An ocean of liquid water hides under Enceladus’ icy surface NASA/JPL/Space Science Institute
There鈥檚 a cosmic snowball fight going on in the Saturn system. The planet’s inner moons are oddly bright, and it may be because one of the moons a little further out is spewing pristine snow at them.
The findings come courtesy of the聽Cassini spacecraft, which ended its mission by flying into Saturn in 2017. It carried with it a radar instrument which used radio waves to examine Saturn鈥檚 frigid moons.
Alice Le Gall at the University of Paris-Saclay in France and her colleagues analysed these radar observations and found that three of the moons, Mimas, Enceladus and Tethys, seem to be twice as bright as we previously thought. They this week at at a joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences in Geneva, Switzerland.
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That can be partly explained by Enceladus: it has huge geysers that spew water from its subsurface ocean into space, which then freezes and snows down on the nearby moons and Enceladus鈥 surface. Le Gall and her colleagues calculated that this layer of ice and snow should be at least a few tens of centimetres thick.
鈥淣ow we know that the snow is actually accumulating, it’s not just a thin veneer but a much thicker layer of water ice,鈥 Le Gall says.
This helps explains why the moons are bright at radio wavelengths, which can penetrate deeper under the surface than visible light. But even deep snow can’t fully account for how bright the moons appear. This suggests something聽else must be buried under the snow or resting on top of it, reflecting the radio waves from the spacecraft鈥檚 radar.
Le Gall and her team are in the process of modelling different structures that could do this – including a layer of snowballs, huge ice spikes, or widespread cracking – but they haven鈥檛 yet found any that match the observations and are also geologically plausible.
鈥淲e have a lot of structures to test, and it鈥檚 actually quite important for future missions that might land on these moons,鈥 says Le Gall. If we want to land there, we need to know first what the surface is like.
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