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.

2004 December 1
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Saturn's Moon Dione from Cassini
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What causes the bright streaks on Dione? Recent and likely future images of this unusual moon by the robot Cassini spacecraft now orbiting Saturn might help us find out. The above image was taken at the end of October from a distance of about one million kilometers. The bright streaks run across some of Dione's many craters, indicating that the process that created them occurred later than the impacts that created those craters. Dione is made of mostly water ice but its relatively high density indicates that it contains much rock inside. Giovanni Cassini discovered Dione in 1684. The Cassini spacecraft is scheduled to photograph Dione at higher resolution in mid-December. Currently, the highest resolution images of Dione remain those taken by the passing Voyager spacecraft in 1980.

Tomorrow's picture: shadow of the rings

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