This story was updated at 2:23 p.m. EDT.
A NASA probe that slammed into the moon's south pole Friday managed to spot the artificial crater carved into the pristine lunar terrain minutes earlier by its partner craft, but scientists have not yet confirmed if the two crashes kicked up a giant plume containing any signs of water ice ? a main goal.
NASA's LCROSS spacecraft slammed a 2.2-ton empty rocket stage ? the equivalent of a sport utility vehicle ? into a crater called Cabeus at 7:31 a.m. EDT (1131 GMT) and recorded the resulting explosion just before making its own death dive and crater four minutes later.
But in those four crucial minutes, the five cameras and four other instruments on the LCROSS shepherding spacecraft recorded the flash of the rocket stage's impact and a telltale sign of the leftover crater. What remains to be seen is whether the crashes created the vast plume of moon dirt that scientists predicted would blast out of the crater up to heights of 6.2 miles (10 km), where it could be lit up by the sun and visible to observers on Earth.
"We saw a crater. We saw a flash," NASA's principal investigator Tony Colaprete told reporters after the $79 million lunar impacts. "So something had to happen in between."
Colaprete said he's thrilled, rather than disappointed like some observers not with the mission team, and had some thoughts on the missing plume.
The plume may have ejected out on an unexpected angle or not risen high enough to be spotted by spacecraft and observers on Earth, Colaprete said, adding that researchers will know more after an in-depth look at the data. The crater left by the Centaur upper stage is about the same size as scientists predicted ? around 66 feet (20 meters) wide.
Colaprete and other LCROSS researchers repeatedly warned that the LCROSS impacts would be difficult to spot from Earth. On Thursday, they described it as seeing "blackness get less black" as the plume exploded outward.
"I'm not convinced it's not in our data yet," Colaprete said. "We've got to go look."
Scientists hoped to be able to scan that portion of the plume from space and Earth to determine if any water ice was present in the debris cloud. Finding proof of buried water ice ? long suggested by the presence of hydrogen-bearing material at the lunar south pole ? could be a boon for NASA since it could be a potential resource for future astronauts.
Last month, scientists announced definitive proof that small amounts of water exist elsewhere on the moon in a molecular form attached to lunar dirt. NASA launched LCROSS ? short for Lunar Crater Observation and Sensing Satellite ? in June along with a powerful orbiter to seek out evidence of water and ice on the moon.
"The moon we thought we knew is not the moon we know now," NASA's chief lunar scientist Mike Wargo told SPACE.com after the LCROSS crashes. "The results that we'll get from LCROSS are an important piece in the puzzle of something that is pretty darn new, the hydration cycle on the moon."
And there are already some other intriguing details puzzling LCROSS scientists.
While no obvious sign of a debris cloud have been confirmed, spectra ? measurements taken in non-visible wavelengths of light ? indicate a signal that suggests an ejecta cloud occurred, Colaprete said. More time is needed to analyze the spectra findings, he added.
During the four minutes between the Centaur crash and the shepherding spacecraft's impact, there was also a strong sodium signal, hinting at some interaction between the impact and the moon's tenuous exosphere of surface material.
"I've got to say that I was blown away by how long this little spacecraft lasted," Colaprete added.
The view from Earth
About 21 professional observatories and a host of amateur skywatchers stretching across the western United States, Hawaii and some overseas sites had fair weather to spot the cloud, but have not yet reported a visible confirmation of the plume.
"We're just looking at the very preliminary images to get a sense of the types of data that have been collected," said Jennifer Heldmann, head of the LCROSS observation campaign. "But it's too early to tell, to make that determination."
Some observatories have already released their early images of the LCROSS lunar crash. Others recorded videos of the Centaur rocket stage and the target crater Cabeus, a 68-mile (98-km) crater partly covered by a permanent shadow because of its location at the lunar south pole.
The Hubble Space Telescope and other satellites and spacecraft, including NASA's Lunar Reconnaissance Orbiter that launched with LCROSS and is currently circling the moon, are also tracking the aftermath of the lunar crashes.
Heldmann said that right now, NASA is awash in data from the moon crashes, especially since all the sites reported pristine viewing conditions.
"We have images. We have video. We have graphs with wavy lines that scientists love," Heldmann said. "We have something for everyone."
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