A comet has a lot to hide. To most people, it’s among the most glamorous objects in the solar system—brilliantly illuminated, racing through space with its glowing tail streaming far behind it. That, at least, is how comets look from great distances, and only when they’re close enough to the sun for the outward-flowing solar wind to light them up and produce those signature tails.
But deeper in space, without the solar floodlights? Not so much. There the comet reveals itself for what it is: a dirty snowball of ice and rock and not a whole lot more.
The resolution of the latest images taken by the spacecraft’s OSIRIS imaging system on July 20th is 330 feet (100 meters) per pixel.
At that resolution, 67P appears to consist of two parts: a smaller head connected to a larger body. The connecting region, the neck, is proving to be especially intriguing.
“One area of the neck seems significantly brighter than surrounding regions,” the post reads.
“This bright region, seen most clearly in the first image, may result from differences in surface composition or grain size. For example, could it be a region of freshly exposed ice or the product of resurfacing. Alternatively, it could be a topographical effect. The cause of this bright region will become clearer once higher-resolution images and spectral data are available.”
Even though the images taken from a distance of 3,400 miles (5,500 kilometers) are still not highly resolved, the scientists are remotely reminded of comet 103P/Hartley, which was visited in a flyby by NASA’s EPOXI mission in 2010.
While Hartley’s ends show a rather rough surface, its middle is much smoother. Scientists believe this waist to be a gravitational low: since it contains the body’s center of mass, emitted material that cannot leave the comet’s gravitational field is most likely to be re-deposited there.
Whether this also holds true for 67P’s neck region is still unclear. Another explanation for the high reflectivity could be a different surface composition. In coming weeks, the OSIRIS team hopes to analyze the spectral data of this region obtained with the help of the imaging system’s filters.
Rosetta mission manger Fred Jansen said much more analysis and modeling will have to be done to determine how best to fly around the weirdly shaped rock, and how to place a lander on it.
“We currently see images that suggest a rather complex cometary shape, but there is still a lot that we need to learn before jumping to conclusions,” he said.
Then mapping can begin to select a touchdown zone for Philae – the small landing robot on Rosetta – in November.
Rosetta will be the first space mission to rendezvous with a comet, follow it as it orbits the Sun, and attempt to send a lander to its surface.