  Measuring the abundance and isotopic composition of noble gases in planetary
atmospheres can answer fundamental questions in cosmochemistry and comparative
planetology. However, noble gases are rare elements, a feature making their
measurement challenging even on Earth. Furthermore, in space applications,
power consumption, volume and mass constraints on spacecraft instrument
accommodations require the development of compact innovative instruments able
to meet the engineering requirements of the mission while still meeting the
science requirements. Here we demonstrate the ability of the quadrupole ion
trap mass spectrometer (QITMS) developed at the Jet Propulsion Laboratory
(Caltech, Pasadena) to measure low quantities of heavy noble gases (Kr, Xe) in
static operating mode and in the absence of a buffer gas such as helium. The
sensitivity reaches 1E13 cps Torr-1 (about 1011 cps/Pa) of gas (Kr or Xe). The
instrument is able to measure gas in static mode for extended periods of time
(up to 48 h) enabling the acquisition of thousands of isotope ratios per
measurement. Errors on isotope ratios follow predictions of the counting
statistics and the instrument provides reproducible results over several days
of measurements. For example, 1.7E-10 Torr (2.3E-8 Pa) of Kr measured
continuously for 7 hours yielded a 0.6 permil precision on the 86Kr/84Kr ratio.
Measurements of terrestrial and extraterrestrial samples reproduce values from
the literature. A compact instrument based upon the QITMS design would have a
sensitivity high enough to reach the precision on isotope ratios (e.g. better
than 1 percent for 129,131-136Xe/130Xe ratios) necessary for a scientific
payload measuring noble gases collected in the Venus atmosphere.
