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Mars Orbiter Image Shows Comet Nucleus is Small
October 20, 2014


The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter captured views of comet C/2013 A1 Siding Spring while that visitor sped past Mars on Sunday (Oct. 19), yielding information about its nucleus.

The images are the highest-resolution views ever acquired of a comet coming from the Oort Cloud at the fringes of the solar system.  Other spacecraft have approached and studied comets with shorter orbits. This comet's flyby of Mars provided spacecraft at the Red Planet an opportunity to investigate from close range.

Images of comet Siding Spring from HiRISE are online at:


The highest-resolution of images of the comet's nucleus, taken from a distance of about 86,000 miles (138,000 kilometers), have a scale of about 150 yards (138 meters) per pixel. Telescopic observers had modeled the size of the nucleus as about half a mile, or one kilometer wide.  However, the best HiRISE images show only two to three pixels across the brightest feature, probably the nucleus, suggesting a size smaller than half that estimate.

For more about HiRISE, visit:


For more about Mars Reconnaissance Orbiter, visit:


For more about comet Siding Spring, including other images of the comet, visit:


Guy Webster  818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.


Comet Siding Spring
These images were taken of comet C/2013 A1 Siding Spring by NASA's Mars Reconnaissance Orbiter on Oct. 19, 2014, during the comet's close flyby of Mars and the spacecraft. Comet Siding Spring is on its first trip this close to the sun from the Oort Cloud at the outer fringe of the solar system.
Image Credit: 
NASA/JPL-Caltech/University of Arizona
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Page Last Updated: October 20th, 2014
Page Editor: Tony Greicius