Mikko Tuomi<p>The common mini-Neptunes typically form with a <a href="https://scicomm.xyz/tags/hydrogen" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>hydrogen</span></a> <a href="https://scicomm.xyz/tags/atmosphere" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>atmosphere</span></a>, resulting in conditions where <a href="https://scicomm.xyz/tags/hydrogen" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>hydrogen</span></a> and the <a href="https://scicomm.xyz/tags/planet" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>planet</span></a>’s molten interior interact for millions to billions of years.</p><p>But the temperatures and pressures involved are so extreme that laboratory experiments to study them are nearly impossible. </p><p>Water and hydrogen would begin to separate deep within the atmosphere leading to rainfall deep inside the planet’s atmosphere as heavier water sinks.</p><p><a href="https://astrobiology.com/2025/03/atmospheres-of-new-planets-might-have-unexpected-mixtures-of-hydrogen-and-water.html" rel="nofollow noopener" translate="no" target="_blank"><span class="invisible">https://</span><span class="ellipsis">astrobiology.com/2025/03/atmos</span><span class="invisible">pheres-of-new-planets-might-have-unexpected-mixtures-of-hydrogen-and-water.html</span></a></p>