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1.
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
2.
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
3.
The Neutral Particle Detector (NPD) of the ASPERA-3 experiment (Analyser of Space Plasmas and Energetic Atoms) on board the
Mars Express (MEX) spacecraft observed an intense flux of H ENAs (energetic neutral atoms) with average energy of about 1.5
keV emitted anisotropically from the subsolar region of Mars. The NPD detected the ENA jet near the bow shock at radial distances
of about 1 R
M from the Martian surface as the spacecraft moved outbound, while the NPD continuously pointed towards the subsolar region.
The jet intensity shows oscillative behavior. These intensity variations occur on two clearly distinguishable time scales.
The majority of the identified events have an average oscillation period of about 50 sec. The second group consists of events
with long-scale variations with a time scale of approximately 300 sec. The fast oscillations of the first group exhibit a periodic structure and are detected in every orbit, while the slow variations of the second group are identified in ∼40% of orbits. The intensity of the fast oscillations have a peak-to-valley ratio about 20 to 30% of the peak intensity. One of the possible mechanisms to explain
fast oscillations is the formation of the low frequency ion waves at the subsolar region of Mars. Slow variations may be explained by either temporal variations in the ENA generation source or by a specific structure of the
ENA generation source, in which hair-like ENA subjets can be present. 相似文献
4.
The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) for the Mars Express Mission 总被引:1,自引:0,他引:1
S. Barabash R. Lundin H. Andersson K. Brinkfeldt A. Grigoriev H. Gunell M. Holmström M. Yamauchi K. Asamura P. Bochsler P. Wurz R. Cerulli-Irelli A. Mura A. Milillo M. Maggi S. Orsini A. J. Coates D. R. Linder D. O. Kataria C. C. Curtis K. C. Hsieh B. R. Sandel R. A. Frahm J. R. Sharber J. D. Winningham M. Grande E. Kallio H. Koskinen P. Riihelä W. Schmidt T. Säles J. U. Kozyra N. Krupp J. Woch S. Livi J. G. Luhmann S. McKenna-Lawlor E. C. Roelof D. J. Williams J.-A. Sauvaud A. Fedorov J.-J. Thocaven 《Space Science Reviews》2006,126(1-4):113-164
The general scientific objective of the ASPERA-3 experiment is to study the solar wind – atmosphere interaction and to characterize
the plasma and neutral gas environment with within the space near Mars through the use of energetic neutral atom (ENA) imaging
and measuring local ion and electron plasma. The ASPERA-3 instrument comprises four sensors: two ENA sensors, one electron
spectrometer, and one ion spectrometer. The Neutral Particle Imager (NPI) provides measurements of the integral ENA flux (0.1–60
keV) with no mass and energy resolution, but high angular resolution. The measurement principle is based on registering products
(secondary ions, sputtered neutrals, reflected neutrals) of the ENA interaction with a graphite-coated surface. The Neutral
Particle Detector (NPD) provides measurements of the ENA flux, resolving velocity (the hydrogen energy range is 0.1–10 keV)
and mass (H and O) with a coarse angular resolution. The measurement principle is based on the surface reflection technique.
The Electron Spectrometer (ELS) is a standard top-hat electrostatic analyzer in a very compact design which covers the energy
range 0.01–20 keV. These three sensors are located on a scanning platform which provides scanning through 180∘ of rotation. The instrument also contains an ion mass analyzer (IMA). Mechanically IMA is a separate unit connected by a
cable to the ASPERA-3 main unit. IMA provides ion measurements in the energy range 0.01–36 keV/charge for the main ion components
H+, He++, He+, O+, and the group of molecular ions 20–80 amu/q. ASPERA-3 also includes its own DC/DC converters and digital processing unit
(DPU). 相似文献
5.
Y. Futaana S. Barabash A. Grigoriev D. Winningham R. Frahm M. Yamauchi R. Lundin 《Space Science Reviews》2006,126(1-4):315-332
As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case
of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board
the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian
exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485
of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed
by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was
most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can
be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation
region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went
out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic
flux variations of the ENA flux at the spacecraft location. 相似文献
6.
Five Years of Stereo Magnetospheric Imaging by TWINS 总被引:1,自引:0,他引:1
Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is the first stereoscopic magnetospheric imager. TWINS is a NASA Explorer Mission of Opportunity performing simultaneous energetic neutral atom (ENA) imaging from two widely-separated Molniya orbits on two different spacecraft, and providing nearly continuous coverage of magnetospheric ENA emissions. The ENA imagers observe energetic neutrals produced from global ion populations, over a broad energy range (1–100 keV/u) with high angular (4°×4°) and time (about 1-minute) resolution. TWINS distinguishes hydrogen ENAs from oxygen ENAs. Each TWINS spacecraft also carries a Lyman-α geocoronal imager to monitor the cold exospheric hydrogen atoms that produce ENAs from ions via charge exchange. Complementing the imagers are detectors that measure the local charged particle environment around the spacecraft. During its first five years of science operations, TWINS has discovered new global properties of geospace plasmas and neutrals, fostered understanding of causal relationships, confirmed theories and predictions based on in situ data, and yielded key insights needed to improve geospace models. Analysis and modeling of TWINS data have: (1) obtained continuous (main phase through recovery) global ion spectra, (2) revealed a previously unknown local-time dependence of global pitch angle, (3) developed quantitative determination of ion fluxes from low altitude ENAs (4) determined dynamic connections between local pitch angle and global ion precipitation, (5) confirmed local-time dependence of precipitating ion temperature, (6) imaged global dynamic heating of the magnetosphere, (7) explained why the oxygen ring current survives longer into recovery than hydrogen, and (8) revealed new global exospheric density features and their influence upon ring current decay rates. Over the next several years of the solar cycle, TWINS observations of three-dimensional (3D) global ion dynamics, composition, origins and destinies are crucial to capture the system-level view of geospace over the full range of geomagnetic and solar activity conditions. 相似文献
7.
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
8.
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
9.
Mitchell Donald G. C:son Brandt Pontus Roelof Edmond C. Hamilton Douglas C. Retterer Kyle C. Mende Steven 《Space Science Reviews》2003,109(1-4):63-75
The magnetospheric O+ population in the 52–180 keV range during storms is investigated through the analysis of energetic neutral atom (ENA) images. The images are obtained from the high energy neutral atom (HENA) imager onboard the IMAGE satellite. At each substorm onset following the commencement of a geomagnetic storm the oxygen ENA display ~30 min intense bursts. Only very weak corresponding features in the 60–119 keV hydrogen ENA can be occasionally seen. The dominating fraction of the oxygen ENA emissions are produced when O+ ions mirror/precipitate at low altitudes, where the number density of the neutral atmosphere is high. During the storm we observed several bursts of oxygen ENA, but it is still not clear how much the O+ content of the ring current increases during the storm main phase. Our observations suggest that the responsible injection mechanism is mass-dependent and scatters the pitch angles. This leads us to favor a non-adiabatic mechanism proposed by (Delcourt, 2002). 相似文献
10.
The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) NASA Mission-of-Opportunity 总被引:3,自引:0,他引:3
D. J. McComas F. Allegrini J. Baldonado B. Blake P. C. Brandt J. Burch J. Clemmons W. Crain D. Delapp R. DeMajistre D. Everett H. Fahr L. Friesen H. Funsten J. Goldstein M. Gruntman R. Harbaugh R. Harper H. Henkel C. Holmlund G. Lay D. Mabry D. Mitchell U. Nass C. Pollock S. Pope M. Reno S. Ritzau E. Roelof E. Scime M. Sivjee R. Skoug T. S. Sotirelis M. Thomsen C. Urdiales P. Valek K. Viherkanto S. Weidner T. Ylikorpi M. Young J. Zoennchen 《Space Science Reviews》2009,142(1-4):157-231
Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a NASA Explorer Mission-of-Opportunity to stereoscopically image the Earth’s magnetosphere for the first time. TWINS extends our understanding of magnetospheric structure and processes by providing simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes ENAs from 1–100 keV with high angular (~4°×4°) and time (~1-minute) resolution. The TWINS Ly-α monitor measures the geocoronal hydrogen density to aid in ENA analysis while environmental sensors provide contemporaneous measurements of the local charged particle environments. By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft, TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the magnetosphere for the first time. This “instrument paper” documents the TWINS design, construction, calibration, and initial results. Finally, the appendix of this paper describes and documents the Southwest Research Institute (SwRI) instrument calibration facility; this facility was used for all TWINS instrument-level calibrations. 相似文献
11.
L. Colangeli J. J. Lopez-Moreno P. Palumbo J. Rodriguez M. Cosi V. Della Corte F. Esposito M. Fulle M. Herranz J. M. Jeronimo A. Lopez-Jimenez E. Mazzotta Epifani R. Morales F. Moreno E. Palomba A. Rotundi 《Space Science Reviews》2007,128(1-4):803-821
The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted
to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the
dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and
time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation
or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The
coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma
evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure
mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10−10 ÷ 4.0 × 10−4 kg m s−1 for velocities up to about 300 m s−1. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10−10 g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties
in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts
demonstrate that GIADA is behaving as expected according to the design specifications.
The International GIADA Consortium (I, E, UK, F, D, USA). 相似文献
12.
Alain Abergel Laurent Verstraete Christine Joblin René Laureijs Marc-Antoine Miville-Deschênes 《Space Science Reviews》2005,119(1-4):247-271
Infrared spectroscopy and photometry with ISO covering most of the emission range of the interstellar medium has led to important
progress in the understanding of the physics and chemistry of the gas, the nature and evolution of the dust grains and also
the coupling between the gas and the grains. We review here the ISO results on the cool and low-excitation regions of the
interstellar medium, where T
gas≲ 500 K, n
H∼ 100–105 cm−3 and the electron density is a few 10−4.
JEL codes: D24, L60, 047
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
13.
The historical evolution of the study of escape of light gases from planetary atmospheres is delineated, and the application of kinetic theory to the ionsphere is discussed. Ionospheric plasma becomes collisionless above the ion-exobase which is located near 1000 km altitude in the trough and polar regions, and which coincides with the plasmapause at lower latitudes. When the boundary conditions at conjugate points of a closed magnetic field line are different, interhemispheric particle fluxes exist from the high temperature point to the low temperature point, and from the point of larger concentrations to the point of smaller concentrations; therefore the charge separation electric field in the exosphere is no longer given by the Pannekoek-Rosseland field. For non-uniform number densities and temperatures at the exobase, the observed r
–4 variation of the equatorial density distribution is recovered in the calculated density distributions. Taking account of plasmasheet particle precipitation does not change very much the electric field and ionospheric ion distributions, at least for reasonable densities and temperatures of the plasmasheet electrons and protons. For field aligned current densities along auroral field lines smaller than 10–5 Am–2, the potential difference between the ion-exobase and plasmasheet is about –3V. In the case of open magnetic field lines the flow speed of hydrogen and helium ions in the exosphere becomes rapidly supersonic as a consequence of the upward directed charge separation electric field, whereas the oxygen ions have a negligible small bulk velocity. Adding a photoelectron efflux decreases the thermal electron escape but does not change significantly the number density distributions. 相似文献
14.
Medium energy neutral atom (MENA) imager for the IMAGE mission 总被引:1,自引:0,他引:1
Pollock C.J. Asamura K. Baldonado J. Balkey M.M. Barker P. Burch J.L. Korpela E.J. Cravens J. Dirks G. Fok M.-C. Funsten H.O. Grande M. Gruntman M. Hanley J. Jahn J.-M. Jenkins M. Lampton M. Marckwordt M. McComas D.J. Mukai T. Penegor G. Pope S. Ritzau S. Schattenburg M.L. Scime E. Skoug R. Spurgeon W. Stecklein T. Storms S. Urdiales C. Valek P. van Beek J.T.M. Weidner S.E. Wüest M. Young M.K. Zinsmeyer C. 《Space Science Reviews》2000,91(1-2):113-154
The Medium Energy Neutral Atom (MENA) imager was developed in response to the Imaging from the Magnetopause to the Aurora for Global Exploration (IMAGE) requirement to produce images of energetic neutral atoms (ENAs) in the energy range from 1 to 30 keV. These images will be used to infer characteristics of magnetospheric ion distributions. The MENA imager is a slit camera that images incident ENAs in the polar angle (based on a conventional spherical coordinate system defined by the spacecraft spin axis) and utilizes the spacecraft spin to image in azimuth. The speed of incident ENAs is determined by measuring the time-of-flight (TOF) from the entrance aperture to the detector. A carbon foil in the entrance aperture yields secondary electrons, which are imaged using a position-sensitive Start detector segment. This provides both the one-dimensional (1D) position at which the ENA passed through the aperture and a Start time for the TOF system. Impact of the incident ENA on the 1D position-sensitive Stop detector segment provides both a Stop-timing signal and the location that the ENA impacts the detector. The ENA incident polar angle is derived from the measured Stop and Start positions. Species identification (H vs. O) is based on variation in secondary electron yield with mass for a fixed ENA speed. The MENA imager is designed to produce images with 8°×4° angular resolution over a field of view 140°×360°, over an energy range from 1 keV to 30 keV. Thus, the MENA imager is well suited to conduct measurements relevant to the Earth's ring current, plasma sheet, and (at times) magnetosheath and cusp. 相似文献
15.
Scott D. Barthelmy Louis M. Barbier Jay R. Cummings Ed E. Fenimore Neil Gehrels Derek Hullinger Hans A. Krimm Craig B. Markwardt David M. Palmer Ann Parsons Goro Sato Masaya Suzuki Tadayuki Takahashi Makota Tashiro Jack Tueller 《Space Science Reviews》2005,120(3-4):143-164
he burst alert telescope (BAT) is one of three instruments on the
Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an
accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to
point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical
observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed
of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a
1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution,
a sensitivity of ∼10−8 erg s−1 cm−2, and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky
hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor. 相似文献
16.
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
17.
David N. Burrows J. E. Hill J. A. Nousek J. A. Kennea A. Wells J. P. Osborne A. F. Abbey A. Beardmore K. Mukerjee A. D. T. Short G. Chincarini S. Campana O. Citterio A. Moretti C. Pagani G. Tagliaferri P. Giommi M. Capalbi F. Tamburelli L. Angelini G. Cusumano H. W. Bräuninger W. Burkert G. D. Hartner 《Space Science Reviews》2005,120(3-4):165-195
he Swift Gamma-Ray Explorer is designed to make prompt multiwavelength observations of gamma-ray bursts (GRBs) and GRB afterglows.
The X-ray telescope (XRT) enables Swift to determine GRB positions with a few arcseconds accuracy within 100 s of the burst onset.
The XRT utilizes a mirror set built for JET-X and an XMM-Newton/EPIC MOS CCD detector to provide a sensitive broad-band (0.2–10 keV) X-ray imager with effective area of > 120 cm2 at 1.5 keV, field of view of 23.6 × 23.6 arcminutes, and angular resolution of 18 arcseconds (HPD). The detection sensitivity
is 2×10−14 erg cm−2 s−1 in 104 s. The instrument is designed to provide automated source detection and position reporting within 5 s of target acquisition.
It can also measure the redshifts of GRBs with Fe line emission or other spectral features. The XRT operates in an auto-exposure
mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source intensity fades.
The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow
each burst for days or weeks.
Dedicated to David J. Watson, in memory of his valuable contributions to this instrument. 相似文献
18.
The Interstellar Boundary Explorer (IBEX) mission is exploring the frontiers of the heliosphere where energetic neutral atoms (ENAs) are formed from charge exchange between interstellar neutral hydrogen atoms and solar wind ions and pickup ions. The geography of this frontier is dominated by an unexpected nearly complete arc of ENA emission, now known as the IBEX ‘Ribbon’. While there is no consensus agreement on the Ribbon formation mechanism, it seems certain this feature is seen for sightlines that are perpendicular to the interstellar magnetic field as it drapes over the heliosphere. At the lowest energies, IBEX also measures the flow of interstellar H, He, and O atoms through the inner heliosphere. The asymmetric oxygen profile suggests that a secondary flow of oxygen is present, such as would be expected if some fraction of oxygen is lost through charge exchange in the heliosheath regions. The detailed spectra characterized by the ENAs provide time-tagged samples of the energy distributions of the underlying ion distributions, and provide a wealth of information about the outer heliosphere regions, and beyond. 相似文献
19.
Energisation of O+ and O+
2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation
E. Kallio A. Fedorov S. Barabash P. Janhunen H. Koskinen W. Schmidt R. Lundin H. Gunell M. Holmström Y. Futaana M. Yamauchi A. Grigoriev J. D. Winningham R. Frahm J. R. Sharber 《Space Science Reviews》2006,126(1-4):39-62
We have studied the loss of O+ and O+
2 ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H+, He++, O+, O+
2) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not
include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside
where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft
have measured the proprieties of escaping atomic and molecular ions, in particular O+ and O+
2 ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create
similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the
properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations
made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by
the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed
at Mars. 相似文献
20.
Vasconcelos Maria Jaqueline Jatenco-Pereira Vera Opher Reuven 《Space Science Reviews》2003,107(1-2):383-386
In this work we examine the damping of Alfvén waves as a source of plasma heating in disks and magnetic funnels of young solar
like stars, the T Tauri stars. We apply four different damping mechanisms in this study: viscous-resistive, collisional, nonlinear
and turbulent, exploring a wide range of wave frequencies, from 10−5Ωi to 10−1Ωi (where Ωi is the ion-cyclotron frequency). The results show that Alfvénic heating can increase the ionization rate of accretion disks
and elevate the temperature of magnetic funnels of T Tauri stars opening possibilities to explain some observational features
of these objects.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献