The gas-to-dust mass ratios found for interstellar dust within the Solar System, versus values determined astronomically for the cloud around the Solar System, suggest that large and small interstellar grains have separate histories, and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and direction of interstellar gas in the cloud surrounding the solar system to derive an in situ value for the gas-to-dust mass ratio, R g/d =94 +46−38 . This ratio is dominated by the larger near-micron sized grains. Including an estimate for the mass of smaller grains, which do not penetrate the heliosphere due to charged grain interactions with heliosheath and solar wind plasmas, and including estimates for the mass of the larger population of interstellar micrometeorites, the total gas-to-dust mass ratio in the cloud surrounding the Solar System is half this value. Based on in situ data, interstellar dust grains in the of 10 −14 to 10 −13 g mass range are underabundant in the Solar System, compared to an MRN mass distribution scaled to the local interstellar gas density, because such small grains do not penetrate the heliosphere. The gas-to-dust mass ratios are also derived by combining spectroscopic observations of the gas-phase abundances in the nearest interstellar clouds. Measurements of interstellar absorption lines formed in the cloud around the solar system, as seen in the direction of ǫ CMa, give−207 for assumed solar reference abundances, and R g/d =551 +61 −251 for assumed B-star reference abundances. These values exceed the in situ value, suggesting either grain mixing or grain histories are not correctly understood, -4or that sweptup stardust is present. Such high values for diffuse interstellar clouds are strongly supported by diffuse cloud data seen towards λ Sco and 23 Ori, provided B-star reference abundances apply. If solar reference abundances prevail, however, the surrounding cloud is seen to have greater than normal dust destruction compared to higher column density diffuse clouds. The cloud surrounding the Solar System exhibits enhanced gas-phase abundances of refractory elements such as Fe + and Mg + , indicating the destruction of dust grains by shock fronts. The good correlation locally between Fe + and Mg + indicates that the gas-phase abundances of these elements are dominated by grain destruction, while the poor correlation between Fe + and H • indicates either variable gas ionization or the decoupling of neutral gas and dust over parsec scalelengths. These abundances, combined with grain destruction models, indicate that the nearest interstellar material has been shocked with shocks of velocity ∼150 km s −1 . If solar reference abundances are correct, the low R g/d value towards λ Sco may indicat...

The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10 −19 and 10 −9 kg in interplanetary space and in the jovian and saturnian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta

No abstract

No abstract

No abstract