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SESAME - Surface Electrical Sounding and Acoustic Monitoring Experiment

SESAME is one of ten experiments on-board the lander Philae of the ESA Rosetta mission (Launch: 2. March 2004) that should
reach comet 67P/ChuryumovGerasimenko in 2014. SESAME comprises the instruments CASSE, DIM, and PP.

Comets have diameters of a few kilometers and thus belong to the smaller bodies of the Solar System, which was formed 4.6 billion years ago. Some scientists assume that impacting comets brought the building blocks of life and the water to the early Earth. As comets remained nearly unaltered since their formation, they can reveal important facts about the conditions and processes during the genesis of the Solar System.

Lander Philae with SESAME sensors (Artist's view: M. Kretschmer)

The major part of a cometary nucleus is composed of water ice and interstellar dust. They were not melted by collisions and radioactive heat like planets and moons. During the larger part of their existence they were stored within the Oort cloud, which is about 50000 times farther from the Sun than Earth. Thus the cometary matter remained "frozen" at temperatures of some –170 °C due to the weak solar insolation.

Due to these circumstances only minor modifications of the  primordial physical and chemical state of comets are expected. Thus comets do not only show their initial chemical composition, but also the largescale build-up as well as the microstructure at the time of their origin. Only after comets are diverted into the inner Solar System by perturbations, they become active  (coma and comet tails form) and become subject to alterations. The activity of comets is governed strongly, apart from the strength of solar irradiation, by the properties of their surface. To understand the processes on the surface and in the interior of comets, measurements of surface parameters (composition, structure, mechanical and electrical parameters) and their variation during a comet day and year are of importance. It is the goal of SESAME to determine several of these parameters.

The integration of the SESAME components as well as the development of the CASSE instrument was coordinated in the Institute of Space Simulation of the German Aerospace Center (DLR) in Köln-Porz in collaboration with the engineering company von Hoerner & Sulger.

Together with scientists from several European countries the DLR Institute of Planetary Research is planning the operation and improving the measuring methods during the years until landing.