This morning, at a hastily arranged press conference, NASA scientists faced a barrage of questions from a frequently skeptical press corps. The questions, however, did not focus on budget issues or plans for future manned missions; instead, the press was concerned about the apparent absence of any visible ejecta from a crater that the Agency had just created by crashing the LCROSS probe into the Moon. NASA seemed very pleased with the data it has obtained, including detailed spectroscopic data, but the press was reflecting the public's desire for a geyser of debris to rise from the impact site and into the field of view of many of the telescopes that were watching.

Regardless of the public expectations, LCROSS clearly performed as planned. It recently separated from the Centaur stage that helped bring it to lunar orbit, and both of the spacecraft were directed towards the Cabeus crater at the Moon's south pole. The Centaur vehicle went first, creating an impact that could be observed from instruments on LCROSS, which followed it in. Less than four minutes later, LCROSS itself struck the lunar surface. The impacts were observed with a variety of telescopes on Earth and in Earth orbit, although the actual site of the impact was obscured by the Cabeus crater walls.

Clearly, a lot of people were hoping that dropping hardware onto the lunar surface would create a spray of debris that would rise above the crater walls, and be visible to the Earth-based observatories. Unfortuntely, from the perspective of the Earth, LCROSS struck not with a bang, but a whimper, as if it had landed on a comfy pillow. NASA scientists spent a lot of the ensuing press conference trying to explain why this didn't necessarily mean that scientists would be disappointed with the data pouring in from instruments around the globe.

Anthony Colaprete, the scientific lead for LCROSS, showed some of the spectroscopic data obtained by the probe's instruments as they approached the lunar surface. From the UV down to the infrared, a time lapse showed signals dropping as LCROSS entered the shadowed region of the crater, until a sudden blip indicated the Centaur's impact. The spatial resolution of the instrument showed that there was a crater in the neighborhood of 18-20m carved out by the impact.

A flash detected by LCROSS (inset, lower right) indicates the Centaur impact.

The woman who coordinated the imaging performed by other observatories, Jennifer Heldmann, described some of the data obtained by a massive network of telescopes that followed the impact, saying, "we have images, we have video, we have graphs with squiggly lines, which scientists love."

The observatories that were able to image the event ranged from Arizona and New Mexico (Apache Point, Magdalena Ridge, and the Vatican Observatory), through California's Mount Wilson and Palomar sites, and included a lot of the best hardware in Hawaii, such as the Keck, Gemini, and Subaru telescopes. Watching from space were the Lunar Reconnaissance Orbiter, which was launched with LCROSS, and the newly refurbished Hubble Space Telescope. A few private satellites that normally do Earth imaging, IKONOS and GeoEye-1, were also redirected to the Moon for the event.

Heldmann showed video from a few observatories that spanned the time of the impact, which decisively revealed nothing—hence all the questioning from the press in attendance. Still, it's possible that imaging processing or specific areas of the spectrum will reveal something, and several of the scientists who spoke were anxious to see what came down from the Hubble, which should have started transmitting its data by the time this article is published. Heldmann also mentioned that the Kitt Peak spectral data indicated ionized sodium, something that Colaprete indicated was picked up by LCROSS as well.

That set off another set of skeptical questions: if scientists had spent the time to pick sodium out of the spectrum, surely they had looked for water? Colaprete tried to explain that sodium vapor is known to be present in the lunar atmosphere, and it creates a distinct spectral line in a clean area of the visible spectrum. Water is typically detected in a crowded area of the IR spectrum, which makes it a lot more challenging to pick out. He simply didn't have time to examine it in detail (in part because he was busy making slides for the press conference), and probably wouldn't discuss it if he had, since detailed analysis of the data would be needed before he'd feel comfortable saying anything conclusive. At the moment, that data was still being shuffled around on thumb drives to everyone who was in place to perform the relevant analysis.

In any case, Colaprete noted that excited sodium ions were an indication that something energetic had happened on the lunar surface, so the absence of a visible plume might simply indicate that the hardware had gone into a slope that forced the plume out sideways, or had impacted on solid rock that limited the amount of material sent upwards.

Overall, the press conference made it clear that the mission worked precisely as planned, in that there's a wealth of observational data to analyze—NASA's Mike Wargo said that scientists are currently just "drinking from the firehose"in order to deal with the volume. The recent findings that suggest the existence of lunar water cycle adds a degree of urgency to the work, but the area struck by LCROSS hasn't seen the sun for as long as two billion years, so there was almost certain to be something interesting lurking there.

Listing image by NASA