Also, we have this follow-on spacecraft that, at impact, is only 600 kilometers away observing with a suite of nine instruments that are specifically designed to look at the impact and look for water. As you mentioned earlier, this follow-on spacecraft even flies through the ejecta plume before making an impact itself. So the LCROSS mission has been specifically designed in much the same way the deep impact mission was specifically designed to impact the body and make measurements of the ejecta plume and remnant materials. We feel we’re going to have a much, much better chance of actually observing the ejecta and that’s the first step to making the measurements.
Also, being as close as we are, we’ll have much, much greater sensitivity. Lunar Prospector was only observed from Earth assets, whereas we’ll be able to observe really up close and personal. This has been demonstrated recently. A year-and-a-half ago or so, the European Space Agency’s SMART-1 spacecraft also crashed into the Moon at the end of its life. It crashed about 27-degrees south of the equator, not in the polar regions, but investigators from the LCROSS team and others tried to observe that impact and had success. The Canada-France-Hawaii Telescope on Mauna Kea did, indeed, observe the flash and the ejecta cloud come up from that spacecraft. Like Lunar Prospector, it was never designed to be an impactor. It was relatively small – a couple hundred kilograms – and also came in at a grazing angle, maybe 2 or 3 degrees above the horizontal. So we feel that LCROSS is going to have a much, much greater chance of success in terms of creating an ejecta cloud that’s observable.
NTB: What types of instruments will be onboard the shepherding spacecraft to observe and analyze this debris plume?
Dr. Colaprete: We have five cameras, three spectrometers, and a special photometer. The five cameras include a visible camera, which is to provide color context imagery so we know precisely where we hit. We have two near infrared cameras that look at wavelengths where water is visible…water ice in particular. What we do with the two cameras is we actually have them looking at two different parts of the wavelength spectrum sensitive to water and by differencing the two images we can actually make a map of where water ice is.
Then we have two mid-infrared, or thermal, cameras. They look at temperatures. They will measure the temperature of the plume and the expanding particle cloud and remnant crater, if there’s any heat left in that crater after impact. We have two of those cameras to work in the same way as the near-infrared cameras. They have filters that look inside and outside of portions of the spectrum that are sensitive to water vapor, so we can difference those images and look for water vapor.
We also have two near-infrared spectrometers. Near infrared spectrometers are very sensitive to water ice and water vapor. We have one that looks down at the impact itself, looking for water ice in the ejecta cloud, and then we have one that looks to the side towards the sun, so as we fly through the ejecta cloud we can monitor how the sunlight is absorbed or scattered away by the ejecta cloud particles. That’s a very sensitive technique to look for various small amounts of water vapor or water ice.
Lastly, we have an ultraviolet visible spectrometer that also looks down at the ejecta cloud and it will be looking at the emission lines from the impact flash, and also scattered light off the ejecta clouds from which we can derive the mineralogy and characteristics of the particles in these ejecta clouds.
Then there’s one last instrument, the Total Luminescent Photometer, which is an instrument built here, by Ames, and it is a very, very fast photometer. It actually measures the flash of the impact itself. The flash lasts only a couple hundred milliseconds, but depending on the brightness and shape of that flash – and by shape I mean the shape of that light curve over time – you can tell how far you penetrated, how strong the material you entered was, even if there was water subliming as you impacted, so this instrument is designed to make very, very precise measurements of very faint signals very quickly. It measures a thousand times a second as the impact occurs.