Beneath the frozen shell of Europa, flakes of ice may float upwards like strange underwater snow. The sparkling landscape formed by this process on the underside of the shell could be a favourable environment for alien life.
On Earth, the ice shelves in Antarctica are the closest analogue to the ice shells of Jupiter鈥檚 moon Europa and Saturn鈥檚 moon Enceladus, which are both thought to host global oceans beneath their frozen surfaces. There are two types of ice in the ice shelves: congelation ice, which starts in one spot and then spreads out as water freezes onto its edges, and frazil ice, which forms when supercooled water turns into ice crystals that then float up to settle beneath the shelf.
at the University of Texas at Austin and her colleagues compared measurements of Antarctic ice with observations and models of the ice on Enceladus and Europa to figure out which sort of ice we should expect there. They found that frazil ice could be common on both worlds, especially in areas where the ice shell is fractured, such as Enceladus鈥� famous 鈥渢iger stripes鈥�.
Advertisement
Both frazil and congelation ice are generally less salty than the ocean water from which they form, but frazil ice tends to be particularly pure at around 0.1 per cent of the salinity of the underlying water. 鈥淗ow the ice freezes matters a lot for how salty the ice would be,鈥� says Wolfenbarger. 鈥淭here鈥檚 a chance that the ice could be a lot more pure than has been previously estimated.鈥�
Understanding the relationship between the salinity of the ice and that of the water could help us understand the conditions in the oceans of Enceladus and Europa, even if we can鈥檛 drill down to sample them directly. The salinity of these oceans is crucial for the possibility of microbial life there, because any organisms may not be able to survive if the water is too salty.
The likely presence of frazil ice is particularly intriguing because it is porous and could bring nutrients from deep underwater up to the bottom of the ice as it snows onto the underside of the shell. 鈥淎t the bottom of the ice shelf it could be pretty mushy, and that鈥檚 an environment that organisms like to inhabit,鈥� says Wolfenbarger. 鈥淲e have actually seen protists in these environments on Earth, which hints that these might be good environments to look for life 鈥� assuming we can get to them.鈥�
Astrobiology
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
