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| Study of the environment around the Rosetta candidate target asteroids |
| The Rosetta spacecraft will fly-by a few asteroids during its course to the final cometary target. The candidate asteroids presently are 3840 Ministrobel (S-type), 2703 Siwa and 140 (C-type).With the limited data presently available on these bodies we calculated some approximate quantities which may be useful to select the fly-by trajectories of the ROSETTA probe. In particular we derived the zones in which particles could stably orbit by analyzing Hills problem of three hierarchical masses--the sun, the asteroid and the orbiting particle. Then, following the approach of Hamilton and Burns, the effects of solar radiation pressure and of the ellipticity of the orbits were also taken into account. In this way for each asteroid we could calculate not only a classical quantity like the radius of the Hill sphere, but also the critical starting orbital distance (as a function of orbital inclination) within which most orbits remain bound to the asteroid, and outside which most escape as a consequence of perturbations. Moreover we determined the orbital stability zone, defined as the union of all the numerically integrated orbits showing long-term stability, for each of the target asteroids. The particular shape of these zones would suggest to have the spacecrafts close approach out of the orbital plane of the asteroids. |
| Publication date: 01 Jun 1999 |
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| The 4.6 micron feature of -SiH groups in silicate dust grains and infrared cometary spectra. |
| Amorphous silicate dust grains have been produced in the laboratory by means of laser ablation of solid targets in different ambient atmospheres. In this work we show that, if the condensation occurs in the presence of hydrogen, the spectra of silicate grains, together with the characteristic 10 and 20 µm features, exhibit an absorption band around 4.6 µm. Such features, absent in the spectra of the same silicate grains produced in an oxygen atmosphere, may be attributed to a fundamental stretching vibration of -SiH functional groups bound into the grains or on their surface. |
| Publication date: 01 Jun 1999 |
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| The International Rosetta Mission |
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| Publication date: 01 Jun 1999 |
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| Geophysical Research Abstracts, Vol. 1, No. 3 (EGS) |
| Several instruments have been described at the annual meetings of the
EGS (European Geophysical Society) and the DPS (Division for Planetary Sciences). The numerous abstracts which were published can be found in:
Geophysical Research Abstracts, Vol. 1, No. 3 (EGS)
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| Publication date: 01 Mar 1999 |
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| The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus. |
| III. First Modeling of a CO-Dominated Coma, with Application to Comets 46 P/Wirtanen and 29 P/Schwassmann-Wachmann I
We present the first gasdynamic simulations of the coma formed by the diffusion from a comet nucleus interior of a volatile molecule at large heliocentic distance. The method used is a generalization of that described in J. F. Crifo et al. (1995, Icarus 116, 77-112). The molecule is assumed to be CO. |
| Publication date: 01 Mar 1999 |
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| Silicates in Hale-Bopp: hints from laboratory studies |
| The recent passage of the Hale-Bopp (C/1995 O1) comet has provided the first opportunity to analyse the infrared spectral properties of a bright comet both from the ground and by the ISO space observatory. Previous works have already been dedicated to study the potential candidates to reproduce the cometary feature at 10 micron observed for different comets. We have applied a similar approach to compare the Hale-Bopp (C/1995 O1) spectra with laboratory data. The best fit has been obtained by using a mixture of crystalline Mg-rich olivine (forsterite), amorphous olivine and amorphous carbon grains. Some constraints on the possible cometary grain types derive from our simulation. Aggregates of submicron particles, composed of amorphous and crystalline olivine and amorphous carbon materials seem to be compatible with the cometary emission. Moreover, the possibility of fitting observational data on a wide IR spectra range, offered by ISO, provides interesting hints about the size distribution of grains responsible for the detected features |
| Publication date: 06 Dec 1998 |
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| VRI imaging of comet 46P/Wirtanen |
| Imaging of comet 46P/Wirtanen was performed in the standard VRI filters on 10 and 11 November 1996 with the 1.0 m telescope of the South African Astronomical Observatory (SAAO). After proper processing and calibration, the images have been used to derive information about the isophote distribution, magnitude and colour indices. We observed a coma extending to at most ~5×10³ km. We derive absolute magnitudes of the coma for the different filters and the colours V-R = 0.18±0.17 and R-I = 0.39±0.16. |
| Publication date: 06 Dec 1998 |
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| Energy balance and the gas flux from the surface of comet 46P/Wirtanen |
| Understanding the power balance at the surface of the nucleus is essential to study the chemical and physical evolution of a comet. Therefore, we present a detailed energy budget analysis for the surface of a model comet in the orbit of 46P/Wirtanen, target comet of the European space craft mission Rosetta, for a variety of parameters and assumptions. We will show that for a fast spinning Jupiter-family comet such as 46P/Wirtanen with a rotation period of about 6 h, a fast rotator approximation underestimates the effective energy input. This yields lower gas fluxes from the surface. For an 100% active, non-dust covered surface we obtain a water gas flux on the order of about 1.5×1028 molecules s-1 at perihelion, assuming a radius of 600 m. The calculated gas flux of water is within the order of measured values for comet 46P/Wirtanen. But our calculated values are maximum gas fluxes at noon—not averaged over one cometary day or taking the lesser insolation at the polar areas into account. Therefore, we conclude that either the radius of comet 46P/Wirtanen may be much larger than the accepted value of 600 m. A radius in the order of 2 km seems more likely to explain the measurements. Or, an other possibility could be that water-ice particles are blown off from the surface like dust particles. This may also increase the effective surface area of sublimation. |
| Publication date: 22 Nov 1998 |
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| H2O+ ions in comets: models and observations |
| An improved magnetohydrodynamic (MHD) model with chemistry is presented. The analysis of the source and sink terms for H2O+ shows that for small comets up to 11% of water molecules are finally ionized. For large comets (such as Halley) this fraction decreases to less than 3%. From the MHD scaling laws a similarity law for the individual ion densities is deduced which takes into account that the mother molecules are depleted by dissociation. This is applied to H2O+ ions. Radial density profiles from model calculations, observations by Giotto near comet Halley, and ground based observations of three comets confirm this scaling law for H2O+ ions. From the similarity law for the density a scaling law for the column density is derived which is more convenient to apply for ground based observations. From these scaling laws methods are derived which allow the determination of the water production rate from the ground based images of the H2O+ ions. Finally, the two dimensional images of model column densities are compared with observations.
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| Publication date: 02 Oct 1998 |
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| Improving Rosetta's Return-Link Margins |
| The Rosetta mission is designed to study in-situ a cometary nucleus' environment and its evolution in the inner Solar System. To be launched in January 2003 by an Ariane-5, Rosetta will rendezvous with Comet P/Wirtanen in 2011, after one Mars- and two Earth-gravity assists, and two asteroid fly-bys. The near-comet operations, which are scheduled to last about 1.5 years, will require a minimum return-link telemetry data rate of 5 kbit/s to meet the scientific goals, with about 14 hours of daily coverage. |
| Publication date: 01 Aug 1998 |
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| Towards a Common Check-out and Control System for Rosetta |
| Definition of the Rosetta ground segment began in 1996 and it soon became clear that a common checkout and mission-control system would be very beneficial for the mission. The chosen approach for achieving this goal was to develop building blocks for the Central Checkout System that can be re-utilised later in the development of the Flight Control System. The Rosetta prime contractor and AIV contractor fully endorsed this approach and the complete system is currently under development. The first delivery of the database system should take place in November 1998, followed by that of the first Central Checkout System in 1999. |
| Publication date: 01 May 1998 |
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| The International Rosetta Mission |
| Direct evidence of the constitution of cometary
volatiles is particularly difficult to obtain, as the
constituents observable from Earth and even
during the flybys of Comet Halley in 1986,
result from physico-chemical processes such
as sublimation and interactions with solar
radiation and the solar wind. What we know
today about cometary material from those
earlier missions and ground-based
observations does, however, demonstrate the
low degree of evolution of cometary material
and hence its tremendous potential for
providing us with unique information about the
make up and early evolution of the solar
nebula. |
| Publication date: 01 Feb 1998 |
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| Robot Technology for the Cometary Landing Mission Rosetta |
| Rosetta is an ESA cornerstone science mission to study, in situ, the environment of cometary nuclei and their evolution in the inner solar system. The main scientific objectives of the mission are to investigate the origin of the solar system by studying the origins of comets and to study the relationship between cometary and interstellar material. To enhance the scientific capabilities of the mission, the orbiter spacecraft will carry one probe, a lander which will land on the comet surface of the comet and perform investigations in situ.
The Rosetta orbiter spacecraft will be launched in 2003 and, after a 9-year cruise, will begin the cometary close observation phase. By 2012 the in situ investigations will be complete. The lander is being developed by combined effort in Germany, Italy, France, the United Kingdom, Hungary, Finland and Austria.
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| Publication date: 01 Jun 1997 |
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