610 research outputs found
Latest results on Jovian disk X-rays from XMM-Newton
We present the results of a spectral study of the soft X-ray emission
(0.2-2.5 keV) from low-latitude (`disk') regions of Jupiter. The data were
obtained during two observing campaigns with XMM-Newton in April and November
2003. While the level of the emission remained approximately the same between
April and the first half of the November observation, the second part of the
latter shows an enhancement by about 40% in the 0.2-2.5 keV flux. A very
similar, and apparently correlated increase, in time and scale, was observed in
the solar X-ray and EUV flux.
The months of October and November 2003 saw a period of particularly intense
solar activity, which appears reflected in the behaviour of the soft X-rays
from Jupiter's disk. The X-ray spectra, from the XMM-Newton EPIC CCD cameras,
are all well fitted by a coronal model with temperatures in the range 0.4-0.5
keV, with additional line emission from Mg XI (1.35 keV) and Si XIII (1.86
keV): these are characteristic lines of solar X-ray spectra at maximum activity
and during flares.
The XMM-Newton observations lend further support to the theory that Jupiter's
disk X-ray emission is controlled by the Sun, and may be produced in large part
by scattering, elastic and fluorescent, of solar X-rays in the upper atmosphere
of the planet.Comment: 17 pages, 7 figures, accepted for publication in a special issue of
Planetary and Space Scienc
X-ray emission from the terrestrial magnetosheath
[1] X-rays are generated throughout the terrestrial magnetosheath as a consequence of charge transfer collisions between heavy solar wind ions and geocoronal neutrals. The solar wind ions resulting from these collisions are left in highly excited states and emit extreme ultraviolet or soft X-ray photons. A model has been created to simulate this X-ray radiation. Published terrestrial exospheric hydrogen distributions and solar wind speed, density and temperature distributions were used in this model. Simulated images were created as seen from an observation point outside the geocorona. The locations of the bow shock and magnetopause are evident in these images. Perhaps this Xray emission can be used to remotely sense the solar wind flow around the magnetosphere. Since similar X-rays are produced in the heliosphere, the challenge will be, however, to eliminate this background emission
Pressure Gradients Driving Ion Transport in the Topside Martian Atmosphere
An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.Magnetic and thermal pressure gradient forces drive plasma flow in the topside ionosphere of Mars. Some of this flow can contribute to ion loss from the planet and thus affect atmospheric evolution. MAVEN measurements of the magnetic field, electron density, and electron temperature, taken over a 3âyear time period, are used to obtain averaged magnetic and thermal pressures in the topside ionosphere versus altitude, solar zenith angle, and latitude. Magnetic pressures are several times greater than thermal pressures for altitudes greater than about 300 km; that is, the plasma beta is less than one. The total pressure increases with altitude in the ionosphere and decreases with increasing solar zenith angle. Using these pressure patterns in the dayside ionosphere to estimate the pressure gradient force in the fluid momentum equation, we estimate horizontal dayâtoânight plasma flow speeds of a few kilometers per second near 400 km
A study of Jupiter's aurorae with XMM-Newton
We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral
emissions as observed by XMM-Newton in Nov. 2003 and compare it with that of an
Apr. 2003 observation. We discover the existence of an electron bremsstrahlung
component in the aurorae, which accounts for essentially all the X-ray flux
above 2 keV: its presence had been predicted but never detected for lack of
sensitivity of previous X-ray missions. This bremsstrahlung component varied
significantly in strength and spectral shape over the 3.5 days covered by the
Nov. 2003 observation, displaying substantial hardening of the spectrum with
increasing flux. This variability may be linked to the strong solar activity
taking place at the time, and may be induced by changes in the acceleration
mechanisms inside Jupiter's magnetosphere. As in Apr. 2003, the auroral spectra
below 2 keV are best fitted by a superposition of line emission most likely
originating from ion charge exchange, with OVII playing the dominant role. We
still cannot resolve conclusively the ion species responsible for the lowest
energy lines (around 0.3 keV), so the question of the origin of the ions
(magnetospheric or solar wind) is still open. It is conceivable that both
scenarios play a role in what is certainly a very complex planetary structure.
High resolution spectra of the whole planet obtained with the XMM-Newton RGS in
the range 0.5-1 keV clearly separate emission lines (mostly of Fe) originating
at low latitudes on Jupiter from the auroral lines due to O. These are shown to
possess very broad wings which imply velocities of ~5000 km/s. Such speeds are
consistent with the energies at which precipitating and charge exchanging O
ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find
good agreement between our measurements and the predictions of recent models.Comment: 16 pages, 17 figures, to be published in 'Astronomy and Astrophysics
Modeling the Enceladus plume--plasma interaction
We investigate the chemical interaction between Saturn's corotating plasma
and Enceladus' volcanic plumes. We evolve plasma as it passes through a
prescribed H2O plume using a physical chemistry model adapted for water-group
reactions. The flow field is assumed to be that of a plasma around an
electrically-conducting obstacle centered on Enceladus and aligned with
Saturn's magnetic field, consistent with Cassini magnetometer data. We explore
the effects on the physical chemistry due to: (1) a small population of hot
electrons; (2) a plasma flow decelerated in response to the pickup of fresh
ions; (3) the source rate of neutral H2O. The model confirms that charge
exchange dominates the local chemistry and that H3O+ dominates the water-group
composition downstream of the Enceladus plumes. We also find that the amount of
fresh pickup ions depends heavily on both the neutral source strength and on
the presence of a persistent population of hot electrons.Comment: 10 pages, 1 table, 2 figure
Science Goals and Overview of the Radiation Belt Storm Probes (RBSP) Energetic Particle, Composition, and Thermal Plasma (ECT) Suite on NASAâs Van Allen Probes Mission
The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASAâs Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the Helium Oxygen Proton Electron (HOPE) sensor, and the Relativistic Electron Proton Telescope (REPT). Collectively they cover, continuously, the full electron and ion spectra from one eV to 10âs of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts. The instruments use those proven techniques along with innovative new designs, optimized for operation in the most extreme conditions in order to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments. The design, fabrication and operation of ECT spaceflight instrumentation in the harsh radiation belt environment ensure that particle measurements have the fidelity needed for closure in answering key mission science questions. ECT instrument details are provided in companion papers in this same issue. In this paper, we describe the science objectives of the RBSP-ECT instrument suite on the Van Allen Probe spacecraft within the context of the overall mission objectives, indicate how the characteristics of the instruments satisfy the requirements to achieve these objectives, provide information about science data collection and dissemination, and conclude with a description of some early mission results
CASTER - a concept for a Black Hole Finder Probe based on the use of new scintillator technologies
The primary scientific mission of the Black Hole Finder Probe (BHFP), part of
the NASA Beyond Einstein program, is to survey the local Universe for black
holes over a wide range of mass and accretion rate. One approach to such a
survey is a hard X-ray coded-aperture imaging mission operating in the 10--600
keV energy band, a spectral range that is considered to be especially useful in
the detection of black hole sources. The development of new inorganic
scintillator materials provides improved performance (for example, with regards
to energy resolution and timing) that is well suited to the BHFP science
requirements. Detection planes formed with these materials coupled with a new
generation of readout devices represent a major advancement in the performance
capabilities of scintillator-based gamma cameras. Here, we discuss the Coded
Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that
represents a BHFP based on the use of the latest scintillator technology.Comment: 12 pages; conference paper presented at the SPIE conference "UV,
X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XIV." To be
published in SPIE Conference Proceedings, vol. 589
Heating Titan's upper atmosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95339/1/jgra19338.pd
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