共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Galli P. Wurz H. Lammer H. I. M. Lichtenegger R. Lundin S. Barabash A. Grigoriev M. Holmström H. Gunell 《Space Science Reviews》2006,126(1-4):447-467
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity. 相似文献
2.
A. Galli P. Wurz S. Barabash A. Grigoriev H. Gunell R. Lundin M. Holmström A. Fedorov 《Space Science Reviews》2006,126(1-4):267-297
We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle
detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at
the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet.
We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach
105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due
to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed.
Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss
rate of hydrogen and oxygen due to the production of ENAs. 相似文献
3.
Yuri N. Kulikov Helmut Lammer Herbert I. M. Lichtenegger Thomas Penz Doris Breuer Tilman Spohn Rickard Lundin Helfried K. Biernat 《Space Science Reviews》2007,129(1-3):207-243
Because the solar radiation and particle environment plays a major role in all atmospheric processes such as ionization, dissociation,
heating of the upper atmospheres, and thermal and non-thermal atmospheric loss processes, the long-time evolution of planetary
atmospheres and their water inventories can only be understood within the context of the evolving Sun. We compare the effect
of solar induced X-ray and EUV (XUV) heating on the upper atmospheres of Earth, Venus and Mars since the time when the Sun
arrived at the Zero-Age-Main-Sequence (ZAMS) about 4.6 Gyr ago. We apply a diffusive-gravitational equilibrium and thermal
balance model for studying heating of the early thermospheres by photodissociation and ionization processes, due to exothermic
chemical reactions and cooling by IR-radiating molecules like CO2, NO, OH, etc. Our model simulations result in extended thermospheres for early Earth, Venus and Mars. The exospheric temperatures
obtained for all the three planets during this time period lead to diffusion-limited hydrodynamic escape of atomic hydrogen
and high Jeans’ escape rates for heavier species like H2, He, C, N, O, etc. The duration of this blow-off phase for atomic hydrogen depends essentially on the mixing ratios of CO2, N2 and H2O in the atmospheres and could last from ∼100 to several hundred million years. Furthermore, we study the efficiency of various
non-thermal atmospheric loss processes on Venus and Mars and investigate the possible protecting effect of the early martian
magnetosphere against solar wind induced ion pick up erosion. We find that the early martian magnetic field could decrease
the ion-related non-thermal escape rates by a great amount. It is possible that non-magnetized early Mars could have lost
its whole atmosphere due to the combined effect of its extended upper atmosphere and a dense solar wind plasma flow of the
young Sun during about 200 Myr after the Sun arrived at the ZAMS. Depending on the solar wind parameters, our model simulations
for early Venus show that ion pick up by strong solar wind from a non-magnetized planet could erode up to an equivalent amount
of ∼250 bar of O+ ions during the first several hundred million years. This accumulated loss corresponds to an equivalent mass of ∼1 terrestrial
ocean (TO (1 TO ∼1.39×1024 g or expressed as partial pressure, about 265 bar, which corresponds to ∼2900 m average depth)). Finally, we discuss and
compare our findings with the results of preceding studies. 相似文献
4.
Mats Holmström 《Space Science Reviews》2006,126(1-4):435-445
Observations and simulations show that Mars' atmosphere has large seasonal variations. Total atmospheric density can have
an order of magnitude latitudinal variation at exobase heights. By numerical simulations we show that these latitude variations
in exobase parameters induce asymmetries in the hydrogen exosphere that propagate to large distances from the planet. We show
that these asymmetries in the exosphere produce asymmetries in the fluxes of energetic neutral atoms (ENAs) and soft X-rays
produced by charge exchange between the solar wind and exospheric hydrogen. This could be an explanation for asymmetries that
have been observed in ENA and X-ray fluxes at Mars. 相似文献
5.
W. Pryor I. Stewart K. Simmons M. Witte J. Ajello K. Toskiba D. McComas D. Hall 《Space Science Reviews》2001,97(1-4):393-399
We model interplanetary H Lyman-α (Lα) observations from Galileo UVS (Ultraviolet Spectrometer) and EUVS (Extreme Ultraviolet Spectrometer) (Hord et al., 1992) and the Ulysses interstellar neutral gas (GAS) instrument (Witte et al., 1992). EUVS measurements near solar maximum (max) in 1990–1992 have a peaked brightness maximum upwind due to a rather isotropic
solar wind charge-exchange ionization pattern (A=0–0.25). GAS measurements from solar minimum (min) in 1997 have a plateau in the upwind direction that we model using Ulysses
SWOOPS (solar wind plasma experiment) solar min data on solar wind density and velocity at different heliographic latitudes.
The isotropic ionization pattern deduced from EUVS at solar max may be consistent with recent SWOOPS results (McComas et al., 2000b, c) that high speed solar wind is absent at high latitudes during solar max. Galileo and Ulysses Lα data favor higher H temperatures (15 000–18 000 K) than previous models.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
The occurrence of waves generated by pick-up of planetary neutrals by the solar wind around unmagnetized planets is an important indicator for the composition and evolution of planetary atmospheres. For Venus and Mars, long-term observations of the upstream magnetic field are now available and proton cyclotron waves have been reported by several spacecraft. Observations of these left-hand polarized waves at the local proton cyclotron frequency in the spacecraft frame are reviewed for their specific properties, generation mechanisms and consequences for the planetary exosphere. Comparison of the reported observations leads to a similar general wave occurrence at both planets, at comparable locations with respect to the planet. However, the waves at Mars are observed more frequently and for long durations of several hours; the cyclotron wave properties are more pronounced, with larger amplitudes, stronger left-hand polarization and higher coherence than at Venus. The geometrical configuration of the interplanetary magnetic field with respect to the solar wind velocity and the relative density of upstream pick-up protons to the background plasma are important parameters for wave generation. At Venus, where the relative exospheric pick-up ion density is low, wave generation was found to mainly take place under stable and quasi-parallel conditions of the magnetic field and the solar wind velocity. This is in agreement with theory, which predicts fast wave growth from the ion/ion beam instability under quasi-parallel conditions already for low relative pick-up ion density. At Mars, where the relative exospheric pick-up ion density is higher, upstream wave generation may also take place under stable conditions when the solar wind velocity and magnetic field are quasi-perpendicular. At both planets, the altitudes where upstream proton cyclotron waves were observed (8 Venus and 11 Mars radii) are comparable in terms of the bow shock nose distance of the planet, i.e. in terms of the size of the solar wind-planetary atmosphere interaction region. In summary, the upstream proton cyclotron wave observations demonstrate the strong similarity in the interaction of the outer exosphere of these unmagnetized planets with the solar wind upstream of the planetary bow shock. 相似文献
7.
Michael W. Liemohn Yingjuan Ma Rudy A. Frahm Xiaohua Fang Janet U. Kozyra Andrew F. Nagy J. David Winningham James R. Sharber Stas Barabash Rickard Lundin 《Space Science Reviews》2006,126(1-4):63-76
Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express.
To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity
to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from
1–2 R
M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside
ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons
are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing
mechanisms are needed to explain the data. 相似文献
8.
H. Noda T. Terasawa Y. Saito H. Hayakawa A. Matsuoka T. Mukai 《Space Science Reviews》2001,97(1-4):423-426
‘The Japanese Mars probe, NOZOMI, is staying in the interplanetary space (1–1.5 AU) until its Mars’ orbit insertion scheduled
in early 2004. Every 16 months on this interplanetary orbit the spacecraft crosses around 1 AU the ‘gravitational focusing
cone’ of the interstellar helium, which are penetrating into the inner heliosphere under the solar gravity. During the first
crossing of the cone in the season of March–May 2000, we observed these helium particles after the solar wind pickup process
with an E/q type ion detector aboard NOZOMI. We have estimated the original temperature of the interstellar helium as 11 000 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Planetary upper atmospheres-coexisting thermospheres and ionospheres-form an important boundary between the planet itself
and interplanetary space. The solar wind and radiation from the Sun may react with the upper atmosphere directly, as in the
case of Venus. If the planet has a magnetic field, however, such interactions are mediated by the magnetosphere, as in the
case of the Earth. All of the Solar System’s giant planets have magnetic fields of various strengths, and interactions with
their space environments are thus mediated by their respective magnetospheres. This article concentrates on the consequences
of magnetosphere-atmosphere interactions for the physical conditions of the thermosphere and ionosphere. In particular, we
wish to highlight important new considerations concerning the energy balance in the upper atmosphere of Jupiter and Saturn,
and the role that coupling between the ionosphere and thermosphere may play in establishing and regulating energy flows and
temperatures there. This article also compares the auroral activity of Earth, Jupiter, Saturn and Uranus. The Earth’s behaviour
is controlled, externally, by the solar wind. But Jupiter’s is determined by the co-rotation or otherwise of the equatorial
plasmasheet, which is internal to the planet’s magnetosphere. Despite being rapid rotators, like Jupiter, Saturn and Uranus
appear to have auroral emissions that are mainly under solar (wind) control. For Jupiter and Saturn, it is shown that Joule
heating and “frictional” effects, due to ion-neutral coupling can produce large amounts of energy that may account for their
high exospheric temperatures. 相似文献
10.
Rosemary Killen Gabrielle Cremonese Helmut Lammer Stefano Orsini Andrew E. Potter Ann L. Sprague Peter Wurz Maxim L. Khodachenko Herbert I. M. Lichtenegger Anna Milillo Alessandro Mura 《Space Science Reviews》2007,132(2-4):433-509
It has been speculated that the composition of the exosphere is related to the composition of Mercury’s crustal materials.
If this relationship is true, then inferences regarding the bulk chemistry of the planet might be made from a thorough exospheric
study. The most vexing of all unsolved problems is the uncertainty in the source of each component. Historically, it has been
believed that H and He come primarily from the solar wind (Goldstein, B.E., et al. in J. Geophys. Res. 86:5485–5499, 1981), Na and K come from volatilized materials partitioned between Mercury’s crust and meteoritic impactors (Hunten, D.M., et
al. in Mercury, pp. 562–612, 1988; Morgan, T.H., et al. in Icarus 74:156–170, 1988; Killen, R.M., et al. in Icarus 171:1–19, 2004b). The processes that eject atoms and molecules into the exosphere of Mercury are generally considered to be thermal vaporization,
photon-stimulated desorption (PSD), impact vaporization, and ion sputtering. Each of these processes has its own temporal
and spatial dependence. The exosphere is strongly influenced by Mercury’s highly elliptical orbit and rapid orbital speed.
As a consequence the surface undergoes large fluctuations in temperature and experiences differences of insolation with longitude.
Because there is no inclination of the orbital axis, there are regions at extreme northern and southern latitudes that are
never exposed to direct sunlight. These cold regions may serve as traps for exospheric constituents or for material that is
brought in by exogenic sources such as comets, interplanetary dust, or solar wind, etc. The source rates are dependent not
only on temperature and composition of the surface, but also on such factors as porosity, mineralogy, and space weathering.
They are not independent of each other. For instance, ion impact may create crystal defects which enhance diffusion of atoms
through the grain, and in turn enhance the efficiency of PSD. The impact flux and the size distribution of impactors affects
regolith turnover rates (gardening) and the depth dependence of vaporization rates. Gardening serves both as a sink for material
and as a source for fresh material. This is extremely important in bounding the rates of the other processes. Space weathering
effects, such as the creation of needle-like structures in the regolith, will limit the ejection of atoms by such processes
as PSD and ion-sputtering. Therefore, the use of laboratory rates in estimates of exospheric source rates can be helpful but
also are often inaccurate if not modified appropriately. Porosity effects may reduce yields by a factor of three (Cassidy,
T.A., and Johnson, R.E. in Icarus 176:499–507, 2005). The loss of all atomic species from Mercury’s exosphere other than H and He must be by non-thermal escape. The relative
rates of photo-ionization, loss of photo-ions to the solar wind, entrainment of ions in the magnetosphere and direct impact
of photo-ions to the surface are an area of active research. These source and loss processes will be discussed in this chapter. 相似文献
11.
E. Nielsen H. Zou D. A. Gurnett D. L. Kirchner D. D. Morgan R. Huff R. Orosei A. Safaeinili J. J. Plaut G. Picardi 《Space Science Reviews》2006,126(1-4):373-388
The Martian ionosphere has for the first time been probed by a low frequency topside radio wave sounder experiment (MARSIS)
(Gurnett et al., 2005). The density profiles in the Martian ionosphere have for the first time been observed for solar zenith angles less
than 48 degrees. The sounder spectrograms typically have a single trace of echoes, which are controlled by reflections from
the ionosphere in the direction of nadir. With the local density at the spacecraft derived from the sounder measurements and
using the lamination technique the spectrograms are inverted to electron density profiles. The measurements yield electron
density profiles from the sub-solar region to past the terminator. The maximum density varies in time with the solar rotation
period, indicating control of the densities by solar ionizing radiation. Electron density increases associated with solar
flares were observed. The maximum electron density varies with solar zenith angle as predicted by theory. The altitude profile
of electron densities between the maximum density and about 170m altitude is well approximated by a classic Chapman layer.
The neutral scale height is close to 10 to 13 km. At altitudes above 180 km the densities deviate from and are larger than
inferred by the Chapman layer. At altitudes above the exobase the density decrease was approximated by an exponential function
with scale heights between 24 and 65 km. The densities in the top side ionosphere above the exobase tends to be larger than
the densities extrapolated from the Chapman layer fitted to the measurements at lower altitudes, implying more efficient upward
diffusion above the collision dominated photo equilibrium region. 相似文献
12.
A Coradini F. Capaccioni P. Drossart G. Arnold E. Ammannito F. Angrilli A. Barucci G. Bellucci J. Benkhoff G. Bianchini J. P. Bibring M. Blecka D. Bockelee-Morvan M. T. Capria R. Carlson U. Carsenty P. Cerroni L. Colangeli M. Combes M. Combi J. Crovisier M. C. Desanctis E. T. Encrenaz S. Erard C. Federico G. Filacchione U. Fink S. Fonti V. Formisano W. H. Ip R. Jaumann E. Kuehrt Y. Langevin G. Magni T. Mccord V. Mennella S. Mottola G. Neukum P. Palumbo G. Piccioni H. Rauer B. Saggin B. Schmitt D. Tiphene G. Tozzi 《Space Science Reviews》2007,128(1-4):529-559
The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe
for Planetary Exploration. VIRTIS, developed in cooperation among Italy, France and Germany, has been already selected as
a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus
Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully
observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars
in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison
– using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative
of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship
with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed
to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the
comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will
be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload
of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral
bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification
of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent
of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied. 相似文献
13.
E. Dubinin M. Fraenz A. Fedorov R. Lundin N. Edberg F. Duru O. Vaisberg 《Space Science Reviews》2011,162(1-4):173-211
Mars and Venus do not have a global magnetic field and as a result solar wind interacts directly with their ionospheres and upper atmospheres. Neutral atoms ionized by solar UV, charge exchange and electron impact, are extracted and scavenged by solar wind providing a significant loss of planetary volatiles. There are different channels and routes through which the ionized planetary matter escapes from the planets. Processes of ion energization driven by direct solar wind forcing and their escape are intimately related. Forces responsible for ion energization in different channels are different and, correspondingly, the effectiveness of escape is also different. Classification of the energization processes and escape channels on Mars and Venus and also their variability with solar wind parameters is the main topic of our review. We will distinguish between classical pickup and ??mass-loaded?? pickup processes, energization in boundary layer and plasma sheet, polar winds on unmagnetized planets with magnetized ionospheres and enhanced escape flows from localized auroral regions in the regions filled by strong crustal magnetic fields. 相似文献
14.
David H. Rodgers Patricia M. Beauchamp Laurence A. Soderblom Robert H. Brown Gun-Shing Chen Meemong Lee Bill R. Sandel David A. Thomas Robert T. Benoit Roger V. Yelle 《Space Science Reviews》2007,129(4):309-326
MICAS is an integrated multi-channel instrument that includes an ultraviolet imaging spectrometer (80–185 nm), two high-resolution
visible imagers (10–20 μrad/pixel, 400–900 nm), and a short-wavelength infrared imaging spectrometer (1250–2600 nm). The wavelength ranges were chosen
to maximize the science data that could be collected using existing semiconductor technologies and avoiding the need for multi-octave
spectrometers. It was flown on DS1 to validate technologies derived from the development of PICS (Planetary Imaging Camera
Spectrometer). These technologies provided a novel systems approach enabling the miniaturization and integration of four instruments
into one entity, spanning a wavelength range from the UV to IR, and from ambient to cryogenic temperatures with optical performance
at a fraction of a wavelength. The specific technologies incorporated were: a built-in fly-by sequence; lightweight and ultra-stable,
monolithic silicon-carbide construction, which enabled room-temperature alignment for cryogenic (85–140 K) performance, and
provided superb optical performance and immunity to thermal distortion; diffraction-limited, shared optics operating from
80 to 2600 nm; advanced detector technologies for the UV, visible and short-wavelength IR; high-performance thermal radiators
coupled directly to the short-wave infrared (SWIR) detector optical bench, providing an instrument with a mass less than 10
kg, instrument power less than 10 W, and total instrument cost of less than ten million dollars. The design allows the wavelength
range to be extended by at least an octave at the short wavelength end and to ∼50 microns at the long wavelength end. Testing
of the completed instrument demonstrated excellent optical performance down to 77 K, which would enable a greatly reduced
background for longer wavelength detectors. During the Deep Space 1 Mission, MICAS successfully collected images and spectra
for asteroid 9969 Braille, Mars, and comet 19/P Borrelly. The Borrelly encounter was a scientific hallmark providing the first
clear, high resolution images and excellent, short-wavelength infrared spectra of the surface of an active comet’s nucleus. 相似文献
15.
M. G. Tomasko R. Boese A. P. Ingersoll A. A. Lacis S. S. Limaye J. B. Pollack A. Seiff A. I. Stewart V. E. Suomi F. W. Taylor 《Space Science Reviews》1977,20(4):389-412
Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated. 相似文献
16.
Helmut Lammer James F. Kasting Eric Chassefière Robert E. Johnson Yuri N. Kulikov Feng Tian 《Space Science Reviews》2008,139(1-4):399-436
The origin and evolution of Venus’, Earth’s, Mars’ and Titan’s atmospheres are discussed from the time when the active young Sun arrived at the Zero-Age-Main-Sequence. We show that the high EUV flux of the young Sun, depending on the thermospheric composition, the amount of IR-coolers and the mass and size of the planet, could have been responsible that hydrostatic equilibrium was not always maintained and hydrodynamic flow and expansion of the upper atmosphere resulting in adiabatic cooling of the exobase temperature could develop. Furthermore, thermal and various nonthermal atmospheric escape processes influenced the evolution and isotope fractionation of the atmospheres and water inventories of the terrestrial planets and Saturn’s large satellite Titan efficiently. 相似文献
17.
R. A. Frahm J. R. Sharber J. D. Winningham P. Wurz M. W. Liemohn E. Kallio M. Yamauchi R. Lundin S. Barabash A. J. Coates D. R. Linder J. U. Kozyra M. Holmström S. J. Jeffers H. Andersson S. Mckenna-Lawler 《Space Science Reviews》2006,126(1-4):389-402
By identifying peaks in the photoelectron spectrum produced by photoionization of CO2 in the Martian atmosphere, we have conducted a pilot study to determine the locations of these photoelectrons in the space
around Mars. The significant result of this study is that these photoelectrons populate a region around Mars bounded externally
by the magnetic pileup boundary, and internally by the lowest altitude of our measurements (∼250 km) on the dayside and by
a cylinder of approximately the planetary radius on the nightside. It is particularly noteworthy that the photoelectrons on
the nightside are observed from the terminator plane tailward to a distance of ∼3 R
M, the Mars Express apoapsis. The presence of the atmospherically generated photoelectrons on the nightside of Mars may be
explained by direct magnetic field line connection between the nightside observation locations and the Martian dayside ionosphere.
Thus the characteristic photoelectron peaks may be used as tracers of magnetic field lines for the study of the magnetic field
configuration and particle transport in the Martian environment. 相似文献
18.
David G. Sibeck R. Allen H. Aryan D. Bodewits P. Brandt G. Branduardi-Raymont G. Brown J. A. Carter Y. M. Collado-Vega M. R. Collier H. K. Connor T. E. Cravens Y. Ezoe M.-C. Fok M. Galeazzi O. Gutynska M. Holmström S.-Y. Hsieh K. Ishikawa D. Koutroumpa K. D. Kuntz M. Leutenegger Y. Miyoshi F. S. Porter M. E. Purucker A. M. Read J. Raeder I. P. Robertson A. A. Samsonov S. Sembay S. L. Snowden N. E. Thomas R. von Steiger B. M. Walsh S. Wing 《Space Science Reviews》2018,214(4):79
Both heliophysics and planetary physics seek to understand the complex nature of the solar wind’s interaction with solar system obstacles like Earth’s magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in context by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the Kelvin-Helmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1–2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles.The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time- and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (\(\sim1~\mbox{keV}\)) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significance of each proposed interaction mode, which can be determined from its occurrence pattern as a function of location and solar wind conditions. Section 3 outlines the physics underlying the charge exchange generation of soft X-rays. Section 4 lists the background sources (helium focusing cone, planetary, and cosmic) of soft X-rays from which the charge exchange emissions generated by solar wind exchange must be distinguished. With the help of simulations employing state-of-the-art magnetohydrodynamic models for the solar wind-magnetosphere interaction, models for Earth’s exosphere, and knowledge concerning these background emissions, Sect. 5 demonstrates that boundaries and regions such as the bow shock, magnetosheath, magnetopause, and cusps can readily be identified in images of charge exchange emissions. Section 6 reviews observations by (generally narrow) field of view (FOV) astrophysical telescopes that confirm the presence of these emissions at the intensities predicted by the simulations. Section 7 describes the design of a notional wide FOV “lobster-eye” telescope capable of imaging the global interactions and shows how it might be used to extract information concerning the global interaction of the solar wind with solar system obstacles. The conclusion outlines prospects for missions employing such wide FOV imagers. 相似文献
19.
Deborah L. Domingue Patrick L. Koehn Rosemary M. Killen Ann L. Sprague Menelaos Sarantos Andrew F. Cheng Eric T. Bradley William E. McClintock 《Space Science Reviews》2007,131(1-4):161-186
The existence of a surface-bounded exosphere about Mercury was discovered through the Mariner 10 airglow and occultation experiments.
Most of what is currently known or understood about this very tenuous atmosphere, however, comes from ground-based telescopic
observations. It is likely that only a subset of the exospheric constituents have been identified, but their variable abundance
with location, time, and space weather events demonstrate that Mercury’s exosphere is part of a complex system involving the
planet’s surface, magnetosphere, and the surrounding space environment (the solar wind and interplanetary magnetic field).
This paper reviews the current hypotheses and supporting observations concerning the processes that form and support the exosphere.
The outstanding questions and issues regarding Mercury’s exosphere stem from our current lack of knowledge concerning the
surface composition, the magnetic field behavior within the local space environment, and the character of the local space
environment. 相似文献
20.
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