After two months of checkout and calibration, NASA's $504 million Lunar Reconnaissance Orbiter was maneuvered into a circular 31-mile-high mapping orbit Tuesday, and scientists said Thursday the spacecraft's instruments are delivering intriguing clues about the possible presence of water ice.
"The moon is starting to reveal her secrets, but some of those secrets are tantalizingly complex," said Michael Wargo, NASA's chief lunar scientist.
Scientists expected the spacecraft to find signs of hydrogen--an indicator of possible water ice deposits--in permanently shadowed craters near the moon's south pole. Ice could be expected from cometary impacts over the past few billion years.
Indeed, one of LRO's instruments shows the temperature in such craters never rises above about 33 kelvin, or minus 400 degrees Fahrenheit. But in a surprise, the spacecraft is detecting signs of hydrogen both inside and outside of such craters.
The observations confirm "there is hydrogen near the lunar south polar region," said Project Scientist Richard Vondrak. "What it also seems to indicate is that the hydrogen is not confined to permanently shadowed craters. Some of the permanently shadowed craters do indeed contain hydrogen. Others, on the other hand, do not appear to have hydrogen. And in addition, there appear to be concentrations of hydrogen that are not confined to the permanently shadowed regions."
Water ice cannot exist in direct sunlight on the surface of the moon.
"However, it can exist below the surface even if the surface is warm," Vondrak said. "So you may have had water deposited, or some other hydrogen-bearing compound like methane or ammonia, that was deposited from a comet or some other event and then was promptly buried.
"And so you could have this buried hydrogen that then would be lasting for long, long periods of time. It would be very durable there. What we don't know is the abundance and how deep it is buried."
The issue is of critical importance to scientists and engineers who envision someday building permanent research stations on the moon, using solar power to break down mined water ice to provide oxygen, water, and hydrogen rocket fuel. Scientists do not yet know if water ice is, in fact, mixed in with the moon's upper soil, only that hydrogen-bearing material of some sort seems to be present.
Equipped with seven state-of-the-art cameras and other instruments, LRO was built to look for suitable landing sites for future manned missions while creating the most detailed lunar atlas ever assembled.
The 4,200-pound solar-powered spacecraft also will measure the solar and cosmic radiation that future lunar explorers will face and map out the surface topology, mineralogy, and chemical composition of Earth's nearest neighbor. One year will be spent scouting future landing sites followed by three years of purely scientific observations.
LRO was launched by an Atlas 5 rocket from the Cape Canaveral Air Force Station in Florida on June 18 along with a companion spacecraft, the $79 million Lunar Crater Observation and Sensing Satellite, or LCROSS. The two spacecraft separated shortly after launch.
LCROSS is designed to guide the Atlas 5's spent Centaur second stage to an impact in a permanently shadowed crater near the moon's south pole on October 9. Instruments aboard LCROSS, LRO, the Hubble Space Telescope, and at observatories on Earth will study the debris thrown up by the crash to look for evidence of ice.
"It could be water, it could be methane, it could by hydrocarbons or organics," said LCROSS Project Manager Dan Andrews. "And so actually from a scientific standpoint, this is incredibly important. Whatever the moon has collected over the last three-and-a-half billion years in terms of water, organics, materials from comets, asteroids, the sun, could be trapped in these pockets on the moon.
"It's a time capsule, it's a window into the past of the entire inner solar system, of Earth," he said. "I see LCROSS and LRO combined as a gateway, a pathfinder to truly understanding even the origins of volatiles, of water, in the inner solar system. The moon is right there, it's right next to us, we can go there much more easily than a lot of other places and make these studies."
LRO Project Manager Craig Tooley said the lunar orbiter is operating in near flawless fashion, with all seven of its instruments now activated and trained on the moon. The craft was maneuvered from its initially elliptical commissioning orbit into a 31-mile-high circular orbit last Tuesday with a three-minute rocket firing over the south pole.
"Commissioning is now complete and all of our seven instruments as well as our spacecraft (are) essentially performing flawlessly," he said Thursday. "So we are certainly ready to proceed on into the mission."