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LRO hints at water on Moon
Posted: September 18, 2009

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NASA's Lunar Reconnaissance Orbiter, LRO, has entered its mapping orbit of the Moon and has already found evidence that hints at widespread hydrogen, and water frost at the south pole.

Neutron flux detections around the lunar south pole from LEND. Image: NASA/Institute for Space Research (Moscow).

LRO is scheduled for a one year primary mission in a polar orbit at roughly 50 kilometres altitude, during which time it will produce the most detailed atlas of the lunar surface and search for resources and safe landing sites for human explorers. “The LRO mission already has begun to give us new data that will lead to a vastly improved atlas of the lunar south pole and advance our capability for human exploration and scientific benefit,” says Richard Vondrak, LRO project scientist at NASA’s Goddard Space Flight Center.

The south pole of the Moon is of great interest because it is strongly believed that water ice exists in the permanently shadowed craters there, brought to the Moon billions of years ago by cometary impacts. First measurements from LRO's Diviner instrument reveal that large areas in the permanently shadowed craters register temperatures of just 33 Kelvin, more than cold enough to store water ice or hydrogen for billions of years, and making them some of the coldest places in the Solar System.

Daytime (left) and nighttime temperatures (right) at the lunar south pole as recorded by Diviner. Purple indicates lowest temperatures (around 40 K) and red to white highest temperatures (400 K). Image: NASA/UCLA.

First results from LRO’s Lunar Exploration Neutron Detector (LEND) – a neutron spectrometer that relies on a decrease in neutron radiation from the lunar surface to indicate the presence of water or hydrogen – supports this hypothesis, and furthermore found evidence for hydrogen all over the Moon. “The surprising thing about the LEND observations is that it indicates that hydrogen is not just confined to permanently shadowed craters,” said Vondrak in last night's dedicated press conference to announce LRO's first results. “Hydrogen cannot exist on its own on the surface in the warmth, but it could exist underground in water, methane or ammonia deposits from comet impacts. What we don't know yet is its abundance or how deeply it is buried.” The accuracy of the hydrogen maps will improve with more observations so scientists will be able to pin down exactly where it is and what form it is in.

LRO’s Lyman Alpha Mapping Project, LAMP, even saw signs of water frost in and around south pole craters including Cabeus A, where the Lunar Crater Observation and Sensing Satellite (LCROSS) will impact on 9 October. LAMP is sensitive to water-ice on the surface and will support LCROSS when LRO passes over Cabaeus A a few minutes after the impact. “LAMP is working well,” says team member Alan Stern. “In fact, LAMP is more sensitive than we expected, which is fantastic.”

Altitude measurements from the LOLA instrument. Image: NASA's Goddard Space Flight Center.

Data from LRO’s Lunar Orbiter Laser Altimeter (LOLA) shows that any future exploration of the terrain at the south pole will be challenging because it is very rough. Using the altimeter to peer into the dark Shackleton crater they discovered very steep slopes of some 30-40 degrees and a craggy floor with ridges 5-10 metres high every 25-50 metres. “It has been in darkness since it formed, 1 to 2 billion years ago,” says LOLA's principal investigator David Smith. “It is treacherous inside, not nice and smooth like we'd prefer it to be [for exploration on the ground].”

This Mini-RF image shows radar imagery of the lunar south pole. Image: NASA/APL/LPI.

As well as searching for resources that could be harnessed by future human explorers, LRO is also characterising the radiation environment of our nearest neighbour. “CRaTER (the Cosmic Ray Telescope for the Effects of Radiation) allows us to get an assessment of the bad guys of long duration missions – space radiation,” says Michael Wargo, NASA chief lunar scientist. During transit to the Moon CRaTER measured high energy charged particles from cosmic rays and solar radiation, gaining count statistics and information on the particles' energies. “It is helping us to understand space radiation. The Moon is beginning to reveal its secrets.”

All of LRO's seven instruments are confirmed as functioning well and by the end of the mission LRO scientists are confident that they will have fully characterised everything about the existence of hydrogen and water at the lunar south pole. “From a science point of view, we would like to understand what the volatile history of the Solar System is, and how they reached the Earth and Moon. Maybe there is a record of this in the permanently shadowed regions,” says Vondrak.

For more information about LRO and LCROSS, be sure to pick up a copy of the October issue of Astronomy Now, onsale in all good newsagents now, or order online here.

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