ABSTRACT: The interaction of the solar wind (SW) with the magnetic field of Mercury is investigated by means of a three dimensional parallelized multispecies hybrid model. A comparison between two mathematical representations of Mercury's intrinsic magnetic field is studied. The first model is an Offset Dipole (OD) having the offset and dipolar moment reported by Anderson et al. (2011). The second model is a combination of a Dipole and a Quadrupole (DQ), the total field is fitted to the offset dipolar field, for northern latitudes greater than 50°. Simulations reproduce the features which characterize Mercury's interaction with the SW, encompassing the Bow Shock (BS), the magnetosheath, the magnetotail, the “cusps” region and the neutral current sheet. Global hybrid simulations of the Hermean magnetosphere run for the OD and DQ models demonstrate that the southern parts of the magnetospheres produced by the OD and DQ models differ greatly in topology and volume meanwhile their northern parts-are quite similar. In particular the DQ model exhibits a dome of closed field lines around the south pole in contrast to the OD. Without further information on the intrinsic magnetic field of the planet in the southern region which should be provided by BepiColombo after year 2020, we can only speculate on the influence of the different magnetic topologies on the magnetospheric dynamics.
Journal of Geophysical Research 10/2012; 117:10228. · 3.02 Impact Factor
ABSTRACT: The exosphere, the tenuous collisionless cloud of gas surrounding Mercury is
still a poorly known object because it is the result of many various
interactions between the surface, the interplanetary medium (Solar wind,
photons and meteoroids), the planetary and the interplanetary magnetic fields.
Many ground-based observations have allowed the detection of intense and
variable sodium emissions at global and local spatial scales, the latter being
mostly concentrated in the polarmid latitude regions. These regions are indeed
the preferred location of solar wind precipitation on the surface of the
planet. In the present paper, by using high resolution Na observations obtained
at the Canary Islands with the THEMIS solar telescope, we analyze the
variability of the sodium exosphere on time-scale of 1 hour and investigate the
possible mechanisms that could explain the exospheric sodium emission
distribution and its dynamics. Our interpretation relates the observed sodium
asymmetries to the combined effects of plasma and photons impacts onto the
Mercury's surface and of sodium diffusion through the upper layer of the
surface. The comparison between data and simulations seems to evidence that,
similarly to what occurs at the Earth, both the magnetic reconnection regimes
of pulsed or quasi-steady reconnection could occur on Mercury, and be
responsible for the observed Na short term variations. In addition to this, a
progressive broadening of the peak regions together with an increase of the
equatorial region seem to corroborate the idea of the role of photon stimulated
desorption, in association with ion sputtering and with global sodium migration
around Mercury as the cause of the observed evolution of the Na exosphere.
ABSTRACT: Recent observations and simulations showed the importance of the upper
atmosphere/ionosphere in the escape processes at Mars. The solar wind
interacts with the Martian ionosphere leading to an ionospheric outflow
into the Martian induced magnetosphere. One of the goals of the
Heliosares project is to simulate this ionospheric outflow, by coupling
a GCM-Ionospheric model, an exospheric model and a Mars-Solar wind
interaction model for different solar conditions. In this presentation,
we will present the 3D dynamical ionospheric core implemented in the
Martian GCM model developed at LMD. This core solves the ions and
electrons dynamics equations including the interaction with the neutral
atmosphere and taking into account the effect of polarization electric
field due to electronic pressure. The numerical approach used to solve
the dynamics equations and the first results of this model will be
presented as well as the future improvements.
AGU Fall Meeting Abstracts. 11/2010; -1:1866.
ABSTRACT: We used a dedicated hemispherical energy analyzer to measure energetic and angular distributions of electrons emitted from molybdenum microtips integrated in a 1 cm2 field emitter array designed by the CEA/LETI laboratory. Such cathodes typically deliver about 25 mA at an extraction voltage of 100 V, and are studied in order to replace heated wires as electron sources for space applications. We find that the energy distribution of the beam strongly depends on the extraction voltage, and is therefore expected to vary across the emission lifetime of the device, at a rate depending both on the alteration of the resistive structure with time and on the fate of adsorbed contaminants at the tip surface. A semi-empirical model of the emitters is proposed and used to determine parameters of energetic and angular distributions. The energy dispersion of the beam is found to increase from 2 eV ± 20% up to 9 eV ± 20% eV, for extraction voltages varying from 40 to 100 V. The mean angular dispersion of the beam is found to be 42° ± 20% when a null electric field is set at the grid extraction surface.
Journal of Physics D Applied Physics 01/2010; 43(6):065501. · 2.54 Impact Factor
ABSTRACT: We performed high spectral resolution observations of Mercury's exosphere on 2005 October 30 and 31 using the European Southern Observatory-New Technology Telescope, La Silla, Chile. The large spectral range, 385-855 nm, of the spectrograph, ESO Multi-Mode Instrument, provides a unique opportunity to search for nonidentified species in Hermian's environment. In this paper, we report a tentative detection of atomic aluminum in the exosphere of Mercury. This detection should be confirmed by further observations and can be used as an upper limit for this element in Mercury's exosphere. We also estimate the upper limit for the column densities of Fe and Si exospheric atoms. Detection of Al, a refractory element, if confirmed, as well as its high exospheric abundance (between 2 and 18) with respect to Ca would suggest either an unexpected surface composition or a relation between exosphere and surface composition that is not well understood.
The Astronomical Journal 03/2009; 137(4):3859. · 4.03 Impact Factor
åp. 05/2008; 482:1015-1029.
ABSTRACT: Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of approximately 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.
Nature 12/2007; 450(7170):646-9. · 36.28 Impact Factor
Nature 11/2007; 450(7170):646-649. · 36.28 Impact Factor
ABSTRACT: 1] A three-dimensional (3-D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O 2 + between 120 and 300 km and the sputtering of the Martian atmosphere by incident O + pickup ions. The reimpacting and escaping fluxes of pickup ions are derived from a 3-D hybrid model describing the interaction of the solar wind with our computed Martian oxygen exosphere. In this work it is shown that the role of the sputtering crucially depends on an accurate description of the Martian corona as well as of its interaction with the solar wind. The sputtering contribution to the total oxygen escape is smaller by one order of magnitude than the contribution due to the dissociative recombination. The neutral escape is dominant at both solar activities (1 Â 10 25 s À1 for low solar activity and 4 Â 10 25 s À1 for high solar activity), and the ion escape flux is estimated to be equal to 2 Â 10 23 s À1 at low solar activity and to 3.4 Â 10 24 s À1 at high solar activity. This work illustrates one more time the strong dependency of these loss rates on solar conditions. It underlines the difficulty of extrapolating the present measured loss rates to the past solar conditions without a better theoretical and observational knowledge of this dependency.
J. Geophys. Res. 01/2007; 112.
ABSTRACT: Atomic hydrogen is an important tracer of the global behaviour and
evolutionary processes of an atmosphere. A method usually used for
determining the abundance of atomic hydrogen is the observation of the
Lyman alpha line at 121.6 nm, excited by resonant scattering of the
solar FUV radiation. During limb observations on 2004 and 2005 the
SPICAM UV imaging spectrometer on Mars Express measured this airglow for
different altitudes and solar zenith angles for a period of medium solar
activity. One spectrum was recorded each second, resulting in more than
1000 spectra for each observation. We will present the data processing,
the calculation of the sky background contribution and the first density
profiles of atomic hydrogen obtained by fitting the data with a model of
hydrogen density and a radiative transfer model. We will compare these
results with previous observations by Mariner 6, 7 and 9. We will also
discuss about the escaping flux deduced from this fitting
AGU Spring Meeting Abstracts. 04/2006; -1:01.
ABSTRACT: On the 11 August 2004, the UV spectrograph Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board Mars Express made the first observation of auroral-type emission on the Martian nightside. In this paper, we describe the results of a new analysis of the observed emission owing to a better calibration of SPICAM UV channel and the use of all spectral information obtained during this observation. Several possibilities for the origin of this emission are discussed. We discussed, in particular, the possible exact geometry of the observation and the possible origins of the Martian aurorae. The emissions measured by SPICAM ultraviolet spectrometer have most probably been produced by electrons with an energy distribution peaking at few tens of eV rather than by electron distributions peaking above 100 eV.
Journal of Geophysical Research 01/2006; 111. · 3.02 Impact Factor
ABSTRACT:  This paper is intended as an introduction to several companion papers describing the results obtained by the SPICAM instrument on board Mars Express orbiter. SPICAM is a lightweight (4.7 kg) UV-IR dual spectrometer dedicated primarily to the study of the atmosphere of Mars. The SPICAM IR spectrometer and its results are described in another companion paper. SPICAM is the first instrument to perform stellar occultations at Mars, and its UV imaging spectrometer (118-320 nm, resolution similar to 1.5 nm, intensified CCD detector) was designed primarily to obtain atmospheric vertical profiles by stellar occultation. The wavelength range was dictated by the strong UV absorption of CO(2) (lambda < 200 nm) and the strong Hartley ozone absorption (220-280 nm). The UV spectrometer is described in some detail. The capacity to orient the spacecraft allows a great versatility of observation modes: nadir and limb viewing (both day and night) and solar and stellar occultations, which are briefly described. The absolute calibration is derived from the observation of UV-rich stars. An overview of a number of scientific results is presented, already published or found in more detail as companion papers in this special section. SPICAM UV findings are relevant to CO(2), ozone, dust, cloud vertical profiles, the ozone column, dayglow, and nightglow. This paper is particularly intended to provide the incentive for SPICAM data exploitation, available to the whole scientific community in the ESA data archive, and to help the SPICAM data users to better understand the instrument and the various data collection modes, for an optimized scientific return.
Journal of Geophysical Research-Planets. 01/2006; 111(E10).
Icarus 11/2005; 178:367-385. · 3.38 Impact Factor
ABSTRACT: In view to prepare Mars human exploration, it is necessary to promote and lead, at the international level, a highly interdisciplinary program, involving specialists of geochemistry, geophysics, atmospheric science, space weather, and biology. The goal of this program will be to elaborate concepts of individual instruments, then of integrated instrumental packages, able to collect exhaustive data sets of environmental parameters from future landers and rovers of Mars, and to favour the conditions of their implementation. Such a program is one of the most urgent need for preparing human exploration, in order to develop mitigation strategies aimed at ensuring the safety of human explorers, and minimizing risk for surface operations. A few main areas of investigation may be listed: particle and radiation environment, chemical composition of atmosphere, meteorology, chemical composition of dust, surface and subsurface material, water in the subsurface, physical properties of the soil, search for an hypothesized microbial activity, characterization of radio-electric properties of the Martian ionosphere. Scientists at the origin of the present paper, already involved at a high degree of responsibility in several Mars missions, and actively preparing in situ instrumentation for future landed platforms (Netlander--now cancelled, MSL-09), express their readiness to participate in both ESA/AURORA and NASA programs of Mars human exploration. They think that the formation of a Mars Environment working group at ESA, in the course of the AURORA definition phase, could act positively in favour of the program, by increasing its scientific cross-section and making it still more focused on human exploration.
Advances in Space Research 02/2004; 34(8):1702-9. · 1.18 Impact Factor
35th COSPAR Scientific Assembly; 01/2004
ABSTRACT: A long term plan of observations of the sodium exosphere of Mercury began in 2002 by using the high resolution echelle spectrograph SARG and a devoted sodium filter at the 3.5 m Galileo National Telescope (TNG) located in La Palma, Canary Islands. This program is meant to investigate the variations of the sodium exosphere appearance under different conditions of observations, namely Mercury's position along its orbit, phase angle and different solar conditions, as reported by previous observations in August 2002 and August 2003 [Barbieri, C., Verani, S., Cremonese, G., Sprague, A., Mendillo, M., Cosentino, R., Hunten, D., 2004. Planet. Space Sci. 52, 1169–1175; Leblanc, F., Barbieri, C., Cremonese, G., Verani, S., Cosentino, R., Mendillo, M., Sprague, A., Hunten, D., 2006. Icarus 185 (2), 395–402].Here we present the analysis of data taken in June 29th and 30th and in July 1st 2005, when Mercury's true anomaly angle (TAA) was in the range 124–130°. The spectra show particularly intense sodium lines with a distinctive peak in emission localized in the southern hemisphere at mid-latitudes. This seems to be a persistent feature related to consecutive favorable IMF conditions inducing localized enhancements of surface sodium density. The comparison with previous data taken by Potter et al. [Potter, A.E., Killen, R.M., Morgan, T.H., 2002. Meteorit. Planet. Sci. 37 (9), 1165–1172] evidences a surprising consistency of the anti-sunward component, which appears to remain constant regardless of the changing illumination and space weather conditions at Mercury.
ABSTRACT: We have studied the production of hot O and C atoms, and hot CO2 and CO
molecules in the martian upper atmosphere and exosphere, through
dissociative recombination of O+ and CO+ ions, and sputtering of the
atmosphere by incident O+ pick-up ions, as a 2 function of the solar
activity. Production and collisional thermalization of the hot particles
in the multispecies CO2 , O and CO upper atmosphere are described by
using an adapted Direct Simulation Monte Carlo. Velocity distributions,
atmospheric loss rates and density profiles are given for suprathermal
O, C, CO and CO2 , at low and high solar activities. At high solar
activity the hot oxygen escape rate estimated from DR of O+ is found to
be less than 2 times the rate estimated from sputtering. The
corresponding sputtered oxygen density is 1.6 lower than the DR density
at 1000km. Sputtering is found to efficiently populate the corona with
molecular species as CO and CO2 at high solar activity, and also to
produce a carbon escape rate that is comparable to that derived from the
major photochemical sources by other authors. Collisions of the
background atmospheric gas with hot O atoms produced in DR of O+ are
found to 2 produce densities of hot heavy molecules as CO2 and CO larger
than 102 cm-3 for exospheric altitudes lower than 1000km, at both high
and low solar activities. At high solar actvity 50% of the sputtered
exospheric oxygen density is seen to originate from dissociations of CO2
molecules subject to the impacting pick-up ions flux. Interestingly, the
hot CO2 density scale height is observed to be process dependent. The
hot oxygen energy distributions associated with sputtering and DR near
the exobase are found to obey distinct decay laws, as a result of the
inclusion of virational excitation of the molecules in the atmosphere.