Saturday, May 3, 2014

Alien Creatures from Another Sandwich

The planet Mars has traditionally been suspected of harboring life forms, at least in its distant past.  This has been a foregone conclusion in much science fiction and fantasy written over the past century.  Intense scientific scrutiny of late has revealed that Mars may indeed have had flowing water on its surface eons ago.  Unfortunately, no evidence of any biological activity has been confirmed yet. 

Attention recently has shifted to Enceladus and Titan, both moons of Saturn, as well as Europa and Callisto, both moons of Jupiter.  All of these satellites appear to have subterranean oceans beneath their icy surfaces.  In some respects, Saturn and Jupiter, the two largest planets in our solar system, together with their numerous moons, constitute miniature solar systems in their own right.  There is also a distant exo-planet called Kepler186f, intriguing because its orbit falls within the habitable zone of its star.  Its size and composition may be similar to Earth.

At the moment, it is believed that the Jovian moon Ganymede may host the conditions necessary for the evolution of life forms—that is, liquid water.  Ganymede is certainly an interesting place.  Though less than half the size of Earth, it may have 25 times the volume of Earth’s oceans—a huge amount of H2O.  It is roughly half ice and half silicate rock, with geologic features suggesting tectonic activity caused by tidal heating.  It basically consists of a core of iron surrounded by a mantle of rock, topped with a shell of ice that may be up to 500 miles thick.  The surface of Ganymede is essentially ice, though there are areas of rock mixed in with the ice.
Ganymede is slightly larger than the planet Mercury; about three quarters the size of Mars, and is the largest moon in the solar system.  (Saturn’s Titan is the second largest moon.)  It has twice the mass of our own moon, as well a very thin atmosphere of oxygen and hydrogen.  Unique among all the moons in our solar system, Ganymede has its own weak magnetic field, possibly related to convection currents in its molten iron core.   Ganymede orbits Jupiter; if it had orbited the sun instead it would qualify as a planet.

Some science fiction here:  what if this frozen planetoid was carefully dislodged from its Jovian orbit and brought into the habitable zone of our sun?  Perhaps it could be lodged in an orbital path between Earth and Mars, and seeded with Earth’s zooplankton to create an atmosphere and the beginnings of a biosphere.  After an eon or two it might become an excellent place to fish.

But is there life on—or inside of—Ganymede now?

According to CNN today, NASA scientists have recently published a study research suggesting that vast amounts of salty water are sloshing about under the moon’s frozen surface.  Alternating layers of ice and salty water, varying in levels of salinity, are arranged in a pattern resembling a ‘club sandwich’, portions of which may interact chemically with rock surfaces.  Scientists speculate, and perhaps hope, that such chemical interactions may have produced at least simple life forms at the bottom of the moon’s enormous oceans. Given that the moon is assumed to have a molten iron core, it would seem possible that there may be a source of warmth as well—perhaps isolated microclimates of relatively warm rock and salty water, though under considerable pressure.

The study’s results were based on an experimental simulations of characteristics thought to exist in the oceans of Ganymede.  Computer models looked at such variables as salinity, water pressure and temperature—evidently there are several different kinds of ice that can form under extreme conditions.  But this is still very speculative, and involves a number of untested assumptions.  Also, a weakness of the study is that the ‘sandwich model’ assumes a stable state, which may not actually exist on Ganymede.

As mentioned in the earlier post about Enceladus, several scientists are proposing a mission to this much smaller moon of Saturn to obtain samples of ice crystals from the geyser sites at its southern pole. Hopefully these can be brought back to earth and examined for extraterrestrial microbes.  (It is striking that as our knowledge of the universe expands, our expectations of encountering alien life forms shrink to the level of single cell organisms.)  In a similar vein, the European Space Agency hopes to send the Jupiter Icy Moon Explorer, (JUICE) to visit three of the Jovian moons after a launch in 2022.  The plan is for JUICE to eventually orbit Ganymede for closer scrutiny.

The prospect of finding life on other planets has been the subject of several earlier posts.  See also:

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