Since CAESAR’s main goal is to collect and return to Earth a bulk sample from a cometary nucleus, the best chance for success is in going to familiar territory.
Comet 67P/Churyumov-Gerasimenko was discovered in 1969 by astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko. It is the most thoroughly studied comet to-date, so CAESAR’s sampling device can be custom-designed for this comet’s surface. The European Space Agency’s Rosetta mission has already orbited the comet for two years from 2014 to 2016, and deployed a lander called Philae to the comet’s surface. Images from Rosetta and Philae show many regions where the comet’s surface is relatively smooth, free of boulders and rugged terrain. These smooth regions represent potential sites where CAESAR would collect its sample using a sampling device designed for the loose sandy material and small rocks seen in images of these regions.
Measurements from Rosetta’s instruments show that these regions are rich in water ice and organics, and CAESAR’s goal is to collect this material and return it to Earth in pristine condition. Bringing these preserved substances back to Earth would allow scientists to determine what role comets played in delivering these necessary ingredients for life to our planet and increase our understanding of how life arose from these chemical building blocks.
View an interactive 3D model of Comet 67P/Churyumov-Gerasimenko
The importance of bringing back a pristine sample is that Comet 67P, like other comets, could be a remnant from the birth of the solar system, and therefore could tell us which organics were already present in the cloud from which the planets formed. Its odd shape suggests that it was formed by a collision between two smaller comets, or that the “neck” region has been carved out by erosion. When a comet passes close to the Sun in its orbit, the increased heat causes the surface to erode when volatile materials, like water and organics, are released as gases—while microscopic particles form a coma around the comet.
Materials in the coma are then blown away from the Sun by solar wind, forming a tail. When a comet passes very close to the Sun, the coma and tail are large and bright enough for us to see in our night sky.
To ensure the safety of the spacecraft and ease of sample collection, CAESAR plans to visit Comet 67P when it is far from the Sun and jets are not as active.
See more of Comet 67P/Churyumov-Gerasimenko at the European Space Agency’s gallery of photos taken by Rosetta.
From the 2018 Lunar Planetary Science Conference.