Of all the geological mysteries of the solar system — and they are legion — perhaps none hold as much intrigue as huge piles of jumbled-up icebergs strewn across the cracked and mottled surface of Europa, Jupiter’s ice-locked moon.
A new theory explains these vast “chaos terrains” as the tips of subsurface lakes that well up and warm the surface. The existence of such lakes would thrill scientists seeking life beyond Earth, a group long drawn to Europa.
Such lakes could provide a habitat for life or act as channels for organic compounds on Europa’s surface to be drawn into the moon’s far deeper ocean, said Don Blankenship, a geophysicist and Europa specialist also at the University of Texas.
In the 1990s, NASA’s Galileo probe found strong evidence of a deep, briny ocean covering the entire moon far beneath the icy surface. The discovery of the moon-girdling ocean immediately prompted speculation that such an environment could foster life. But to do so, scientists said, organic compounds from Europa’s surface would need to find their way through the ice.
Subsurface lakes — and the process that creates them — would provide just such channels.
“If Europa is habitable, we need to get material from the surface down into the deep interior, down into the ocean,” Schmidt said.
Beyond raising hopes for one day finding life on Europa, the theory neatly explains the chaos terrains that litter half of the moon’s surface.
“If you didn’t know you were looking at Europa, you would think you were looking at icebergs calving off Greenland or the Antarctic ice sheets,” said Kevin Hand, who studies Europa at NASA’s Jet Propulsion Laboratory and was not involved in the work. “These iceberg-riddled features have presented quite a conundrum.”
To solve the mystery, Schmidt and Blankenship point to the way glacier-covered volcanoes behave in Iceland.
Deep warmth from these volcanoes melts the glaciers from below. A lens of water forms under the icy surface and moves upward. Eventually, the warm water breaks through. A flood gushes.
The surface of Europa is too cold for any liquid water. But as warm water seeps up, heated from the planet’s mantle below, it would break the surface ice into a jumble of miles-long icebergs. The icebergs then flip, float and freeze in place.
“It’s a vigorous process,” Schmidt said. “Material is getting thrown around. Icebergs are flipping over. Brines are going up and coming back down.”
Blankenship used a kitchen analogy. “It’s like a Cuisinart operating at the surface,” he said.
Schmidt arrived at the theory after she traveled to Antarctica, which hosts a hundred or more subsurface lakes. One, Lake Vostok, holds intrigue as a possible home for exotic life on Earth. A Russian team has repeatedly tried to drill through three miles of ice to reach the lake for study.
If such subsurface lakes exist on Europa, they would hold more water than all five Great Lakes, Schmidt said.
“I think they present a compelling story,” Hand said of the research group. “Unfortunately, we have very limited data from Europa.”
Schmidt acknowledges that the idea is still a theory.
But there is a way to test it: Fly another probe to Europa and peer beneath its surface with powerful radar.
Blankenship has spent more than a decade helping NASA plan such a mission. So far, funding has not arrived.
“I’m 57 now,” he said. “I’d love to see the subsurface of Europa before I die.”
Hand, also involved in planning a Europa mission but decades younger, offered the same message.
“It’s time to go back,” he said.