An article published in the journal “Nature” reports a reconstruction of the trajectory of ESA’s Rosetta mission’s Philae lander in its touchdown on the surface of comet 67P/Churyumov-Gerasimenko. A team of researchers examined data collected by the Rosetta space probe and the Philae lander to find out where the latter made its second touchdown on the comet, which was followed by further bounces before finally landing. The study also showed that the affected materials contained an abundant amount of ice as soft as freshly laid snow, to the point of being described as softer than cappuccino froth.
On November 12, 2014, the Rosetta mission’s Philae lander made the first landing of a human vehicle on a comet. It was supposed to be a controlled landing, complete with a harpoon system to anchor to the surface of an object with very low gravity which made its weight very limited. Instead, Philae started bouncing and stopped only after about two hours.
The image (Touchdown 1: ESA/Rosetta/Philae/ROLIS/DLR; all other images: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Analysis: O’Rourke et al (2020)) shows the points of the various landings made by the lander Philae on the surface of comet 67P/Churyumov-Gerasimenko.
Philae’s mission was very limited, yet what appeared to be half failure still allowed for valuable data to be gathered. Almost six years later, their study, combined with other data collected by Rosetta, led to new findings about what happened to Philae and about comet 67P/Churyumov-Gerasimenko.
In particular, the Philae lander’s ROsetta MAgnetometer and Plasma monitor (ROMAP) instrument and the Rosetta spacecraft’s Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) instrument were crucial to finding the area where Philae bounced off the comet 67P/Churyumov-Gerasimenko for the second time. During that event, the ROMAP boom struck the surface generating a characteristic signal that showed its movement relative to Philae allowing to estimate the duration of the lander’s penetration into the ground. The correlation between the ROMAP data and those of the Rosetta RPC magnetometer allowed to determine the exact orientation of Philae.
According to the data analysis, Philae spent nearly two minutes at the point of second surface contact, a duration determined by the very low gravity of comet 67P/Churyumov-Gerasimenko. The lander didn’t simply bounce but also “plowed” a portion of the surface, leaving traces that were detected by various instruments, even in the images. The signs discovered have a shape that earned the region the nickname “skull-top”.
It was possible to estimate the porosity of the boulder hit by the Philae lander and establish that the ice beneath its surface is soft, to the point of being defined softer than cappuccino froth. This discovery is interesting because it opens up the possibility of future missions that include collecting comet samples to return to Earth.
Comets are considered fossils dating back to the early history of the solar system and also contain organic compounds, so being able to analyze them in depth would offer further information about it. Comets may have “seeded” the Earth with those organic compounds, so their examination could help to better understand the development of life on Earth and the possibilities that they favor the emergence of life on other planets.
