The ice crust of Jupiter’s moon Europa hides a lake as large in volume as the American Great Lakes, say scientists studying images from NASA’s Galileo spacecraft. If true it would be the most promising place in the Solar System to look for extraterrestrial life.
The scientists focused on two images showing bumpy features called chaos terrains. Based on similar processes seen with Earth-based ice shelves and volcanoes covered by glaciers, they developed a four-step model to explain how these features form on Europa.
The chaos terrains could be ice shelves floating on subsurface lakes; cracking and churning as they do so. It appears to resolve several conflicting observations that sometimes show that the ice shell is thick, and sometimes that it is thin. Dr Louise Prockter of Johns Hopkins University’s Applied Physics Laboratory (APL) says, “For quite some time, Europa geologists have been struggling to figure out what these features are and how they form. This is the first time that anyone has come up with an end-to-end model that explains what we see on the surface.”
What’s more, in their paper published in the journal Nature, the scientists say that there should be many more such lakes waiting to be discovered. Although the idea of Europa harbouring an ocean under its icy shell has been around for a while, whether this means the moon could actually support any life has been a source of heated debate for years.
The problem is that the open question of the ice crust’s thickness is a crucial one for biology. As co-author on the paper, Dr Wes Patterson of APL says, “Europa’s subsurface harbours much of what we believe is necessary for life. But, chemical nutrients found at the surface are likely vital for driving that biology.”
Dr Britney Schmidt of Texas University’s (Austin) Institute for Geophysics, and lead author on the paper says, “One opinion in the scientific community has been that if the ice shell is thick, that’s bad for biology: it might mean that the surface isn’t communicating with the underlying ocean.”
In other words if the ice crust is too thick then it is unlikely to crack all the way down to the ocean below. Thus the two sets of chemicals necessary for biochemistry never mix, and the ocean would remain sterile. The presence of the lakes would be the solution. Even if the crust was thick, subsurface lakes (sourced by the ocean below) could act as ‘mixing chambers’ for all of the required chemicals, meaning that Europa could support an ecosystem.
The scientists are confident that their terrain model is correct. However, because the inference is that the lakes lie several kilometres below the surface, the only true confirmation of their existence would come from a future mission designed to probe the ice shell. Prockter says, “If we’re ever to send a landed mission to Europa, these areas would be great places to study.”
The Galileo spacecraft orbited Jupiter from 1995 to 2003 when it was deliberately crashed into the planet’s clouds to avoid accidentally contaminating the moons at some time in the future.
Kulvinder Singh Chadha is a UK-based freelance science writer, and a former assistant editor of Astronomy Now magazine. He has an astrophysics degree from the University of Hertfordshire.
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