In situ mass spectrometry during the Lutetia flyby

During the Rosetta flyby at asteroid Lutetia the ROSINA instrument tried to detect a thin exosphere of the asteroid. Although the instrument is sensitive enough to detect even very tenuous gases at a density level of 1cm−3 the Lutetia exosphere could not be unambiguously detected due to spacecraft outgassing, which was not constant because of the changing solar aspect angle. An upper limit for a water exosphere density at the flyby distance of 3160km of (3.5±1.0)×103cm−3 was deduced from the measurements. ► ROSINA measured mass spectra all through the Lutetia flyby. ► Signal is dominated by spacecraft outgassing. ► An upper limit for a water exosphere density at the flyby distance of 3160km of (3.5±1.0)×103cm−3 was deduced.