Making planets

Exoplanets are planets that orbit stars other than our Sun, so they're outside of our solar system. The first exoplanet orbiting a sun-like star, discovered in 1995, is called 51 Pegasi b. This discovery completely changed the way we look at our solar system and the possibilities of the universe. This planet orbits its star in under a week. It is the size of Jupiter, about 11 times the radius of Earth, but orbits 20 times closer to its star than we are to the Sun.

The most common size of exoplanet in our galaxy is non-existent in our solar system. These planets are sub-Neptune in size. Neptune is the smallest of our gas giants, sitting at the furthest distance from our Sun and mostly made of hydrogen and helium. Earth is the largest rocky planet in our system. About 50% of discovered planets are actually somewhere between the size of Earth and Neptune. The big question this poses is what they are made of: are they super-sized rocks, called super-Earths, or compressed gas giants, called mini-Neptunes?

From the discovery of 51 Pegasi b, a hot Jupiter sitting right next to its star and heated by radiation, to the Kepler mission showing a galaxy filled with super-Earths, we have a fundamental question: what are their atmospheres made of? An atmosphere defines the environment and where a planet formed in the first place.

We expect to discover atmospheres dominated by hydrogen and helium, which are hard to measure. We look for tiny components, such as water vapor, CO2, and methane. The relationship between carbon monoxide and methane can tell us a huge amount about the chemical and thermal structure of an atmosphere.

Very early on, we used the Hubble Space Telescope to look for water vapor, which is one of the most common molecules in the entire universe. We find it orbiting black holes, in star formation regions, and across our solar system. We expected water to be mixed within these atmospheres, but we found less than expected.

The study of exoplanets requires a whole team of scientists together to make discoveries. The amazing diversity of worlds requires different questions and techniques. Our communities require experts in observations, data analysis, stars, and chemists to understand alien chemical networks. Science isn't done on its own anymore, and exoplanets is a perfect field to show how community comes together.

If I was to single out one misconception in the field, it is that we're all looking for aliens. What we're looking for is understanding about how these planets are made and how the dynamics of a system might change the way a world sees the universe. We want to fundamentally understand the physics, chemistry, and mechanisms behind these extreme environments; it is not always about aliens.