BOULDER, Colo. — Think of it as some sort of extraterrestrial axiom: Look for places on a celestial body where the sun doesn’t shine.
NASA planners are now orchestrating America’s return to the moon, with many experts hoping to hang their space helmet on the likelihood that ice is stored within permanently shadowed craters at the lunar poles.
Just one look is all it takes to see that the moon has natural "beauty marks" — a landscape peppered by meteorites, micrometeorites and comets.
Most of these impactors showered water ice on the moon. Any of that ice surviving those cosmic crashes would be strewn across the lunar landscape and rapidly vaporize. But some of that ice — even down to individual molecules — could have wound up trapped inside supercold, permanently shadowed lunar craters.
Such an ice resource is considered invaluable if processed to create life-sustaining oxygen and water, even transformed into rocket fuel for propelling spacecraft beyond the moon. However, whether or not this material — spotted by lunar orbiters of years past — is actually water ice or hydrogen is open to question.
If, indeed, appreciable near-surface water ice is resident in polar "cold traps" on the moon, it would be a storehouse of scientific knowledge as well as a resource bonanza.
Early this year, President Bush spelled out a strategy for space exploration beyond low Earth orbit. For the moon, the White House marching orders to NASA were:
- Undertake lunar exploration activities to enable sustained human and robotic exploration of Mars and more distant destinations in the solar system.
- Starting no later than 2008, initiate a series of robotic missions to the moon to prepare for and support future human exploration activities.
- Conduct the first extended human expedition to the lunar surface as early as 2015, but no later than the year 2020.
- Use lunar exploration activities to further science, and to develop and test new approaches, technologies and systems, including use of lunar and other space resources, to support sustained human space exploration to Mars and other destinations.
NASA strategists have already begun pointing to the lunar south pole and its possible stockroom of ice as the place of choice for an initial encampment of explorers.
Nailing the lunar ice story
As a first robotic step back to the moon, NASA is moving out on the Lunar Reconnaissance Orbiter, or LRO, and will soon announce the scientific payload this craft will carry. The planning date for LRO launch is Oct. 15, 2008.
"In my view the LRO payload will ‘nail’ the lunar ice story as best one can do from orbit, and pave the way for a surface-based follow-on," said Jim Garvin, NASA chief scientist in Washington.
LRO’s powerful payload will enable different measurement approaches that can address the issue of lunar ice in the upper few feet of lunar topside, Garvin told Space.com.
"We need a chemical fingerprint," said Alan Stern, a planetary scientist and director of the Southwest Research Institute's Department of Space Studies in Boulder. "If there is water ice in the proportions earlier spacecraft data indicated, and I stress ‘if’ … that would be very exciting for exploration and science."
Stern said the ice would have come from meteoritic and cometary sources, or it might have been created by reaction in the lunar soil. LRO and its battery of instruments can basically get at the answer, but it’s clear that the true tale won’t come from any one sensor, he said.
Given independent sensor techniques with different strengths, "LRO can be the definitive mission for both finding and mapping the distribution of lunar ice with enough confidence to send landers/rovers down to specific ice deposits for more detailed study," Stern said.
Delving into water ice by going to the moon may be like getting a comet sample return, Stern said. "It would be sort of a meta-comet sample return if you find significant quantities."
Perhaps by coring down through layers of lunar ice and finding layers, the probe could find the signatures of different impacts with different parent bodies, Stern suggested. "So that could be very valuable scientifically in terms of understanding comets … which are, of course, relics from the formative days of our solar system. But from an exploration standpoint, it’s about producing water for humans and rocket engines," he added.
Europe has already got a jump start on pinpointing what might be lurking in those sun-shy craters. Now looping the moon is the European Space Agency’s SMART-1 probe.
"SMART-1 is equipped with sensors to peek in the permanent night at the bottom of polar craters," said Bernard Foing, ESA’s chief scientist and SMART-1 project scientist.
Foing said SMART-1 ground controllers will use the spacecraft to peer into dark polar targets with sensors for far longer periods of exposure time than for illuminated parts of the moon. "Even though there is no direct sunlight, the light reflected from the rims of craters could amount to 50 Earthshine … so this could be measurable," he said.
Using SMART-1’s advanced multicolor micro-camera, Foing continued, that device will map and look for albedo variations inside shadowed craters. Albedo is the fraction of light that is reflected by a body or surface.
By employing SMART-1’s Infrared Spectrometer, Foing said, a search for the "specific spectral fingerprint of water ice" is also scheduled.
"If there are water layers trapped from bombardments from comets and water-rich asteroids, a core in lunar ice would give us access to a unique historical record of ice, volatiles and possibly organics that were delivered to the Earth-moon system," Foing noted.
"If there is not enough water ice there but only enhanced solar wind hydrogen,
future exploration will rely on combining H and O, to make H2O water … like we
do in the chemistry classroom," Foing suggested. "This artificial water might be cleaner to drink than cometary melt!"
Ice picks in the tool kit
There are several science questions that can be addressed by the ability to conduct on-the-spot analyses of ice deposits in the lunar poles, said Ben Bussey, a lunar expert at the John Hopkins University Applied Physics Laboratory in Laurel, Md.
"There is uncertainty as to what is the physical nature of any ice deposit. One scenario is that essentially you have layers with different ice concentrations separated by dry regolith. If this is the case then a core sample would provide information on the impact history of the Earth-moon system," Bussey pointed out.
Bussey said that geochemical analyses of ice deposits will provide information on the composition of the impacting bodies. Analysis of isotopic ratios of that material should indicate approximately where in the solar system the impactor originated, he said.
While not directly targeted to an on-the-ground study of lunar ice, a moon landing mission is being assessed by NASA. It could serve as a template for robot landers armed with ice picks in their tool kit.
NASA is reviewing a New Frontiers project dubbed Moonrise — a lunar South Pole-Aitken Basin sample return mission. Michael Duke is principal investigator for Moonrise, based at the Colorado School of Mines in Golden.
Moonrise would involve two identical landers on the surface near the moon's south pole and the return of about 5 pounds (over 2 kilograms) of lunar materials from a region of the moon's surface believed to harbor materials from the mantle of our celestial neighbor, Duke explained.
If Moonrise gets the go-ahead, this mission must be ready for launch no later than June
30, 2010, within a mission cost cap of $700 million.
Be it trapped water ice or hydrogen, it’s all good news from the Moon.
That’s the stance of Alan Binder, director of the Lunar Research Institute in Tucson, Ariz. He was the principal investigator for Lunar Prospector, a NASA Discovery mission launched in January 1998 that operated in lunar orbit for 19 months.
Lunar Prospector found quantities of hydrogen at both the north and south lunar poles. That finding seemed to back data gleaned a few years earlier by the Pentagon’s Clementine moon probe. Scientists on the project contend that Clementine revealed the presence of ice at the bottom of a permanently shadowed crater near the moon's south pole.
"Until we go down on the surface, so to speak, and get absolute confirmation, we can only say that Lunar Prospector found large amounts of hydrogen on the moon," Binder said.
"It’s totally irrelevant what form the hydrogen is in … whether it’s solar wind-implanted hydrogen or whether it is water. We just have to know what equipment to take. That’s because you harvest solar-wind hydrogen one way and you harvest the water ice another way. It’s still good news," Binder explained.
"In both cases, it’s the hydrogen that is the valuable thing," Binder concluded, "because there’s plenty of oxygen around. We know that you can crack the rocks and get the metal and oxygen out."