It’s not entirely clear yet how Earth got its oceans, although it’s likely that it was a mixture of cometary impacts and water effusing from the planet’s hellish depths several billion years ago. A new paper posted to the preprint server arXiv has suggested that, on other worlds, oceans may appear in an even more dramatic manner.
As first spotted by New Scientist, this hypothesis – courtesy of a team of researchers at the German Aerospace Center (DLR) – focuses on worlds whose atmospheres are rich in hydrogen and oxygen.
When taking the form of free gas molecules, they can become quite explosive if ignited by a sudden burst of energy; say, a bolt of lightning. This reaction releases a lot of thermal energy, and the surrounding air expands rapidly. At the same time, it releases a quantity of water – the result of hydrogen and oxygen combining.
The Berlin-based team was curious as to what proportions and amounts of atmospheric oxygen and hydrogen were required to trigger such a paroxysm. Could there be a world out there whose atmosphere featured significant water-forming blasts like this, and if so, how much water could they produce?
Sure, Earth’s atmosphere contains a fair bit of oxygen, but there’s nowhere near enough hydrogen to cause a violent explosion every single time there’s a thunderstorm. The team’s calculations suggest that so-called Super-Earths – rocky worlds whose mass greatly exceeds that of our own, but remains below that of ice giants like Neptune – are good candidates.
Specifically, those that orbit pre-main sequence red dwarf stars are suspected of sometimes having large amounts of free oxygen produced when it’s separated from water molecules via high-energy interactions in the atmosphere.
Despite hydrogen’s ability to escape most planets due to its low molecular weight, Super-Earths are also likely to be relatively rich in free hydrogen too if their gravitational fields can attract enough from the gaseous matter floating within the same planetary system.
When these gases accumulate, and the atmosphere reaches the thrilling-sounding “combustion-explosion limit”, a lightning strike, or even some casual cosmic ray bombardment, it can cause the spark that creates water at, well, lightning speeds – along with “modest amounts” of hydrogen peroxide.
The team’s study concludes that large amounts of H2 and O2 can react in this way to form “up to about 10 Earth oceans” on these Super-Earths.
“The water production would be instantaneous – of the order of seconds or less,” lead author Dr John Lee Grenfell, of the DLR, told IFLScience.
One major caveat though is that this oxygen generally emerges from pre-existing water in the first place, which means that instead of new oceans being created, you're essentially recycling old ones. Grenfell points out, though, that “if the oxygen comes from other sources – for example from carbon dioxide being split by light – then the answer is no… you don’t need water to form water.”
In any case, “the explosion mechanism is still a way to slow down water loss on the planet, so that’s good for life.”
The team's study also notes that, as oxygen can accumulate via photochemical reactions without the need for photosynthetic life, their work “has important repercussions for interpreting O2 gas as a biosignature.”
In case you're wondering, this isn't the only over-the-top weather out there in the cosmos.
Saturn’s Titan, for example, has a methane-driven climate whose winds blow over electrified sand dunes. Io has planetwide sulfurous snowfall every time in steps into Jupiter’s shadow, and the snow on Mars appears almost out of nowhere. Some exoplanets are so superheated by their host stars that it rains pebbles and boulders on oceans of lava.
Sure, Earth has bomb cyclones – but compared to the rest of the galaxy, our meteorology’s a bit meh, really.