A new analysis of data gathered by the CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission) instrument, a radar onboard ESA’s Rosetta spacecraft and its Philae lander, confirms that solar radiation has significantly modified the surface of comet 67P/Churyumov-Gerasimenko as it travels through space between the orbits of Jupiter and Earth.
ESA’s Philae lander at work on comet 67P/Churyumov-Gerasimenko. Image credit: ESA / AOES Medialab.
The CONSERT radar was designed to probe the nucleus of 67P/Churyumov-Gerasimenko with radio waves at 90 MHz frequency. The experiment involved two antennas sending precise signals to each other.
But when Philae lander went missing upon landing on November 2014, scientists had to work with estimated values.
It took nearly two years to find out where the lander was. In September 2016, its exact position was retrieved within the area identified by CONSERT.
“We managed to define the region where the lander was with a margin of about 150 m (492 feet),” said study co-lead author Dr. Wlodek Kofman, a researcher at the University Grenoble Alpes and the Centrum Badan Kosmicznych Polskiej Akademii Nauk.
“The real landing site was in this region.”
“Precise 3D models of the comet with Philae in the picture allowed us to revisit the measurements and improve our analysis of the interior,” he added.
This graphic shows the signal connecting the CONSERT instrument on Philae, on the surface of comet 67P/Churyumov-Gerasimenko, to the one on the Rosetta orbiter. The fan like appearance is a result of the motion of Rosetta along its orbit, with the colors marking the separate signal paths as the orbit evolves. The image below shows the signals in more detail, propagating inside the comet from Philae to the points from where they leave the comet to the orbiter. The curving is a result of the projection of its paths on the bumpy surface of the comet. The bluer color indicates more shallow paths (just a few centimeters), while the redder tones show where the signals penetrated below 100 m (328 feet) in depth. Image credit: Kofman et al, doi: 10.1093/mnras/staa2001.
The time for the signal to travel between CONSERT’s two antennas offered insights into the comet’s nucleus, such as porosity and composition.
Dr. Kofman and colleagues discovered that rays propagated at different velocities, indicating varying densities within the comet.
“The relative permittivity of the materials is found to range from about 1.7 to 1.95 in the shallow subsurface (< 25 m) and about 1.2 to 1.32 in the interior,” the scientists said.
“These differences indicate different average densities between the shallow subsurface and the interior of comet.”
“They can be explained by various physical phenomena such as different porosities, the possible compaction of surface materials, or even perhaps different proportions of the same materials,” they added,
“This strongly suggests that the less dense interior has kept its pristine nature.”
The findings were published in the Monthly Notices of the Royal Astronomical Society.
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Wlodek Kofman et al. 2020. The interior of Comet 67P/C-G; revisiting CONSERT results with the exact position of the Philae lander. MNRAS 497 (3): 2616-2622; doi: 10.1093/mnras/staa2001
