What we have learned about the Martian magnetic field

Dolginov, Sh. Sh.

doi:10.1007/bf00054322

Cited by 17 publications

(6 citation statements)

References 50 publications

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“…Opinions differ concerning either the existence or, if extant, the order of magnitude of a field for Mars [Smith, et al 1965;Russell, 1987;Dolginov, 1987;ford, 1991]. If Stevenson [1983] is correct that the core is stably stratified and there is no other mechanism for stirring to produce a dynamo, it should fall further below any lines drawn on the figures for the planets with known fields, as evidenced by Venus.…”

Section: Discussionmentioning

confidence: 99%

“…There are two basic problems of having a unique and accurate estimate of the planetary magnetic moments. 1987;Russell, 1987Russell, , 1989 and Mars [Ness, 1979;Dolginov, 1987;Axford, 1991] are the maximum possible, partly for this reason. Indeed, the fields induced by the Cytherian ionosphere [Luhmann, 1991] make it difficult to observe any weak internal field even from a low altitude [see also Russell, 1993].…”

Section: Magnetic Momentsmentioning

confidence: 99%

See 1 more Smart Citation

The magnetic bode fallacy

Cain¹,

Beaumont²,

Holter³

et al. 1995

J. Geophys. Res.

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The magnetic moments and angular momenta of Solar System bodies are compared to evaluate the statistical reality of the relation that has come to be called the "magnetic Bode law." Runcorn has suggested that this "law", giving a slope of about 3/5 on a log-log plot, is only a geometrical effect of the angular momenta being proportional to the fifth power of radius and the magnetic moment the cube. The best fit hne to the six planets with nonzero magnetic fields is log(m/m,) = -0.2 (+0.2) + 0.82 (-1-0.05)log(L/L,), where the subscripts denote the values for Earth. The value 0.82 is shown to be consistent with the 3/5 slope once estimation bias is accounted for. Monte Carlo analysis was used to construct (2500) synthetic solar systems from the variables representing the range of the planer's radii, densities, coefficients of inertia, periods of rotation, and surface poloidal field intensity. If these variables are considered independent, it was found that the probability of obtaining a slope as different from 0.6 as suggested by Runcorn is 34%, but only a 0.2% chance of obtaining values that are so linear as the actual data on this plot. If instead the covariances of the actual planets are included in the analysis, the mean slope is 0.82 with small deviation, but the odds of obtaining such a tight fit as that observed in the actual Solar System becomes 63%. It is concluded that considering the lack of physical plausibility of the correlations between the physical parameters besides field, the strong correlation with rotation as an important factor in computing the angular momentum is spurious. Comparisons are done using both the angular momenta of the whole planet, and the theorized magnetoactive shells and cores. The conducting volumes are also compared with the poloidal dipole fields external to these magnetoactive regions. The studies show that the volumes of the magnetoactive regions appear to be related to the strength of the poloidal field just outside, and that the tighter trend for the log momentum versus log dipole moment plots is mainly due to the geometric factor suggested by Runcorn. Plots of field just outside these regions versus their volumes show that the Earth and Io have significantly higher fields than those predicted by a line extending from the giant planets to Mercury. Such a line also does not miss Dolginov's estimate for Mars by a half order of magnitude. The upper limit of field of Venus falls 3 orders below this trend. If Mars has a core theorized to be some 1780 km in radius, a weak dynamo resulting in a surface field close to the limiting 10-100 nT range suggested by earlier spacecraft observations is not inconsistent with the trend of the other planets. The deviation of Earth and Io from a line joining the other planets is thought to be due to the added vigor of convection from their extra sources of energy. For Earth this would likely be caused by freezing of the inner core whereas for Io the enhancement would be from tidal heating as previously suggested. Paper number 95JE00504. 0148-...

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Section: Discussionmentioning

confidence: 99%

Section: Magnetic Momentsmentioning

confidence: 99%

The magnetic bode fallacy

Cain¹,

Beaumont²,

Holter³

et al. 1995

J. Geophys. Res.

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“…Small observational limits on the Martian magnetic dipole moment (( 1-5 x 1022 G-cm3; Dolginov [1987]; Russell [1987]) combined with scaling estimates from the terrestrial case (~ 4.5 x 1024 G-cm3; e.g. Russell [1987]) make it unlikely that Mars has an intrinsic core-dynamo magnetic field at present.…”

Section: Introductionmentioning

confidence: 99%

A crustal magnetization model for the magnetic field of Mars: A preliminary study of the Tharsis Region

Hood

Hartdegen

1997

Geophysical Research Letters

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Abstract. Crustal magnetic field anomalies are calculated at several altitudes above the Tharsis region on Mars assuming a source region consisting of uniformly magnetized subsurface volcanic constructs. The subsurface structure is consistent with a proposed model for the evolution of the Tharsis province based on geologic and tectonic evidence.The maximum thicknesses of subsurface volcanic deposits are constrained by gravity and topography data. Mean magnetization intensities are assumed to be comparable to those of SNC meteorites. Because reversals of the former Martian dynamo are neglected, the calculated field magnitudes may represent an upper limit on actual fields to be expected above the Tharsis region. Maximum field magnitudes at 300 km altitude are in the range 1-5 nT and would be marginally detectable by an orbiting magnetometer.

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“…The present Martian magnetic field is the subject of continuing controversy. Based on data obtained from the Russian Mars 2 and 3 (1971) and 5 (1974) orbiters and American Mariner 4 fly-by spacecraft, analyses have been presented for (Dolginov 1987) and against (Russell 1987) a present weak Martian mag netic field. The upper limit to any Martian dipole moment is approximately 2 x 10" 6 * * * * * * * * * 16 Am2, corresponding to an equatorial surface field of about 50 nT (Dol ginov 1987).…”

Section: Sn C M Eteorites and Th E M Artian M Agn Etic Fieldmentioning

confidence: 99%

The magnetism of meteorites and early Solar System magnetic fields

Collinson

1994

Phil. Trans. R. Soc. Lond. A

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The characteristics of the remanent magnetization of chondrite, achondrite and shergottite, nakhlite and chassignite (SNC) meteorites are described, and interpretation in terms of magnetizing fields in the ancient Solar System discussed. The magnetism of ordinary chondrites is commonly scattered in direction within samples, implying magnetization of constituent fragments before accumulation. The magnetic history of these meteorites is uncertain because of lack of knowledge of the origin and properties of tetrataenite, an ordered FeNi alloy often carrying the bulk of the magnetization. Achondrites also often possess scattered magnetization, the primary component probably being acquired during cooling after differentiation of the parent body. A magnetizing field of internal origin is possible. Estimates of magnetizing field strength are in the approximate range 5-100 μ T, with carbonaceous chondrites showing the highest values. The SNC meteorites, probably originating on Mars, provide evidence for a weak, ancient Martian magnetic field of the order 1 μ T.

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What we have learned about the Martian magnetic field

Cited by 17 publications

References 50 publications

The magnetic bode fallacy

The magnetic bode fallacy

A crustal magnetization model for the magnetic field of Mars: A preliminary study of the Tharsis Region

The magnetism of meteorites and early Solar System magnetic fields

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