Ptolemy operations and results during the Lutetia flyby

Abstract

The September 5th 2008 Rosetta flyby of asteroid 2867 Šteins raised tantalising questions concerning the possibility of outgassing and extant exospheres surrounding small bodies within the asteroid belt. With this in mind and recognising the size and composition of asteroid 21 Lutetia it was decided to attempt a detection of such possible outgassing using a number of Rosetta instruments, including Ptolemy, a miniature gas chromatograph isotope ratio mass spectrometer aboard the lander Philae. Ptolemy collected 5 sets of mass spectra at hourly intervals during the Lutetia encounter; 2 background measurements either side of close approach and an exosphere detection measurement as the spacecraft passed over the subsolar point. An increase in pressure was detected at the subsolar point but the cause (exosphere or spacecraft) was unresolved with the realisation that any such detection is hindered by outgassing from the spacecraft and instrument itself. Constraints are placed on the properties of Lutetia exosphere, structure and production rates. The experience gained is used to provide suggestions for future missions or spacecraft events aimed at the detection and characterisation of the exospheres of Solar System bodies.