64 research outputs found
A Distribution of Large Particles in the Coma of Comet 103P/Hartley 2
The coma of comet 103P/Hartley 2 has a significant population of large
particles observed as point sources in images taken by the Deep Impact
spacecraft. We measure their spatial and flux distributions, and attempt to
constrain their composition. The flux distribution of these particles implies a
very steep size distribution with power-law slopes ranging from -6.6 to -4.7.
The radii of the particles extend up to 20 cm, and perhaps up to 2 m, but their
exact sizes depend on their unknown light scattering properties. We consider
two cases: bright icy material, and dark dusty material. The icy case better
describes the particles if water sublimation from the particles causes a
significant rocket force, which we propose as the best method to account for
the observed spatial distribution. Solar radiation is a plausible alternative,
but only if the particles are very low density aggregates. If we treat the
particles as mini-nuclei, we estimate they account for <16-80% of the comet's
total water production rate (within 20.6 km). Dark dusty particles, however,
are not favored based on mass arguments. The water production rate from bright
icy particles is constrained with an upper limit of 0.1 to 0.5% of the total
water production rate of the comet. If indeed icy with a high albedo, these
particles do not appear to account for the comet's large water production rate.
production rate.
Erratum: We have corrected the radii and masses of the large particles of
comet 103P/Hartley 2 and present revised conclusions in the attached erratum.Comment: Original article: 46 pages, 17 figures, 5 tables, published in
Icarus. Erratum: 5 pages, 1 table, accepted for publication in Icaru
Techniques for Galactic Dust Measurements in the Heliosphere
Galactic interstellar dust (ISD) is the major ingredient in planetary
formation. However, information on this important material has been extremely
limited. Recently the Ulysses dust detector has identified and measured
interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above
. Inside this distance it could not reliably distinguish
interstellar from interplanetary dust. Modeling the Ulysses data suggests that
up to 30 % of dust flux with masses above at 1~AU is of
interstellar origin. From the Hiten satellite in high eccentric orbit about the
Earth there are indications that ISD indeed reaches the Earth's orbit. Two new
missions carrying dust detectors, Cassini and Stardust, will greatly increase
our observational knowledge. In this paper we briefly review instruments used
on these missions and compare their capabilities. The Stardust mission [{\em
Brownlee et al.}, 1996] will analyze the local interstellar dust population by
an in-situ chemical analyzer and collect ISD between 2 and 3~AU from the Sun.
The dust analyzer on the Cassini mission will determine the interstellar dust
flux outside Venus' orbit and will provide also some compositional information.
Techniques to identify the ISD flux levels at 1~AU are described that can
quantify the interstellar dust flux in high-Earth orbit (outside the debris
belts) and provide chemical composition information of galactic dust.Comment: Accepted for Journal of Geophysical Research, 6 figures, Late
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
Shape, Density, and Geology of the Nucleus of Comet 103P/Hartley 2
Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33 km in length. Surface features are primarily small mounds 1%. The shape may be the evolutionary product of insolation, sublimation, and temporary deposition of materials controlled by the objects complex rotation
Shape, density, and geology of the nucleus of Comet 103P/Hartley 2
a b s t r a c t Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33 km in length. Surface features are primarily small mounds <40 m across, irregularly-shaped smooth areas on the two lobes, and a smooth but variegated region forming a ''waist'' between the two lobes. Assuming parts of the comet body approach the shape of an equipotential surface, the mean density of Hartley 2 is modeled to be 200-400 kg m Ă3 . Such a mean density suggests mass loss per orbit of >1%. The shape may be the evolutionary product of insolation, sublimation, and temporary deposition of materials controlled by the object's complex rotation
Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta
Cometary ices are rich in CO2, CO and organic volatile
compounds, but the carbon content of cometary dust was only measured for
the Oort Cloud comet 1P/Halley, during its flyby in 1986. The COmetary
Secondary Ion Mass Analyzer (COSIMA)/Rosetta mass spectrometer
analysed dust particles with sizes ranging from 50 to 1000Â ÎŒm, collected
over 2 yr, from 67P/Churyumov-Gerasimenko (67P), a Jupiter family
comet. Here, we report 67P dust composition focusing on the elements C
and O. It has a high carbon content (atomic | |â )
close to the solar value and comparable to the 1P/Halley data. From
COSIMA measurements, we conclude that 67P particles are made of nearly
50 per cent organic matter in mass, mixed with mineral phases that are
mostly anhydrous. The whole composition, rich in carbon and non-hydrated
minerals, points to a primitive matter that likely preserved its
initial characteristics since the comet accretion in the outer regions
of the protoplanetary disc.</p
Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/ChuryumovâGerasimenko
The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m sâ1)
in the environment of comet 67P/ChuryumovâGerasimenko (hereafter 67P).
In these particles, carbon and nitrogen are expected mainly to be part
of the organic matter. We have measured the nitrogen-to-carbon (N/C)
atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with
an averaged value of 0.035 ± 0.011. This is compatible with the
measurements of the particles of comet 1P/Halley and is in the lower
range of the values measured in comet 81P/Wild 2 particles brought back
to Earth by the Stardust mission. Moreover, the averaged value
found in 67P particles is also similar to the one found in the insoluble
organic matter extracted from CM, CI and CR carbonaceous chondrites and
to the bulk values measured in most interplanetary dust particles and
micrometeorites. The close agreement of the N/C atomic ratio in all
these objects indicates that their organic matters share some
similarities and could have a similar chemical origin. Furthermore,
compared to the abundances of all the detected elements in the particles
of 67P and to the elemental solar abundances, the nitrogen is depleted
in the particles and the nucleus of 67P as was previously inferred also
for comet 1P/Halley. This nitrogen depletion could constrain the
formation scenarios of cometary nuclei.</p
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