Why is looking at an exoplanet’s atmosphere up close so important?
Exoplanet scientists are already characterising the atmospheres of large and hot exoplanets. We’ve found evidence of lots of clouds, water vapour, methane and other molecules and atoms, as well as evidence of winds. The next stage is pushing the envelope towards smaller and cooler planets.
Large planets have thick atmospheres, which makes them easy to detect and characterise. It also helps if the planet is hot because heat puffs the atmosphere up, making it larger and easier to detect. Small, cool planets, like Earth, have very thin atmospheres, and this is very challenging for our current telescopes. While we’re waiting for the next generation of telescopes like the Extremely Large Telescope (ELT) and the James Webb Space Telescope, astronomers are still looking for the most favourable exoplanets for characterisation.
It helps a lot if the exoplanets are relatively nearby – within about 100 light years – transiting and are very close to their parent stars. However, most planets do not transit their parent stars, and we’re interested in more than just close-in planets. Beyond the 2020s, when starlightblocking technologies like coronagraphs and starshades become more advanced, we will be directly imaging a greater diversity of planets. We will be able to characterise not only exoplanet atmospheres, but also exoplanet surfaces.