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.

2000 November 1
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

Double Asteroid 90 Antiope
Credit: W. Merline (SwRI), et al.

Explanation: This eight-frame animation is based on the first ever images of a double asteroid! Formerly thought to be a single enormous chunk of rock, asteroid 90 Antiope resides in the solar system's main asteroid belt between Mars and Jupiter. Now, these premier images reveal Antiope to actually consist of two 50 mile wide asteroids separated by about 100 miles. Like weights on each end of an elastic string, the pair mutually orbit their center of mass, or balance point in the space between them, once every 16.5 hours. Binary asteroids and asteroids with moons are believed to be rare, but observations of their orbits allow a direct determination of asteroid masses and densities. Surprisingly, Antiope and known asteroid-moon systems are found to have densities closer to ice than rock, despite their relatively dark and unreflective surfaces. These sharp images were made at the Keck Observatory atop the Hawaiian volcano Mauna Kea using newly developed adaptive optics technology to overcome the blurring effect of Earth's atmosphere.

Tomorrow's picture: Galaxies Collide

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/GSFC
& Michigan Tech. U.