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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