The right combination of gases could put exoplanets through an explosive sea change. Hydrogen and oxygen in an atmosphere can ignite and leave behind water, a reaction that could dump oceans onto a planet鈥檚 surface.
at the German Aerospace Centre in Berlin and his colleagues calculated how oxygen could build up in a planet鈥檚 atmosphere and combine with hydrogen to create water. They found that at high enough temperatures, the combination could combust or explode, lighting up the planet鈥檚 sky with a ball of fire.
Large rocky planets near dwarf stars tend to have atmospheres rich in hydrogen. This gas is pulled into a planet鈥檚 gravitational control from the disk of dust and gas surrounding its star. If there is a way for oxygen to build up, such as from sunlight splitting up molecules of water or ice on the surface, a small burst of energy like a thunderbolt or a cosmic ray can cause the mixture to ignite.
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In a burst of heat, sound, and light, the hydrogen and oxygen would combine to form water, which would then rain back down to the ground. 鈥淏ut it鈥檚 not like rain on Earth, where you have condensation droplets forming gradually in the atmosphere,鈥� says Grenfell. 鈥淚t would be a much more rapid fallout of water.鈥� Depending on the temperature, the water could form huge steam plumes or pour down as if buckets of water spilled from the skies all at once.
Rocket fire atmospheres
This is the same reaction that takes place in some rocket engines, generating the energy that pushes the rocket upward, the flame that shoots out of its thrusters and the steam that billows away as exhaust.
Such a reaction in a planet鈥檚 atmosphere could form water oceans on the surface at lightning speed. All life as we know it requires water, so this could enhance a rocky world鈥檚 habitability.
While this chemical reaction is well-known, at the Massachusetts Institute of Technology sees one big problem when it comes to exoplanets: the model requires the planet to have water in the first place to supply the oxygen that then reacts with hydrogen. 鈥淵ou do not end up with more water than you started with,鈥� he says.
Nevertheless, if聽ultraviolet light from the planet鈥檚 star is going to destroy the water on its surface, this is a way to get that water back to the ground. The development of life as we know it needs access to liquid water over long timescales, so if alien water cycles play out this way, oceans on other worlds could be replenished and stick around.
鈥淚t would keep water in the form of an ocean on the surface for longer,鈥� he says. 鈥淥bviously a big explosion isn鈥檛 what you would intuitively think is good for life, but in this case it could be.鈥�
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Read more: Ocean-covered planets may not be the places to search for life
