Comet C/2013 Siding Spring hurtled past Mars October 19 and NASA's Mars Reconnaissance Orbiter (MRO) took the lead in beaming back fine images of its pristine nucleus taken during the closest approach.

The images were acquired by the High-Resolution Imaging Science Experiment (HiRISE) camera on board the MRO. With the instrument accurately depicting brightness and details, astronomers observed the comet has a smaller nucleus than previously thought.

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According to NASA, the images showed the part likely to be the nucleus was only two to three pixels across, suggesting a size half that originally modeled. Prior to the comet's flyby near the Red Planet, telescopic observation led to models estimating the size of the nucleus at about one kilometer. 

The observation presents images of the comet with a complete dynamic range, including the nucleus and coma. A comet consists of an icy lump of materials in the core, known as the nucleus.

As the comet comes closer to the Sun, the ice on the nucleus starts turning into gas and forms a cloud called a coma. HiRISE images were overexposed photos in which the coma was enhanced so astronomers could fully identify its size.

"It's excitingly fortunate that this comet came so close to Mars to give us a chance to study it with the instruments we're using to study Mars," affirmed Mark Lemmon from NASA's Opportunity science team. "The views from Mars rovers, in particular, give us a human perspective, because they are about as sensitive to light as our eyes would be."

Coming from the Oort Cloud a light year away from the Sun, Siding Spring is on its first foray into the inner solar system. The rare phenomenon could give humankind fresh insights into what materials led to the formation of the Solar System eons ago.  

TagsSiding Spring, Comet Flyby, Comet C1/2013 A1, NASA, Mars Reconnaissance Orbiter (MRO), High-Resolution Imaging Science Experiement, Orbiter, HiRISE, comet