30Aug2014

Our Understanding Of How Planets Formed

Planet Formation

Image credit: Lynette Cook for Gemini Observatory/AURA

Have you ever wondered how planets are formed? For hundreds of years astronomers have imagined how it could have formed and formed theories around these ideas as more and more evidence came into the picture.

However, we can only observe after the fact planets have formed so it makes it a little difficult to study. There are ways around this and the Hubble Space Telescope has helped scientists all over uncover the mystery of how planets are formed. Let’s take a look.

From our understanding we know that a star and its planets form out of a collapsing cloud of gas and dust within a larger cloud, which is called a nebula. Some of these gasses and dust are leftovers from supernovas and colliding stars. As gravity starts to take over and pulls in the materials together, the cloud compresses, churns, and gets hotter. What you would see is a hot core or the birth of a star.

The fun isn’t over yet. The cloud around the star starts to churn as the inherent motion within kicks in. The ring of dust and gas gets exceedingly more compressed and starts to rotate all in the same direction. Soon it gets thinner and flatter as it spins more and more, like spinning cosmic pizza dough. The stellar disk or “protoplanetary disks” as astronomers call them, is where the magic happens and planets are born.

Protoplanetary disk dust

Artist’s impression of a proto-planetary disc forming around a star

As everything is moving in the same direction you have a scene of a cosmic shooting gallery. In this shooting gallery, dust or rocks collide together and form into larger rocks. You can think of this when you see dust bunnies form on the ground, as they swirl around and clump together to make larger dust balls. As these rocks swirl around the protoplanetary disk it catches some of the gasses flying around and get bigger and bigger.

Soon they start forming more into the familiar shape of a planet or the beginnings of a “planetesimals.” In the inner disk most of the gas has either been gobbled up by the star or cleared out already. This leads to the formation of smaller rocky planets closer to the star. In the outer area of the disk there is still ice, dust, and gasses looming around. This additional material allows the planetesimals farther from the star to grow larger as it accumulates dust, gas, and ice.

Eventually, the path for each planet starts to clear out and be able to travel around the star. The really cool picture that you should visualize now is that hundreds of these planetesimals are forming at the same time. It also means that they inevitably meet up and collide. If their paths cross at the right time and they’re moving fast enough – CRASH – right into each other sending debris every which way. However, if they are travelling slowly and moving toward each other then gravity can gently mend the two together.

If the two pieces of rock or participants are further away, their gravitational encounter can pull the body off the course. This means trouble as it can send these participants flying across lanes of traffic and causing multiple collisions. So you can imagine how active the process is and extremely dangerous for anyone within it. After millions of years of countless encounters and collisions the dust starts to settle and you are left with many larger and fewer planets that dominate their area. Source: BrownSpaceman

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