Last month, the European Space Agency Rosetta’s space probe arrived at the comet known as 67P/Churyumov–Gerasimenko, thus becoming the first spacecraft to ever rendezvous with a comet. As it continues on its way to the Inner Solar System, Rosetta’s sensing instruments have been studying the surface in detail in advance of the attempted landing of it’s Philae probe.
Because of this, Rosetta has been able to render a map of the various areas on the surface of the comet, showing that it is composed of several different regions created by a range of forces acting upon the object. Images of the comet’s surface were captured by OSIRIS, the scientific imaging system aboard the Rosetta spacecraft, and scientists analyzing them have divided the comet into several distinct regions, each characterized by different classes of features.
All told, areas containing cliffs, trenches, impact craters, rocks, boulders and parallel grooves have been identified and mapped by the probe. Some of the areas that have been mapped appear to be caused by aspects of the activity occurring in and around the nucleus of the comet, such as where particles from below the surface are carried up by escaping gas and vapor and strewn around the surface in the surrounding area.
So detailed are these images that many have been captured at a resolution of one pixel being equal to an area of 194 square centimeters (30 square inches) on the comet surface. Dr. Holger Sierks, OSIRIS’ Principal Investigator from the Max Planck Institute for Solar System Science, puts it into perspective:
Never before have we seen a cometary surface in such detail. It is a historic moment – we have an unprecedented resolution to map a comet… This first map is, of course, only the beginning of our work. At this point, nobody truly understands how the surface variations we are currently witnessing came to be.
The newly-generated comet maps and images captured by the instruments on Rosetta will now provide a range of detail on which to finalize possible landing sites for the Philae probe to be launched to the surface . As such, the Rosetta team will meet in Toulouse, France, on September 13 and 14 to allocate primary and backup landing sites (from a list of sites previously selected) with much greater confidence.
At the same time, Rosetta has revealed quite a bit about the outward appearance of the comet, and it aint pretty! More often than not, comets are described as “dirty snowballs” to describe their peculiar composition of ice and dust. But Rosetta’s Alice instrument, which was installed by NASA, has sent back preliminary scientific data that shows that the comet is more akin to a lump of coal.
Alice is one of eleven instruments carried aboard Rosetta and one of three instrument packages supplied by NASA for the unmanned orbiter. Essentially, it’s a miniature UV imaging spectrograph that looks for thermal markers in the far ultraviolet part of the spectrum in order to learn more about the comet’s composition and history. It does this by looking specifically for the markers associated with noble gases, such as helium, neon, argon, and krypton.
The upshot of all this high-tech imaging is the surprising discovery of what 67P/Churyumov-Gerasimenko looks like. According to NASA, the comet is darker than charcoal. And though Alice has detected oxygen and hydrogen in the comet’s coma, the patches of barren ice that NASA scientists had expected aren’t there. Apparently, this is because 67P/Churyumov-Gerasimenko is too far away from the warmth of the sun to turn the ice into water vapor.
We’re a bit surprised at just how unreflective the comet’s surface is and how little evidence of exposed water-ice it shows.
Launched in 2004, Rosetta reached 67P/Churyumov-Gerasimenko by a circuitous route involving three flybys of Earth, one of Mars, and a long detour out beyond Jupiter as it built up enough speed to catch up to the comet. Over the coming months, as the Rosetta spacecraft and comet 67P move further into the solar system and approach the sun, the OSIRIS team and other instruments on the payload will continue to observe the comet’s surface for any changes.
Hence why this mission is of such historic importance. Not only does it involve a spacecraft getting closer to a comet than at time in our history, it also presents a chance to examine what happens to a comet as it approaches our sun. And if indeed it does begin to melt and breakdown, we will get a chance to peer inside, which will be nothing less than a chance to look back in time, to a point when our Solar System was still forming.