Ptolemy – an Instrument to Measure Stable Isotopic Ratios of Key Volatiles on a Cometary Nucleus

Abstract

A fundamental goal of cometary studies is to determine the exact relationship between these bodies and the Solar System -the question(s) can be summarised as follows: did comets originate during the same events that spawned the Sun and planets, are they more primitive bodies that record a pre-solar history, or are they interstellar materials collected in relatively more recent times? Now, whatever the origin of comets, it is entirely possible that they could, in part, contain interstellar or presolar components -indeed, it seems rather likely in light of the fact that primitive meteorites contain such entities. These particular components are likely to be refractory (dust, macromolecular organic complexes, etc.). Of more relevance to the issues above are the volatile constituents, which make up the bulk of a comet's mass. Since these materials, by their very nature, volatilise during perihelion passage of a comet they can, in some instances, be detected and measured spectroscopically. Perhaps the most useful species for isotopic investigations are C 2 , HCN and CN. Unfortunately, spectroscopic measurements can only currently be made with accuracies of ±10 to ±20%. As such it is very often not practical to conclude anything further than the fact that isotopic measurements are compatible with "solar" values, which tends to imply an origin from the margins of the solar accretion disk. But there is another problem with the spectroscopic measurements -since these are made on gaseous species in the coma (and relatively minor species at that) it is impossible to be certain that these represent the true nuclear values. In other words, if the processes of sublimation, active jetting, and photochemistry in the coma impart isotopic fractionation, the spectroscopic measurements could give a false impression of the true isotope ratios. What is required is an experiment capable of measuring isotopic ratios at the very surface of a comet. Herein we describe the Ptolemy instrument, which is included on the Philae lander as part of the Rosetta mission to 67P/Churyumov-Gerasimenko. The major objective of Ptolemy is a detailed appraisal of the nature and isotopic compositions of all materials present at the surface of a comet.

Influence of spacecraft outgassing on the exploration of tenuous atmospheres with in situ mass spectrometry

“…[39] Figure 11 shows results of an interference test with the Rosetta lander PHILAE [Bibring et al, 2007] as well as an attempt to combine measurements with Ptolemy, a gas chromatograph mass spectrometry sensor onboard the lander [Wright et al, 2007]. Both units are mounted on the spacecraft −x panel and are therefore clearly outside the DFMS FOV.…”

Volatile Analysis by Pyrolysis of Regolith for planetary resource exploration

“…More recently, the Thermal and Evolved Gas Analyzer (TEGA) instrument on the Phoenix Mars lander heated polar regolith samples up to 9S0°C and analyzed the evolved gases using a mass spectrometer [22]. The Rosetta mission, currently on its way to comet 67P/Churyumov-Gerasimenko, includes two evolved gas mass spectrometer instuments, the Cometary Sampling and Composition (COSAC) experiment [23] and Ptolemy [24]. These instruments contain very small pyrolysis ovens, capable of heating to 600°C and 800°C, respectively.…”

Kronos: exploring the depths of Saturn with probes and remote sensing through an international mission

“…Elements of the GAS designed to improve the precision of the measurements are adapted from in situ calibration, static mass spectrometry, gas separation, chemical processing techniques and advanced pumping systems developed for the Rosetta mass spectrometer Ptolemy [59] and presently under development for the 2009 Mars Science Laboratory [60]. The mass spectrometer is a quadrupole mass spectrometer similar to more than a dozen that have been developed at the NASA Goddard Space Flight Center and successfully operated in the upper atmosphere of the Earth and Venus.…”