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.

2010 November 8
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

700 Kilometers Below Comet Hartley 2
Credit: NASA, JPL-Caltech, UMD, EPOXI Mission

Explanation: What kind of comet is this? Last week, NASA's robotic EPOXI spacecraft whizzed past Comet 103P/Hartley, also known as Comet Hartley 2, and recorded images and data that are both strange and fascinating. EPOXI was near its closest approach -- about 700 kilometers away -- when it snapped the above picture. As expected, the comet has indeed shown itself to be a tumbling iceberg orbiting the Sun between Earth and Jupiter. However, unexpected features on the images have raised many questions. For example, where are all the craters? Why is there a large smooth area around the middle? How much of Comet Hartley 2 is a loose pile of dust and ice shards? Future analyses and comparisons to other comet nuclei may answer some of these questions and, hopefully, lead to a better general understanding of comets, meteors, and the early Solar System.

Tomorrow's picture: thin galaxy

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