A Living Ocean on a Jovian Moon?

Jupiter's watery Europa may be the best bet for life elsewhere in the solar system

  • Share
  • Read Later
Time & Life Pictures / Getty Images

Jupiter's moon 'Europa'

If you went by news coverage alone, you’d think there’s only one world in the solar system aside from Earth worth studying—and that, of course, is Mars. NASA’s Curiosity rover is inching its way across the Red Planet’s Gale Crater; the Opportunity rover has entered its tenth year of exploration in a region some 5,000 miles (8,000 km) away; and a new rover, named InSight, is on the schedule for a 2016 launch. Why all that attention? In a word, water. Mars had plenty of it once, enough that life might have been able to take hold and could still, in theory, be hanging on in still-wet pockets below the surface.

But another world in our Solar System doesn’t have to look to the past for its maritime days. Jupiter’s moon Europa not only had water, it has it—likely a vast, globe-girdling ocean, 60 mi. (96 km) deep, just beneath a comparatively thin, 2-mi. (3.2 km) rind of ice. Gravitationally plucked by the tidal tugging of its sister moon Io and Jupiter itself, Europa retains a hot interior, which keeps the water comparatively warm and even pulsing. If that doesn’t sound like a place that could cook up life, nothing does. The only ingredients missing to make Europa’s ocean a potential home to living things have been salt and organic compounds. Now, according to a study about to be published in The Astronomical Journal, they’re not missing anymore. A dip in the waters of Europa, the paper concludes, could be very much like a dip in our oceans, perhaps with all the biology that implies.

Long before astronomers could know Europa’s composition for sure, they suspected that it might be covered in ice. It’s brighter in color than most of the Solar System’s other moons, and in the early 1970’s, telescopes detected what was interpreted as frost on the surface. In 1979, Voyager 2 spotted what appeared to be a network of cracks on Europa’s surface as it whizzed past Jupiter—stronger evidence that it wasn’t just frost, but almost certainly real ice.

(MORE: Voyager 1 at the Threshold of Forever)

When the Galileo probe showed up about two decades later, it became clear that Europa’s ice coating was thick—but more important, the cracks, now clearly evident, meant the ice was floating, forever being fractured and re-fractured by the movement of the ocean below and the flexing of the moon itself. Neighboring Io is continually squeezed the same way, but there isn’t much water there, so the internal heating leads instead to sulfur-spewing volcanoes.

None of this meant Europa had the ingredients for life: you could keep a tank of sterile water warm and churning for 4.5 billion years and at the end, all you’d have would be the same tank of sterile water. Finding evidence of the organics and salt was the key, and that has at last been provided, thanks to a set of observations by the giant Keck II telescope in Hawaii.

The work was conducted by Caltech planetary scientist Mike Brown, who first used the Keck to study Europa 15 years ago and found evidence of salt straightaway—sort of. Those observations showed that Europa has a thin atmosphere containing sodium atoms—which is a sign of salt, but what kind? If it’s sodium chloride—plain table salt and ocean salt—the odds of life might be boosted considerably. With the optics the Keck had at the time, that was a hard thing to determine; it was even hard for Galileo spacecraft, despite its eight years in Jovian orbit.

“The big problem with any spacecraft,” says Brown, “is that they’re already old when you launch them,” meaning the design is locked in at the beginning of the years-long assembly process. “They started building [Gaileo] in 1977, but it wasn’t done for another 15 years.”

(MORE: Did a Distant Solar System Send Life to Earth?)

New optics on the Keck have sharpened the telescope’s vision considerably, and when Brown and his colleague Kevin Hand, of NASA’s Jet Propulsion Laboratory, looked at Europa anew, they were at last able to tease out information showing that the salt on the surface is magnesium sulfate. The naïve—and disappointing—assumption would be that the material must have bubbled up from the water below, and that the oceans are rich in sulfur. The picture, however, was more complex than that. Magnesium sulfate is found only on one side of the moon—the side that faces Io, which means that the sulfur is coming from that moon’s volcanic exhaust, and is not native to Europa at all.

That doesn’t suggest the Europan ocean is salt-free. Indeed, it must be salty because the moon has a magnetic field, which means it has to be electrically conductive, something that fresh water isn’t and salt water is. And since magnesium sulfate salt is ruled out, that leaves sodium chloride—good old-fashioned sea salt—as the next best choice. At least that’s the inevitable—if yet unproven—deduction. “We haven’t actually detected either chlorine or sodium chloride,” says Brown, “so this is still a speculation.”

Still, it’s a speculation with big implications. The fractures on the surface have always suggested that the water in the ocean is not entirely trapped by the crust, but instead bubbles up and back down, with the chemistry of the ice above and the water below commingling. It’s statistically inevitable that Europa has been bombarded by many comets during its long lifetime, and since comets are known to contain carbon-based organic compounds, the oceans would be laced with the stuff too, rounding out the recipe for biology.

(MORE: Explosion On Jupiter: Did the Planet Take a Hit For Earth?)

“I’m not an expert on life,” says Brown. “But I do know that if you dip a net in the ocean here, you’re bound to pick up something.” Even if you could not get your net two miles deep into the Europan ocean, simply sampling the surface ice would tell you a lot. “You could just land on the surface, dig up a scoop, and know what the chemistry of the ocean really is,” says Brown.

That kind of hands-on study is not likely to happen soon; even a robot lander would be too ambitious (read: too expensive) for the current NASA. Instead, the agency is thinking about a probe called the Europa Clipper, which would orbit Jupiter and make flybys as little as 10 miles above the Europan surface. Armed with far better instruments than Galileo’s vintage electronics, it would nail down the chemistry on the moon’s surface. If that chemistry is life-friendly, the case for a lander would be much stronger—and perhaps irresistible. We’ve never before encountered seawater, after all, that didn’t have at least a little something swimming around in it.

VIDEO: Life in the Universe: Easy or Hard?

86 comments
frish
frish

Life, as in self replicating molecules, may exist in many portions of the Universe.

The leap from microbial life to human type life is probably as difficult as life starting altogether.

Unless we are the first, or the only we can detect within our sphere of perception, I suspect "intelligent life" has existed before, somewhere.

If our type intelligence were "selected for' by the Universe, we'd be knee deep in BEMs and LGM (bugged eyed monsters and little green men).

ilincaandrei
ilincaandrei

@SETIInstitute Billions are spent for "defense" ' . Just 1% of that would make such an incredible difference.To bad we have politicians- --

KeckObservatory
KeckObservatory

Great story Mr. Lemonick. Great job synthesizing information from Dr. Brown -- one of the astronomical greats!

DavidLueder
DavidLueder

While I'd support the sampling and studying of Europa's surface ice for what we might learn from it, i'm highly skeptical of a life scenario there.  It simply doesn't logically follow that just because life is abundant in our oceans, it must be abundant wherever we find salt water.   That'd be ignoring everything we know about our delicately balanced ecosystems.

John
John

I think it was a central plot point in one of Arthur C. Clarke's sequels to 2001, either 2010, or 2061, but they do encounter amphibious life in one of those books on Europa.

auronlu
auronlu

It's not just Europa, either.

I waved at Europa tonight through a backyard telescope. We had the Galileo probe orbiting Jupiter for years, taking photos of Europa's iceberg surface, but news media deemed it unsexy and didn't cover it.  Cassini dropped a probe through the cloud tops of Titan, an enormous achievement -- and splashed down -- yes, SPLASHED DOWN -- on a muddy, slushy plain on Titan, taking photos of rain clouds and mountains and fog on the way in, and it has YET to make the news; it's the only other moon where humans have landed a spacecraft. Cassini has used radar to penetrate Titan's thick clouds and capture images of its rivers, its lakes larger than the Great Lakes that grow and shrink from seasonal monsoons. Cassini has also seen enormous geysers erupting from Enceladus, spraying Saturn with so much water that it's altered Saturn's chemistry. And then there are the ice volcanoes on Triton.

For some reason -- possibly savvy social media PR -- the Mars Curiosity rover FINALLY broke through the news media firewall that has declared space news off-limits since shortly after the Challenger disaster stopped selling papers. So much has been discovered, unseen, because the news media didn't think it worth reporting. It may be time to do some retrospectives to pick up the slack, between news media's busy schedule of posting puppy videos and puff pieces. 

jsheff
jsheff

"... and a new rover, named InSight, is on the schedule for a 2016 launch."

Actually, no, InSight is a stationary lander, not a rover.


kskrz
kskrz

@TIME: Jupiter's moon Europa may be the best bet for life elsewhere in the solar system | ti.me\/15QTn56Uq8” Very interesting!

dslevy
dslevy

Road trip! RT @TIME: Jupiter's moon Europa may be the best bet for life elsewhere in the solar system | ti.me\/15QTn56I8d

gauravgangurde2
gauravgangurde2

%s saw this on discovery 10 years ago. It's cold temperature will still be a disadvantage. %s's %s

SwiftrightRight
SwiftrightRight

@auronlu I still remember that. The probe had an acoustic sensor. Actually listening to the wind on another planet was SO cool and yet less the 9500 humans have heard it. 

Hadrewsky
Hadrewsky

@auronlu 

That aint water raining on Titan - it is liquid methane


Ya should actually know wtf you are talking about for christs sake

Joyoverkill
Joyoverkill

@hutchinaaron muskyfish journal just followed me. a new personal high in hygiene! but ferreals I'mma escape this whack hole in 10 c u soon

iHumanist
iHumanist

@Hadrewsky @auronlu Easy, Hadrewsky. Titan DOES in fact have water AND liquid methane and ethane. The rain itself is methane, but there is a subsurface ocean of liquid water on Titan. There's no reason to get so upset...