M. I. Verigin

The dependence of the Martian magnetopause and bow shock on solar wind ram pressure according to Phobos 2 TAUS ion spectrometer measurements

The location of the Martian magnetopause and that of the bow shock are studied on the basis of three-dimensional solar wind proton spectra measured by the TAUS spectrometer on board Phobos 2 in its 56 circular orbits. The clear and strong dependence of the areomagnetopause position on solar wind ram pressure was revealed, while the position of the bow shock was practically independent of this parameter. In the power law expression telling the dependence of the Martian magnetotail thickness D on the solar wind ram pressure: D∼(ϱυ²)−1/k, the power index turned out to be k∼5.9±0.5. The close coincidence of this index with k = 6 for a dipole geomagnetic field, and the large areomagnetotail thickness compared with the planetary diameter, suggest that an intrinsic dipole magnetic field is likely to be an important factor in the solar wind interaction with Mars. On the other hand, the relatively stable position of the subsolar point of the Martian magnetopause and unambiguous induction effects observed by the Phobos 2 MAGMA magnetic experiment in the magnetotail indicate the essential role of an induced magnetic field, too. The weak dependence of the terminator bow shock position on the solar wind ram pressure may be related to the relatively stable position of the subsolar magnetopause.

Calculated ionization rates, ion densities, and airglow emission rates due to precipitating electrons in the nightside ionosphere of Mars

The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.

The Martian magnetic field environment: Induced or dominated by an intrinsic magnetic field?

Abstract Even though magnetic field and plasma in-situ measurements near Mars from the 1989 PHOBOS-2 project and from earlier missions are available, the existence of an Martian intrinsic magnetic field is still controversial. In this study we analyze data of the PHOBOS-2 magnetic field experiments MAGMA and FGMM and use the upstream solar wind parameters of the TAUS and ASPERA experiments. Different methods are used to investigate the influence of the interplanetary magnetic field (IMF) and of a possible weak intrinsic field on the solar wind interaction with Mars : The compressibility of plasma boundaries, the correlation between upstream IMF and tail properties and between magnetic field structures and planetary rotation. The study shows that the magnetic field in the tail is strongly correlated with the upstream IMF suggesting that the Martian magnetotail is induced, at least to a large extent. Compressibility studies reveal a weak dependence of the plasma boundaries on the solar wind dynamic pressure but the bow shock location appears to be not affected by the Martian longitude within the accuracy of our measurements. We conclude that an intrinsic planetary field, if it exists, does not play a major role in the interaction between the solar wind and Mars.

Analysis of the 3-D shape of the terrestrial bow shock by interball/magion 4 observations

Abstract Location and shape of the terrestrial bow shock are analyzed using MAGION 4 (sub satellite of INTERBALL 1) crossings of this boundary and upstream solar wind parameters measured by the WIND spacecraft. Different crossing points were mapped to the Sun — Earth line and to the terminator plane using an analytical model of the planetary bow shock previously developed for the Martian bow shock investigation. Analysis of the subsolar bow shock position as a function of Alfvenic Mach number ( M a ) revealed fine effect that this boundary tends to approach the Earth when M a is decreasing for field-aligned flow of the solar wind, while for non field-aligned flow the bow shock moves away from the planet. Asymmetry of the terrestrial bow shock in the terminator plane is found for non field-aligned flow with anisotropic Friedrichs diagrams.

On the problem of the Martian atmosphere dissipation: Phobos: 2 TAUS Spectrometer results

The measurements of proton spectra obtained by the TAUS spectrometer on board the Phobos 2 spacecraft in elliptical orbits near Mars are presented. A strong deceleration of the solar wind upstream of the Martian bow shock was revealed. It can be caused by the mass loading of the plasma flow by ions originating from the hot oxygen/hydrogen corona of Mars and/or by protons specularly reflected from the bow shock. In the first case the deceleration of the solar wind by about 100 km/s implies that the hot oxygen corona of Mars could be several times denser than it was anticipated to be (at least during the observation period that was close to solar cycle maximum). Furthermore, the loss of planetary oxygen through the corona appears to be the main process of oxygen loss from Mars. The upper limit of loss rate for such a process is determined to be 1026 oxygen atoms or 2.5 kg of oxygen per second.

Calculated densities of H3O+(H2O)n,NO2− (H2O)n, CO3− (H2O)n and electron in the nighttime ionosphere of Mars: Impact of solar wind electron and galactic cosmic rays

We have calculated the densities of positive ions and negative ions in the ionosphere of Mars at solar zenith angle 106° between height interval 0 km and 220 km. This model couples ion-neutral, electron neutral, dissociation of positive and negative ions, electron detachment, ion-ion, ion-electron recombination processes through 117 chemical reactions. Of the 34 ions considered in the model, the chemistry of 17 major ions (O 2 + , NO + , CO 2 + , H 3 O + H 2 O, H 3 O + (H 2 O) 2 , H 3 O + (H 2 O) 3 , H 3 O + (H 2 O) 4 , O 2 + CO 2 , H 3 O + , CO 4 - , CO 3 - , CO 3 - H 2 O, CO 3 - (H 2 O) 2 , NO 2 - H 2 O, NO 2 - (H 2 O) 2 , NO 3 - H 2 O, and NO 3 - (H 2 O) 2 ) are discussed in this paper. At altitude below 70 km, the electron density is mainly controlled by hydrated hydronium ions and water clusters of NO 2 - and CO 3 - . The ions O 2 + and NO + dominate above this altitude. This calculation suggests that the ionosphere of Mars contains F and D peaks at altitude ~130 km and ~30 km due to precipitation of solar wind electron and galactic cosmic rays respectively. F peak is mainly produced by O 2 + after heavy loss of CO 2 + with atomic oxygen. D peak occurs due to high efficiency of electron attachment to Ox molecules, which entails that concentration of negative ions is higher than that of electron below 30 km. These results are compared with radio measurements made by Mars 4 and Mars 5 in the nighttime ionosphere.

Planetary bow shocks: Asymptotic MHD Mach cones

A direct approach for determining the asymptotic MHD Mach cone is formulated and solved. An implicit analytical solution enables the calculation of the asymptotic downstream slope of MHD Mach cones at any clock angle for arbitrary Ms, Ma, and ϑbv. The solution obtained includes all previously known symmetric cases. The elongation and shift of the asymptotic fast mode shock cross-section are studied for a wide range of upstream plasma parameters as well as its unusual ‘chopped’ shape under certain conditions. Our results may be useful for planetary shock modeling and MHD numerical codes verification.

Plasma properties from the upstream region to the cometopause of comet P/Halley: Vega observations

Based on the Plasmag-1 plasma measurements on board Vega-1 and -2, evidence is provided for the deceleration upstream, for the heating at and for the thermalization and deceleration behind the bow shock of comet Halley. In the cometosheath region two separate ion populations are observed: the first one consists of cometary ions being picked up in the vicinity of the point of observation; the energy of these ions coming from the solar direction decreases much faster than the energy of the solar wind ions. The second one consists of cometary ions being picked up by the solar wind far away from the point of observation. Considerable oscillations in the plasma flow direction occur in the cometosheath region.

Temperature and density variations in the dusk and dawn plasmasphere as observed by interball tail in 1999 – 2000

Abstract The data on cold ion fluxes measured by the ALPHA 3 instrument on Interball-Tail in July – October 1999 when the spacecraft crossed the dusk side outer plasmasphere, and in January – April 2000 when it crossed the dawn side plasmasphere are analyzed. Correlation of cold ion parameters in the plasmasphere with indices of geomagnetic activity and parameters of the external solar wind flow is examined. In the innermost observed part of the dawn plasmasphere ion temperature is increasing with MLT from post midnight to prenoon. In the outermost plasmasphere no temperature dependence on MLT was observed. It is revealed that cold ion density in the dusk and dawn side outer plasmasphere is increasing with increasing solar wind ram pressure.

The flaring of the Martian magnetotail observed by the Phobos 2 spacecraft

Spacecraft observations from the Earths magnetotail show that the flaring angle depends on the downtail distance, the upstream solar wind dynamic pressure and the Bz component of the interplanetary magnetic field [Petrinec and Russell, 1993]. Measurements from the Phobos 2 spacecraft along a circular orbit at 2.8 Mars radii allow a similar study of the Mars magnetotail. Under the assumption that the magnetic pressure in the Martian tail lobes is much greater than the plasma pressure in the lobe, we use the pressure balance condition between the tail lobe magnetic pressure and the normal component of the solar wind pressure to infer the angle at which the tail magnetopause flares. As in the case of the terrestrial magnetotail, the flaring angle of Mars tail depends on the solar wind dynamic pressure, but this angle (at 2.5 RM) is about one half the terrestrial value (at 17 RE). The median inferred flaring angle is about 13°.