Saturday, June 14, 2014

NASA Cassini Image: Flyby of Saturn's moon Phoebe

As it entered the Saturn system, NASA's Cassini spacecraft performed its first targeted flyby of one of the planet's moons.

On June 11, 2004, Cassini passed Phoebe, the largest of Saturn's outer or "irregular" moons, at an altitude of just 1,285 miles (2,068 kilometers).

This was the sole close flyby of one of the outer moons of Saturn in the entire Cassini mission.

This montage of two views is published by the Cassini team to mark the 10th anniversary of the Phoebe flyby.

The image on the left side shows Cassini's view on approach to Phoebe, while the right side shows the spacecraft's departing perspective.

Most of the left-side view was previously released as PIA06073; an area on its upper right side is newly filled in here.

Most of the view on the right side has not previously been released, although the crater at upper left is seen in PIA06074.

Phoebe's shape is approximately spherical (see PIA06070 and PIA15507 for more details), with a diameter of 136 miles (219 kilometers) on its longest axis and 127 miles (204 kilometers) on its shortest axis, which is also the rotation axis. This is approximately 16 times smaller than Earth's moon.

For several reasons, Phoebe is thought to be a captured object that does not share a joint origin with Saturn and the inner, "regular" satellites.

It orbits in a retrograde direction, opposite to the direction of Saturn's other major moons.

Its overall density was determined by Cassini scientists to be quite large for a moon of Saturn.

The prevailing view is that Phoebe might have formed in the Kuiper Belt, far beyond the orbit of Saturn. It might thus be a small cousin of the largest Kuiper Belt object, Pluto.

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