37 research outputs found
Interstellar Dust Inside and Outside the Heliosphere
In the early 1990s, after its Jupiter flyby, the Ulysses spacecraft
identified interstellar dust in the solar system. Since then the in-situ dust
detector on board Ulysses continuously monitored interstellar grains with
masses up to 10e-13 kg, penetrating deep into the solar system. While Ulysses
measured the interstellar dust stream at high ecliptic latitudes between 3 and
5 AU, interstellar impactors were also measured with the in-situ dust detectors
on board Cassini, Galileo and Helios, covering a heliocentric distance range
between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the
inner solar system is altered by the solar radiation pressure force,
gravitational focussing and interaction of charged grains with the time varying
interplanetary magnetic field. The grains act as tracers of the physical
conditions in the local interstellar cloud (LIC). Our in-situ measurements
imply the existence of a population of 'big' interstellar grains (up to 10e-13
kg) and a gas-to-dust-mass ratio in the LIC which is a factor of > 2 larger
than the one derived from astronomical observations, indicating a concentration
of interstellar dust in the very local interstellar medium. Until 2004, the
interstellar dust flow direction measured by Ulysses was close to the mean apex
of the Sun's motion through the LIC, while in 2005, the data showed a 30 deg
shift, the reason of which is presently unknown. We review the results from
spacecraft-based in-situ interstellar dust measurements in the solar system and
their implications for the physical and chemical state of the LIC.Comment: 10 pages, 2 b/w figures, 1 colour figure; submitted to Space Science
Review
Galileo dust data from the jovian system: 2000 to 2003
The Galileo spacecraft was orbiting Jupiter between Dec 1995 and Sep 2003.
The Galileo dust detector monitored the jovian dust environment between about 2
and 370 R_J (jovian radius R_J = 71492 km). We present data from the Galileo
dust instrument for the period January 2000 to September 2003. We report on the
data of 5389 particles measured between 2000 and the end of the mission in
2003. The majority of the 21250 particles for which the full set of measured
impact parameters (impact time, impact direction, charge rise times, charge
amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in
radius), most of them originating from Jupiter's innermost Galilean moon Io.
Their impact rates frequently exceeded 10 min^-1. Surprisingly large impact
rates up to 100 min^-1 occurred in Aug/Sep 2000 when Galileo was at about 280
R_J from Jupiter. This peak in dust emission appears to coincide with strong
changes in the release of neutral gas from the Io torus. Strong variability in
the Io dust flux was measured on timescales of days to weeks, indicating large
variations in the dust release from Io or the Io torus or both on such short
timescales. Galileo has detected a large number of bigger micron-sized
particles mostly in the region between the Galilean moons. A surprisingly large
number of such bigger grains was measured in March 2003 within a 4-day interval
when Galileo was outside Jupiter's magnetosphere at approximately 350 R_J
jovicentric distance. Two passages of Jupiter's gossamer rings in 2002 and 2003
provided the first actual comparison of in-situ dust data from a planetary ring
with the results inferred from inverting optical images.Comment: 59 pages, 13 figures, 6 tables, submitted to Planetary and Space
Scienc
One year of Galileo dust data from the Jovian system: 1996
The dust detector system onboard Galileo records dust impacts in circumjovian
space since the spacecraft has been injected into a bound orbit about Jupiter
in December 1995. This is the sixth in a series of papers dedicated to
presenting Galileo and Ulysses dust data. We present data from the Galileo dust
instrument for the period January to December 1996 when the spacecraft
completed four orbits about Jupiter (G1, G2, C3 and E4). Data were obtained as
high resolution realtime science data or recorded data during a time period of
100 days, or via memory read-outs during the remaining times. Because the data
transmission rate of the spacecraft is very low, the complete data set (i. e.
all parameters measured by the instrument during impact of a dust particle) for
only 2% (5353) of all particles detected could be transmitted to Earth; the
other particles were only counted. Together with the data for 2883 particles
detected during Galileo's interplanetary cruise and published earlier, complete
data of 8236 particles detected by the Galileo dust instrument from 1989 to
1996 are now available. The majority of particles detected are tiny grains
(about 10 nm in radius) originating from Jupiter's innermost Galilean moon Io.
These grains have been detected throughout the Jovian system and the highest
impact rates exceeded . A small number of grains has been
detected in the close vicinity of the Galilean moons Europa, Ganymede and
Callisto which belong to impact-generated dust clouds formed by (mostly
submicrometer sized) ejecta from the surfaces of the moons (Kr\"uger et al.,
Nature, 399, 558, 1999). Impacts of submicrometer to micrometer sized grains
have been detected thoughout the Jovian system and especially in the region
between the Galilean moons.Comment: accepted for Planetary and Space Science, 33 pages, 6 tables, 10
figure
Four years of Ulysses dust data: 1996 to 1999
The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse (, perihelion distance 1.3 AU, aphelion distance 5.4 AU). Between
January 1996 and December 1999 the spacecraft was beyond 3 AU from the Sun and
crossed the ecliptic plane at aphelion in May 1998. In this four-year period
218 dust impacts were recorded with the dust detector on board. We publish and
analyse the complete data set of both raw and reduced data for particles with
masses to g. Together with 1477 dust impacts
recorded between launch of Ulysses and the end of 1995 published earlier
\cite{gruen1995c,krueger1999b}, a data set of 1695 dust impacts detected with
the Ulysses sensor between October 1990 and December 1999 is now available. The
impact rate measured between 1996 and 1999 was relatively constant with about
0.2 impacts per day. The impact direction of the majority of the impacts is
compatible with particles of interstellar origin, the rest are most likely
interplanetary particles. The observed impact rate is compared with a model for
the flux of interstellar dust particles. The flux of particles several
micrometers in size is compared with the measurements of the dust instruments
on board Pioneer 10 and Pioneer 11 beyond 3 AU (Humes 1980, JGR, 85,
5841--5852, 1980). Between 3 and 5 AU, Pioneer results predict that Ulysses
should have seen five times more ( sized) particles than
actually detected.Comment: accepted by Planetary and Space Science, 22 pages, 8 figures (1
colour figure
On the origin and evolution of the material in 67P/Churyumov-Gerasimenko
International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects
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Dust Flux Monitor instrument for the Stardust mission to comet Wild 2
[1] The Dust Flux Monitor Instrument ( DFMI) is part of the Stardust instrument payload. The prime goal of the DFMI is to measure the particle flux, intensity profile, and mass distribution during passage through the coma of comet Wild 2 in January 2004. This information is valuable for assessment of spacecraft risk and health and also for interpretation of the laboratory analysis of dust captured by the Aerogel dust collectors and returned to Earth. At the encounter speed of 6.1 km/s, the DFMI measurements will extend over the particle mass range of 8 decades, from 10(-11) to > 10(-3) g. A secondary science goal is to measure the particle flux and mass distribution during the similar to 7 year interplanetary portions of the mission, where, in addition to measurements of the background interplanetary dust over the radial range 0.98 AU to 2.7 AU, multiple opportunities exist for possible detection by the DFMI of interplanetary meteor-stream particles and interstellar dust. The DFMI consists of two different dust detector systems: a polyvinylidene fluoride ( PVDF) Dust Sensor Unit (SU), which measures particles with mass 10(-4) g. The large Whipple shield structures provide the large effective sensitive area required for detection of the expected low flux of high-mass particles
Isophot observations of comet Hale-Bopp - First results
Comet Hale-Bopp has been observed five times with ISOPHOT, the photometer on board the Infrared Space Observatory (ISO), four times before its perihelion passage at heliocentric distances of 4.92, 4.58, 2.93 and 2.81 AU, and at 3.91 AU postperihelion. Each time, multi-filter photometry covering the range between 3.6-175 mu m with eight to ten filters was performed to sample the spectral energy distribution of the comet. These measurements were used to determine dust temperatures for the cometary coma. The evolution of the strength of the silicate feature can be followed in the data as well as the flux deficit at longer wavelengths
The Stardust mission: Returning comet samples to earth
Stardust is an approved NASA mission that will collect large numbers of cometary particles and return them to Earth for laboratory analysis. The collected samples will be processed at the Curatorial Facility at the NASA
Johnson Space Center in Houston, Texas, where they will be allocated to investigators in a manner similar to the existing lunar sample, cosmic dust, and Antarctic meteorite programs. We urge all investigators interested in primitive materials to begin seriously considering what they would like to do with the samples when they are returned to Earth.
Stardust is the fourth mission in the new NASA Discovery program. It is highly focused on sample return and, following Discovery guidelines, is a low-cost, rapid-development project. The mission will launch in February
1999, fly past Comet Wild 2 on January 1, 2004, and return samples to Earth on January 13, 2006. The spacecraft will collect particles by direct impact into low-density silica aerogel during a 6.1-km/s flyby approaching within 150 km of the nucleus. The particles, ranging in size up to >200 μm, will penetrate several hundred particle diameters into the aerogel, where they will remain until they are extracted in the curatorial facility. The best model of the comet dust production indicates that Stardust will collect more than 20,000particles>15 μmin diameter in its 1000 cm^2 area of collection surface