There has been a lot of publicity this year about the search for "potentially habitable planets," specifically in the much coveted area around stars where the "Goldilocks" temperature is "just right" for liquid water to exist.
The irony is, however, that the nearest form of extraterrestrial life in the solar system may only be 1 billion miles away, say astrobiologists.
At that distance, the sun is a feeble 1/100th its brightness as seen from Earth, and therefore temperatures are a chilly -330 Fahrenheit (-200 degrees Celsius). The majority of solar system bodies out there froze rock solid billions of years ago.
But an unlikely oasis is Saturn's frost-covered moon Enceladus. This would be a place for life on the edge, so said scientists at a recent meeting of the Enceladus Focus Group at the SETI Institute in Mountain View, Calif.
In Voyager spacecraft photos taken in the early 1980s, Enceladus is clearly seen to have a young surface. Whole craters appear to be wiped out by smoother, and therefore, younger terrain. This was seen as evidence of water-ice volcanoes.
But we had to wait for NASA's Cassini orbiter to arrive at Saturn to see the moon’s geyser-like eruptions.
Cassini found unusually warm temperatures in Enceladus' south polar region. These hot tracks run the length of four giant fissures, dubbed "tiger stripes."
The gouges have geysers spewing water vapor and organic chemicals into space. They leave little doubt that there is a warm saltwater ocean inside the moon, possibly containing the basic chemistry of life: carbon, nitrogen, ammonia and methane, among other elements.
Though a billion miles from the sun, this is a hot moon, no doubt kept molten by the gravitational tug of Saturn and its other satellites.
By contrast, Mars is much more unyielding in giving up any secrets of a potentially hidden biosphere. Reported observations of methane plumes — which might be biological in origin — are controversial. Landers and rovers have found evidence of a watery past, but life must be hidden underground and perhaps inches out of reach of today’s robot explorers.
The same goes for Jupiter's moon Europa, which is entombed in ice. There could be a thriving biosphere in a global ocean down under. But getting to it is problematic. It requires penetrating miles of rock-hard ice or carpet-bombing thinner areas on the crust to trigger manmade geysers.
But Enceladus is conveniently spewing its ocean into space. It would be a comparatively easy trawl for an astrobiology mission to fly though the plumes and bring biological samples back to Earth.
The only problem is fuel costs; getting to Saturn and back would be a multi-decade mission with today's rockets. We definitely would need nuclear propulsion to provide enough oomph to shorten round-trip transit times.
The unique Enceladean condition may be archetypal of many habitats in our Milky Way galaxy for microbial life. For example, a planet orbiting close to a cold brown dwarf adrift in space might get enough tidal pumping to maintain a warm interior. The same goes for any number of satellites orbiting far-flung planets that do not huddle closely to the fires of their stars.
To find our comic cousins out there, we still need to find true Earth clones. But Enceladus could be further evidence that, when it comes to the suspected ubiquity of life in the cosmos, the meek do inherit the Galaxy.