ASU search for water on moon seeks important answers
Researcher Craig Hardgrove explains science behind NASA mission that marked university as major player in space exploration
Arizona State University’s NASA mission to visit a metal asteroid is just beginning, but the first mission that marked the school as a major player in space exploration has been under way for more than a year.
LunaH-Map, the Lunar Hydrogen Polar Mapper, will launch in September 2018. Its task will be to find water and ice at the south pole of the moon, and map the deposits.
ASU Now spoke with principal investigator Craig Hardgrove, an assistant professor in the School of Earth and Space Exploration about the science behind the mission, what will be built on its discoveries, and why there isn’t a hockey rink buried on the moon.
Why look for water and ice on the moon? It can be used for fuel and drinking water in the push to Mars, saving an enormous amount of space and payload weight on spacecraft.
“That’s the geologic question we’re trying to answer about the moon: how much (water and ice) is there on a moderate spatial scale, so we can send a rover and really get at how much water is there,” Hardgrove said.
Scientists aren’t sure about how water and ice appear on the moon. It is likely deposited by two things: solar wind or passing asteroids and comets. Protons from solar wind are implanted into the lunar surface, then they combine with an electron to form a hydrogen atom. The hydrogen atom binds with oxygen and forms hydroxyl atoms.
Asteroids and comets carry water. “Those are dirty ice balls, basically,” Hardgrove said, carrying 50 to 80 percent water. As they get close to the sun, they shed water.
“Those could be passing by, depositing water on bodies like the moon,” he said. “So maybe that’s the explanation for why it’s enriched in certain regions and not others.”
LunaH Map will carry a neutron counter. As it flies over the south pole of the moon, it measures neutrons that leak from the moon’s surface. There’s a base number of counts you’d expect for a dry moon: around 50 parts per million water.
“Very, very dry,” Hardgrove remarked. “At the pole, it’s maybe 200, up to 500 parts per million and in some small regions we know that it’s 5000 to 50,000 parts per million, it’s really enriched. We just don’t know exactly where those regions are.”
No one knows where the hydrogen is, or how much of it is there. And is it all implanted by solar wind? It’s an important geologic question. If it is, maybe the small amounts of hydrogen at the poles have moved around somehow, possibly by meteorite impacts. Maybe the moon’s poles have moved throughout geologic time. Scientists aren’t sure, but hydrogen gets remobilized and concentrated in permanently shadowed craters at the poles.
No one knows how much is there. Hardgrove suspects it’s on the order of a couple hundred parts per million. There isn’t a good answer for why you would get 5,000 parts per million or 50,000 parts per million. That’s around five percent water – a lot for the moon. Certain parts of Mars have that much water – the north pole of Mars is pure ice – but the moon isn’t Mars, and no one knows how that much water appears on the moon.
How would you find out whether the water came from an asteroid or comet, or somehow was inherent to the moon? A rover would have to collect samples and analyze isotope ratios with a mass spectrometer.
The maps LunaH Map will create may be used by NASA to decide where to land a rover to do exactly that.
“We’re talking about identifying regions that are several kilometers wide where hydrogen is enriched,” Hardgrove said. “And then NASA could plan for future missions where you want to land your rover, because now we’re on the scale of the landing ellipse. NASA will know that the hydrogen is somewhere in that patch of ground.”
That mission, called Resource Prospector, is already in the planning stages. It’s going to have to be one of the toughest rovers ever built, because it’s going to dip its toe into one of the coldest places in the solar system, places which have never, ever seen sunlight. Think as low as -400 degrees below Fahrenheit.
Electronics and hardware may not be able to survive. The rover will carry the same instrument LunaH Map will: a neutron detector. What the rover would do is land in the illuminated areas and do what NASA calls “toe dips” into the darkness.
“Resource Prospector could toe dip in, scoop and come back out and do the analysis,” Hardgrove said. “But they’re worried that if they take that sample out, all of the water, if it’s in there, it’s just going to sublimate immediately. So then they have to do their analysis in the dark to figure out how much is actually there, or seal it up somehow. It’s a difficult problem to figure out how to assess what’s really down there, just because it’s some of the coldest parts of the solar system.”
Any ice down there would be bound up somehow with the regolith, the loose dust, dirt, and rock covering the bedrock. It would have to be extracted for human use with some kind of refining process. It won’t be like chipping ice off a cliff and melting it on a winter camping trip. And, while golf has been played on the moon, it is unlikely hockey will enjoy the same privilege.
“We don’t think it’s like an ice skating rink or anything,” Hardgrove said. “That would be a very different method for moon formation than anything we’re familiar with.”
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