Europa: Life in our Solar System?

2 Feb
This article first appeared in the February 2012 edition of an awesome new science magazine called Guru. You can download the magazine for free here.

Please listen carefully. There is life on Europa. I repeat: there is life on Europa…like huge strands of wet seaweed, crawling along the ground…Imagine an oak tree…flattened out by gravity…Tendrils, stamens, waving feebly…”

Europing for a miracle

Tendrils, stamens, waving feebly (credit: George L Smyth)

Professor Chang is stranded on Jupiter’s icy moon, Europa. His air supply is rapidly running out and he’s got no chance of being rescued; all he can do is die with dignity and hope that somebody hears his final radio message.

“I’ve only two requests to make…When the taxonomists classify this creature, I hope they’ll name it after me. And – when the next ship comes home – ask them to take our bones back to China.”

Fiction becoming fact

If this sounds like science fiction, well, that’s because it is. This gloomy scenario takes place near the beginning of 2010: Odyssey Two, Arthur C. Clarke’s sequel to his most famous novel, 2001: A Space Odyssey.

In Odyssey Two, Clarke imagines Europa to be teeming with extraterrestrial life, sustained by a liquid ocean beneath the moon’s surface. He was undoubtedly inspired by images sent back by the Voyager space probes during the late 1970s, which revealed Europa’s surface to be covered with a smooth shell of ice, raising the possibility of an underground watery ocean.

Europa has since become one of our Solar System’s most enigmatic bodies. Evidence now points to a huge ocean under its icy surface, possibly containing twice as much water as all of the Earth’s oceans combined. And where there’s water, life is often not too far away. Suddenly, Arthur C. Clarke’s story doesn’t seem quite so outlandish…

A hidden ocean

Most of what we know about Europa comes from the Galileo spacecraft, named after Galileo Galilei, the discoverer of Jupiter’s four largest moons: Io, Ganymede, Callisto, and, of course, Europa, which is about the same size as our own Moon. Launched by NASA in 1989, Galileo (the spacecraft, not the man) took six years to make the epic journey to Jupiter, and went on to spend eight years orbiting the gas giant and making a series of daring flybys past Jupiter’s moons.

Thanks to this mission, we now have some stunning close-up shots of Europa. Although hardly any craters mark the moon’s surface – a sign of its young age – dark lines crisscross the entire globe, like veins and arteries under a translucent skin. These fractures in Europa’s crust are a result of Jupiter’s immense gravitational pull on its delicate moon.

Europa in all its glory (credit: NASA/JPL/Ted Stryk)

Europa’s skin is also freckled with rough, jumbled regions of ice known as “chaos terrains”. In November last year, a team of US astronomers led by Britney Schmidt at the University of Texas proposed that these terrains are formed above huge underground lakes. When water trickles into cracks in the overlying ice, floating icebergs are created, like ice cubes bobbing in a glass of water. According to the researchers, chaotic regions are formed when this floating ice refreezes.

Another piece of evidence for Europa’s underground water comes from Galileo’s measurements of fluctuations in the magnetic field around Europa, pointing to the presence of some kind of conducting layer below the surface. The most likely candidate? A salty ocean!

Life on Europa?

In Arthur C. Clarke’s novel, Europa’s life forms are dumb, plant-like creatures that spend most of their lives rooted to the seabed. But if we could travel to the real Europa and peer under its glacial shell, what might we expect to discover?

“We’re not going to be finding little green men, unless they can hold their breath for an awfully long time,” says Lewis Dartnell, an astrobiologist at University College London. “The ocean on Europa is different from Earth’s oceans in that it’s sealed by an ice layer, so it’s dark and there’s no possibility for photosynthesis or growing by sunlight.”

Life on Europa? (credit: Dave Gray for Guru Magazine)

This means that any life in Europa’s oceans – most likely simple microbes such as bacteria ­– needs to get energy from somewhere else. One possibility is hydrothermal vents on the seafloor that spew out heated water. We already know that these exist in the shadowy depths of Earth’s oceans, and that they provide a habitat for “anaerobic” microbes which are able to survive without oxygen. This has led astrobiologists to speculate that similar life might be found in Europa’s oceans.

Indeed, Lewis Dartnell believes that Europa may now have overtaken Mars as the most likely habitat for extraterrestrial life in our Solar System: “A long time ago, Mars was warm and wet, but it’s very cold and dry now,” says Dartnell. “Life on Mars may well have been driven to extinction, or only survive deep beneath the surface of the planet. On the other hand, the evidence from Europa is that it still has a wet environment, so there might be life on Europa today.”

What’s next?

The Galileo mission ended in 2003 when NASA sent the spacecraft on a kamikaze dive into Jupiter’s atmosphere. Galileo’s fuel supply was nearly depleted, and NASA was desperate not to contaminate precious Europa with earthly bacteria.

Our next close encounter with Europa will probably not be for another fifteen years, possibly even longer. One campaign still on the drawing board is the Europa Jupiter System Mission, originally planned as a joint NASA-ESA (European Space Agency) project and scheduled for launch in 2020. However, NASA has since pulled out of the project due to budget cuts, so ESA may now go it alone with the renamed Jupiter Icy Moon Explorer mission.

Whenever it happens, the next mission will give us an even closer glimpse of our Solar System’s most intriguing moon. One day, it may be possible to send a probe down to analyse Europa’s ice – perhaps even a nuclear-powered “cryobot” that can tunnel all the way to the moon’s inky ocean.

The cutest little cryobot (credit: Dave Gray for Guru Magazine)

And who knows what we might find down there. Arthur C. Clarke’s exotic creatures? Probably not. But simple life? A lot of scientists wouldn’t bet against it.

Further reading:

ResearchBlogging.org

Greenberg, R (2008). Unmasking Europa: The Search for Life on Jupiter’s Ocean Moon. Praxis/Springer.

ResearchBlogging.orgKivelson MG, Khurana KK, Russell CT, Volwerk M, Walker RJ, & Zimmer C (2000). Galileo magnetometer measurements: a stronger case for a subsurface ocean at Europa. Science, 289 (5483), 1340-3 PMID: 10958778

ResearchBlogging.orgSchmidt BE, Blankenship DD, Patterson GW, & Schenk PM (2011). Active formation of ‘chaos terrain’ over shallow subsurface water on Europa. Nature, 479 (7374), 502-5 PMID: 22089135

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