Home sweet home? (Image: Detlev Van Ravenswaay/Science Photo Library)

How do you solve a problem like Europa? The icy moon of Jupiter is thought to host a vast ocean beneath its frozen crust, making it an ideal target to look for life beyond Earth. But the tiny world also has a perfect storm of problems – a poorly mapped surface, a space environment full of powerful radiation, geysers that may or may not exist – that make designing such a mission tricky.

Last week, more than 200 scientists and engineers met at NASA’s Ames Research Center in Mountain View, California, to chart a course for detecting life in Europa’s seas. This isn’t mere wishful thinking: NASA’s 2016 budget gave a dedicated mission to the icy moon the green light, with a launch date for the probe by the mid-2020s.

“We’re going to do a Europa mission,” NASA science administrator John Grunsfeld told the meeting. “If there’s something trapped in that water, and we potentially have the opportunity to see it, it could be transformative.”


For decades, mission planners assumed that any probe sent to explore Europa’s watery secrets would need to land on the surface, drill through the ice and swim through the inky deep. That changed in 2013, when a team used Hubble data to conclude that 200-kilometre-tall geysers were spraying from near Europa’s south pole. All engineers would need to do is reach orbit to taste the moon’s interior.

That’s good news for the best-studied mission design, a $2.1 billion concept known as the Europa Clipper. To avoid Jupiter’s harsh radiation belts, the Clipper wouldn’t land on the moon’s surface or even orbit it directly, but instead orbit Jupiter and make regular fly-bys of Europa.

If the geysers are active when an orbiter passes by, it could fly through the spray and collect a sample. But how do we tell if anything lives in it? The instruments scientists typically use to find microbes in droplets on Earth are too bulky and finicky to send across the solar system. Instead, astrobiologists rely on a technique known as mass spectrometry, which identifies the chemicals in a sample.

The presence of organic molecules could be a clue to life, but they can also form through abiotic processes. Complex organic molecules are much tougher to randomly assemble. Only life can put together something as intricate as chlorophyll, for instance, which has a long hydrocarbon tail and a flower-like head containing nitrogen, oxygen and magnesium.

“The probability of this just forming in high abundance is essentially zero,” Lee Cronin of the University of Glasgow, UK, told the meeting as he presented his “universal life detector”. This would use mass spectrometry to identify complex chemicals, with the assumption that a high number is a hint of life.

Another idea is to use an array of antibodies, the chemicals your immune system produces to recognise invaders. Antibodies have evolved to grab hold of just about any organic molecule and could be arranged on a chip to snag and categorise chemicals in a Europa sample, suggested Chris McKay of NASA Ames. He also pushed the idea of checking the biochemicals for their chirality, or handedness. Life on Earth only uses left-handed amino acids, and life elsewhere might have a similar preference.

We might not catch them alive, though. Any Europa microbes shot out of a geyser would be boiled and then fried in Jupiter’s powerful radiation. But that doesn’t bother McKay: a freshly killed microbe has the same biochemistry as a living one. “Death is just another form of life,” he said.

Ice punch

But it might not be that easy. Europa’s geysers haven’t been spotted again, suggesting they are either relatively rare, or the initial observation was a fluke.

Charles Hibbitts of Johns Hopkins University in Baltimore, Maryland, has an alternative idea: punch through the ice. We could smash a precision impactor into Europa’s surface and send the orbiting spacecraft through the resulting plume to collect a sample, similar to NASA’s Deep Impact mission, which shot a projectile at a comet in 2005.

If we find evidence of past plume activity on Europa, that would be the perfect place to dive bomb, Hibbitts said, because it might increase our odds of hitting the subsurface ocean.

Rather than rely on a robot, some would like to get a bit of Europa back to Earth. Isik Kanik of NASA’s Jet Propulsion Laboratory presented a modified version of his team’s Life Investigation For Enceladus (LIFE) mission, originally designed to capture a sample from Saturn’s geyser-erupting moon Enceladus and bring it home. He described a sample return mission as “the gift that keeps on giving”, because the samples “can be analysed and reanalysed for generations to come”.

There’s just one problem: even a small sample would take a lot of additional fuel to climb out of Jupiter’s colossal gravity.

Small and dedicated might be the way to go. A proposal from David Mauro of NASA Ames called Europa Plume Chaser would send two small satellites to Jupiter, each carrying a camera and some miniaturised instruments. The first would scout for plumes, hopefully giving scientists enough information to direct the second probe through a plume. Tiny satellites have the potential to transform deep space science, and even New Scientist is getting in on the action with our TEENSY mission, a crowdfunded spacecraft for Europa exploration.

A mission to Europa has a lot of wind in its sails. But instruments will have to be selected soon to make the targeted launch date. As it may be decades before NASA sends another probe we should make an effort to find life now. “The clock is ticking,” Grunsfeld said. “I just hope we don’t miss this remarkable opportunity.”

This article will appear in print under the headline “Seeking alien life in Europa’s icy seas”