumea even has a ring system around it! Our New Horizons spacecraft, after visiting Pluto recently, is still travelling and is aiming to reach 2014 MU69 on 1st January 2019 which will help us to understand this belt better. Scieni also predict a planet X or planet 9 that exists near this belt which has a strong gravitational pull. But our solar system doesn’t even end here, it continues even further where Eris, another dwarf planet exists! Our solar system is contained within a crescent moon shaped cloud formed by solar winds which is called as Heliosphere and which is again thought to surrounded by Oort’s cloud whose existence is still isn’t proved. Till now, only 2 human made objects have left Heliosphere, which are voyager 2 and Voyager 1 but soon there would be many more. Different objects in the solar system are waiting to be discovered, the only thing we need to be successful in any field is curiosity and hardwork. Keep staring above an keep asking questions!