moon's river

The smooth surface of Europa could hide a life-filled ocean.Courtesy of NASA.
  A living ocean near Jupiter?
whoa, is that kenneth starr in the corner?Does the evidence of a liquid ocean we've just seen on Jupiter's moon Europa indicate that this moon houses extraterrestrial life? A wild thought. But let's start with an ol' Why Files tradition -- a few facts to ground all this speculation.

What exactly do we know about Europa? A lot, considering that the moon never gets closer than 630 million kilometers to Earth.


bullet Jupiter's fourth-largest moon is slightly smaller than Earth's moon.

Europa's average distance from Jupiter is 671,000 kilometers; it rotates in 3.55 days.


bullet Europa's surface is covered with frozen water at a nippy -260 Fahrenheit.


bullet Most of Europa's mass is concentrated in the center. "There's really dense material on the inside, and really not dense material on the outside," says Geoff Collins, a geology graduate student at Brown University. "So that's why we think there's a water layer."


bullet A rain of organic chemicals probably reaches Europa's surface courtesy of comets and asteroids.


bullet Here's what NASA knows about Europa.


  Does this add up to life?
Of course not. But don't forget that life on Earth apparently originated in water. And scientists have found life in unbelievably bizarre crannies on Earth, including inside cracked rocks more than one mile beneath the surface, inside rocks in the desert, at temperatures of minus 10 degrees Celsius, and above boiling temperature in water emerging from deep-sea vents. The current picture seems to be this: Life occupies just about any niche available on Earth, from the hottest to the coldest.

Although it's conceivable that life may also exist in any tolerable extraterrestrial niche, this argument by analogy only proves that the possibility of life on Europa should be taken seriously. The speculation got a boost in 1996 when scientists announced they'd found traces of life on a Martian meteorite. The announcement has fueled a lively scientific debate as nay-sayers began poking holes in the original argument. See "Ames Tackles the Riddle of Life" in the bibliography.

James Head of Brown University says Europa seems to have three conditions considered essential for life: organic molecules (ferried in by asteroids and comets), heat and liquid water. Taken together, he says, there's a decent possibility that Europa is or was alive. "You have to think that a layer of water could harbor life."

Getting a closer look
The evidence is already intriguing enough for scientists to ask for funding (That's news?) to search further. Head notes that President Clinton's 1999 budget includes a mission to depart for Jupiter in 2003. The satellite would actually orbit Europa, carrying a radar instrument able to penetrate the ice and map any ocean that's present. A second instrument would measure Europa's surface accurately enough to register changes pointing to the presence of subsurface water.

If all the signals were positive, the logical next step would be to visit that ocean, with a drill or a melt-thru-the-ice robot probe. We won't stress the enormous technical problems this would entail: It's daunting enough to pierce several kilometers of ice, grab samples, and return to the surface on Earth. (In February, 1998, Russian scientists finally drilled to the bottom of the Antarctic ice cap, to a depth of 3650 meters.)

Pulling off that stunt on a moon whose climate makes Antarctica seem tropical will be slightly tougher, particularly when the moon is so distant that radio waves take at least 35 minutes to reach it from Earth. And there's a final complication: the probe must be sterile, to avoid contaminating Europa's ocean with Earthly life. To get some practice, NASA and Russian scientists may begin exploring a hidden lake under the Antarctic ice cap (see "Russian Outpost Readies for Otherworldy Quest" in the bibliography).

Read all about watery moons!


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