Computer Science – Performance
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..705a&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Computer Science
Performance
Scientific paper
The Lunar Ejecta and Meteorites (LEAM) experiment was deployed by the Apollo 17 astronauts in the Taurus-Littrow area of the moon in December 1972. The science objectives of LEAM were (1) to investigate the interplanetary dust flux (primary particles) bombarding the lunar surface; (2) to investigate the properties of the lunar ejecta (secondary) particles; (3) to follow the temporal variability of these fluxes along the lunar orbit; and (4) to observe interstellar particles. The design and expected performance was similar to the dust experiments flown on Pioneers 8 and 9 in heliocentric orbits [1]. They responded to plasma generated by hypervelocity dust impacts. The pulse height generated was a function of mv2.6 of the particle (where m [g] is its mass and v [km/s] is its impact velocity) with a detection threshold of typically m = 10-13 g at v = 25 km s-1. Particle velocity was measured directly by its time of flight between two films spaced 5 cm apart. The LEAM contained three sensor systems. The east sensor was pointed 25° north of east, so that once per lunation its field of view swept into the direction of the interstellar dust flow. The west sensor was pointing in the opposite direction, while the up sensor was parallel to the lunar surface and viewing particles coming from above. Only the west sensor was lacking the front film. It was designed to identify low-speed ejecta impacts that were not expected to penetrate the front film. It soon became evident that most events registered by the sensors had to be attributed not to meteorites or lunar ejecta but to slow moving, highly charged lunar surface dust. Most puzzling were two facts: (1) the event rates increased with the passage of the terminators and (2) the events registered in the front film only and with the maximum possible pulse height. The event rate started to increase up to 60 hours before the local sunrise and persisted after sunrise for about 30-60 hours. In this interval the east sensor's rates were up to 100 times higher than the normal background rates, while the rates of the west and up sensors increased somewhat less. No increased rates were observed during lunar eclipses. Two subsequent studies were performed to support the evidence: a theoretical work to model the response of the electronics [2] and an experimental study of the LEAM flight spare model [3]. The studies had similar conclusions: Extremely slow moving particles (v<100 m s-1) generate a LEAM response up to and including the maximum pulse height if the particles carry a positive charge Q>10-12 C. Both studies suggest that the LEAM events are consistent with the sunrise/sunset-triggered levitation and transport of slow moving, highly charged lunar dust particles.
Auer Stefan
Berg Otto E.
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