Shergottites, nakhlites and the Chassigny meteorites (SNC group) may have originated on Mars. The shergottites are medium-grained basalts, the nakhlites are pyroxenites and the Chassigny is a dunite. The SNC group is petrologically diverse but differs from all other known achondrites in terms of mineral chemistry, the redox state, the oxygen isotopic composition and the radiometric ages. The SNC stones are mafic and ultramafic cumulate rocks with mineralogies that indicate rapid cooling and crystallization from tholeiitic magmas which contained water and experienced a high degree of oxidation. The characteristics suggest formation from a large parent body, i.e., a planet, but not earth. The estimated ages for the rocks match the estimated ages for several mapped Martian volcanoes in the Tharsis region. Additionally, the elemental and isotopic abundances of atmospheric gases embedded in melts in the SNC stones match Viking Lander data for the Martian atmosphere. However, reasons are cited for discounting the possibility that a large meteorite(s) collided with Mars about 180 myr ago and served as the mechanism for ejecting the SNC stones to earth.

SNC meteorites: Clues to Martian petrologic evolution?

When the supersonic solar wind reaches the neighborhood of a planetary obstacle it decelerates. The nature of this interaction can be very different, depending upon whether this obstacle has a large-scale planetary magnetic field and/or a well-developed atmosphere/ionosphere. For a number of years significant uncertainties have existed concerning the nature of the solar wind interaction at Mars, because of the lack of relevant plasma and field observations. However, measurements by the Phobos-2 and Mars Global Surveyor (MGS) spacecraft, with different instrument complements and orbital parameters, led to a significant improvement of our knowledge about the regions and boundaries surrounding Mars.

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The plasma Environment of Mars

[1] The 3-D velocity distribution functions of nonthermal ions observed in the vicinity of the Moon have been analyzed to understand the interaction between the solar wind and the Moon. The observation was made during the lunar swing-by of the Nozomi spacecraft, and the closest approach was about 1.6 RL from the Moon's surface. Both Nozomi and the Moon were located in the solar wind, and nonthermal ions were observed only when the spacecraft was very close to the Moon. The nonthermal ions were measured by a Particle Spectrum Analyzer/Ion Spectrum Analyzer (PSA/ISA) on board the Nozomi. After analyses and careful examination of the 3-D velocity distribution of the nonthermal ions, the characteristics of the nonthermal ions were revealed as follows: The nonthermal ions have a partial ring structure in the phase space, they are protons, their source location is the dayside of the Moon, and they have large velocities when they are generated. We propose the following scenario of a solar wind interaction with the Moon: The electromagnetic field in the vicinity of the Moon must have a dynamic structure, possibly a miniature bow shock associated with a local magnetic anomaly, where some of the solar wind protons are deflected violating their first adiabatic invariant. After the deflection, they move under the force of the convection electric field and gyrate around the magnetic field in the solar wind. This motion forms a partial ring structure with large initial velocities in the velocity phase space.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JA009366

Moon-related nonthermal ions observed by Nozomi: Species, sources, and generation mechanisms

A model for thermal evolution of the Martian mantle and core and for the evolution of the Martian magnetic field is developed by expanding the planetary thermal history model of Stevenson et al (1983) and using the energy balance equations from that work Several parameter values are chosen differently from those of the Stevenson model, including those for mantle density, core radius, core density, central pressure, and pressure at the core-mantle boundary The model is further modified to allow calculations of lithosphere thickness through time According to the model, the core contains a light alloying constituent, assumed to be sulfur The results of calculations show that a small Martian magnetic field can be generated by a weakly convecting liquid core

Thermal history of Mars and the sulfur content of its core

[1] Mars Global Surveyor (MGS) Magnetometer (MAG) data provide constraints on magnetic morphology at Mars, including the relative importance of the solar wind and of crustal magnetic sources. We analyze MAG data to characterize the upstream interplanetary magnetic field (IMF) and confirm trends in the magnetic field expected from the solar wind interaction with a planetary atmosphere, including increases at the shock and magnetic pile-up boundary (MPB), postshock turbulence, and field line draping around the Martian obstacle. Crustal magnetic sources locally modify the solar wind interaction, adding variability to the Martian magnetic environment that depends on planetary rotation. We identify trends in the vector magnetic field with respect to altitude, solar zenith angle, and planetary location. Crustal sources influence the magnetic field to different altitudes above different regions, and the influence of the strongest source extends to 1300–1400 km. The draped IMF partially controls the field topology above crustal sources, and crustal magnetic field lines reconnect to this field in a systematic fashion that depends upon Mars' geography, IMF strength, and IMF orientation.

/pdf/martian-magnetic-morphology-contributions-from-the-solar-1nspoue9w6.pdf

Martian magnetic morphology: Contributions from the solar wind and crust

The magnetic field in the close proximity of planet Mars according to data from Mars 2 and Mars 3 spacecraft is discussed The magnetometers on the spacecraft detected a field whose intensity near the orbital periapses was 7 to 10 times higher than the interplanetary field at the distance of the Martian orbit The nature of the observed field is described

/pdf/magnetic-field-in-the-very-close-neighborhood-of-mars-32h6wwg5k8.pdf

Magnetic field in the very close neighborhood of Mars according to data from the Mars 2 and Mars 3 spacecraft

Experimental data obtained by the magnetometers on Mars 3 (1972) at heights of 1000 km on the day side and Mars 5 (1974) at heights up to 9000 km on the dusk and night sides during opposite polarities of the interplanetary magnetic field show that Mars has an intrinsic magnetic field. The magnetic moment of the Martian dipole is M ≈ 64Rm³ = 2.5·1022 G cm³, and the equatorial dipole field at the surface of the planet is 64 γ. The topology of lines of force on the day and night sides can be explained best if we assume that the magnetic dipole axis of Mars is tilted less than 15°–20° from the rotation axis. The bow shock position observed on the day side is in agreement with the hypothesis of an intrinsic Martian magnetic field.

The magnetic field of mars according to the data from the Mars 3 and Mars 5

The residual field from Cosmos 49 is presented in chart form. This map displays vast areas (1000–4000 km across) of negative and positive ΔT (the T are differences between measured and model fields) that are of the order of a few tens of gammas. The external field does not exert any essential influence on the ΔT distribution. The frequency spectrum of ΔT is similar to that of the model field used for the greater part of the chart, but within the ‘contrast zones’ the ΔT spectrum contains higher harmonics. There is no apparent correlation between the ΔT distribution and near-surface anomalies or the thickness of the magnetoactive layer of the earth's crust. The correlation with heat flow distribution is somewhat more distinct within certain regions. It appears that the greater part of ΔT is due to a poor representation of the main geomagnetic field. However, the authors do not exclude the possibility of intermediate anomalies of inductive origin within the mantle, which could contribute to the higher-frequency part of the ΔT spectrum.

Residual geomagnetic field from the satellite Cosmos 49

This paper is devoted to a description of the problems related to the experiment and the experimental data concerning the field of the moon which were obtained during the flight of the second Soviet cosmic rocket. As a consequence of the analysis of the measuring apparatus' sensitivity threshold, according to measurement data in a weak geomagnetic field, some 45,000 to 60,000 km from the center of the earth, and of the analysis of noise level in the orbital space of the moon, coupled with measurements directly near the moon and up to 55 km from its surface, no notable magnetic field of the moon was revealed. It is estimated that the dipole magnetic moment of the moon must be smaller than 1/10,000 of the earth's magnetic moment.

Investigation of the Magnetic Field of the Moon

The data of three-times repeated magnetic survey of the section of Lunokhod-2 route 1.5 km long are analyzed. The linear size of the regions of magnetic field anomalies disclosed is 200–300 m. The results of magnetic survey near the tectonic break of Straight Rille and near the south rim of crater Le Monnier were used for estimation of rock magnetization in situ. It is shown that mare basalts in south-east region of crater Le Monnier have oblique magnetization (at the angle c30° to horizon). The magnitude of magnetization is × 5 × 10−5 G cm g−1. The south-east slope of the crater Le Monnier is magnetized roughly vertically, the upper limit of magnetization of the rocks of the rim is c 1 × 10−5 G cm3 g−1. The results of an analysis of 160 magnetic field variations recorded by Lunokhod-2 indicate that the horizontal components of variations have nearly linear polarization. The principal axes of hodographs stretch in the direction north-west-south-east. Such a polarization of variations may be due to an increase of the thickness of the upper isolated layer under Mare Serenitatis.

Sh. Sh. Dolginov

Papers

Magnetic field in the very close neighborhood of Mars according to data from the Mars 2 and Mars 3 spacecraft

The magnetic field of mars according to the data from the Mars 3 and Mars 5

Residual geomagnetic field from the satellite Cosmos 49

Investigation of the Magnetic Field of the Moon

Study of magnetic field, rock magnetization and lunar electrical conductivity in the Bay Le Monnier