An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports a study indicating that the interior of the nucleus of comet 67P/Churyumov-Gerasimenko is porous and less dense than its surface. A team of researchers reviewed data collected by ESA’s Rosetta space probe and its Philae lander’s CONSERT instrument. The signals exchanged between them through the cometary nucleus propagated at different speeds, indicating a varying density of its interior. This suggests that solar radiation changed the surface, making it less porous.
The mission of the Rosetta space probe ended on September 30, 2016, with a landing on the surface of comet 67P/Churyumov-Gerasimenko which caused its destruction. The huge amount of data collected over time kept on being examined, and there are also the data collected by the Philae lander, which was built precisely to land on the comet but literally bounced off its surface and was operational for just a little longer than two days. Despite its limited success, Philae made it possible to obtain very useful data on the comet.
One of the instruments of the mission was CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission), a radar with two antennas, one on Rosetta and one on Philae. The exchange of 90 MHz radio signals made it possible to probe the interior of comet 67P/Churyumov-Gerasimenko. The subsequent creation of precise 3D models of the nucleus allowed to analyze the data collected by CONSERT to obtain indications on its porosity and composition.
The image (ESA/Rosetta/Philae/CONSERT) shows at the top a graph with the signals connecting the CONSERT instrument of the lander Philae to that of the Rosetta space probe. The graph is fan-shaped due to Rosetta’s movements in its orbit while the colors indicate the different signal paths as the orbit changed. Below the details of the signals as they propagate within the nucleus from Philae to the points where they leave the comet to reach Rosetta. The paths are projected onto the surface and therefore are curved in the image. The colors indicate the depth of the paths from blue indicating the lowest to red indicating the greatest, where the signals exceeded 100 meters in depth.
There are discussions about the interpretation of these results, but Wlodek Kofman, one of the lead authors of this study, believes they suggest that the less dense interior of the comet 67P/Churyumov-Gerasimenko retained its original pristine nature. Instead, the surface was modified by solar radiation.
The extraordinary Rosetta mission continues to offer insights into comet research. These objects are perhaps the most primitive in the solar system and offer information on its formation. They carry various chemical compounds, including organic ones, which they probably scattered around, reaching the Earth as well.
