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Life in our solar system April 17, 2006

Posted by dr. gonzo in Space.
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This most excellent article, 8 worlds where life might exist, by Seth Shostak, Senior Astronomer at the SETI Institute, sums up the worlds in our system that may potentially harbor some form of extraterrestrial life.

His list includes: Earth (of course), Venus, Mars, Titan, Europa, Ganymede, Callisto and Enceladus.

Venus is the longest shot. From Shostak's article:

"David Grinspoon, at the Southwest Research Institute, notes that the thick, sulfuric acid-ridden clouds of this planet might be a stable environment for floating life. Venusian acidophiles – analogs to a type of bacteria that can withstand highly acidic environments on Earth – might eke out an existence there. “It’s a long shot,” Grinspoon admits, but he insists that we shouldn’t rule out life on this nearby world."

Mars has long been the target of astrobiologists.

Titan became a target of much speculation following the landing of the Huygens probe in Jan. 2005. Continued examination of Titan is planned by the Cassini orbiter, which is presently exploring the Saturnian system.

From Shostak's article:

"David Grinspoon has suggested that the Sun’s weak ultraviolet light might rip apart some of these atmospheric compounds, producing acetylene. Falling into the liquid lakes of methane and ethane below, this gas (best known for firing blowtorches on Earth) could serve as a food for microscopic life. Unlikely? Yes. Impossible? No."

Evidence continues to mount for the existence of these liquid lakes on Titan's surface, as well as possible river-like drainage channels and seas.

The other four candidate bodies are satellites of large, gas giants in our star system.

Ganymede, Callisto and Europa are three of the largest four Jovian moons, together with Io they are know as the Galilean satellites.

There is a fair amount of evidence due to its changing magnetic field that a subsurface ocean exists on Europa around ten miles below the ice covered exterior. At the bottom of this ocean it is possible that volcanic vents exist, similar to those on Earth which provide energy and food for primitive lifeforms. No Europa mission is yet budgeted but NASA scientists acknowledge that it is a priority target for astrobiology. Still, no mission.

Ganymede and Callisto show similar evidence for subsurface oceans.

Enceladus, a Saturnian moon, was recently shown to have a system of geysers spewing water ice into space. It is thought that these geysers are fed by liquid water reseviors below the surface, kept liquid through tidal heating. Enceladus is the first extraterrestrial world where we have found convincing evidence of liquid water. And on Earth where there is water, there is life.

I would like to add one additional world to Shostak's most excellent list. Ceres, the largest of the asteroids and target of the recently reinstated DAWN mission. A subsurface ocean has also been modeled on Ceres.

DAWN co-investigator Mark Sykes said this of Ceres on The Planetary Society Blog:

"Ceres is the largest surviving protoplanet between Mars and Jupiter, has differentiated with a rocky core and ice-rich mantle, and may have a subsurface ocean — which could make it rival Europa in importance for astrobiology."

There are a number of missions in operation that are helping us understand some of these bodies. Mars has been and is the target of numerous missions. DAWN will help us understand Ceres. Titan warrants further investigation, perhaps a rover mission of some sort. However, Europa and Enceladus are among the targets that must be priortized for exploration long before ever considering other missions to land humans on the moon again. Science suffers at the hands of a near sighted president.

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