June 14, 2010

Jupiter’s Io A Plausible Contender For Life

Jupiter's moon Io could be a potential target to look for extraterrestrial life.

Io is the innermost of Jupiter's large moons and has the most volcanic activity in the solar system, with plumes of matter rising 186 miles above the surface.

This activity is due to Jupiter's powerful gravitational pull, which causes Io's tormented solid crust to bulge up and down 328 feet or more, generating intense heat in Io due to friction.

Io generally is considered a poor candidate for life because of all the radiation Jupiter blasts it with.  Also, no organic molecules have been detected on its surface, and it has only an extremely thin atmosphere devoid of detectable water vapor.

"Everyone right away tends to categorically exclude the possibility of life on Io," astrobiologist Dirk Schulze-Makuch at Washington State University told Space.com.

However, conditions on Io still might have made it a friendlier habitat in the distant past.  Schulze-Makuch said that there is a chance life might have survived to the present day.

"Life on the surface is all but impossible, but if you go down further into the rocks, it could be intriguing," he said. "We shouldn't categorize it as dead right away just because it's so extreme."

Computer models suggest that the moon formed in a region around Jupiter where water ice was plentiful.  Io's heat, combined with the resulting possibility of liquid water, could have made life plausible.

"There must have been quite a lot of water on Io shortly after formation, judging from the amount of water ice on Europa and Ganymede," said Schulze-Makuch. 

This water would have been stripped from Io's surface by Jupiter's radiation within 10 million years.  Life could have retreated underground at this point, where water might still be abundant, and geothermal activity and sulfur compound could provide microbes with sufficient energy to survive.

Schulze-Makuch said that although no organic molecules have been detected on the moon's surface, that does not mean they do not exist underground.  Jupiter's radiation would quickly destroy any organic compounds that once existed on the surface or that may today still emanate from the subsurface.

Schulze-Makuch suggests that the many lava tubes thought to exist on Io could serve as an especially favorable environment for life by protecting organisms from radiation.

The lava tubes could also provide thermal insulation, trapping moisture and providing nutrients like sulfurous compounds.  He also said that microbes are common in lava tubes on Earth, from ice and volcano zones in Iceland to hot sand-floored tubes in Saudi Arabia, and lava tubes are the most plausible cave environment for life on Mars.

The primordial soup that any life on Io might have derived from was likely based on water, but the solvent of choice for organisms might have drastically changed later on as the moon transformed.

Hydrogen sulfide is one choice because it is abundant in Io's shallow subsurface and remains a liquid from negative 123 to negative 76 degrees Fahrenheit. 

"I'm exploring with colleagues whether sulfur compounds could work as solvents of life," Schulze-Makuch noted.

Because of the wild extremes Io faces as it orbits Jupiter one possible survival strategy for life would be to remain dormant most of the time, only reverting back when nutrients were rich.

"It'd be much easier for life to take a beating if it goes dormant regularly," Schulze-Makuch said.

Schulze-Makuch said that although Europa and Ganymede are higher priority targets for future exploration missions, Io should not be neglected. 

"Much insight could be gained by sending a radiation-resistant robotic probe capable of detecting the chemistry and physical state of subsurface and surface liquids on Io," he noted, perhaps as part of a larger mission to the Jovian system.

"I know the chances of life on Io are low, and even if there is some microbial life in lava tube caves in its crust, in the short term there's no way for us to get there," he added. "But let's not totally exclude Io only because it seems strange or foreign."

If a mission to Io is extraordinarily lucky enough to find life in such an unlikely environment, "then it would make life elsewhere in the galaxy seem much more likely," Schulze-Makuch said. "It would really broaden our horizons."

Schulze-Makuch published his ideas in the February-March issue of the Journal of Cosmology.


On the Net: