The structure of cometary dust - first results from the MIDAS Atomic Force Microscope onboard Rosetta

Abstract:

A decade after launch the European Space Agency’s Rosetta spacecraft has finally arrived at comet 67P/Churyumov–Gerasimenko. Unlike previous cometary missions, Rosetta is not a flyby, limited to taking a snapshot of the comet at a single heliocentric distance. Instead, Rosetta intercepted the comet prior to the onset of major activity and will chart its evolution during its perihelion passage and beyond.

Such a unique mission requires a unique payload; as well as the more typical remote sensing instruments, Rosetta also carries sensors to sample in situ the gas and dust environment. One of these instruments is MIDAS, an atomic force microscope designed to collect dust and image it in three dimensions with nanometre resolution. Equipped with an array of sharp tips, four of which are magnetised to allow magnetic force microscopy, MIDAS exposes targets to the incident flux after which they are moved to the microscope for analysis.

As well as extending coverage of the dust size distribution down to the finest particles, MIDAS has the unique capability to determine the shape of pristine particles - to determine, for example, if they are compact or fluffy, and to look for features which may be diagnostic of their formation environment or evolution. The magnetic mode lets MIDAS probe samples for magnetic material and to map its location if present.

Having been operating almost continuously after hibernation imaging empty targets before exposure, the first exposures were performed when Rosetta entered 30 km bound orbits. The first MIDAS images and analyses of collected dust grains are presented here.