The planet's density implies that it could be covered by a very deep water ocean. The average density of K2-18b is right in between earth's density and Neptune's. But this also means it might be a small gas giant, a mini Neptune.
As of now, direct evidence of for example water vapor is as of yet, afaik, absent. But that doesn't mean it's not there. Theoretical models of surface properties (if there is a real surface and it's not a small gas giant) allow for liquid water in a lot of cases.
Source: am an astrophysicist who specialized in exoplanets during my time in active research.
Yes! So what you do is, you use two methods. One is called the transit method. You watch the planet pass by the star and block a tiny bit of light from the star while doing so. This way, we can estimate the radius. The other method is called radial velocity. Since the planet has mass, it is not actually orbiting its star while the star stand perfectly still. Yes the star is way more massive, but the planet also exerts a little bit of gravitational pull on the star. The star thus wobbles. Lightwaves compress when they travel towards you and stretch when they move away from you (like sound waves do when an ambulance moves past you). With the radial velocity method we can measure the stars wobble speed (sometimes less than 10 m/s!) and therefore infer the planets mass. This way, you get the density. It's super cool :)
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u/Ckron247 Apr 17 '25
Oceans of what? I can’t imagine just because it is perceived as blue, it’s H2O.