Date: February 6, 2012
Title: A Frosty Moon
Podcasters: Nancy Atkinson with Dr. Randy Gladstone
Organization: NASA Lunar Science Institute
The previous podcast about the lunar ionosphere referenced by Dr. Gladstone:
Music: “Amelia” by Ben Bedford from his “Land of the Shadows” CD. http://benbedford.com/
Description: There’s even more water on the Moon, now with a frosty flavor! Over the past couple of years, spacecraft observations have been helping scientists re-write the book on our understanding of the Moon, especially in recognizing water, found in various forms on the lunar surface and subsurface. The latest frosty news comes from the Lyman Alpha Mapping Project or the LAMP instrument aboard NASA’s Lunar Reconnaissance Orbiter. Joining us today to tell us more is Dr. Randy Gladstone from the Southwest Research Institute who is on the science team for LAMP.
Bios: The NLSI brings together leading lunar scientists from around the world to further NASA lunar science and exploration.
Dr. Randy Gladstone is a scientist at the Southwest Research Institute in the SwRI Space Science and Engineering Division.
Nancy Atkinson is a science journalist and is the Senior Editor for Universe Today http://www.universetoday.com.
Sponsor: This episode of the “365 Days of Astronomy” podcast is sponsored anonymously and is dedicated to the international dark-sky association www.darksky.org.
Nancy Atkinson: There’s even more water on the Moon! Hi, this is Nancy Atkinson for the NASA Lunar Science Institute. Over the past couple of years, spacecraft observations have been helping scientists re-write the book on our understanding of the Moon, especially in recognizing water, found in various forms on the lunar surface and subsurface. The latest frosty news comes from the Lyman Alpha Mapping Project or the LAMP instrument aboard NASA’s Lunar Reconnaissance Orbiter. Joining us today to tell us more is Dr. Randy Gladstone from the Southwest Research Institute who is on the scien team for LAMP. Welcome, Dr. Gladstone and thanks for being with us.
Dr. Randy Gladstone: Thanks, Nancy.
Nancy: Could you tell us about the LAMP instrument on LRO, what it does and how it does it?
Gladstone: Sure. LAMP is what is called an imaging spectrograph, so it work likes a telescope but also has a spectrograph that breaks the light up into different colors. It operates at ultraviolet wavelengths, far shorter than the human eye wavelengths. So, any photons ago into LAMP, we count them one by one. There are not very many of them at those wavelengths, it’s pretty dim but LAMP is able to observe them all and record when it saw them and where they came from. So it is able to not only break the light up into colors, but to see spatially where the light is coming from .
Nancy: LAMP has been looking into deep dark craters on the Moon with its ultraviolet eyes. What has it been seeing?
Gladstone: Ah, well, it is designed it specifically the to concentrate on Lyman alpha light which is the light that hydrogen atoms like to admit. Again this is much shorter than eyes can see but there’s a lot of hydrogen in the universe including a hydrogen wind from interstellar space that blows through the solar system and the Sun shining on these hydrogen atoms lights up the night sky quite a bit. If you could see Lyman alpha you could see it never gets really dark; it only gets like twilight brightness, so that’s why we picked that wavelike to look in the permanently shadowed regions because it provides an illumination source for looking inside these dark craters that never see sunlight. And when we did that, again because there are so few of these photos so we have count them for a long time, so we’ve been looking at these permanently shadowed regions every orbit of the Lunar Reconnaissance Orbiter which is about hundred and 13 minutes, a little under two hours, but we’ve been adding up photons from LAMP for the last couple years of this mission in order to get enough to build up a map.
Nancy: And what are you finding as far as water?
Gladstone: Well, the interesting thing is that these permanently shadowed craters seem to be a lot darker; less reflective in these wavelengths in the ultraviolet than the region right outside the crater that sees some sunlight occasionally with the seasons. The one thing that sort of indicates is that the soil in these permanently shadowed regions is fluffier. Now another thing we see we also use besides the Lyman alpha from the interstellar hydrogen wind blowing through solar system, we also just use regular stars — the stars are bright at Lyman Alpha wavelengths and longer wavelengths, too. The stars shine all the time on the night side and into the permanently shadowed regions and using the starlight we found that the color at the ultraviolet wavelike is a little brighter, the longer ultraviolet wavelengths, than it is at Lyman Alpha. That indicates to us, it seems the most likely explanation for that is a little bit of water frost of the surface, like one or two percent — nothing you’d really notice, but one or two percent of the soil has water frost in it, right at the surface and that makes the reflection of the soil a little brighter at the longer ultraviolet wavelengths — just a little bit.
Nancy: So is findings frost on the Moon pretty surprising?
Gladstone: It was a little surprising, but not entirely because that’s what LAMP was designed to look. We planned to go look for this but we didn’t really think that we would see much because, again, this Lyman alpha light, the same light source that we were using destroys water on the surface, usually. It breaks apart the water molecules and destroys and frost that is there, and it was thought this should happen at a fast enough rate that frost shouldn’t accumulate in these permanently shadowed regions. But it turns out it isn’t quite so fast; it’s about you 15 times slower than we originally thought and that is based on lab work that has been done shining ultraviolet light on frost and seeing how it breaks up. So, these earlier estimates that people had used were kind of overestimating how short a lifetime frost would have on the Moon’s surface. So we were a little surprised but when we went back and looked at these rates, it turned out that it was possible for frost accumulate in these permanently shadowed regions.
Nancy: The “fluffy” type soils that LAMP is finding is reminiscent of the description by the LCROSS team, the Lunar Crater Observation and Sensing Satellite mission from 2009, of the type of regolith that the LCROSS spacecraft found when the impactor slammed into a crater at the lunar south pole. The scientists described the regolith there as “fluffy,” as well. Have you been able to bring together the findings between the two missions and start to figure out what that combination tells you about the Moon?
Gladstone: It is interesting, it does seem like those two measurements are consistent, the two permanently shadowed regions seemed to have fluffy or porous soil in them. This is indirect evidence from us and from them, the LCROSS mission, but it’s consistent with what we would expect. In an earlier podcast that you had with Bill Farrell about the lunar ionosphere, he talked about the electric fields that get generated at the terminator of the Moon and how that can levitate dust and in thesepermanently shadowed regions when the dust comes back down, it can create what has been called fairy castle structures that are fluffy and so that is sort of my gut feeling, that there’s those kinds of structure in these permanently shadowed regions is sort of elaborate, fluffy soils there.
Nancy: Fairy castles and frost on the Moon is certainly not something we were thinking of forty years ago when the Apollo missions went to the Moon! So, all this water that’s been found on the Moon recently is a departure from the thinking of the past 40 years that the Moon was bone dry what are the feelings of lunar scientists — are you all of you excited, baffled, or perplexed? What’s the general consensus on all of these new findings
Gladstone: Well, personally I still think of the Moon is still being bone dry but there are these little regions, the permanently shadowed regions are really, really fascinating. They have them on Mercury too, and it’s just because of the peculiar spin axis of the these two bodies that these craters of the North and South pole of Mercury and the Moon are never able to see the Sun, and that makes them get very, very cold and what happens is that anything that hits them sticks. So, water that lands there after bouncing around on the surface of the Moon, a water molecule hits one of these permanently shadowed regions, and then it sticks. But anything that is bouncing around sticks, too. And this has been predicted for long time that we would find a lot of volatiles there. During the LCROSS impact our instrument actually a found Mercury coming out of that soil too. So there is more than just water there, there is probably all kinds of things collected there over a billion years that these things have been stable.
So yeah, I’m very excited by these findings and I think that a next mission or something for NASA to try would be to go to one of these permanently shadowed regions and dig in the soil, like a core sample and measure the volatiles that comes out of the soil is you warm it up.
Nancy: So what’s next for the lamp instrument and your team?
Gladstone: LAMP is still looking, mapping out and trying to better signal-to-noise, to make better maps basically, of the entire Moon. We are also looking off more and more now that the LRO mission is run by the Science Directorate at NASA, originally it was run by the Exploration Directorate and our job was to map out the possible resources of the polar regions for a future Moon base. But now it is run by NASA science directorate, we get to do less exploration oriented science, so one of the things are looking for is the lunar atmosphere. So we normally point straight down at underneath, strait down at the nadir, but to look at the atmosphere it is better to look sort of tangentially along the surface towards the horizon so we’re doing that more and more and looking for gases that are on Moon. They are very, very tenuous as another podcast said. The Moon doesn’t really have an atmosphere; it is more like an exosphere. There are just a few gas molecules bouncing around and they don’t even collide with one another. We are looking for those. We think we’ve seen helium gas around the Moon which is has been seen before. And we’re looking for argon which has also been seen before, but we haven’t seen yet, so we’re still trying see how that atmosphere varies from place to place on the Moon and what makes it come and go, things like that.
Nancy: Thanks again to Dr. Randy Gladstone from the Southwest research Institute for sharing the latest findings from the lamp instrument for more information check out the lamp website at www.boulder.swri.edu/lamp
End of podcast:
365 Days of Astronomy
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