archive: SETI [ASTRO] Searching For Life On Jupiter's Moon Europa

SETI [ASTRO] Searching For Life On Jupiter's Moon Europa

Larry Klaes ( )
Thu, 10 Dec 1998 09:07:36 -0500

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>Date: Wed, 9 Dec 1998 17:58:25 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Searching For Life On Jupiter's Moon Europa
>Reply-To: Ron Baalke <>
>Stanford University
>CONTACT: David F. Salisbury, News Service
>(650) 725-1944, e-mail:
>December 9, 1998
>Searching For Life On Jupiter's Moon Europa
>If the icy surface of Europa conceals a liquid ocean, which seems
>likely, then the Jovian moon will become one of the hottest spots in the
>system to look for alien life.
>Europa Orbiter, a NASA mission in the early planning stages, that is
>for launch in 2003, is being designed specifically to look for evidence of a
>Europan ocean. If one is found, Europa and Earth would be the only two worlds
>in the solar system where liquid water is known to exist. And liquid water is
>thought to be essential for the development of life.
>Christopher Chyba -- the Carl Sagan Chair for the Study of Life in the
>Universe at the SETI Institute and a consulting professor of geological and
>environmental sciences at Stanford -- chairs the science definition team for
>the mission. At the American Geophysical Union meeting in San Francisco, he
>summarized the current evidence for an ocean on Europa and described the
>instrument package that his team has proposed for the next Europa mission.
>Europa looks something like a cracked cue ball. The possibility that a liquid
>water ocean may lurk beneath its ice crust was first raised at the time of
>the Voyager missions in the late 1970s, but was reinforced in 1996 when
>images of Europa's surface were beamed to Earth by the Galileo spacecraft.
>The images showed areas where the surface ice has been broken up and shifted
>around like pieces of a jigsaw puzzle, leading Ronald Greeley from Arizona
>State University to propose that the Europan icebergs must be lubricated
>from below by warm ice or liquid water.
>Since then, "there has been a convergence of evidence that supports the
>existence of a liquid ocean on Europa," Chyba said.
>* In addition to the iceberg-like areas, Galileo imagery has revealed an
>impact crater that appears to have been filled in at the bottom, areas that
>appear to show localized melting near the surface, and other features
>consistent with a liquid layer below the ice;
>* Galileo's onboard magnetometer, which measures magnetic fields, has
>measured fluctuations that are consistent with the magnetic effects of
>currents flowing in a salty ocean;
>* Lack of cratering on Europa's surface indicates that it is very young --
>less than 10 million years -- which suggests that it is being continually
>resurfaced, possibly by frost falling from liquid water geysers encountering
>Europa's frigid surface temperatures, which hover at -170 degrees Celsius;
>* Theoretical estimates of the amount of heat produced by the gravitational
>push and pull exerted on Europa by the other Jovian moons indicate that it
>should be adequate to warm the moon's interior enough to sustain a liquid
>"All these lines of evidence point to a liquid water ocean," Chyba said.
>The investigations that the science definition team has suggested for the
>proposed $250 million Europa Orbiter include imaging, altimetry, gravity
>measurements and subsurface radar soundings.
>"The most decisive measurements are likely to come from the altimetry and
>gravity measurements," Chyba said.
>As Europa travels in a slightly eccentric orbit around Jupiter, tides are
>raised, similar to the lunar tides on Earth. If the distant satellite
>a deep ocean covered by the thin ice crust, then the tidal movements
should be
>fairly large, producing a 30-meter rise and fall each 3.5 days. But if the
>moon is solid ice the deformation would be only a meter or so. The altimeter
>and gravity measurements independently would measure this effect.
>These measurements should be definitive for the case of a global ocean, but
>would be more difficult to interpret if the liquid layer takes the form of a
>number of discontinuous seas, Chyba said.
>In that case, a radar sounder might provide the needed data. Radar is
>routinely used to sound ice on Earth. That is how Lake Vostok -- a body of
>water about the size of Lake Ontario buried under 3,700 meters of ice in
>Antarctica -- was discovered. A clean interface between water and ice can
>be seen clearly in radar reflections. Depending on the consistency of the
>Europan ice, a radar sounder should be capable of penetrating somewhere
>between a kilometer and several kilometers into the crust.
>"Even if the radar sounder did not find clear evidence of liquid water,
>it would still provide us with extremely valuable information about the
>subsurface geological features," Chyba said.
>Another possible instrument is an infrared spectrometer. Such a device could
>provide information about the chemical composition of Europa's surface,
>including the presence of organic molecules.
>The decision on which instruments the orbiter will carry will be made next
>year. The selection will be particularly difficult because the spacecraft
>will have an extremely small payload of about 20 kilograms, he said.
>"If the orbiter confirms that Europa has a liquid ocean, then it will become
>one of hottest places in the solar system, along with Mars, to search for
>life. In this case there will be an entire program of exploration, likely
>involving a series of spacecraft to Europa." But if the Moon does not conceal
>such an ocean, then it will move down significantly on the space agency's
>priority list, he said.
> ###
>Related links:
>Galileo Europa home page