Shadows on Saturn

The shadows of Enceladus (left) and Titan (right) on Saturn's cloud tops.

The shadows of Enceladus (left) and Titan (right) on Saturn's cloud tops.

These two views from NASA’s Cassini spacecraft, currently in orbit around Saturn, show the huge difference in scale between it’s largest Moon, Titan, and a smaller one, Enceladus—even though the moons themselves are not in view.

On the left is a view taken with Saturn”s rings almost edge-on. On the planet’s clouds, just below the rings, can be seen a dark spot—this is the shadow being cast by Enceladus. The moon itself is a long way off to the left and not visible in this frame. Enceladus is about 500 kilometres in diameter.

On the right is another view with almost the same geometry, but this time there is a huge shadow on Saturn’s clouds, stretched out by the curve of the planet. This is the shadow of Titan, Saturn’s largest planet and one that is currently the target of many investigations.

Titan has a thick, nitrogen atmosphere, similar to what Earth’s atmosphere is thought to have been like billions of years ago. Titan is 10 times bigger than Enceladus, with an average diameter of 2,576 kilometres.

A view of the surface of Titan, taken by the Huygens probe

A view of the surface of Titan, taken by the Huygens probe after it landed on January 14, 2005

On January 14, 2005, the Huygens probe—which had been carried by Cassini all the way from Earth—descended through Titan’s clouds and landed safely on its surface. It found a frozen world, but one that sometimes experiences rain and rivers of methane and ethane at super-cold temperatures.

In just a couple of days from now, July 7, Cassini will make another close fly-by of Titan—swooping over the moon at a distance of only 1,005 kilometres—and will train its suite of instruments on the thick clouds and frozen surface.

The left-hand view above was taken from a distance of around 1.7 million kilometres from Saturn, while the right-hand view was from around 2.1 million kilometres.

Story by Jonathan Nally, Editor,

Images courtesy NASA / JPL / Space Science Institute.

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