Craters in the Dark …

Friday, October 9th, 2009

The moon has two new craters in it today, courtesy of NASA and the LCROSS mission. Along with hundreds of thousands of other people, I got up before 4:00 this morning to watch the live coverage of the impact. It was … well, anticlimactic. But I’ll get to that below.

It gave me an amazing sense of deja vu to see live coverage, from a NASA spacecraft, of the moon getting larger and larger. It’s been only 37 years since the last time … Welcome back, moon! Nice to see you again!

Impact site is below and to the left of the prominent crater (center). NASA photo.

Of course, this was very different from the Apollo missions. The difference was especially apparent when the second spacecraft (the “shepherding satellite”) hit the moon. There was no astronaut saying from the moon, “Tranquillity Base here. The Eagle has landed.” Instead, we got the flight controller saying from a control room in Mountain View, California, “Flight shepherding spacecraft impact, stations report LOS [loss of signal]. Last tracking at 11:35:35.054 seconds.” And then, that was it. From the operational point of view, the mission was over. The controllers got up, exchanged high fives, and started milling about the control room. If this had been a manned mission, or even a soft landing of a robotic mission, the work would be just beginning. It was weird for it to be over so abruptly.

Just a few seconds earlier, there was an interesting comment from the science control room: “We confirm thermal signature of the crater over mid-IR camera.” For anyone wanting live, real-time science, this was it. As the chief scientist, Tony Colaprete, explained later in the press conference, the infrared camera saw a distinct bright spot, a little over a pixel wide, that was the hot, newly formed crater from the Centaur rocket impact. He was clearly jazzed about this detection, which they weren’t sure that they were going to be able to make. The ultraviolet spectrometers also got excellent readouts that should contain lots of information about the material that was thrown up by the impact. But Colaprete wouldn’t say, or even speculate, what they have seen yet. The main thing he wanted to emphasize was that the instruments worked and they got the data they wanted.

The press conference was kind of interesting to watch because it was clear that the story the media found interesting was exactly the opposite of the spin that NASA would like to put on the landing. None of the four speakers mentioned this, but it was clearly written on one of the slides taken from an Earth-based telescope: No plume detected.

Reporters are trained, of course, to look for the elephant in the room that nobody is talking about. They homed in on what Tony Colaprete, Jennifer Heldmann and Michael Wargo weren’t saying — the fact that none of the ground-based telescopes were reporting any visual evidence of the impact. I really think that the scientists should have acknowledged this up front. A lot of the publicity and a lot of the planning of the mission was built around the premise that the debris plume would be visible from Earth, certainly through the big professional telescopes in California and Hawaii, but even through a 10-12 inch amateur telescope. But it wasn’t. I think that the reporters were right to question the scientists on why no plume was seen (yet) and what this might mean.

However, though “no plume” might be the big news story at the moment, it is very far from the end of the story. The scientific work of the mission is just beginning. The press conference was held two hours after impact. But the more relevant time frames are two days (the time that will be spent with the full science team at NASA-Ames collecting data), two weeks (when they will meet again and start drawing their initial conclusions), and two months (when they are likely to make a public announcement of the results). Tony Colaprete and Michael Wargo made the following very important points:

1. It is not clear yet that the plume wasn’t detected. Further image processing could reveal that it was there, but fainter than expected. “Gray on black,” as Wargo said.
2. Even if the plume wasn’t detected, the crater was detected, and it was about the expected size. Its thermal signal will give a lot of information about what was at the impact site.
3. Colaprete kept coming back over and over to the point that “spectra are where the science is at.” The spectrometers are more sensitive than the cameras, and they tell you what the chemicals are that you are looking at. For the most part the readout is not instant (although Colaprete did talk about a clear sodium line).
4. Finally, Wargo reminded the reporters that this was an experiment. An experiment, by definition, is something whose result you don’t know in advance. You might have a prediction or a theory, but until you do the experiment you just aren’t sure what is going to happen. So the plume was smaller or darker or less dramatic than expected. That will still tell us something.

So the press conference was an interesting clash of cultures. The media like pretty pictures, big explosions, and dramatic discoveries. They don’t like to wait. The scientists, as Jennifer Heldmann said, like “squiggly lines” (like the output of a spectrometer). They understand the value of patience and gathering all the evidence before you reach a conclusion.

If you want to know whether LCROSS saw water ice on the moon, your best bet is to stay tuned. The answer is likely to come out at the American Geophysical Union (AGU) meeting in December, in San Francisco. I’ll be there!

P.S. Maybe I was wrong about the media spin being different from the NASA spin. Here’s a mainstream media article that barely mentions the lack of a visible plume.

Tags: anticlimax, deja vu, ice, impact, LCROSS, plume, science culture, spectrometer, squiggly lines
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