Observations of magnetic anomaly signatures in Mars Express ASPERA-3 ELS data

Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic ‘anomaly’ regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere.     

Structure of the martian wake

We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field.     

First ENA observations at Mars: Subsolar ENA jet

The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4-7) × 10⁵ cm⁻² sr⁻¹ s⁻¹ in the energy range 0.3-3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region, but this can not be explained in the frame of MHD models.     

Accretion of matter by condensed objects

The equations of motion for steady-state spherical symmetric flow of matter into or out of a condensed object (e.g. neutron stars, black holes, etc.) are displayed and solved for simple polytropic gases. It appears that infalling matter may be heated as hot as 10¹²K and that X-ray luminosities of the order of 10³⁷ erg s^–1 could result. The two fluid (electrons and ions separately) approach is also examined and it is shown that electrostatic fields of the order of 10⁵ V m^–1 are required near the surface of the object. Such fields are not strong enough to significantly modify the space-time metric.     

Quarter-wave ULF pulsations

Recent theoretical work has predicted the possible existence of “quarter-wave” ULF pulsation resonances, in which the wave electric field has a near-node in one ionosphere and an antinode in the conjugate ionosphere. Eigenvalues are derived for quarter-wave toroidal and guided poloidal resonances for a range of L-values and plasma density distributions. From these eigenvalues, resonant periods can be obtained.Three pulsation events with anomalously long periods (when interpreted as half-waves) are examined in the light of these results. It is decided that only one event is a good candidate for quarter-wave status; this event seems likely to be a driven resonance effectively in the quarter-wave guided poloidal mode.     

First ENA observations at Mars: Solar-wind ENAs on the nightside

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future.     

Ion escape at Mars: Comparison of a 3-D hybrid simulation with Mars Express IMA/ASPERA-3 measurements

We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction.     

On the interaction between differential rotation and magnetic fields in the Sun

We have performed 3-D numerical simulations of compressible convection under the influence of rotation and magnetic fields in spherical shells. They aim at understanding the subtle coupling between convection, rotation and magnetic fields in the solar convection zone. We show that as the magnetic Reynolds number is increased in the simulations, the magnetic energy saturates via nonlinear dynamo action, to a value smaller but comparable to the kinetic energy contained in the shell, leading to increasingly strong Maxwell stresses that tend to weaken the differential rotation driven by the convection. These simulations also indicate that the mean toroidal and poloidal magnetic fields are small compared to their fluctuating counterparts, most of the magnetic energy being contained in the non-axisymmetric fields. The intermittent nature of the magnetic fields generated by such a turbulent convective dynamo confirms that in the Sun the large-scale ordered dynamo responsible for the 22-year cycle of activity can hardly be located in the solar convective envelope.     

Petrology and provenance of a very‐low‐titanium picrite clast in lunar highland regolith breccia 15295

Clast 100 in regolith breccia 15295 could be a key to resolving the relationship(s) between mare basalts and lunar picritic glasses. The clast is basaltic, with texture, mineralogy, mineral compositions, and calculated bulk composition suggesting that it crystallized in a thick lava flow or shallow intrusive body from a very‐low‐titanium (VLT) basaltic magma. The estimated bulk composition of clast 15295,100 is primitive (i.e., magnesian) compared to those of known VLT basalts, and is very close to those of VLT picritic green glasses, especially the Apollo 14 A green glass. From these similarities, we infer that clast 15295,100 is a crystalline product of a picritic magma similar to the Apollo 14 A glass. Clementine and M³ remotely sensed data of the lunar surface were used to find areas that have chemical compositions consistent with those of clast 15295,100, not only near the Apollo 15 site, but in a broad region surrounding the site. Two regions are consistent with clast's 15295,100 compositional data. The larger region is in southern Mare Imbrium, and a smaller region is in the eastern half of Sinus Aestuum. These locations should be considered as candidates for future missions focusing on sample science.