LPOD-Feb6-08

CIRCLES GALORE

image from Herb Frey, NASA Goddard Space Flight Center. The middle globe is centered at 0° longitude, the left globe at 120°W, and the right is at 240°W.

The lunar surface is the culmination of everything that has happened to it over the last 4.5 billion years. The earliest intense period of cratering is preserved only in the highlands and even there younger craters obscure the older ones. The oldest craters on the Moon that are still detectable are the large impact basins. From examination of Apollo, Orbiter and terrestrial images about 45 basins have been identified. Now NASA scientist Herb Frey has found another possible 47 basins using a technique he perfected in studying the ancient history of Mars. On that planet the MOLA laser altimeter provided such a dense mesh of elevations that ancient basins could be detected as broad depressions even though nothing was visible in the morphology. There isn't a similar topographic grid for the Moon so Herb made do with the best we have. And that is the Unified Lunar Control Net which is a less precise, more widely spaced grid. These three views show in solid circles the known basins and newly discovered ones as dashed. Do you see the prominent basins on the Earth-facing side: Imbrium, Serenitatis, Crisium and Humorum? There are only a few new basins on the nearside - especially in Procellarum, but many on the farside. If these ancient basins are confirmed with the greatly improved altimetry data coming from the Chinese and Japanese lunar orbiters, they will provide new inputs about the deep history of the Moon.

Chuck Wood

Related Links
Today the abstracts from the March 2008 Lunar and Planetary Science Conference went online. There are many 2 page abstracts about the Moon.

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