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Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

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egy, called Power In that would allow for an earlier insertion into the mapping orbit. The talk summarizes this strategy, showing<br />

on a slide the planned transition orbits. There are shots of the Martian moon, Phobos, taken from the Viking spacecraft, as Ms Dodd<br />

explains that the trajectory will allow the orbiter to make new observations of that moon. She also explains the required steps to<br />

prepare for mapping after the spacecraft has achieved the mapping orbit around Mars. The lecture ends with a picture of Mars<br />

from the Observer on its approach to the planet.<br />

CASI<br />

Orbit Insertion; Spacecraft Orbits; Mars Probes; Earth-Mars Trajectories; Transfer Orbits; Spacecraft Maneuvers; Orbital<br />

Maneuvers<br />

<strong>2000</strong>0064061 Hawaii Univ., Hawaii Inst. of Geophysics <strong>and</strong> Planetology, Honolulu, HI USA<br />

Formation of a Martian Pyroxenite: A Comparative Study of the Nakhlite Meteorites <strong>and</strong> Theo’s Flow<br />

Friedman, R. C., Hawaii Univ., USA; Taylor, G. J., Hawaii Univ., USA; Treiman, A. H., Lunar <strong>and</strong> Planetary Inst., USA; Meteorites<br />

<strong>and</strong> Planetary Science; 1999; <strong>Volume</strong> 34, pp. 919-932; In English<br />

Contract(s)/Grant(s): NAG5-4212; NAGw-3684; NAGw-5098<br />

Report No.(s): SOEST-Publ-4886; HIGP-Publ-1077; Copyright; Avail: Issuing Activity<br />

The unusual composition of the nakhlites, a group of pyroxenitic martian meteorites with young ages, presents an opportunity<br />

to learn about nonbasaltic magmatic activity on another planet. However, the limited number of these meteorites makes unraveling<br />

their history difficult. A promising terrestrial analog for the formation of the nakhlites is Theo’s Flow in Ontario, Canada. This<br />

atypical, 120 m-thick flow differentiated in place, forming distinct layered lithologies of peridotite, pyroxenite, <strong>and</strong> gabbro.<br />

Theo’s pyroxenite <strong>and</strong> the nakhlites share strikingly similar petrographies, with concentrated euhedral to subhedral augite grains<br />

set in a plagioclase-rich matrix. These two suites of rocks also share specific petrologic features, mineral <strong>and</strong> whole-rock compositional<br />

features, <strong>and</strong> size <strong>and</strong> spatial distributions of cumulus grains. The numerous similarities suggest that the nakhlites formed<br />

by a similar mechanism in a surface lava flow or shallow intrusion. Their formation could have involved settling of crystals in<br />

a phenocryst-laden flow or in situ nucleation <strong>and</strong> growth of pyroxenes in an ultramafic lava flow. The latter case is more likely<br />

<strong>and</strong> requires steady-state nucleation <strong>and</strong> growth of clusters of pyroxene grains (<strong>and</strong> olivine in the nakhlites), circulating in a<br />

strongly convecting melt pool, followed by settling <strong>and</strong> continued growth in a thickening cumulate pile. Trapped pockets of intercumulus<br />

liquid in the pile gradually evolved, finally growing Fe-enriched rims on cumulus grains. With sufficient evolution, the<br />

melt reached plagioclase supersaturation, causing rapid growth of plagioclase sprays <strong>and</strong> late-stage mesostasis growth.<br />

Author<br />

Meteorites; Peridotite; Pyroxenes; Mineralogy; Nakhlites<br />

<strong>2000</strong>0064115 Washington Univ., Dept. of Earth <strong>and</strong> Planetary Sciences, Saint Louis, MO USA<br />

Geology of the Smythii <strong>and</strong> Marginis Region of the Moon: Using Integrated Remotely Sensed Data<br />

Gillis, Jeffrey J., Washington Univ., USA; Spudis, Paul D., Lunar <strong>and</strong> Planetary Inst., USA; Journal of Geophysical Research;<br />

Feb. 25, <strong>2000</strong>; ISSN 0148-0227; <strong>Volume</strong> 105, No. E2, pp. 4217-4233; In English; Original contains color illustrations<br />

Contract(s)/Grant(s): NAG5-6784<br />

Report No.(s): Paper 1999JE001111; LPI-Contrib-985; Copyright; Avail: Issuing Activity<br />

We characterized the diverse <strong>and</strong> complex geology of the eastern limb region of the Moon using a trio of remote-sensing data<br />

sets: Clementine, Lunar Prospector, <strong>and</strong> Apollo. On the basis of Clementine-derived iron <strong>and</strong> titanium maps we classify the highl<strong>and</strong>s<br />

into low-iron (3-6 wt % FeO) <strong>and</strong> high-iron (6-9 wt % FeO) units. The association of the latter with basalt deposits west<br />

of Smythii basin suggests that the highl<strong>and</strong> chemical variation is the result of mixing between basalt <strong>and</strong> highl<strong>and</strong> lithologies. Mare<br />

Smythii <strong>and</strong> Mare Marginis soils are compositionally similar, containing moderate iron (15-18 wt % FeO) <strong>and</strong> titanium (2.5-3.5<br />

wt % TiO2). Smythii basin, in addition to the basalt deposits, contains an older, moderate-albedo plains unit. Our investigation<br />

reveals that the dark basin plains unit has a distinct albedo, chemistry, <strong>and</strong> surface texture <strong>and</strong> formed as a result of impact-mixing<br />

between highl<strong>and</strong> <strong>and</strong> mare lithologies in approximately equal proportions. Clementine iron <strong>and</strong> maturity maps show that swirls<br />

along the northern margin of Mare Marginis have the same iron composition as the surrounding nonswirl material <strong>and</strong> indicate<br />

that the swirl material is bright because of its low agglutinate content. Gravity data for the eastern limb show high, positive Bouguer<br />

gravity anomalies for areas of thin basalt cover (e.g., Smythii basin <strong>and</strong> complex craters Joliot, Lomonosov, <strong>and</strong> Neper). We<br />

deduce that the uplift of dense mantle material is the primary (<strong>and</strong> mare basaltic fill the secondary) source for generating the concentration<br />

of mass beneath large craters <strong>and</strong> basins.<br />

Author<br />

Moon; Remote Sensing; Lunar Geology; Lunar Soil; Lunar Composition<br />

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