Snow on Enceladus adds to evidence for subsurface ocean

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.

Credit: NASA/JPL-Caltech/Space Science Institute

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.

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