Washington, Oct 21 (IANS): NASA's Mars Reconnaissance Orbiter successfully captured views of the comet C/2013 A1 Siding Spring when it whizzed past Mars Sunday, obtaining key information about its nucleus.

The images taken by the High-Resolution Imaging Science Experiment (HiRISE) show only two to three pixels across the brightest feature, probably the nucleus, suggesting a size smaller than half the estimate, NASA stated.

Telescopic observers had modelled the size of the nucleus at about 1 km wide.

"The images are the highest-resolution views ever acquired of a comet coming from the Oort Cloud at the fringes of the solar system," the US space agency said in a statement.

The comet's flyby of Mars provided spacecraft near the Red Planet an opportunity to investigate from close range.

The highest-resolution of images of the comet's nucleus, taken from a distance of about 138,000 km, was with a scale of about 138 metres per pixel.

The comet whizzed past within about 139,500 kms of Mars Oct 19.

Siding Spring originated in the Oort Cloud, a spherical region of space surrounding our sun and occupying space between 5,000 and 100,000 astronomical units.