Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2005 May 30
See Explanation. Clicking on the picture will download the highest resolution version available.

A Great White Spot on Rhea
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What caused this great white spot on the surface of Saturn's moon Rhea? The spot was first noticed last year by the robot Cassini spacecraft now orbiting Saturn. Cassini's flyby of Rhea in April imaged in the spot in great detail. Astronomers hypothesize that the light-coloured spot is the result of a relatively recent impact on the surface of the icy moon. The impact that likely created the crater also splashed light-coloured material from the interior onto the darker surface. Rhea spans 1,500 kilometres across and is the second largest moon of Saturn after Titan. Rhea sports several other light coloured surface features that are, as yet, not well understood.

Tomorrow's picture: trifid starscape

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