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31.
A. Milillo P. Wurz S. Orsini D. Delcourt E. Kallio R. M. KILLEN H. Lammer S. Massetti A. Mura S. Barabash G. Cremonese I. A. Daglis E. De Angelis A. M. Di Lellis S. Livi V. Mangano K. Torkar 《Space Science Reviews》2005,117(3-4):397-443
Mercury is a poorly known planet, since the only space-based information comes from the three fly-bys performed in 1974 by
the Mariner 10 spacecraft. Ground-based observations also provided some interesting results, but they are particularly difficult
to obtain due to the planet’s proximity to the Sun. Nevertheless, the fact that the planet’s orbit is so close to the Sun
makes Mercury a particularly interesting subject for extreme environmental conditions. Among a number of crucial scientific
topics to be addressed, Mercury’s exosphere, its interaction with the solar wind and its origin from the surface of the planet,
can provide important clues about planetary evolution. In fact, the Hermean exosphere is continuously eroded and refilled
by these interactions, so that it would be more proper to consider the Hermean environment as a single, unified system – surface-exosphere-magnetosphere.
These three parts are indeed strongly linked to each other. In recent years, the two missions scheduled to explore the iron
planet, the NASA MESSENGER mission (launched in March 2004) and the ESA cornerstone mission (jointly with JAXA) BepiColombo
(to be launched in 2012), have stimulated new interest in the many unresolved mysteries related to it. New ground-based observations,
made possible by new technologies, have been obtained, and new simulation studies have been performed. In this paper some
old as well as the very latest observations and studies related to the surface-exosphere-magnetosphere system are reviewed,
outlining the investigations achievable by the planned space-based observations. This review intends to support the studies,
in preparation of future data, and the definition of specific instrumentation. 相似文献
32.
Helmut Lammer Eric Chassefière Özgür Karatekin Achim Morschhauser Paul B. Niles Olivier Mousis Petra Odert Ute V. Möstl Doris Breuer Véronique Dehant Matthias Grott Hannes Gröller Ernst Hauber Lê Binh San Pham 《Space Science Reviews》2013,174(1-4):113-154
The evolution and escape of the martian atmosphere and the planet’s water inventory can be separated into an early and late evolutionary epoch. The first epoch started from the planet’s origin and lasted ~500 Myr. Because of the high EUV flux of the young Sun and Mars’ low gravity it was accompanied by hydrodynamic blow-off of hydrogen and strong thermal escape rates of dragged heavier species such as O and C atoms. After the main part of the protoatmosphere was lost, impact-related volatiles and mantle outgassing may have resulted in accumulation of a secondary CO2 atmosphere of a few tens to a few hundred mbar around ~4–4.3 Gyr ago. The evolution of the atmospheric surface pressure and water inventory of such a secondary atmosphere during the second epoch which lasted from the end of the Noachian until today was most likely determined by a complex interplay of various nonthermal atmospheric escape processes, impacts, carbonate precipitation, and serpentinization during the Hesperian and Amazonian epochs which led to the present day surface pressure. 相似文献
33.
The natural damped frequencies and the response to translational excitation of a viscous liquid in a circular cylindrical container are obtained. The response of the liquid surface elevation above its equilibrium position, as well as the viscous liquid force in x-direction due to translational excitation in this direction have been numerically evaluated. In this analysis the side wall adhesive boundary conditions have been satisfied, while only the normal bottom condition has been observed. This makes the results of the analysis applicable to liquid height ratio h/a>1. 相似文献
34.
Herbert I. M. Lichtenegger Helmut Lammer Yuri N. Kulikov Shahin Kazeminejad Gregorio H. Molina-Cuberos Rafael Rodrigo Bobby Kazeminejad Gottfried Kirchengast 《Space Science Reviews》2006,126(1-4):469-501
The heating of the upper atmospheres and the formation of the ionospheres on Venus and Mars are mainly controlled by the solar
X-ray and extreme ultraviolet (EUV) radiation (λ = 0.1–102.7 nm and can be characterized by the 10.7 cm solar radio flux).
Previous estimations of the average Martian dayside exospheric temperature inferred from topside plasma scale heights, UV
airglow and Lyman-α dayglow observations of up to ∼500 K imply a stronger dependence on solar activity than that found on
Venus by the Pioneer Venus Orbiter (PVO) and Magellan spacecraft. However, this dependence appears to be inconsistent with
exospheric temperatures (<250 K) inferred from aerobraking maneuvers of recent spacecraft like Mars Pathfinder, Mars Global
Surveyor and Mars Odyssey during different solar activity periods and at different orbital locations of the planet. In a similar
way, early Lyman-α dayglow and UV airglow observations by Venera 4, Mariner 5 and 10, and Venera 9–12 at Venus also suggested
much higher exospheric temperatures of up to 1000 K as compared with the average dayside exospheric temperature of about 270
K inferred from neutral gas mass spectrometry data obtained by PVO. In order to compare Venus and Mars, we estimated the dayside
exobase temperature of Venus by using electron density profiles obtained from the PVO radio science experiment during the
solar cycle and found the Venusian temperature to vary between 250–300 K, being in reasonable agreement with the exospheric
temperatures inferred from Magellan aerobraking data and PVO mass spectrometer measurements. The same method has been applied
to Mars by studying the solar cycle variation of the ionospheric peak plasma density observed by Mars Global Surveyor during
both solar minimum and maximum conditions, yielding a temperature range between 190–220 K. This result clearly indicates that
the average Martian dayside temperature at the exobase does not exceed a value of about 240 K during high solar activity conditions
and that the response of the upper atmosphere temperature on Mars to solar activity near the ionization maximum is essentially
the same as on Venus. The reason for this discrepancy between exospheric temperature determinations from topside plasma scale
heights and electron distributions near the ionospheric maximum seems to lie in the fact that thermal and photochemical equilibrium
applies only at altitudes below 170 km, whereas topside scale heights are derived for much higher altitudes where they are
modified by transport processes and where local thermodynamic equilibrium (LTE) conditions are violated. Moreover, from simulating
the energy density distribution of photochemically produced moderately energetic H, C and O atoms, as well as CO molecules,
we argue that exospheric temperatures inferred from Lyman-α dayglow and UV airglow observations result in too high values,
because these particles, as well as energetic neutral atoms, transformed from solar wind protons into hydrogen atoms via charge
exchange, may contribute to the observed planetary hot neutral gas coronae. Because the low exospheric temperatures inferred
from neutral gas mass spectrometer and aerobraking data, as well as from CO+
2 UV doublet emissions near 180–260 nm obtained from the Mars Express SPICAM UV spectrograph suggest rather low heating efficiencies,
some hitherto unidentified additional IR-cooling mechanism in the thermospheres of both Venus and Mars is likely to exist.
An erratum to this article can be found at 相似文献
35.
The intense stellar UV radiation field incident upon extra-solar giant planets causes profound changes to their upper atmospheres. Upper atmospheric temperatures can be tens of thousands of kelvins, causing thermal dissociation of H2 to H. The stellar ionizing flux converts H to H+. The high temperatures also drive large escape rates of H, but for all but the planets with the smallest orbits, this flux is not large enough to affect planet evolution. The escape rate is large enough to drag off heavier atoms such as C and O. For very small orbits, when the hill sphere is inside the atmosphere, escape is unfettered and can affect planet evolution. 相似文献
36.
Present natural data bases for abundances of the isotopic compositions of noble gases, carbon and nitrogen inventories can
be found in the Sun, the solar wind, meteorites and the planetary atmospheres and crustal reservoirs. Mass distributions in
the various volatile reservoirs provide boundary conditions which must be satisfied in modelling the history of the present
atmospheres. Such boundary conditions are constraints posed by comparison of isotopic ratios in primordial volatile sources
with the isotopic pattern which was found on the planets and their satellites. Observations from space missions and Earth-based
spectroscopic telescope observations of Venus, Mars and Saturn's major satellite Titan show that the atmospheric evolution
of these planetary bodies to their present states was affected by processes capable of fractionating their elements and isotopes.
The isotope ratios of D/H in the atmospheres of Venus and Mars indicate evidence for their planetary water inventories. Venus'
H2O content may have been at least 0.3% of a terrestrial ocean. Analysis of the D/H ratio on Mars imply that a global H2O ocean with a depth of ≤ 30 m was lost since the end of hydrodynamic escape. Calculations of the time evolution of the 15N/14N isotope anomalies in the atmospheres of Mars and Titan show that the Martian atmosphere was at least ≥ 20 times denser than
at present and that the mass of Titan's early atmosphere was about 30 times greater than its present value. A detailed study
of gravitational fractionation of isotopes in planetary atmospheres furthermore indicates a much higher solar wind mass flux
of the early Sun during the first half billion years.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
Becker R.H. Clayton R.N. Galimov E.M. Lammer H. Marty B. Pepin R.O. Wieler R. 《Space Science Reviews》2003,106(1-4):377-410
Variations in the isotopic ratios of volatile elements in different reservoirs on the terrestrial planets carry information
about processes that operated on the planets since their formation. Comparisons between primordial planetary compositions,
to the extent they can be determined, may help us understand the planetary formation process. This working group report summarizes
our knowledge of terrestrial planet volatile inventories.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
39.
After a short abstract of the theory for the gyroscope, the theory for the gyrovibrator,1 an angular rate-measuring device, is presented. It is shown that, in contrast to the theory given by Diamantides,1 the output signal and the natural frequency of the vibrating body depend on all three principal moments of inertia of the vibrating body. 相似文献
40.
Fred Goesmann Helmut Rosenbauer Reinhard Roll Cyril Szopa Francois Raulin Robert Sternberg Guy Israel Uwe Meierhenrich Wolfram Thiemann Guillermo Munoz-Caro 《Space Science Reviews》2007,128(1-4):257-280
Comets are thought to preserve the most pristine material currently present in the solar system, as they are formed by agglomeration
of dust particles in the solar nebula, far from the Sun, and their interiors have remained cold. By approaching the Sun, volatile
components and dust particles are released forming the cometary coma. During the phase of Heavy Bombardment, 3.8--4 billion
years ago, cometary matter was delivered to the Early Earth. Precise knowledge on the physico-chemical composition of comets
is crucial to understand the formation of the Solar System, the evolution of Earth and particularly the starting conditions
for the origin of life on Earth. Here, we report on the COSAC instrument, part of the ESA cometary mission Rosetta, which
is designed to characterize, identify, and quantify volatile cometary compounds, including larger organic molecules, by in
situ measurements of surface and subsurface cometary samples. The technical concept of a multi-column enantio-selective gas
chromatograph (GC) coupled to a linear reflectron time-of-flight mass-spectrometer instrument is presented together with its
realisation under the scientific guidance of the Max-Planck-Institute for Solar System Research in Katlenburg-Lindau, Germany.
The instrument's technical data are given; first measurements making use of standard samples are presented. The cometary science
community is looking forward to receive fascinating data from COSAC cometary in situ measurements in 2014. 相似文献