New high-res maps suggest little water in moon

by Anne Minard on February 12, 2009

Lunar global topographic map obtained from Kaguya (SELENE) altimetry data shown in Hammer equal-area projection. Credit: Hiroshi Araki et al. 2009

Lunar global topographic map obtained from Kaguya (SELENE) altimetry data shown in Hammer equal-area projection. Credit: Hiroshi Araki et al. 2009

New maps of the moon from Japan’s Kaguya (SELENE) satellite suggest a lunar surface too rigid to allow for any liquid water, even deep below.

The new view is unveiled in one of three new papers in this week’s issue of the journal Science based on Kaguya (SELENE) data. In it, lead author Hiroshi Araki, from the National Astronomical Observatory of Japan, and international colleagues report that the Moon’s crust seems to be relatively rigid compared to Earth’s and may therefore lack water and other readily evaporating compounds. The new map is the most detailed ever created of the Moon, and reveals never-before-seen craters at the lunar poles.

“The surface can tell us a lot about what’s happening inside the Moon, but until now mapping has been very limited,” said C.K. Shum, professor of earth sciences at Ohio State University, and a study co-author. “For instance, with this new high-resolution map, we can confirm that there is very little water on the Moon today, even deep in the interior. And we can use that information to think about water on other planets, including Mars.”

Using the laser altimeter (LALT) instrument on board the Japanese Selenological and Engineering Explorer (SELENE) satellite, Araki and his colleagues mapped the Moon at an unprecedented 15-kilometer (9-mile) resolution. The map is the first to cover the Moon from pole to pole, with detailed measures of surface topography, on the dark side of the moon as well as the near side. The highest point — on the rim of the Dririchlet-Jackson basin near the equator — rises 11 kilometers (more than 6.5 miles) high, while the lowest point — the bottom of Antoniadi crater near the south pole — rests 9 kilometers (more than 5.5 miles) deep. In part, the new map will serve as a guide for future lunar rovers, which will scour the surface for geological resources.

But the team did something more with the map: they measured the roughness of the lunar surface, and used that information to calculate the stiffness of the crust. If water flowed beneath the lunar surface, the crust would be somewhat flexible, but it isn’t, the authors say. They add that the surface is too rigid to allow for any liquid water, even deep within the Moon. Earth’s surface is more flexible, by contrast, with the surface rising or falling as water flows above or below ground. Even Earth’s plate tectonics is due in part to water lubricating the crust.

Araki and his team say Mars, on a scale of surface roughness, falls somewhere between the Earth and the Moon — which suggests there may have once been liquid water, but that the surface is now very dry.

In the second Kaguya/SELENE study, lead author Takayuki Ono of Japan’s Tohoku University and colleagues describe debris layers between the near-side basalt flows, which suggest a possible period of reduced volcanism in the Moon’s early history. They propose that global cooling was probably a dominant driver of the shaping of lunar maria on the moon’s near side starting about 3 billion years ago. 

The third paper was authored by Noriyuki Namiki of Japan’s Kyushu University and his colleagues, who report gravity anomalies across the Moon’s far side indicating a rigid crust on the far side of the early Moon, and a more pliable one on the near side.

Source: Science

Polar topographic maps obtained from Kaguya (SELENE) altimetry data. Credit: Hiroshi Araki et al. 2009

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