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NASA moon orbiter begins two-year science mission

Posted: September 20, 2010

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As NASA shifts its focus away from moon as the next destination for human space travelers, the agency's lunar orbiter has completed a long-planned transition from an exploration to a scientific mission.

Artist's concept of LRO. Credit: NASA
Command of the Lunar Reconnaissance Orbiter was handed over Thursday from NASA's exploration division to the science directorate, completing a yearlong mission devoted to scouting potential landing sites for future manned and robotic visits.

"LRO is now in the very capable hands of the science mission directorate," said Michael Wargo, the chief lunar scientist in NASA's exploration department.

Wargo said the first phase of LRO's mission was a "spectacular success."

Circling a scant 31 miles above the moon, LRO has catalogued data collections from seven instruments designed to create a chemical and topographic atlas of the lunar surface, search for water ice, and characterize the radiation environment.

LRO will operate for at least the next two years, and officials plan to propose another extension in 2012, assuming the spacecraft and instruments are still in good shape, according to Richard Vondrak, the mission's project scientist at the Goddard Space Flight Center.

"We have resources on-board the spacecraft that could potentially take it quite a bit longer than that," Wargo said.

Scientists say LRO's daily work won't change much over the next two years, but the objectives will be geared toward pure scientific research instead of paving the way for human voyages.

The strategy shift has been planned since LRO's launch in June 2009, before the Obama administration began its push to cancel NASA's plans to return astronauts to the moon.

Under the White House's proposal, which is still being debated in Congress, the space agency would develop human missions to asteroids as a stepping stone to an eventual journey to Mars. The strategy would bypass the moon.

When astronauts do return to the moon, they will be armed with LRO data on resources and terrain hazards.

"The original intention of LRO was to provide the information needed for the continued safe and effective exploration of the moon," Wargo said. "That included identification of hazards, being able to have, in effect, a lunar atlas that is unprecedented in its precision and accuracy."

But a concept to robotically gather samples from a giant impact basin near the moon's south pole and return them to Earth could be the next mission to lean on LRO's findings.

Artist's concept of the MoonRise mission concept. Credit: NASA

One of three candidates for NASA's next medium-class New Frontiers probe, the MoonRise mission would touch down in the moon's South Pole-Aitken Basin, the site of an ancient impact event that carved a cavity more than 1,500 miles wide.

Scientists think the event excavated rock from deep below the lunar surface that could hold clues on the formation of the Earth and the moon. Returning those rocks to a laboratory on Earth could yield untold discoveries, according to researchers.

MoonRise is pitted against probes to Venus and a nearby asteroid. If selected, the MoonRise mission would launch before the end of 2018.

Scientists announced another round of LRO results last week, including observations of the South-Pole Aitken Basin, or SPA.

The orbiter's Diviner payload takes the temperature of the lunar surface and uses infrared sensors to search for rocks and determine their chemical make-up.

So far, Diviner has not found any evidence of exposed rocks from the lunar mantle at SPA, the oldest and deepest impact site on the moon. If there are outcrops of mantle rock inside the crater, they are likely mixed in with other material from the lunar crust.

"The new Diviner data will help in selecting the appropriate landing sites for potential future robotic missions to return samples from SPA," said Benjamin Greenhagen, a planetary scientist at NASA's Jet Propulsion Laboratory. "We want to use these samples to date the SPA-forming impact and potentially study the lunar mantle, so it's important to use Diviner data to identify areas with minimal mixing."

Researchers last week also announced new findings from LRO's laser altimeter, which sends out pulses of light and measures their returns to construct precise maps of lunar terrain.

The instrument surveyed 5,000 craters across the moon and confirmed that older highland regions show more scarring from large comet and asteroid collisions, indicating the most massive impacts occurred in the early history of the moon.

The question is when the largest impacts stopped occurring.

A topographic map of the Orientale impact basin. Credit: NASA/Goddard/MIT/Brown
According to James Head, a professor of geological sciences at Brown University, the expansive Orientale impact basin formed 3.8 billion years ago was a turning point in lunar history. Only smaller, younger craters lie inside Orientale's ejecta field.

"Using the crater counts from the different impact basins and examining the populations making up the superposed craters, we can look back in time to discover when this transition in impactor populations occurred," Head said.

The moon's crater record is an important analog for what Earth experienced in the same period. Most ancient craters on Earth have eroded beyond detection.

The laser altimeter is also crucial in the search for boulders and rocks that could pose safety risks for future landers.

"It's providing the information necessary for planning additional missions, whether they be robotic or a crewed return to the moon," Wargo said.

The discoveries announced last week address the moon's bombardment history and surface-shaping geological processes, two of the top five science objectives for LRO's research mission.

They give LRO a "running start" on its science mission, according to Vondrak.