Underground pools of salt water may be common on Jupiter’s moon, Europa, according to researchers who believe the sites could be promising sites to search for signs of extraterrestrial life.
Evidence of shallow puddles, not far below the frozen surface of the Jovian moon, emerged when scientists noticed that giant parallel ridges extending hundreds of miles over Europe were strikingly similar to surface features detected on the Greenland ice sheet.
If the vast ice ridges crisscrossing Europe formed in a similar way to those in Greenland, pockets of groundwater might be ubiquitous in the body and help distribute life-giving chemicals from the ice crust to the salty ocean that lurks far away.
“Liquid water near the surface of the ice crust is really a provocative and promising place to imagine life after you’ve got a bullet,” said Dustin Schroeder, assistant professor of geophysics at Stanford University. “The idea that we could find a signature that would suggest a promising pocket of water like this, I think, is very exciting.”
Europa is 2,000 miles wide, which is slightly smaller than Earth’s moon. It became a major contender in the search for life elsewhere when observations from ground-based telescopes and the Transiting Space Probe found evidence of a deep ocean 10 to 15 miles below its icy surface.
Europa’s ocean is estimated to be about 40 to 100 miles deep, so even though it’s a quarter of the Earth’s width, it may contain twice as much water as all of Earth’s oceans combined.
Despite all that is known about Europa, images of the frozen body have thrown up long-standing mysteries. The first is the presence of wide double edges that cover the surface like scars. The ridges can be up to 300 meters (1,000 ft) high and are separated by half-mile wide valleys.
The Stanford University team got its start with an academic presentation on Europa mentioned intriguing diploids. Images of the features reminded scientists of a much smaller double edge they observed in northwest Greenland. Armed with radar and other observations of Greenland’s hills, they set out to understand how they formed.
“On the Greenland ice sheet, there is a feature of small double ridges that are very similar to those we see on the surface of Jupiter’s moon Europa,” said Riley Culberg, a doctoral candidate and geophysicist at Stanford University. “And the exciting reason we’ve had this analog advantage in Greenland is that we’ve been trying to figure out what makes the double spurs over Europe for about 20 years.”
Writing Nature CommunicationsThe researchers described how Greenland’s double ice ridges, which are about 50 times smaller than those in Europe, formed when shallow pools of groundwater froze and repeatedly broke the surface, steadily rising ridges. “It’s like when you put a soda can in the freezer and it explodes. That kind of pressure is what pushes the edges on the surface up,” Kohlberg said.
In Greenland, water drains into underground pockets of surface lakes, but in Europe, scientists suspect liquid water is being pushed toward the surface from the underlying ocean through fractures in the ice crust.
They added that this movement of water could help circulate chemicals essential for life in the ocean of Europe.
It’s “reasonable” that Europa’s hills were formed by upward water pressure, said Michael Manga, a professor of Earth and planetary sciences at the University of California, Berkeley, who was not involved in the research.
But the questions remain. “I wonder why the features are so much smaller on Earth,” he said. While Earth’s stronger gravity could explain why the hills are lower here than in Europe, it’s unclear why the valleys between them also narrow.
NASA Europa Clipper MissionScheduled to launch in 2024, it is expected to shed light on how the double spurs form as it makes a detailed survey of Jupiter’s moon and investigates whether it harbors conditions suitable for life.