Shooting The Moon: A high-tech look at lunar topography
The Moon is typically seen bathed in the white light of the sun. Like Earth viewed from above, in its full state it looks like a perfect sphere, as smooth as a snooker ball. In fact, as scientists from Arizona State University in Tempe have just revealed in a high-resolution Moon map, it has a topography that is as varied and in places extreme as anything on our planet.
In the course of its monthly elliptical orbit, the Moon moves around Earth at an average distance of roughly a quarter of a million miles. Space is a harsh environment, and the Moon has virtually no atmosphere, extremes of temperature (from -233°C at night to +123°C in the day), and no human presence—which makes mapping it tricky.
To do it, the multinational team behind this image first designed a new Wide Angled Camera (WAC) capable of withstanding the vicissitudes of outer space. They then hitched a lift for it on a spacecraft: the Lunar Reconnaissance Orbiter (LRO), which was launched by NASA in 2009 and has already gone beyond its initial mission to spend a year in close orbit of the Moon. The palm-sized WAC was mounted on the LRO, which flies at an average altitude of 50km (30 miles) above the Moon’s surface. Each picture it takes covers a swathe 70km wide.
As the LRO is constantly circumnavigating the Moon, with each orbit 30km (in ground distance) from the last, the pictures it takes overlap, giving a stereo view of almost every patch of lunar ground, every month. About 69,000 of these images were sent back and fed into a computer, which used them to build an accurate model of almost all the terrain. The bits at extreme latitudes that the WAC couldn’t survey—the holes at the poles—were covered by another laser instrument on board, known as LOLA (Lunar Orbiter Laser Altimeter).
But it was only when the models were shaded, to give a sense of the relief, and coloured in with different altitudes shown by different colours, that the topography was transformed into a living landscape—of craters, mountains and the vast basalt plains that early astronomers mistook for seas and lakes. “I could not be more pleased with the quality of the map,” said Mark Robinson, who heads the Arizona team. “It’s phenomenal. The richness of detail should inspire lunar geologists around the world for years to come.”