Q. What are LCROSS’s scientific achievements thus far?
Observation data taken by near-infrared spectrometers. The red curve shows the spectral model of a mixture of water vapor and ice. The yellow areas indicate water absorption bands. (Courtesy of NASA)
Observation data taken by the ultraviolet/visible spectrometer. The arrows point to characteristic emission lines of a compound of water and dust. (Courtesy of NASA)
Images of the Centaur rocket (left) and the flash of its impact (right) taken by the LROSS near-infrared camera. (Courtesy of NASA)
The greatest achievement thus far is the confirmation of the presence of water on the Moon. LCROSS impacted the Cabeus crater near the South Pole. The crater is permanently shadowed, without any sunlight, and it had been assumed that such a region had the highest likelihood of the presence of water. LCROSS consists of the shepherding spacecraft and the Centaur rocket. The rocket crashed into the Cabeus crater first, followed by the satellite about five minutes later. We investigated the composition of the materials ejected by the impact, and found water vapor and dust in the upper layer and heavy materials in the lower layer. Evidence of the presence of water was found in both layers.
To be more precise, the data acquired by the near-infrared spectrometers on LCROSS matched the spectral data of a mixture of water vapor and ice. No other compounds would match better than this. Moreover, the data taken by the ultraviolet/visible spectrometer showed the spectral signature that indicates the presence of a hydroxyl group formed when water is broken down by sunlight. This has raised the possibility of the presence of a much greater quantity of water in wider areas on the Moon than previously expected.
In addition to these findings, LCROSS obtained a tremendous amount of data, which is currently in analysis. Unfortunately, I’m in the middle of writing papers and cannot talk about it now, but we are definitely getting a lot of amazing data. It is all very exciting, so please anticipate new discoveries. Q. Many people were expecting to see a cloud of dust when LCROSS impacted the Moon. But that didn’t happen. Did you get depressed?No. We knew going into Cabeus that it would be very hard. We were going to limit our ground-based observations, and we tried to get that across to the public. The day before impact I did a number of press interviews, and I told them, "Look, what you’ll probably see, if anything, is darkness turning a little gray. You’re not going to see something spectacular." But then, even ourselves, NASA, we would show an artist’s conception of a big blast. People always expect some dramatics, but that’s not how science works.
To put it in perspective, from our vantage point on our shepherding spacecraft, we saw a dust cloud that, 20 seconds after impact, was the size of San Francisco, and we were observing it from as far away as Los Angeles. So that kind of puts into perspective that this impact was quite spectacular, at least in terms of its dimensions and its viewability. We observed the dust cloud from six hundred kilometers away, and it got quite immense. The fireball that came out was moving at about two kilometers per second, and went as far as four kilometers to either side just seconds after impact. And then we had this debris cloud shoot up to 15-20 kilometers in altitude very quickly, a vapor cloud that escaped from the crater at 1000 degrees. All that was not necessarily expected, but it was certainly dramatic. But it was not a bright cloud as seen from Earth, and that was a bit unexpected.
Some people had been expecting a large explosion and were disappointed. But in a way that was good in the sense that we got millions of people to look at the Moon, and think about it, and this really highlighted the incredible lunar exploration that’s gone on in the last few years, with all the various peoples - from JAXA to India, to China, to the United States - exploring the moon. So the controversy over this mission was good in that sense. I am happy that people celebrated these missions, and were looking at our Moon on impact night, and continue to do so. LCROSS showed that there is still so much for us to find out about the Moon, and that has caught people’s attention. I think that LCROSS’s achievements will lead to the next planetary explorations.
Q. What are your thoughts about the KAGUYA mission, which observed the moon from 2008 to 2009?
Lunar Explorer KAGUYA (Courtesy of Akihiro Ikeshita)
It was a spectacular mission in so many ways, and it was very important for us at NASA and LCROSS. It helped our understanding of the craters and the poles, and it was instrumental in our success. KAGUYA’s topography data helped us select and rule out certain targets that we wouldn’t have been able to assess properly otherwise. I worked with the principal investigator of KAGUYA’s Terrain Camera as well, to evaluate targets, so both those instruments, the laser altimeter and the terrain camera, were very important. Q. Japan is planning SELENE-2, a lunar explorer with a robot that will search and analyze the lunar surface. How does that project look to you?LCROSS certainly has captured everyone’s attention. It shows the moon is a unexplored wilderness that we don’t fully understand, and it raised more questions, which is a great thing. That’s how you know you’re doing good exploration and good science: you’re raising more questions than you’re answering. So I think getting back there and touching the surface again is fundamental to the next steps, to really taking what we’ve learned in these missions such as LCROSS and proceeding forward. In that sense, I am looking forward to new lunar missions.
