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.

2006 January 1
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

The Largest Rock in the Solar System
Credit: Voyager 1, NASA

Explanation: There, that faint dot in the center - that's the largest rock known in our Solar System. It is larger than every known asteroid, moon, and comet nucleus. It is larger than any other local rocky planet. (Nobody knows for sure what size rocks lie at the cores of Jovian planets, or orbit other stars.) It used to be the largest rock of any type known until earlier last year. The Voyager 1 spacecraft took the above picture of the giant space rock in 1990 from the outer Solar System. This rock is so large its gravity makes it nearly spherical, and holds heavy gases near its surface. Today, this rock starts another orbit around its parent star, for roughly the 5 billionth time, spinning over 350 times during each trip. Happy Gregorian Calendar New Year to all the human inhabitants of this rock we call Earth.

Tomorrow's picture: sun pillar

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
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