Some first results from Lunar Reconnaissance Orbiter (or, I love LOLA)
Posted by Emily Lakdawalla
17-09-2009 14:09 CDT
As of Tuesday (September 15), Lunar Reconnaissance Orbiter (or LRO as I suppose I'm going to be forced to call it -- I really really wish they'd run a naming contest and given this bird a more graceful, one-word name) is now in its low, circular, science orbit and is gathering data. It launched on June 18 and has been in orbit since the 23rd. During the last two months, it's been far from idle. It's been in its commissioning phase -- turning on its science instruments one by one, gathering some preliminary data, running multiple instruments at a time, then running through tests like moving solar panels while taking a photo to see how badly it smears the image data.
So this morning they held a press briefing to showcase some of the early data captured through the commissioning phase. There was only one instrument principal investigator on the panel, and I was thrilled to see that it was David Smith, the head of the Lunar Orbiter Laser Altimeter or LOLA.
Why is LOLA so thrilling? It's because our understanding of lunar topography is pretty lousy. It's as lousy as Martian topography was before Mars Global Surveyor arrived with its Mars Orbiter Laser Altimeter, or MOLA. MOLA absolutely revolutionized our understanding of Mars as a planet. It showed us what was high and what was low. It revealed features that were invisible in photos but whose subtle effects were noticeable in topography. And it created a precise control network for photos of the Martian surface from all the different orbiters that have been there in the past. With apologies to the MOC team, I think that MOLA topography was the greatest result of the Mars Global Surveyor mission; it's a critical data set that won't be supplanted for decades.
So I'm looking forward to LOLA doing the same to usher in a flurry of new discoveries about the Moon. LOLA gathers data along a line directly beneath the spacecraft, so it will take a long time for it to cover the entire globe. But since LRO is a polar orbiter, all those ground tracks converge at the poles, so the first map shows pretty good coverage of the south pole. It's absolutely lovely, the data set we've been missing for The Moon. There is wonderful detail. There are flat-floored craters and central peak craters. There's a couple of peak ring craters. I'm intrigued by the "wall" of bright red high elevation peaks that march across the image from its center to the right-hand edge. I can't say whether that's just an accidental wall built up from overlapping crater rims, or if it's an incredibly degraded bashed up remnant of some ancient great big impact basin. Whatever it is, it's cool.Here's a lovely visualization that they put together at GSFC. It shows you how they built up the topographic map with lots and lots of ground tracks, and then names some of the south polar craters. Shackleton crater overlaps the pole itself. Toward the end of the movie we circle around to Cabeus and Cabeus A -- that being the recently chosen target for the upcoming LRO impact. You can view it in HD resolution on Facebook here (even if you're not a Facebook member, I think).
mith went on to present a little bit of his data that crossed Shackleton crater, which overlaps the Moon's south pole. I've always believed that people fail to appreciate the power of looking at single MOLA ground tracks crossing features on Mars -- these topographic profiles contain higher-resolution information than is available in the digital terrain model versions of the topographic data sets. Likewise, I think that LOLA ground tracks across features of interest will provide powerful data for scientists interested in lunar geology. But as Smith pointed out, these topographic profiles will also be important to people interested in exploration on the ground, whether it be by humans or robots. First here's the image, then I'll tell you what Smith said about it: Smith said (and this was transcribed from the live briefing, so any mistakes in transcription are mine): "Spots on the LOLA profile are 25 meters apart. It goes up and down 5 or 10 meters in height. So over a distance of 25 meters you have a very large variation in surface elevation. It presents something of a difficulty if you were trying to drive over the surface. If you are interested in Shackleton, it's a great crater in many respects if you're thinking about ice. It's been in darkness probably ever since it formed. But slopes are sufficiently steep that you've got to be concerned about them. And the bottom is a pretty treacherous surface, not as smooth as you'd like it to be if you'd like to explore. This is pretty typical of craters." Food for thought.
Some other interesting early results came from Diviner, an instrument that measures the temperature of the surface:About these, LRO project scientist Richard Vondrak said: "Over the last six weeks, Diviner has been mapping the Moon. These are the first two composite maps of the temperature of the lunar surface. Blue indicates temperatures below about 100 K (-300 F); the left-hand map shows daytime temperatures. Daytime temperatures reach 380 K (220 F), hotter than the boiling point of water. The significance of temperature variations is that it's driven not just by elevation of the Sun but also by the shadowing that occurs due to the topography of the surface. Diviner has found out that during the daytime in the permanently shadowed regions, the temperature never gets above 35 K, which is extremely cold, and is low enough to permanently trap volatiles such as water. Early indications from Diviner are that permanently shadowed regions at the lunar south pole are perhaps the coldest part of the solar system, colder than any other region that has been identified in the solar system." Later on in the briefing, during the question-and-answer period, he reiterated that last point, saying it was "colder than Pluto."
They showed this pretty picture from the Mini-RF instrument without much comment except that it was instrumental in helping with the selection of Cabeus A as the target of LCROSS. Also significant -- but unmentioned -- is the fact that this Mini-RF is a duplicate of the one that was flying on the Chandrayaan-1 mission; in a sense, that instrument team is continuing work that began a year ago.
This image from LEND, the Russian-built Lunar Exploration Neutron Detector, really stirred up the press. Vondrak commented that the early results do show hydrogen as predicted in permanently shadowed regions near the south pole. "The surprising thing about the LEND observations is that while it confirms that there is hydrogen near the lunar south pole region, it also seems to indicate that the hydrogen is not confined to permanently shadowed regions. Some contain hydrogen; some do not; and in addition there appear to be concentrations that are not confined to permanently shadowed regions." When the press asked a bunch of questions about what this means, he answered, "you're asking the same questions that the science team members are."Here's another one where it's too early to say much about the data, from an instrument called LAMP that's looking for surface water ice frost in the permanently shadowed areas near the south pole. As with Mini-RF, LAMP is a copy of an instrument that's flying elsewhere, on not one but two spacecraft. It's nearly identical to the ALICE instruments on both the Rosetta comet mission and the New Horizons Pluto/Kuiper Belt mission. The neatest thing about LAMP is that it doesn't rely on sunlight to illuminate craters; it relies on Lyman-alpha radiation from nearby space and stars, so, like mini-RF and LOLA it can "see" into those dark areas on the Moon. I'll close with a bit of eye candy from the Lunar Reconnaissance Orbiter camera, of a bit of sunlit rim of Shackleton crater. The full image is mostly black and serves as a reminder that cameras can only do so much for us in these permanently shadowed regions; it's marvelous to have so many instruments on LRO that can "see in the dark," one way or another, to teach us more about what might be lurking in that darkness. Here's a video version; again, go to Facebook to see it in HD.
ll of these data sets focused on the south pole for two main reasons. First is that LRO's preliminary orbit was an elliptical one, with its perilune close to the south pole -- in fact, closer to the pole than it is now in its nominal orbit. So its highest-resolution data for the whole mission was being gathered on the south pole during the commissioning phase. The other reason -- I'm sure, a related one -- is that they needed the south polar data to map out the impact site for LCROSS. Now that LRO is in its science orbit, it's looking at the whole Moon. I am eagerly awaiting the first global lunar topographic map. They didn't tell me how long that wait was going to be, but the nominal mission is only a year in length -- so by this time next year we should have our first reliable global map of lunar topography to tie all other data to. Yay!
Or read more blog entries about: