The Champollion cometary molecular analysis experiment

The Chemical Analysis of Released Gas Experiment (CHARGE), is one of several investigations selected for the Champollion New Millennium DS4 Mission. CHARGE is presently being designed to carry out a detailed molecular and isotopic analysis of material collected for the surface and several centimeters below the surface of comet Tempel I. The highest priority scientific issues addressed by this investigation include: the chemical conditions present in the region of cometary formation; the chemical changes during cometary formation and over the lifetime of the comet; the relationship of comets to other primitive and more evolved bodies in the solar system and to the parent interstellar cloud; the contribution of cometary material to the atmospheres and oceans of planets; and the nature of the mixture of ices and dust grains which give rise to the coma and extended sources of gas as a comet approaches perihelion. CHARGE will be designed to thermally process samples of solid phase material from near the ambient temperature to approximately 900 K. Gases evolved from the frozen ices will be continuously analyzed as a function of sample temperature by a quadrupole mass spectrometer with a mass range of 2 to 300 amu. A broad range of major and trace species, both organic and inorganic, from the gases evolved from the solid samples will undergo both chemical and cold trapping for subsequent analysis by gas chromatograph mass spectrometer (GCMS) analysis. CHARGE technology heritage includes the Galileo Probe Mass Spectrometer (Niemann et al., 1996) that successfully measured the composition of Jupiter's atmosphere in December of 1995. The landed portion of the mission will enable analysis of subsurface materials and allow identification of organic species present at sub-parts per million mole-fraction in the nucleus. Prior to the landed operations, CHARGE will carry out measurements from orbit for a period of several weeks.