![]() ![]() The gravitational tug of Enceladus on Cassini allowed the moon’s mass to be estimated, giving a value for the density of the body. This observation has been known for many years, ever since the Voyager 2 mission took the first images of Enceladus and determined its radius, so allowing its volume to be calculated. The moon has a density low enough to imply mainly ice with a small, rocky core. Researchers came a step closer to solving the puzzle when they looked at the internal structure of Enceladus. This would be sufficient power for a city the size of Chicago. The effect, however, is insufficient to account for the power required to keep the geysers active – calculated to be in the order of 5GW. Enceladus is in orbital resonance with the similar-sized moon Dione, which affects the shape of Enceladus’ orbit around Saturn. For instance tidal interaction with our own moon is responsible for the ebb and flow of water on Earth. NASAįor several years, scientists have favoured the explanation of “tidal heating” – a result of interactions between planetary-sized bodies. Any model that purported to explain the heat source had also to account for its focused nature – the ocean is global, but why is only the south polar region active?Īrtist’s impression showing Cassini driving through geysers. There are almost no impact craters in the tiger stripes region, so it must be very young, of the order of a million-years-old. The temperature of the stripes is higher than that of the rest of the icy crust, so it was assumed that they must be cracks in the ice. The geysers are associated with features known as “tiger stripes” – a set of four, parallel depressions, about 100km long and 500m deep. But what scientists have failed to explain is what heat source could be powering this activity.Īs more observations of the location of the plumes were made, the mystery of the missing heat source increased. ![]() A subsequent observation that hydrogen was present in the plumes led to an additional conclusion, that hydrothermal activity – chemical reactions due to the interaction of water and rock – was taking place. It was because of these geysers that scientists could work out that Enceladus must have an ocean below its icy crust and that the ocean is active (convecting). The geysers are plumes of salty water-ice mixed with traces of carbon dioxide, ammonia, methane and other hydrocarbons that erupt along cracks in Enceladus’ south polar region. Now new research, published in Nature Astronomy, suggests this ocean has existed within Enceladus for a very long time – possibly long enough to create the conditions to develop life. ![]() As a result, this small, icy moon is currently regarded as a potential host for life, and so no chance was taken that it might become contaminated by the Cassini spacecraft. With its curtain of geysers and internal ocean, Enceladus is unique. The reason for the “grand finale” was to guard against the possibility that Cassini might crash into one of Saturn’s moons – in particular Enceladus. We recently bade farewell to the Cassini spacecraft, which after 13 years of faithfully orbiting Saturn and its moons was directed to plunge into the giant planet’s atmosphere. ![]()
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