Saturn’s New Moons

The Cassini spacecraft has found evidence of lightning and two tiny moons orbiting the ringed planet.

Saturn is proving to be full of surprises. The Cassini spacecraft, now at just the beginning of its 4-year mission to the planet, has already discovered two new moons and a slew of lightning storms on the ringed planet.

 

This photo, taken by a camera aboard the Cassini spacecraft, shows one of Saturn’s newly discovered, tiny moons (framed by box).

 

NASA, JPL, Space Science Institute

Astronomers from the Space Science Institute in Boulder, Colo., discovered the moons in pictures that Cassini took in early June. The moons are tiny. They appear to be the smallest ones ever discovered around Saturn. Both take about a day to orbit the planet. They lie between the paths of two larger moons, Mimas and Enceladus.

One of the new moons is called S/2004 S1. It’s 194,000 kilometers from Saturn’s center and measures about 3 kilometers across. The other moon, called S/2004 S2, is 211,000 kilometers from Saturn’s center and measures about 4 kilometers across.

The new discoveries could make scientists rethink their ideas about other parts of the solar system, especially about the Kuiper Belt—a stash of icy bodies that lies way out at the edge of the solar system.

Astronomers have long assumed that the Kuiper Belt is full of small comets, each about the size of a house. These comets would zoom past Saturn at high speeds. If such comets were common out there, though, they would probably ram into Saturn’s small moons, smashing them to bits. Because this apparently hasn’t happened, the Kuiper Belt’s supply of small comets might be smaller than expected.

 

This illustration shows how lightning above Saturn would generate high-frequency radio waves that could be detected by the Cassini spacecraft.

 

NASA, JPL, University of Iowa

Cassini has also detected bursts of lightning on Saturn. The storms seem to form at fairly high latitudes, and they don’t last very long. In the early 1980s, the Voyager spacecraft found a different storm pattern. Voyager recorded long-lasting storms located close to the planet’s equator.

The difference, astronomers suggest, has to do with a change in season. Two decades ago, Saturn’s rings cast a shadow near the planet’s equator. This put the cold, shaded part of Saturn’s atmosphere next to the hottest part. The result would be turbulent conditions that could produce large storms. Now, it’s summer in Saturn’s southern hemisphere, and the rings cast a broad shadow over the northern hemisphere. Under these conditions, long-lived storms appear to occur less often.

What will Cassini find next? Stay tuned. There’s much more to come. —E. Sohn

Going Deeper:

Cowen, Ron. 2004. Saturn watch: Cassini finds two new moons and lightning. Science News 166(Aug. 21):115-116. Available at http://www.sciencenews.org/articles/20040821/fob2.asp .

Sohn, Emily. 2004. Ringing Saturn. Science News for Kids (July 28). Available at http://www.sciencenewsforkids.org/articles/20040728/Feature1.asp .

______. 2004. Search for a missing moon. Science News for Kids (April 28). Available at http://www.sciencenewsforkids.org/articles/20040428/Note3.asp .

______. 2004. Planets on the edge. Science News for Kids (April 7). Available at http://www.sciencenewsforkids.org/articles/20040407/Feature1.asp .

Additional information about the discovery of two new moons orbiting Saturn can be found at saturn.jpl.nasa.gov/news/press-releases-04/20040816-pr-a.cfm (NASA Jet Propulsion Laboratory).

Information about the discovery of lightning on Saturn is available at www.nasa.gov/mission_pages/cassini/media/cassini-080504.html (NASA).

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