Date: June 3, 2010

Title: Mysterious Moon Rocks

Podcaster: NASA Lunar Science Institute

Organization: NASA Lunar Science Institute (NLSI) – http://lunarscience.arc.nasa.gov/

Description: Using data from NASA’s Moon Mineralogy Mapper (M3) on India’s Chandrayaan-1 spacecraft, teams of researchers recently found two new kinds of Moon rocks: one was “hidden” on the far side of the Moon, the other has been hiding in plain sight.

Music: “Aquaspheres” from Dr. Sounds, from Magnatune

Bio: The NLSI brings together leading lunar scientists from around the world to further NASA lunar science and exploration.

Nancy Atkinson is a science journalist and is the Senior Editor for Universe Today.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Graham Hewett “For my wife Cecilia who puts up with all the geeky things I do.”

Transcript:

Voice: You are listening to the NASA Lunar Science Institute podcast which highlights the latest news information of the Moon, on the Moon and from the Moon. It is produced from the NASA Lunar Science Institute at the Ames Research Center in Moffett Field, California.

Nancy Atkinson: There’s a mystery on the Moon! Hi, this is Nancy Atkinson for the NASA Lunar Science Institute. Thanks to the Moon Mineralogy Mapper instrument or M cubed, on the Chandrayann-1 spacecraft, scientists have found two different kinds of never-before-seen lunar rocks – one kind on the far side of the Moon and the other staring right at us on the near side. The composition and location of these new rock types are puzzling lunar scientists. To learn more about these mysterious Moon rocks, we talked with Dr. Carle Pieters from Brown University who is the Principal Investigator for M cubed as well as Dr. Jessica Sunshine from the University of Maryland, a co- investigator with the project.

Dr. Pieters tells us about the newly found rocks on the far side.

Dr. Carle Pieters: The rock type on the far side of the Moon that is so unusual is a magnesium spinel lithology. Now, what that means is that there is a mineral called spinel that is typically an iron, magnesium, aluminum oxide. The particular kind of this mineral that we found is a magnesium end member with a little bit of iron in it. Which is called basically a spinel, a normal definition of a spinel. So that’s the mineral specifically. Now what’s unusual about the minerals that we found on the far side is that the general geology of this particular area is common on the moon. It’s class of crater that are called basins, these are over 300 km in diameter, so they are huge! It’s a big hole in the ground that was formed early in lunar history about 4 billion years ago. We don’t know the exact dates, but we know they were early. This period ended about 3.8 billion years ago. The Moon’s surface is peppered by these major basins. Now, what we normally see when we look at this particular basin on the far side, it’s the Moscoviense Basin on the far side. It’s a very, quite typical wonderful basin on the far side of the Moon that has excavated quite normal plagioclase rich lithology, which was later filled with basaltic rich mare lavas. So it is quite a typical large basin in terms of all the compositional properties we have measured.

But what we noticed by looking in detail at the spectral properties of the material, and in particular the material along the inner-most ring of this basin, which has mostly likely exposed the deepest materials from the crust, we noticed there were a few little areas that were unusual – spectroscopically unusual. So, of course we investigated those in more detail. And found that these unusual areas had a whole list of properties that were quite perplexing. First of all they were unusual, but not unusual in the same way. There are three primary different compositions and two we had seen elsewhere, although not at this particular location, and these are compositions that are rich in iron bearing minerals called pyroxene and olivine and so we see small areas of these pyroxenes and olivines and we say ‘Hmm, that’s interesting!’

They are widely separated, and that was a mystery in itself. But then the third kind of mineral we had never seen before, and what is interesting is not only is there an unusual abundance of this particular mineral, but it also has a lack, an absence of the minerals that we are more familiar with, the pyroxenes and olivines that we see elsewhere. So there are several mysteries that are interwoven here. One is why do we have a concentration of this spinel mineral and however it got concentrated in this area, why aren’t the other minerals that we are familiar with also there, because they are not. So this is a big mystery and it is a very exciting one because now we have to reexamine our understanding of the character of the lunar crust, in particular to the depths that might have been tapped by this enormous basin and that we are now looking at exposed on the surface.

Nancy: Dr. Pieters said there is also a related question about this region on the Moon.

Pieters: Not only are these unusual areas, and they are only about a kilometer or two in size, unusual compositionally, but in every method we’ve been able to look at thus far, in every wavelength and resolution, they have no other distinguishing properties. Typically, on the Moon to indentify an usual composition we look for a fresh crater that has excavated and exposed material on the surface of the Moon. These areas have no fresh craters, no disturbance at all across their surface, even at the highest resolution that is seen with the LROC (Lunar Reconnaissance Orbiter Camera) instrument which measures a half a meter resolution. These are old surfaces that have been undisturbed but have an extremely unusual composition. And even the space weathering that has occurred on the surface throughout the billions of years of history on the Moon has not erased their unusual compositions. So, they are unusual for the kind of compositions we see, but they are also unusual because they have no identifying property that allows us to identify them in our imagery which is quite unusual for features on the surface of the Moon.

Nancy: Now let’s move to the near side of the Moon, where Dr. Sunshine was given a specific task.

Dr. Jessica Sunshine: One of the things I was asked to be in charge of was looking for anomalies, things that just didn’t look like the rest of the Moon. And of course you never know what’s going to happen under those circumstances. Carle had already discovered that there seemed to be some magnesium spinel on the far side of the Moon and I went looking to see where else it was, and found that the only place that we had anything that looked like the spinel mineral in data we had at the time was on the near side and it was an extremely large deposit in the middle of the central nearside, almost exactly dead center at zero zero. And we started looking a little more carefully and realized that it wasn’t really the same kinds of things that Carle found, which truly was a new rock type on the far side of the Moon, but something usual about the regions that we had already known was full of what we call dark mantle deposits or pyroclastic deposits, which is firefountaining deposits, which we have going on in Iceland right now. We have lava and gas, explosive eruptions over large areas of the Moon, about the size of Massachusetts. And we knew that three of them were there, it just turned out that one fo them was compositionally different from the other ones, and in particular it had the kind of spinel which is a chromite, because it has chrome in it, and now we’re busy trying to figure out why this deposit is different from the one next door, and what does it mean. And we’re still working that process out as we speak.

Nancy: I asked Dr. Sunshine what it’s like to find something new like this on the side of the Moon that humans have looked at for millennia.

Dr. Sunshine: Yeah, I tend to title my talks on the subject something like, “Hidden in Plain Sight” because they are! Its right there and I think this is a really fascinating part of this because we have been starring at the Moon, as humanity for millennia and if our eyes were slightly different we would see this one really dark spot in the middle of the Moon that is different from anywhere else.

Nancy: And these discoveries couldn’t have been made without the Chandrayaan-1 spacecraft and the Mcubed instrument.

Sunshine: Mcubed is able to see, if you will, it collects data over amuch broader range of light than our human eyes can. We can all see the rainbow, we’re all familiar with that, from blue to red, but there is light at shorter wavelengths, which we call ultraviolet, and particularly for this case, there is light at shorter wavelengths called infrared, and Mcubed goes farther into the infrared than humans can see and it is there we are able to see diagnostic fingerprints of different kinds of minerals. So I suspect there are certain kinds of bugs who would look at the Moon and would have known these deposits are there because their vision goes into the infrared!

Nancy: So, Dr. Pieters, does these new discoveries tell us there are still more mysteries to find on the Moon?

Pieters: Oh, absolutely! We’ve just barely scratched the surface here. This is thrilling from a spectroscapist’s point of view, of course, but also from someone who is trying to understand how planets work, and in particular how this wonderful small body in our neighborhood is telling us about the characteristics of crustal evolution and fundamental properties of planetary surfaces.

Voice: To find out more about this topic, visit our website at www.lunarscience.nasa.gov. Any opinions expressed are the individuals and do not necessarily reflect the opinion of NASA or the NASA Lunar Science Institute. This podcast is produced for educational purposes only. On behalf of the NASA Lunar Science Institute, thanks for listening.

End of podcast:

365 Days of Astronomy
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