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Posts Tagged ‘Carle Pieters’

More from the AGU: Pink Moon, White Mountains

Friday, December 18th, 2009

 

My last two posts were about the American Geophysical Union meeting, held this week in San Francisco. The meeting is now over, but I’m not done writing about it yet — not by a long shot!

In 1971, Nick Drake recorded a song called “Pink Moon” that became a posthumous hit in 1999 when it appeared in a Volkswagen commercial. Now it turns out that he was really on to something. On Wednesday afternoon, Carle Pieters, the lead scientist for the Moon Mineralogy Mapper on Chandrayaan-1, the Indian spacecraft that circled the moon for ten months, talked about her discovery of a new, magnesium-rich pink spinel.

Well, okay, it isn’t really a pink moon. But if you go to the moon’s far side and land your spacecraft on the edge of the Moscoviense basin — a very attractive place, with one of the few maria on the moon’s far side — she says that you can dig up all the pink spinel that you want.

Because we have never landed anything on the moon’s far side — human, robot, or other — we’ll have to wait a while to find out if she is right. The evidence from the Moon Mineralogy Mapper (M-cubed for short) is a very distinctive spectrum, with no absorption at 1 micron and a “whopping” (Pieters’ technical term) absorption band at 2 microns, that is totally unlike any other known moon rocks but a very good match for pink spinel measured in the laboratory.

Jessica Sunshine also talked about spinel, but hers is very dark, not pink, and is probably mostly chromite. M-cubed found this deposit — also previously unknown — at only one place on the near side of the moon, a region called Sinus Aestuum. Why only there? Dunno. How much is there? Dunno. But this would be a great spot to explore once we start sending robots or astronauts back to the moon. (2015? 2020? 2100? Never?)

The good thing, and the bad thing, about both of these talks is that they were just good ol’ talks about rocks, the sort of things that geologists like to talk about when the press isn’t watching. Lest we forget, M-cubed was not really intended to look for water ice. The whole business about water was really an unexpected bonus. If they had really expected to see water, they would have made the spectrometer sensitive out to 3.6 microns. (3 microns is enough to see the peak absorption bands of hydroxyl and water at 2.7 and 2.8, but not the full spectra.)

Neither Pieters’ nor Sunshine’s findings are going to make headlines, but they are good examples of a scientific instrument doing what it was meant to do, and finding new stuff. The take-home message for non-geologists is just that the moon is not a homogeneous place; it has stuff we haven’t seen before and it most likely has stuff we haven’t even thought of yet. The other message is that all of these discoveries allow us to piece together a few more puzzle pieces to understand lunar geology.

In the case of the spinel, Larry Taylor explained in his talk how these deposits were probably formed by secondary intrusions of magma into the anorthosite layer at the top of the lunar magma ocean. In her final talk, Pieters also mentioned the magma ocean, which is believed to have encircled the moon immediately after its formation by a giant impact. She said that M-cubed found a “massive amount” of anorthosite in the Inner Rook Mountains in Mare Orientale, which she described as “very strong evidence for the magma ocean hypothesis.”

This comment made me sit up in surprise. I tend to think of the magma ocean as a done deal; I wrote about it in my book as one of the major discoveries, perhaps the major discovery, of the Apollo missions. Why would you care about proving something you already know?

The reason is that in science, nothing is ever really a done deal. A hypothesis may eventually become a theory, and it may become conventional wisdom, but you always want to collect new data and look for new evidence. The magma ocean hypothesis is based on a few anorthositic dust samples and anorthositic rocks collected by the Apollo astronauts. Until now, we hadn’t really seen any large-scale structures made of anorthosite. Now we have seen a whole mountain range of the stuff, or at least Pieters thinks we have, from orbit. The next thing to do is send a geologist there and see if she is right. Do we have any volunteers to go and look for Carle Pieters’s white mountain range?

Tags: anorthosite, Carle Pieters, Chandrayaan-1, Jessica Sunshine, Larry Taylor, lunar magma ocean, Mare Orientale, Moon Mineralogy Mapper, Moscoviense, Sinus Aestuum, spinel
Posted in Future exploration, Media, Meetings, Missions, Science | 1 Comment »

Water on the Moon — Bring your Buckets!

Friday, November 13th, 2009

As usual, the LCROSS press conference had a lot of Power Point slides, but probably the most memorable thing about it was an empty 2-gallon industrial bucket. Tony Colaprete, the lead scientist for the mission, said: “I’m here today to tell you that yes, indeed, we found water on the moon, and we didn’t just find a little, but we found a significant amount.” Then he held up the bucket. ”In the 20-30 meter wide impact crater that LCROSS made, we found about a dozen of these 2-gallon buckets. And that is probably a lower bound.”

Let me back up and give a little bit of context. Earlier missions, Clementine and Lunar Prospector, had found evidence for water ice but no direct proof. This year, three different missions simultaneously reported proof of water ice, because they detected not just the spectral signature of hydrogen (H) but also the hydroxyl molecule (OH). [It doesn't take too much knowledge of chemistry to see that hydrogen, H, plus hydroxyl, OH, equals water, HOH.] Not only that, the hydroxyl comes and goes over the course of a lunar day, which suggests that there is some chemistry going on at the moon’s surface. Carle Pieters, the principal investigator for the Chandrayaan-1 mission’s Moon Mineralogy Mapper, estimated that you could get a liter of water from a football field-sized area of the moon’s surface. This was exciting news, but as a reality check, it still makes the moon drier than Earth’s driest desert.

LCROSS has found an oasis in the desert. It was targeted for a specific crater near the south pole, Cabeus, where remote sensors had detected a high concentration of hydrogen. It excavated a 30-meter crater, only a third the size of a football field. Within that region, it dug up not just a liter of water, but 100 liters. Again, for context, one reporter asked Colaprete how this compares with Earth’s driest deserts. He said, “If you stand on that beach [the sandy spot where LCROSS impacted], I can say that it is wetter than some deserts on Earth.”

Does this contradict the Chandrayaan-1 findings? Of course not. It just re-emphasizes how little we know. Chandrayaan-1′s measurements were taken over a broad swath of the moon. By comparison, LCROSS is just looking at a tiny pinprick on the surface. Also, Chandrayaan-1 was measuring only the water that is right at the surface, up to a few microns deep. On the other hand, LCROSS excavated to several meters below the surface. To me that was one of the most exciting things about LCROSS; unlike measurements from orbit, it really sees what is underground. (However, it turns out that I was not entirely correct when I thought that LCROSS would be the first mission to do this. Radar measurements can penetrate one or two meters. Chandrayaan-1 carried a radar instrument on board, but those results have not been published yet. When they do get published, Paul Spudis promises me that they will be good.)

So basically, we now have one data point where we had zero before. We know that at one particular location, we have found an oasis. It remains to be seen exactly how concentrated the water ice is there, how heterogeneous it is, how hard it is to find other areas with lots of water, how deeply it is buried, etc. Not only that, there is a whole new suite of questions: How does water get to the moon? Once it’s there, how does it get transported to the poles? There are lots of theories, and at this point absolutely no way to choose among them.

What we have here is the appearance, in less than two months (since Pieters’ paper), of a whole new field of science that didn’t exist before: lunar hydrology. The next step, of course, will be for the LCROSS team to continue analyzing their data and nail down the concentration of water at their impact site. Also, LRO (the Lunar Reconnaissance Observer) will continue making large-scale observations  to figure out where else on the moon we might find water. But then, if we’re really serious about following up on this discovery, the next step needs to be a lunar rover (or even several of them) to poke around these permanently shadowed craters and start answering the questions in the previous paragraph.

There was one other very interesting thing mentioned at the press conference, which Colaprete was clearly eager to say more about but he just doesn’t have the data yet. LCROSS found lots of other volatile elements in the debris plume and/or the vapor cloud released by the impact. These may include:

  • carbon dioxide
  • methane
  • methanol
  • ethanol
  • ammonia
  • other organic molecules

The case for these is not as clear yet as the case for water. Colaprete said that it is absolutely certain that some of them are present, but they can’t yet pin down which ones and in what amounts. The science team is going to continue working hard to answer those questions, but they felt that the detection of water was so clear and of such overriding importance that they voted to go public with it now (instead of waiting another month, as per the original plan). But still, stay tuned for news about these other volatile compounds, because this story ain’t over yet.

Tags: buckets, carbon dioxide, Carle Pieters, Chandrayaan-1, hydrology, LCROSS, LRO, methane, oasis, Paul Spudis, Tony Colaprete, volatile compounds, water
Posted in Media, Missions, NASA, Science | No Comments »

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