Selected microprobe analysis of the Morasko meteorite and micrometeorites
(in per cent) Meteorite Kamacite Taenite O Si S 0.02 0.01 Fe 95.42 80.49 Ni 6.49 18.08 Mg Al Mn Total 101.1 98.6 [Fe.sub.3][0.sub.4] Fe00H Micrometeorites
with low Ni content Sample 3/11 Sample PS/40 O 1.35 0.005 Si 1.18 0.004 S 0.01 0.001 Fe 55.93 62.97 Ni 0.001 0.001 Mg Al Mn Total 58.47 * 62.98 * [Fe.sub.3][0.sub.4] 77.2 86.9 Fe00H 88.9 100.1 Micrometeorite
with high Ni content Sample 4/KKH O 6.77 Si 0.64 S Fe 87.04 Ni 4.66 Mg 0.05 Al 0.57 Mn 0.27 Total 100.0 [Fe.sub.3][0.sub.4] Fe00H * OH and O bounded with Fe were not analysed
A RECENT EUROPEAN STUDY has confirmed that a silent cosmic rain of micrometeorites
is falling on us.
Using a model of impact delivery and a known estimate of micrometeorite
flux at Mercury, Bruck Syal was able to estimate how often cometary material would impact Mercury, how much carbon would stick to Mercury's surface, and how much would be thrown back into space.
Hemenway of Dudley Observatory pioneered studies like this one, but the origins of many micrometeorites
The researchers also identified micrometeorite
damage and the breakdown of Teflon mountings, which may have left deposits on the back of the reflector.
Fortunately, 3 billion years of micrometeorite
bombardments have eroded the rough flows into smooth rolling plains.
Rather, the smoothness may stem from micrometeorite
Second, if it's punctured by a micrometeorite
, the holes will be unlikely to line up in such a way that sunlight will scatter onto the primary mirror.
The NASA researcher notes that magnesium fluoride coatings exposed to natural radiation in space during 10 months of the five-year Long-Duration Exposure Facility (LDEF) mission (SN: 11/11/89, p.314) showed only minor degradation -- consistent with micrometeorite
and atmospheric contaminants but not with instrinsic radiation damage, he says.
While chondritic fragments are the most abundant type of micrometeorite
, scientists previously had thought that unmelted grains were extremely rare.
Among these agencies are agitation by micrometeorite
impacts, electrostatic effects, and evaporation-condensation cycles.
Moreover, crystalline water ice typically lasts only 10 million years before it's destroyed, which points to possible resurfacing, perhaps by micrometeorite
impacts converting existing surface ices to crystalline form by flash-heating.