Subsequent Orbital Evolution Research Articles

Recognizing mercurian meteorites

Abstract— With the recent realization that some meteorites may come from Mars and the Moon, it is worthwhile to consider whether meteorites from Mercury could exist in our collections and, if so, whether they could be recognized. The current state of ignorance about Mercury both increases the potential scientific value of mercurian meteorites and aggravates the problem of identifying them. Here, we review evidence supporting the possibility of impact launch and subsequent orbital evolution that could deliver rocks from Mercury to Earth and suggest criteria that could help identify a mercurian meteorite. Mercurian rocks are probably differentiated igneous rocks or breccias or melt rocks derived therefrom. Solar nebula models suggest that they are probably low in volatiles and moderately enriched in Al, Ti, and Ca oxides. Mercurian surface rocks contain no more than 5% FeO and may contain plagioclase. A significant fraction may be volcanic. They may possess an unusual isotopic composition. Most pristine mercurian rocks should have solidification ages of ∼3.7 to ∼4.4 Ga, but younger impact‐remelted materials are possible. Because we know more about the space environment of Mercury than we do about the planet itself, surface‐exposed rocks would be easiest to identify as mercurian. The unique solar‐to‐galactic cosmic‐ray damage track ratio expected in materials exposed near the Sun may be useful in identifying a rock from Mercury. Mercury's magnetic field stands off the solar wind, so that solar‐wind implants in mercurian regolith breccias may be scarce or fractionated compared to lunar ones. Mercurian regolith breccias should contain more agglutinates (or their recrystallized derivatives) and impact vapor deposits than any other and should show a higher fraction of exogenic chondritic materials than analogous lunar breccias. No known meteorite group matches these criteria. A misclassified mercurian meteorite would most likely be found among the aubrites or the anorthositic lunar meteorites.

Poynting-Robertson effect and small eccentric orbits

Perturbation equations of celestial mechanics in application to solar electromagnetic radiation are investigated. Special attention is payed to nearly circular orbis. Results of Klacka and Kaufmannova (1992) are generalized and various initial semi-major axes are taken into acount. Time-averaged (during one period) eccentricity decreases only during the first 25% of the total time of inspiralling toward the Sun. The value 25% hods for all initial values of semi-major axes (initialy circular orbits are supposed). The orbits become more and more eccentric in the subsequent orbital evolution.

Charged dust in the outer planetary magnetospheres

The dynamics of the electrostatic disruption products of fragile interplanetary dust aggregates which are initially electrically charged on entering the Jovian plasmasphere is considered. The detailed orbits of these charged particles, which are shown to be confined to the equatorial plane, are computed. It is found that the fragments with radii typically about 1 micron are magnetogravitationally trapped within the plasmasphere due to the velocity-induced oscillation of their surface potentials. It is suggested that the distribution of micrometeroid dust within the Jovian magnetosphere, observed by Pioneer 10 and the recent Voyager, is a result of the magnetogravitational trapping and subsequent orbital evolution of these charged dust particles.