Saturn

When the Cassini spacecraft swung past Saturn in 2006, it found the sun eclipsed by the planet’s disc and the sun’s rays shining through the planet’s rings, a spectacular effect caught on camera. Planet Earth can be seen as a pale blue dot to the left at 10 o’clock just beyond the bright rings and before the diffuse outer rings.

Now is the time to view Saturn which will be visible in our evening skies throughout the summer months.

Over the course of the next few years, till 2017, the rings will slowly pitch towards us, making it easier to discern their structure. The Cassini division divides the two bright bands and was first seen by Cassini, astronomer Royal to Louis XIV. On evenings of perfect “seeing”, you should be able to see the Encke division which skirts the end of the outer bright ring. The outer diffuse bands were only discovered by extra-terrestrial probes.

The rings are only about 100 m thick and disappear when viewed edge on, which last happened in 2009. They are made of tiny grains and larger clumps of ice and dust, about 95% being water ice.

Beyond the rings, circle eight moons in regular orbit, five of which can be viewed in an amateur telescope, and beyond them, dozens of asteroids and planetary fragments in wildly irregular orbits which have been captured by Saturn’s gravitational field. In all, 62 moons have now been identified.

Of the regular moons, Titan is the largest and can be seen clearly in its 16 day orbit round the planet. It’s one of the largest moons in the solar system, second only to Jupiter’s moon, Ganymede and bigger than the planet Mercury. With an atmosphere of methane gas which can precipitate as rain, Titan has seas and lakes and a landscape of mountains, rivers and shorelines. It’s not quite paradise since temperatures never rise above the glacial, but methane provides a source of organic chemicals which could seed life in this outpost of the solar system.

Towards Saturn from Titan, you may also pick out the dimmer moons: Rhea, Dione, Tethys and Enceladus.

The most difficult to see is Enceladus but it’s another gem of the solar system, an icy place of violence and spectacle. Its proximity to Saturn means it’s subject to gravitational pummelling which causes icy material to erupt out in giant plumes that trail behind the moon forming the outermost of Saturn’s bright rings, seen for the first time by the planetary probe Cassini. Who knows, maybe life also lurks on this enigmatic moon?

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