The possibility of Life on Europa
The combination of interior heat, liquid water, and infall of organic material from comets and meteorites, means that Europa has the key ingredients for life. Europa, like Mars and the Saturn moon Titan, is a laboratory for the study of conditions that might have led to the formation of life in the Solar System. At present, though, there is not a shred of evidence for the existence of any form of life on Europa. However, we can say that some of the conditions are right for life; and with a little informed speculation it is possible to say that if life exists anywhere in the Solar System other than Earth then it will exist on, or rather in, Europa.
Europa has an ensemble of interlaced cracks in its surface, reminiscent of cracks in an egg-shell, that indicate active tectonics within the ice sheet. A strong inference is that these fissures have been eruptive sites from which liquid water has intermittently flowed out onto the satellite's surface erasing the traces of impact craters. Because Io, the innermost Jovian satellite, supports highly active volcanic systems driven by internal tidal friction, the suspicion lurks that similar, although much less intense, heating may exist in the subsurface of Europa, accounting for the resurfacing processes that involve the effusion of water onto the planetary surface.
Black Smokers on Earth
One of the most compelling insights to emerge from 15 years of
research on submarine volcanic-hydrothermal systems on earth is the idea
that volcanos in the presence of liquid water can sustain life on this
planet (such as the black smokers shown to the right, which are
found at mid-ocean ridges on Earth) and perhaps other planets.
Whether life can originate in such
systems is controversial, but the evidence in unequivocal regarding the
linkages between volcanic processes as we know them and abundant
carbon-based life forms on and below the sea-floor in the vicinity of
active spreading centers.
Life needs liquid water, a warm localized environment, hot-spots - say around 273 to 500 Kelvin ( 0 C to 227 C or 32 to 425 F) - from freezing at normal atmospheric pressure to boiling at high pressure - the right chemicals and time to get started. It also needs a little stirring around, a shield from excessive radiation, and a little gravity to allow centrifugal separation of suspended particulates.Many informed planetary scientists are certain that Europa supplies some of these conditions, and we are fairly certain that it could supply the others. The required warm environment could come from geothermal vents, such as are found on the mid-ocean ridges of Earth. These black smokers are rich in essential life nutrients and whole isolated ecosystems live in the vicinity of such places, from simple bacteria to fish. The temperature of the smokers can be well above boiling point (327 C or 620 F) and they can release obnoxious chemicals such as sulfur. But primitive life still flourishes, and flourishes well.
Lake Vostok
In the 1970s, a lake the size of Lake Ontario was discovered in Antartica under 2.5 miles of glacier ice. For a diagram, see
here. This lake has been separated from the rest of the world for over half a million years. The discovery in recent years that life may well exist down there gives some idea of whether life might exist in the underground oceans of Europa.
It's clear: we need to explore below Europa's icy surface