An artist's impression of the interior of Saturn's moon Enceladus, based on
data from the Cassini space probe suggesting the moon contains a
water ocean beneath its south pole.
Water = Life
- Evidence from Cassini spacecraft suggests a large body of liquid water beneath the surface of Saturn's moon Enceladus.
(The Guardian) - Researchers have discovered a deep saltwater ocean on one of the many small moons that orbit Saturn, leading scientists to conclude it is the most likely place in the solar system for extraterrestrial life to be found.
Gravitational field measurements taken by Nasa's Cassini space probe revealed that a 10km-deep ocean of water, larger than Lake Superior, lurks beneath the icy surface of Enceladus at the moon's south pole.
David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena, said the body of water was so large it "may extend halfway or more towards the equator in every direction. It might even extend all the way to the north."
The presence of a saltwater ocean a billion kilometres from Earth more than satisfies Nasa's long-held mantra of "follow the water" to find signs of alien life, but water is not the only factor that makes Enceladus such a promising habitat. The water is in contact with the moon's rocky core, so elements useful for life, such as phosphorus, sulfur and potassium, will leach into the ocean.
The first hint that Enceladus might harbour a subterranean ocean came in 2005 when Nasa's Cassini spacecraft photographed extraordinary jets of water vapour blasting out of fissures in the moon's south pole. The source of the water was a mystery, and an ocean of liquid water was only one possibility.
The latest discovery, reported in the journal, Science, gives scientists the strongest indication yet that the source of water vapour coming from Enceladus is a large body of water underneath the surface of the icy moon.
An international team led by Luciano Iess at the Sapienza University in Rome inferred the existence of the ocean after taking a series of exquisite measurements made during three fly-bys between April 2010 and May 2012, which brought the Cassini spacecraft within 100km of the surface of Enceladus.
As Cassini sped past the Saturnian moon, researchers used Nasa's Deep Space Network of giant antennas to monitor signals reaching Earth from the spacecraft's onboard radio. They looked for subtle shifts in the frequency of the radiowaves, which revealed whether the spacecraft was speeding up or slowing down. The measuring technique exploits the Doppler effect, which explains why the siren of a police car has a higher pitch as it approaches, and a lower pitch as it heads away.
|If we do find alien life I am willing to bet |
it will be very, very pissed off.
Cassini, the scientists discovered, sped up and slowed down by a few millimetres per second as it flew past Enceladus. Some of the change in speed was down to variations in the gravitational field of the moon as a result of different densities of material under the surface.
When scientists first speculated that Enceladus might contain an ocean of water, one of the greatest puzzles was how the ice could be heated to make liquid water. Stevenson and his colleagues believe that gravitational forces that act on Enceladus as it orbits Saturn essentially knead the moon, producing enough heat inside to melt the ice. The process is known as tidal heating.
Enceladus is not the only moon in the solar system to have a subsurface ocean. Europa, a much larger moon that orbits Jupiter, has a more extensive, global ocean under the surface. But Enceladus has excited scientists because the vapour plumes from the south pole are known to contain organic molecules. These, along with basic elements, a source of heat and liquid water, make Enceladus a prime candidate in the search for alien organisms.
"The question is what conditions do you need to form life and, of course, we don't know what temperature the ocean is today, nor do we know what it was back in the geological past. But it's conceivable that it was warm enough, with circulation of water coming from the silicate core as well, to allow life to form even if today that ocean is maintained by antifreeze and is slightly below the freezing point," said Jonathan Lunine, a member of the team at Cornell University in New York. The antifreeze in question is salt, which reduces the temperature at which water freezes.
I suspect any aliens we find will be hungry