Saturn's largest moon, Titan, remains an enigma, explored only by remote sensing from Earth, and by the Voyager and Cassini spacecraft. The most puzzling aspects include the origin of the molecular nitrogen and methane in its atmosphere, and the mechanism(s) by which methane is maintained in the face of rapid destruction by photolysis. The Huygens probe, launched from the Cassini spacecraft, has made the first direct observations of the satellite's surface and lower atmosphere. Here we report direct atmospheric measurements from the Gas Chromatograph Mass Spectrometer (GCMS), including altitude profiles of the constituents, isotopic ratios and trace species (including organic compounds). The primary constituents were confirmed to be nitrogen and methane. Noble gases other than argon were not detected. The argon includes primordial 36Ar, and the radiogenic isotope 40Ar, providing an important constraint on the outgassing history of Titan. Trace organic species, including cyanogen and ethane, were found in surface measurements.

Abstract. The Galileo probe mass spectrometer determined the composition of the Jovian atmosphere for species with masses between 2 and 150 amu from 0.5 to 21.1 bars. This paper presents the results of analysis of some of the constituents detected: H2, He, Ne, Ar, Kr, Xe, CH4, NH3, H20 , H2S , C 2 and C3 nonmethane hydrocarbons, and possibly PH 3 and C1.4He/H2 in the Jovian atmosphere was measured to be 0.157 _+ 0.030. 13C/12C was found to be 0.0108 +_ 0.0005, and D/H and 3He/4He were measured. Ne was depleted, -<0.13 times solar, Ar -<1.7 solar, Kr -<5 solar, and Xe -<5 solar. CH 4 has a constant mixing ratio of (2.1 _+ 0.4) x 10 -3 (•2C, 2.9 solar), where the mixing ratio is relative to H 2. Upper limits to the H20 mixing ratio rose from 8 x 10 -7 at pressures <3.8 bars to (5.6 _+ 2.5) x 10 -5 (•60, 0.033 _+ 0.015 solar) at 11.7 bars and, provisionally, about an order of magnitude larger at 18.7 bars. The mixing ratio of H2S was <10 -6 at pressures less than 3.8 bars but rose from about 0.7 x 10 -5 at 8.7 bars to about 7.7 x 10 -5 (328, 2.5 solar) above 15 bars. Only very large upper limits to the NH 3 mixing ratio have been set at present. If PH 3 and CI were present, their mixing ratios also increased with pressure. Species were detected at mass peaks appropriate for C2 and C3 hydrocarbons. It is not yet clear which of these were atmospheric constituents and which were instrumentally generated. These measurements imply (1) fractionation of 4He, (2) a local, altitudedependent depletion of condensables, probably because the probe entered the descending arm of a circulation cell, (3) that icy planetesimals made significant contributions to the volatile inventory, and (4) a moderate decrease in D/H but no detectable change in (D + 3He)/H in this part of the galaxy during the past 4.6 Gyr. IntroductionThe Galileo probe mass spectrometer (GPMS) obtained useful data concerning the composition of the Jovian atmosphere along the probe trajectory between pressure levels of 0.51 and 21.1 bars. Among species detected were H 2 and HD, 3He and 4He; the isotopes of the noble gases Ne, Ar, Kr, and Xe; the volatiles CH4, NH 3, H20 , H2S; a chlorine compound which may have been HC1, and a large number of C2 and C3 nonmethane hydrocarbons (NMHCs). Mixing ratios, or data capable of being translated into mixing ratios, have been obtained from the mass spectra acquired by direct sampling of the atmosphere and information provided by two enrichment cells for numerous species. Striking aspects of the abundance profiles were (1) the very low mixing ratios of condensable volatiles such as H2S and H20 at pressures <8 bars and their gradual increase at higher pressures along the probe trajectory, InstrumentThe GPMS has been described in detail [Niemann et al., 1992]. A quadrupole mass filter scanning in integral mass steps from 2 to 150 atomic mass units (amu) provided mass analysis. A one half-second integration time was allotted to each mass step. A secondary electron multiplier detected the ions transmitted by the mass filter. The ...

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission's main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet's activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N2 and 13C from 12CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources

In this paper, we use data from the Dynamics Explorer 2 (DE 2) satellite and a theoretical simulation made by using the National Center for Atmospheric Research thermosphere/ionosphere general circulation model (NCAR‐TIGCM) to study storm‐induced changes in the structure of the upper thermosphere in the low‐ to middle‐latitude (20°‐40°N) region of the winter hemisphere. Our principal results are as follows: (1) The winds associated with the diurnal tide weaken during geomagnetic storms, causing primarily zonally oriented changes in the evening sector, few changes in the middle of the afternoon, a combination of zonal and meridional changes in the late morning region, and mainly meridional changes early in the morning. (2) Decreases in the magnitudes of the horizontal winds associated with the diurnal tide lead to a net downward tendency in the vertical winds blowing through a constant pressure surface. (3) Because of these changes in the vertical wind, there is an increase in compressional heating (or a decrease in cooling through expansion), and thus temperatures in the low‐ to middle‐latitudes of the winter hemisphere increase. (4) Densities of all neutral species increase on a constant height surface, but the pattern of changes in the O/N2 ratio is not well ordered on these surfaces. (5) The pattern of changes in the O/N2 ratio is better ordered on constant pressure surfaces. The increases in this ratio on constant pressure surfaces in the low‐ to middle‐latitude, winter hemisphere are caused by a more downward tendency in the vertical winds that blow through the constant pressure surfaces. Nitrogen‐poor air is then advected downward through the pressure surface, increasing the O/N2 ratio. (6) The daytime geographical distribution of the modeled increases in the O/N2 ratio on a constant pressure surface in the low‐ to middle‐latitudes of the winter hemisphere correspond very closely with those of increases in the modeled electron densities at the F2 peak.

The composition of the jovian atmosphere from 0.5 to 21 bars along the descent trajectory was determined by a quadrupole mass spectrometer on the Galileo probe. The mixing ratio of He (helium) to H2 (hydrogen), 0.156, is close to the solar ratio. The abundances of methane, water, argon, neon, and hydrogen sulfide were measured; krypton and xenon were detected. As measured in the jovian atmosphere, the amount of carbon is 2.9 times the solar abundance relative to H2, the amount of sulfur is greater than the solar abundance, and the amount of oxygen is much less than the solar abundance. The neon abundance compared with that of hydrogen is about an order of magnitude less than the solar abundance. Isotopic ratios of carbon and the noble gases are consistent with solar values. The measured ratio of deuterium to hydrogen (D/H) of (5 +/- 2) x 10(-5) indicates that this ratio is greater in solar-system hydrogen than in local interstellar hydrogen, and the 3He/4He ratio of (1.1 +/- 0.2) x 10(-4) provides a new value for protosolar (solar nebula) helium isotopes. Together, the D/H and 3He/4He ratios are consistent with conversion in the sun of protosolar deuterium to present-day 3He.