Subterranean saltwater pools may be common on Jupiter’s moon Europa, according to researchers who believe the sites could be promising spots to look for signs of extraterrestrial life.
Evidence of shallow puddles not far beneath Jupiter’s moon’s frozen surface emerged when scientists noticed that giant parallel ridges stretching hundreds of kilometers across Europa were strikingly similar to surface features discovered on the Greenland ice sheet.
If the vast ice ridges criss-crossing Europe formed in a manner similar to Greenland, pockets of groundwater could be ubiquitous in the body, helping disperse life-giving chemicals from the ice crust to the salty ocean far away.
“Liquid water near the surface of the ice crust is really a provocative and promising place to imagine life after a bullet,” said Dustin Schroeder, an assistant professor of geophysics at Stanford University. “I’m very excited about the idea that we might find a signature that points to a promising water bag like this.”
Europa is 2,000 miles across, which is slightly smaller than Earth’s Moon. It became a key competitor in searches 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.
Europe’s ocean is estimated to be 40 to 100 miles deep, so despite being a quarter the width of Earth, it can hold twice as much water as all of Earth’s oceans combined.
Despite what is known about Europa, images of the frozen body have long posed a mystery. The first is the presence of wide double ridges that cover the surface like scars. The ridges can be as high as 300 meters (1,000 feet) and are separated by valleys half a mile wide.
The Stanford University team began with an academic presentation on the intriguing diploids mentioned in Europe. Images of the feature reminded scientists of a much smaller double ridge they observed in northwestern Greenland. Armed with radar and other observations of the Greenland hills, they set out to understand how they formed.
“There is a feature of small double ridges on the Greenland ice sheet that are very similar to those we see on the surface of Jupiter’s moon Europa,” said Riley Culberg, a graduate student and geophysicist at Stanford University. “And the exciting reason we had this analogous advantage in Greenland is that we’ve been trying to figure out what constitutes the double spurs over Europe for about 20 years.”
Writing in Nature Communications, the researchers described how Greenland’s twin 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 you put a soda can in the freezer and it explodes. That kind of pressure pushes the edges up on the surface,” Kohlberg said.
In Greenland, water flows into underground pockets of surface lakes, but in Europe scientists suspect that liquid water from the ocean below is being pushed to the surface through fractures in the ice crust.
They added that this water movement could help circulate chemicals essential to life in Europe’s oceans.
It’s “reasonable” that the hills of Europe 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 with the research.
But the questions remain. “I wonder why the features on Earth are so much smaller,” he said. While Earth’s stronger gravity might explain why the hills are lower here than in Europe, it’s unclear why the valleys in between also get narrower.
NASA’s Europa-Clipper mission, scheduled for launch in 2024, is expected to shed light on how the binary spurs form by conducting a detailed survey of Jupiter’s moon and whether it offers conditions suitable for life .