Observatories in Chile scan the sky taking pictures of the young exoplanetary systems. Here there are just discs of gas and dust- a new star just about to be born. We must observe these discs to answer the fundamental questions about how our very own solar system was formed. These discs also show us the planetary formation that takes place.
This observatory in Chile observed a young star- only about a million years old. Planets had already been starting to form around the star/ Astronomers noticed that there were these rings around the star which had very little or almost no dust. It tells us that most planets form pretty quickly.
A star first starts its life as a cloud of dust and gas. Slowly the gas and dust clump together and collapse under their own gravity. As it squeezes in it spins faster and a lot of material is spun out. To build planets you need heavy elements in their gaseous form. A planet may seem huge when it reaches maturity, but its origin is from very tiny and minuscule dust particles. Due to the electrostatic forces the dust that meets in the cloud clumps together. These dust particles are incredibly tiny, the size of the particles beneath your sofa. This dust soon becomes centimetre-sized pebbles. At this stage due to physical reasons, the pebbles stop growing. They cannot stick to each other and bounce off of each other. Hence, we can say that there is a limit to which dust can grow.
Electrostatic forces are too weak to make a planet. However, the pebbles are capable of making a ring-like structure and the gas circling them slows the pebbles’ rotations and the pebbles eventually form planetesimals so that gravity can take over.
The Voyager travelled through the Kuiper belt. The Kuiper belt is a belt somewhat close to the edge of the solar system. It is a spectacular place filled with rocks and ice and the relics of the early solar system. The Voyager saw something spectacular. It witnessed a 22-mile rock. The rock was 2 planetesimals stuck together and they looked stuck by glue. They were bonded together by gravity and ice and friction. These are the very planet-building fossils that scientists were searching for. This was the missing link that shows us that dust forms pebbles which in turn create planetesimals about 10-10 miles long.
Although the planets are born equally, they are two sides of opposite poles. They are smaller near the Sun and grow larger as the distance increases. The Sun plays a critical role in the chemistry of the solar system. Heavy metals that survive the heat from terrestrial planets- Mercury, Venus, Earth and Mars. 250 million miles from the Sun- you hit the frost line. Water freezes here and there is a lot more material for larger planets to form. Ice helps in planet formation as it can bond very easily, this helps make colossal cores. Once you have a core about 20-30 times the Earth’s size it becomes effortless for gas to fall in- the process becomes uncontrollable. This is how you can make a huge planet.
Although, after running a few simulations, planetary scientists discovered that core accretion did not work on Jupiter. This process should take 100 million years but that is long. We found out that the Sun attacked the protoplanetary disc hence gas moved out fast. The protoplanetary disc lasted for about only 5 million years; Jupiter had to have formed fast for it did not have 100 million years of material to grow this large. Astronomers think that Jupiter rapidly builds its core before the gas is blown away and captures it. Huge numbers of small pebbles are present and planetesimals can consume a large number of pebbles.
If we use pebbles to model the solar system something strange is visible, pebbles reach the size of the Earth pretty quickly and another 100 smaller Earth-like rocky planets are formed. Clearly, something else is going on. The small planet wants to probably get larger but faster growing and larger planets like Jupiter gobble most of the pebbles up. The small one starves but the bigger one eats more. Pebbles helped Jupiter grow into the Solar System’s largest planet.
We see a variety of planets in our Solar System. Small terrestrial ones like Mercury, Venus, Earth and Mars and large planets like Jupiter. Nonetheless, computer simulations suggest that Mars could have been a much bigger planet than it is today. Mars is smaller than the mass of the Earth. It seems that something took a huge chunk of Mars out of the solar system. That 'something' being Jupiter.
As the protoplanetary disc pushes Jupiter closer to the Sun, its immense gravity pushes some planetesimals away from the region of Mars- driving away the material that Mars wanted. If Jupiter did not drive all that material we would have a mega Mars - 10 times the size it is today. Nevertheless, if Jupiter made its way near the Sun, it should still be here. Yet Jupiter was not the only planet that migrated. Saturn also moved and yanked back Jupiter into the outer solar system again.
Mars is not the only planet shaped by Jupiter’s existence. Scientists observe that there is more water on the Earth than there should be. This could be due to the contribution from the far parts of the solar system. Water-rich minerals were present millions of millions of miles away. How is it possible that Earth contains those? When Jupiter migrates it passes through the disc that contains water-rich minerals and showers Earth with that material.
The last stage of growing a rocky planet is the last collision stage. When Earth started forming it was hot, filled with lava and inhospitable, but something collided with the Earth and made a completely different planet. A shockwave covered the planet. 2000-degree rock water created a cloud of spinning vapourised rock. The Earth and moon begin to form. The moon soon emerges from the rock cloud and vapour.
The formation of planets in each star system is not yet clear to planetary scientists and astronomers though they hope to figure out the formation of planets soon. We can just hope and wait.
Bibliography:
Mark, Stephen. “How To Build A Planet” Discovery+. 21 Feb, 2021. Video. 5 Jul, 2022.
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