As Saturn approaches its August 11th equinox (during which the Sun will be directly above the gas giant’s equator at noon for 27 months), the Cassini Equinox Mission can do some moonlet spotting. During this time, sunlight will cast long shadows of any object protruding from the 10 metre-thick rings.
In this case, hidden inside Saturn’s B-ring, a moonlet with a diameter of approximately 400 metres becomes obvious when sunlight hits the rings edge-on. The result is a very obvious 25 mile-long shadow. This discovery wouldn’t have been possible during any other time, as Cassini can only see the small rock because of its shadow. If the Sun was above or below the rings, no shadow would be cast, and therefore no moonlet would be visible.
Saturn experiences an equinox twice every Saturnian year (once every 15 terrestrial years), and NASA planned the Cassini mission to coincide with this interesting period to economise on the position of the Sun, spotting small objects like this little satellite…
In October 2008, Cassini flew very close to the surface of Saturn’s icy moon Enceladus. From a distance of only 50 km from the moon, the spacecraft was able to collect samples of a plume of ice. In an earlier “skeet shot”, Cassini captured detailed images of the cracked surface, revealing the source of geysers blasting the water into space. At the time, scientist were able to detect that it was in fact water ice, but little else would be known until the molecular weight of chemicals in the plume could be measured and analysed.
At the European Geophysical Union meeting in Vienna this week, new results from the October Enceladus flyby were presented. Frank Postberg and colleagues from the Max Planck Institute for Nuclear Physics have discovered traces of sodium salts and sodium bicarbonate in the plume for the first time.
It would appear that these chemicals originated in the rocky core of the moon and were leached from the core via liquid water. The water was then transported to the surface where it was ejected, under pressure, into space. Although scientists are aware that the chemical composition in the plume may have originated from an ancient, now frozen, sub-surface ocean, the freezing process would have isolated the salt far from the surface, preventing it from being released.
“It is easier to imagine that the salts are present in a liquid ocean below the surface,” said Julie Castillo of NASA’s Jet Propulsion Laboratory in Pasadena, California. “That’s why this detection, if confirmed, is very important.”
This is the best evidence yet that Enceladus does have a liquid ocean, bound to cause a stir amongst planetary scientists and re-ignite excitement for the search for life living in a salty sub-surface ocean.