Planetary scientists believe that small impacts regularly bombard the Moon, but until recently, they’ve had no way to distinguish new craters from the already pockmarked lunar surface.
In 2009, NASA’s Lunar Reconnaissance Orbiter (LRO) arrived at the Moon and began taking high-resolution photographs. By comparing pictures taken early in the mission with more recent images, the LRO camera team has discovered more than two-dozen new impact craters – including an 18-meter-wide crater caused by a bright flash on March 17, 2013.
Transcripts of “New Craters on the Moon”
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What is LRO?
LRO is this amazing spacecraft that has seven science instruments on it, and it's been in orbit around the Moon since June of 2009. And it's collecting all sorts of data to help NASA make really good decisions in the future about where to send robotic spacecraft and humans, and to address fundamentally-important science questions not only about the Moon, but about the solar system in general.
I'm Mark Robinson, and I'm the principal investigator of the Lunar Reconnaissance Orbiter Camera.
What is LROC?
Okay, what is LROC? That's a great question. Sounds like one camera, Lunar Reconnaissance Orbiter Camera, but it's not. It's actually three cameras. There are two identical narrow angle cameras that are very high resolution, they have pixels about this big [spreads hands], 50 centimeters, and it was designed so that you could look at a human scale on the surface to find safe and engaging landing sites. Then there's a third camera, wide-angle camera, which is literally about this big [15 centimeters]. It maps the Moon in UV and visible wavelengths, and its key purpose is to look at compositional differences for both scientific and resource evaluation.
Finding New Impact Craters
It's not easy to find new impact craters because most of them are very small. The only way we can really do this is if we have a before image and an after image, and we've been in orbit for four years now. So what we're doing now is we're going back to images that were taken in the first year or two, put them on a computer screen, and blink them. And then it becomes really obvious, "Oh, look, there's a new crater there!" because it wasn't in the before, it's in the after, before after, and we call these temporal pairs.
So now we have several thousand pairs, and to sit down and look at every single pixel in all those images would probably take one person, you know, ten or twenty or thirty years. So we started working on an algorithm, or a computer program, that searches the images by using a little template, the before and after pairs, and it automatically finds them. It gets like about a 90% success rate. So far we've found hundreds of changes on the surface. Many of them are too small to really know for sure if they're craters or if they're secondary craters, but we have found over 25 that are absolutely, positively confirmed craters, you can see the rim and the ejecta, and we've also made this amazing discovery that we find secondary craters related.
Hunting the March 17 Crater
There was a bright flash that was recorded by a video camera by a team at Marshall Space Flight Center, and it was the brightest flash they recorded so it must be therefore one of the biggest craters, and so they were really interested for us to take a picture, can you see the crater? Because they predicted how big it was going to be based on the energy but this is all a model, and so it's a great opportunity to actually calibrate their model.
So we took a picture centered on their coordinates, and we didn't find a crater. We found these enigmatic little splotches, there was something...disturbance of the soil that wasn't in the original image, but we didn't know what it was. So we thought, okay, well their coordinates are off a little bit, because their pixels are really big from their camera, in fact their pixels are bigger than our image footprints. So we said, okay, no problem we'll move over to the west and we'll take a - you know, we're building up a mosaic.
So the next month comes around, we take a picture and we do the same thing, look at the before, look at the after image: no crater. But more of these splotches...but also in that image we saw what looked like very faint rays, and we thought, "Boy, I wonder if those are actually rays from a crater?" So we just did this simple exercise of drawing lines and see where they converged.
And then so the next month we came around, remember this is the third opportunity, we center the field of view of the camera right on that latitude-longitude, boom take another picture, comes down and there it is: beautiful 18-meter-diameter crater. And then we started looking and now we've got three of these, and there's hundreds of these little splotches that we're finding, these rays, and then we have the big picture: you could see that the splotches are actually lined up. These very small clods of ejecta were thrown out ten, twenty, thirty kilometers away, that's thirty-thousand meters compared to an 18-meter-diameter crater, so it's a very exciting discovery.
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