Friday, 30 March 2012

NASA releases new Cassini images of Saturn's moons Enceladus, Janus and Dione.

Saturn has fifty-three named moons, of which thirteen are larger than 50 km in diameter, and seven large enough to have formed a roughly spherical shape due to their own mass. Another nine unnamed moons of Saturn have confirmed orbits; the exact number of moons orbiting the planet is hard to assess, since each of the billions of tiny particles that make up Saturn's rings could potentially be seen as a moon.

The 33 largest moons of Saturn, showing comparative size and the order in which they orbit. NASA/JPL.

The orbits of Saturn's moons. Lunaf.com.

The Cassini Probe has been orbiting Saturn since June 2004, sending back scientific data and images of the planet and its moons. This week NASA released new images of three of the moons, Enceladus, Janus and Dione sent back by Cassini in the last few days.

Enceladus is the sixth largest moon of Saturn, with a diameter of 500 km. It orbits at a distance of 238 000 km, within the planet's E ring. Enceladus is a geologically active body, on which volcanic activity was observed near its south pole by Cassini in 2005. The surface of Enceladus is made up of a number of distinct terrains, some thought to be less than 100 million years old.

Image of Enceladus from 111 809 km. Taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Image of Enceladus from 232 197 km. Taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Image of Enceladus from 48 759 km. Taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Image of Enceladus from 31 881 km. Taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Janus is a small irregularly shaped moon, roughly 203 × 185 × 152.6 km. It orbits Saturn at roughly 151 500 km, in an almost identical orbit to another moon, Epimetheus, which caused some confusion for astronomers trying to establish the orbital parameters of what they had assumed was a single moon. The surface of Janus is heavily cratered, with some craters exceeding 30 km in diameter. The moon has a low density, which combined with its irregular shape, leads some planetary scientists to conclude it is a rubble pile rather than a solid object.

Image of Janus taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Image of Janus taken by the Cassini Probe on 27 March 2012, and received on Earth on 28 March.

Dione is the forth largest moon of Saturn, and the fifteenth largest moon in the Solar System (since it is bigger than all the known smaller moons combined, this is an important distinction, the fifteen largest moons really are a different class of object). Dione orbits Saturn at about 377 400 km. It is a spherical object with an icy, crater covered surface, though its high density suggests it has a large rocky core.

Image of Dione from 78 998 km. Taken by the Cassini Probe on 28 March 2012, and received on Earth on the same day.

Image of Dione from 80 171 km. Taken by the Cassini Probe on 28 March 2012, and received on Earth on the same day.

Image of Dione from 44 528 km. Taken by the Cassini Probe on 28 March 2012, and received on Earth on the same day.

Image of Dione from 44 028 km. Taken by the Cassini Probe on 28 March 2012, and received on Earth on the same day.

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