Published online 23 October 2007 | Nature | doi:10.1038/news.2007.182
Corrected online: 24 October 2007

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The sunniest spot on the Moon

SMART-1 data indicates good spot for lunar base.

This hill (in the box, lower left) gets sunlight in the morning and the evening all through the summer.Courtesy of the researchers

On top of a hill near the south pole of the Moon is a sunny spot that might make the ideal place for a lunar outpost, according to preliminary analysis of data from the European Space Agency (ESA) satellite SMART-1.

Ben Bussey, from the Applied Physics Laboratory in Laurel, Maryland, and colleagues found the spot by looking at images from ESA’s SMART-1 mission, which orbited the Moon for a year and a half before crash-landing there in September 2006. The Advanced Moon micro-Imager Experiment (AMIE) took shots of the Moon's surface throughout SMART-1's mission.

After close analysis, the group found a hill on a ridge to the southwest of Shackleton crater at the south pole, that he says is constantly illuminated during the lunar southern summer. In each summer 'day', as the Moon turns once on its axis with respect to the Sun and orbits the Earth once (that takes just more than 27 Earth days), the hilltop stays firmly in sunshine, Bussey told the International Lunar Exploration Working Group International Conference on Exploration and Utilisation of the Moon in Sorrento, Italy, on 23 October.

“A lunar outpost on this hill would have constant solar energy during the summer.”

Ben Bussey
Applied Physics Laboratory

“I think this is the most illuminated place near the south pole, and potentially the most illuminated place on the Moon,” Bussey says.

The hill makes a great candidate for any future lunar base. “A lunar outpost on this hill would have constant solar energy during the summer,” explains Bussey.

Coupled to that, it’s near to both a region that is known to be in the dark constantly, and to a source of water ice — a useful resource and place of interest for scientists looking for evidence of meteorite impacts and volatile molecules.

Land of the midnight sun

On Earth, the 23° tilt of our axis to the Sun ensures that a large area gets all-day sunlight in the southern summer. On the Moon this angle is only 1.5°, resulting in a smaller area that might experience constant summer light. But it was previously unknown whether mountains, hills or dips in this area might throw shadows that block the sunshine at certain times of day. Alternatively a large hill might peak out of the shadows all year round, to catch a bit of winter light too. Bussey's hill is the best bet for this so far.

Bussey and his colleagues haven't yet analysed AMIE pictures from the southern winter, but he is working on these data now. Identifying the hill of interest in the array of photos is a time-consuming process, he says.

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A 1999 study using data from NASA’s moon-mapping mission Clementine also took photos of this hill, but in low resolution. Snaps from that mission hint that the hill doesn't catch the winter sunlight. But the improvement in resolution with the AMIE data means it is now possible for engineers to look more closely at the topography, and work out where and how to best position solar panels to get the maximum power.

For human habitation, a spot that is lit permanently, all year, would be the ideal. Bussey does not think this is likely anywhere on the Moon. “I think everywhere, unfortunately, gets dark,” he says. 

Corrected:

This article originally implied that Bussey was working alone; the work is instead a team effort.
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