How do we know what planets are made of and why should we care?

Before we talk about planets we need to understand the stars.

More importantly how stars are born.

 

Stars form in gas clouds, also known as interstellar clouds. Regions in space with gaseous elements. When stars form their new gravity causes the cloud around them to compress into a disc. These are known as accretion discs. Accretion discs look like frisbees, also like frisbees they spin around the star.

 

Why is any of this relevant?

Well as an accretion disc spins the matter within it bumps into each other slowly growing in size, like snowballs but with rocks instead of snow. Over time this process forms planets, moons, asteroids, etc. Basically most of the stuff you find in a solar system is made through this snowball method.

 

Before the invention of more powerful telescopes, we used to think there were only planets in our solar system, but in recent decades we found out that most stars have planets. So every star we see in the night sky likely has its own solar system.

Meaning there are millions if not billions of planets in the universe. Scientists now are trying to find out what these so-called exoplanets are made of and if they can support life.

 

It can be difficult to study exoplanets since they don’t emit any light, so scientists use methods like spectroscopy to study gas clouds instead.

You might be wondering “How are those two things related?”.

Well, when scientists study the makeup of a gas cloud or accretion disc they know that any planet that forms out of it will have roughly the same composition.

 

Why does a planet’s composition matter though?

Planets need to have certain compounds to be able to sustain life. For example, they need carbon, oxygen and hydrogen for organic molecules. Phosphorus and sulphur are also vital for sustaining life, as they are needed to make some organic molecules. If they find a planet that has the basic building blocks for life then we can study it further.

Who knows we might even find another Earth.

 

Source:

Öberg, K. I., & Bergin, E. A. (2021). Astrochemistry and compositions of planetary systems. Physics Reports, 893, 1–48. https://doi.org/10.1016/j.physrep.2020.09.004