Europa’s tantalizing plumes spur NASA mission to search for life

Phantom plumes of icy water, spewing from Jupiter’s moon Europa, are intriguing space scientists who met in Mountain View last week to plan a new NASA effort to probe the moon’s frozen, fractured surface for evidence of life.

The giant gas planet Jupiter, nearly 500 million miles from Earth, holds scores of moons, and mysterious Europa, roughly the size of our own moon, is one of the strangest.

A tangled chaos of long brown-hued cracks and deep, ridged fissures on Europa’s surface marks areas that have been disrupted, melted and frozen again. Scientists believe the surface covers a vast ocean of water hundreds of miles deep, with a hot rocky core at the center.

For years NASA scientists and engineers have been designing a mission to orbit Europa with a spacecraft tentatively named Clipper. It would circle the moon for more than three years, making 45 flybys, to study its surface with ice-penetrating radar and seek signs of life in the deep ocean beneath. The cost estimate:

$2 billion.

That concept had been slowly moving through the bureaucratic jungle of NASA headquarters in Washington until three years ago when the Hubble Space Telescope detected sporadic plumes of icy water vapor rising 125 miles high above Europa’s surface near its south pole.

The plumes haven’t been seen since 2012, but as news has spread among scientists who seek signs of life in space — from Mars to the exoplanets around distant solar systems — there’s a growing call for action.

“We’ve just jumped on the plume finding,” said Christopher McKay, a space geophysicist at NASA’s Ames Research Center and a fervid exobiologist who spoke to the hundred scientists at last week’s meeting there.

“There’s real enthusiasm in that bunch,” he said. “Before Hubble spotted the plumes we didn’t know whether we really had an ocean on Europa, we didn’t know whether there was water, and it was a tough place for astrobiology — but now it doesn’t look so tough.”

Evidence of volcanoes

The plumes offer powerful evidence of volcanic activity on Europa that would fracture the moon’s thick, icy crust, causing the water from the ocean below to erupt above the surface, the scientists say.

“That ocean could be a soup of organics, and we’ll take finding life there whether it’s dead or alive — because dead is evidence of life anyway,” McKay said.

While engineers spoke of fleets of “CubeSats” — foot-square mini-satellites first developed at Stanford and Cal Poly — that could fly through Europa’s putative plumes, McKay proposed that a Clipper orbiting mission could send down a “small focused lander.” It could, he said, explore the region where Europa’s plumes have erupted and pick up remnants of the icy material to analyze them for evidence of amino acids, life’s basic chemicals.

David Senske, a NASA geologist at the Jet Propulsion Laboratory in Pasadena, noted that the icy plumes may or may not erupt again since the Hubble telescope has only detected them once, “but if they exist,” he said, “they offer an incredible opportunity in our search for life.”

Cynthia Phillips, a senior research scientist at the SETI Institute in Mountain View, displayed images of Europa’s southern region taken 20 years apart by the historic Voyager and Galileo missions in the late ’70s and ’90s, which revealed no changes in the icy crust nor evidence of plumes caused by volcanic activity.

“A mission to Europa has been at the top of NASA’s list for decades,” she said, “but now the reality of the plumes has rekindled all our excitement.”

To Phillips, a new mission to the moon more than 400,000 miles from Jupiter will be an opportunity to harvest crucial new images of Europa’s fractured surface. By being compared to the images she has gathered from nearly 40 years ago, they could reveal a history of powerful changes in the surface of the restless moon, and fresh insights into its ocean below, she said.

Promising opportunity

The vision of a new spacecraft seeking signs of life in fresh plumes of water vapor erupting from Europa’s frozen crust is not lost on NASA’s leadership. Last week, John Grunsfeld, a cosmic ray physicist, veteran astronaut and now the agency’s chief scientist, was there to cheer the planners on.

“We’re going to do a Europa mission,” he told them. “It’s too good a chance to miss, so let’s think outside the box or in it. Let’s get your best ideas out on the table.”

David Perlman is The San Francisco Chronicle’s science editor. E-mail: dperlman@sfchronicle.com