排序方式: 共有7条查询结果,搜索用时 156 毫秒
1
1.
2.
K. C. Hansen T. Bagdonat U. Motschmann C. Alexander M. R. Combi T. E. Cravens T. I. Gombosi Y.-D. Jia I. P. Robertson 《Space Science Reviews》2007,128(1-4):133-166
The plasma environment of comet 67P/Churyumov-Gerasimenko, the Rosetta mission target comet, is explored over a range of heliocentric
distances throughout the mission: 3.25 AU (Rosetta instruments on), 2.7 AU (Lander down), 2.0 AU, and 1.3 AU (perihelion).
Because of the large range of gas production rates, we have used both a fluid-based magnetohydrodynamic (MHD) model as well
as a semi-kinetic hybrid particle model to study the plasma distribution. We describe the variation in plasma environs over
the mission as well as the differences between the two modeling approaches under different conditions. In addition, we present
results from a field aligned, two-stream transport electron model of the suprathermal electron flux when the comet is near
perihelion. 相似文献
3.
A.A. de Almeida D. Trevisan Sanzovo G.C. Sanzovo R. Boczko R. Miguel Torres 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1993-2000
In an attempt to evaluate correlations between several properties of comets we report the results of a cometary research involving a criterious analysis of gas and dust mass production rates in Comets 67P/Churyumov-Gerasimenko (main target of Rosetta Mission), 1P/Halley, Hyakutake (C/1996 B2), and 46P/Wirtanen and make a comparison between them. 相似文献
4.
W. Riedler K. Torkar H. Jeszenszky J. Romstedt H. St. C. Alleyne H. Arends W. Barth J. V. D. Biezen B. Butler P. Ehrenfreund M. Fehringer G. Fremuth J. Gavira O. Havnes E. K. Jessberger R. Kassing W. Klöck C. Koeberl A. C. Levasseur-Regourd M. Maurette F. Rüdenauer R. Schmidt G. Stangl M. Steller I. Weber 《Space Science Reviews》2007,128(1-4):869-904
The International Rosetta Mission is set for a rendezvous with Comet 67 P/Churyumov-Gerasimenko in 2014. On its 10 year journey
to the comet, the spacecraft will also perform a fly-by of the two asteroids Stein and Lutetia in 2008 and 2010, respectively.
The mission goal is to study the origin of comets, the relationship between cometary and interstellar material and its implications
with regard to the origin of the Solar System. Measurements will be performed that shed light into the development of cometary
activity and the processes in the surface layer of the nucleus and the inner coma.
The Micro-Imaging Dust Analysis System (MIDAS) instrument is an essential element of Rosetta’s scientific payload. It will
provide 3D images and statistical parameters of pristine cometary particles in the nm-μm range from Comet 67P/Churyumov-Gerasimenko.
According to cometary dust models and experience gained from the Giotto and Vega missions to 1P/Halley, there appears to be
an abundance of particles in this size range, which also covers the building blocks of pristine interplanetary dust particles.
The dust collector of MIDAS will point at the comet and collect particles drifting outwards from the nucleus surface. MIDAS
is based on an Atomic Force Microscope (AFM), a type of scanning microprobe able to image small structures in 3D. AFM images
provide morphological and statistical information on the dust population, including texture, shape, size and flux. Although
the AFM uses proven laboratory technology, MIDAS is its first such application in space. This paper describes the scientific
objectives and background, the technical implementation and the capabilities of MIDAS as they stand after the commissioning
of the flight instrument, and the implications for cometary measurements. 相似文献
5.
Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission
to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of
dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time,
impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments
and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe
the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence
on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when
more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because
model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained
for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and
most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the
in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible
by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production
rate of 67P/C–G are those of a fairly typical comet. 相似文献
6.
《Space Science Reviews》2007,128(1-4):433-506
The Optical, Spectroscopic, and Infrared Remote Imaging System OSIRIS is the scientific camera system onboard the Rosetta
spacecraft (Figure 1). The advanced high performance imaging system will be pivotal for the success of the Rosetta mission.
OSIRIS will detect 67P/Churyumov-Gerasimenko from a distance of more than 106 km, characterise the comet shape and volume, its rotational state and find a suitable landing spot for Philae, the Rosetta
lander. OSIRIS will observe the nucleus, its activity and surroundings down to a scale of ~2 cm px−1. The observations will begin well before the onset of cometary activity and will extend over months until the comet reaches
perihelion. During the rendezvous episode of the Rosetta mission, OSIRIS will provide key information about the nature of
cometary nuclei and reveal the physics of cometary activity that leads to the gas and dust coma.
OSIRIS comprises a high resolution Narrow Angle Camera (NAC) unit and a Wide Angle Camera (WAC) unit accompanied by three
electronics boxes. The NAC is designed to obtain high resolution images of the surface of comet 67P/Churyumov-Gerasimenko
through 12 discrete filters over the wavelength range 250–1000 nm at an angular resolution of 18.6 μrad px−1. The WAC is optimised to provide images of the near-nucleus environment in 14 discrete filters at an angular resolution of
101 μrad px−1. The two units use identical shutter, filter wheel, front door, and detector systems. They are operated by a common Data
Processing Unit. The OSIRIS instrument has a total mass of 35 kg and is provided by institutes from six European countries. 相似文献
7.
Philippe L. Lamy Imre Toth Björn J. R. Davidsson Olivier Groussin Pedro Gutiérrez Laurent Jorda Mikko Kaasalainen Stephen C. Lowry 《Space Science Reviews》2007,128(1-4):23-66
In 2003, comet 67P/Churyumov–Gerasimenko was selected as the new target of the Rosetta mission as the most suitable alternative
to the original target, comet 46P/Wirtanen, on the basis of orbital considerations even though very little was known about
the physical properties of its nucleus. In a matter of a few years and based on highly focused observational campaigns as
well as thorough theoretical investigations, a detailed portrait of this nucleus has been established that will serve as a
baseline for planning the Rosetta operations and observations. In this review article, we present a novel method to determine
the size and shape of a cometary nucleus: several visible light curves were inverted to produce a size–scale free three–dimensional
shape, the size scaling being imposed by a thermal light curve. The procedure converges to two solutions which are only marginally
different. The nucleus of comet 67P/Churyumov–Gerasimenko emerges as an irregular body with an effective radius (that of the
sphere having the same volume) = 1.72 km and moderate axial ratios a/b = 1.26 and a/c = 1.5 to 1.6. The overall dimensions
measured along the principal axis for the two solutions are 4.49–4.75 km, 3.54–3.77 km and 2.94–2.92 km. The nucleus is found
to be in principal axis rotation with a period = 12.4–12.7 h. Merging all observational constraints allow us to specify two
regions for the direction of the rotational axis of the nucleus: RA = 220°+50°
−30° and Dec = −70° ± 10° (retrograde rotation) or RA = 40°+50°
-30° and Dec = +70°± 10° (prograde), the better convergence of the various determinations presently favoring the first solution. The phase function,
although constrained by only two data points, exhibits a strong opposition effect rather similar to that of comet 9P/Tempel
1. The definition of the disk–integrated albedo of an irregular body having a strong opposition effect raises problems, and
the various alternatives led to a R-band geometric albedo in the range 0.045–0.060, consistent with our present knowledge of cometary nuclei. The active fraction
is low, not exceeding ~ 7% at perihelion, and is probably limited to one or two active regions subjected to a strong seasonal
effect, a picture coherent with the asymmetric behaviour of the coma. Our slightly downward revision of the size of the nucleus
of comet 67P/Churyumov-Gerasimenko resulting from the present analysis (with the correlative increase of the albedo compared
to the originally assumed value of 0.04), and our best estimate of the bulk density of 370 kg m−3, lead to a mass of ~ 8 × 1012 kg which should ease the landing of Philae and insure the overall success of the Rosetta mission. 相似文献
1