Some of the most extreme planets ever found beyond our Solar System are making astronomers re-evaluate how rocky planets develop and the atmospheres they retain.
These highly irradiated exoplanets, which are also known as lava planets are so hot they can cause rocks to melt, yet some have recently been shown to retain thick atmospheres for billions of years.
Researchers at Stanford University are attempting to introduce a different planetary regime termed the “cosmic sandbar.” If valid, the theory may help account for why lava-covered planets found that they actually had significant atmospheres under enormous radiation from their stars.
Recall that scientists have the ‘cosmic shoreline’ idea; basically it describes where rocky planets (harder closer to the star) start losing their atmospheres to space. As one approaches a star; stellar radiation increases in strength. But several lava worlds seem to fall on the wrong side of that division.
A notable example is the super-Earth 55 cancri e which sits very close to its star. The James Webb Space Telescope has revealed it to have a thick atmosphere despite the intense radiation it is subjected to.
More and more evidence like this is appearing with additional observations of hot rocky planets which do not conform to the usual picture. The new model implies an important role for the molten rock.
Rather than just losing atmosphere gases to space, a lava-covered planet can gain and lose gases to its molten surface; while some gases are lost to space, others are replaced through outgassing of the planetary interior.
If these processes were to reach equilibrium, the atmosphere would be likely to survive for billions of years.
They characterize this as a new domain, a cosmic sandbarbeyond the official “cosmic shoreline”that is, a circumstance where atmospheric attrition due to stellar radiation is compensated for by outgassing from the molten interior of a planet.
Maybe that balance accounts for Really some worlds a lot closer to the stars than Mercury is to the Sun and still hold on to thick gassy atmospheres.
The model also takes into account the planet’s evolution.
For example, as the planet cools and its surface solidifies, active volcanoes can cease to erupt meaning the flow of gases from the interior to the atmosphere can be fundamentally altered. When this occurs may determine if the planet ends up with a substantial atmosphere or is almost airless.
The number of lava planets currently known, and that are being observed, is rapidly increasing due to a new interest taken by observation from the James Webb Telescope.
The reason is NASA reporting in March that Webb observations of TOI-561 b indicated that the firey super-Earth has a rich volatile atmosphere overlying an enormous magma ocean, unlike a bare rocky surface.