Until relatively recently, it was thought that the best, or perhaps only, place to look for life elsewhere in the solar system was Mars. The other inner planets were much too hot while the outer gas and ice giants were far too cold – the chances of any kind of life being found, even microbes, was considered extremely unlikely at best.
Along with Jupiter’s moon Europa, a tiny Saturnian moon, Enceladus, has become one of the most fascinating places in the solar system and a prime target in the search for extraterrestrial life. Its outward appearance is that of a small, frozen orb, but it revealed some surprises when the Cassini spacecraft gave us our first ever close-up look at this little world – huge geysers of water vapour spewing from its south pole. The implications were thought-provoking: Enceladus, like Europa, may have an ocean of liquid water below the surface. Unlike Europa however, the water is apparently able to make it up to the surface via fissures, erupting out into space as giant plumes.
Now, a new project sponsored by the German Aerospace Center, Enceladus Explorer, was launched on February 22, 2012, in an attempt to answer the question of whether there could be life on (or rather, inside) Enceladus. The project lays the groundwork for a new, ambitious mission being proposed for some time in the future…
Saturn’s tiny moon Enceladus was the centre of attention for the Cassini spacecraft again last week, with beautiful new photos being released of the moon and its water vapour geysers erupting from the south pole. Some views show surface detail on the moon, some are of the geysers themselves and there is a very nice shot of Enceladus silhouetted against Saturn and its rings in the background. There is even a dual ultraviolet stellar occultation in which two of the stars in the belt of the constellation Orion are seen shining through the plumes! Even though these are still raw, unprocessed images, they again capture the beauty of Enceladus and the Saturnian system…
Until fairly recently, the search for life elsewhere in the solar system has focused primarily on Mars, as it is the most Earth-like of all the other planets in the solar system. The possibility of finding any kind of life farther out in the outer solar system was considered very unlikely at best; too cold, too little sunlight, no solid surfaces on the gas giants and no atmospheres to speak of on any of the moons apart from Titan…
Enceladus, a small icy moon of Saturn, is one of the most active places in the solar system, with dozens of geysers of water vapour and ice particles erupting from warmer fissures near the south pole, a big surprise when they were first discovered by the Cassini spacecraft several years ago. Since then, the debate has focused on their origin, but the latest evidence continues to indicate that the most likely explanation is that the plumes emanate from a subsurface reservoir of liquid water which somehow stays heated enough on this cold world to remain liquid.
A new study indicates that the geysers have probably been active for up to 100 million years. This estimate is based on the fact that a deep layer of snow blankets much of the moon, which forms when ice particles from the plumes settle back onto the surface. The “snow” is a very fine powder which coats the surface at an average rate of less than one thousandth of a millimetre per year. Yet in places the snow is 100 metres thick. This means it must have taken tens of millions of years to accumulate this much, and that such long-lived activity is most easily explained by a reservoir of liquid water beneath the surface.
Other evidence previously discussed also points to liquid water, notably that the plumes are composed of water vapour and ice particles with large amounts of salts mixed in, very similar in composition to salt water oceans on Earth. There are also various organic molecules in the plumes found by Cassini (which has flown through and directly sampled the material in them), and the combination of water, heat and organics have made Enceladus a new favourite spot in the search for extraterrestrial life.
It was also noted during the Division of Planetary Sciences / European Planetary Science Congress (DPS/EPSC) meeting going on now, that the mass of the plumes being primarily slower, salt-rich particles and the amount of ice particles in the plumes also both support a liquid water origin (courtesy of Emily Lakdawalla’s Twitter feed).
Cassini also just took some new photographs of the geysers which are actually like a very fine mist, but look dramatically beautiful when backlit by the sun.