For the first time, astronomers have gotten a close look at the core of a comet from the Oort cloud.
On October 19, comet Siding Spring whizzed within 138,000 kilometers of NASA’s Mars Reconnaissance Orbiter, putting the spacecraft in a perfect position to snap images of the comet. NASA’s Opportunity rover has also beamed back its view of Siding Spring from the surface of the Red Planet.
Because of the speed of the icy boulder and its distance from the MRO, the images aren’t as crisp as those taken by Rosetta at 67P/Churyumov-Gerasimenko, which was born in the Kuiper belt. But the fuzzy dots seen in the Mars orbiter images do give hints that Siding Spring’s cometary core is small, only 0.5 kilometers across. The new images are also the first of the core of a comet that takes longer than 200 years to orbit the sun.