Tag Archives: Moon

LCROSS saw water

LCROSS infrared spectrum
LCROSS infrared spectrum

LCROSS crashed into the Moon last month, although the lack of a visible plume in the real-time video feed made the impact less exciting than it could have been. But the lack of a visible plume is hardly a failure, since LCROSS was sent to do science, not make a flashy impact.

And it looks like LCROSS has managed to find exactly what it was sent to find on the Moon. Analysis of the near-infrared and ultraviolet spectra as LCROSS passed through the plume kicked up by the impact of the Centaur rocket upper stage indicates that the plume contained water. And not the piddling amount of water that seems ubiquitously present on the rest of the Moon: there must be significant reservoirs of water at Cabeus crater. Just how much water there might be remains to be seen, as well as the identity of other compounds that appear to have been detected in the impact plume.

Source of the Moon's water

Remember how NASA's M3 instrument on ISRO's Chandrayaan-1 spacecraft confirmed the sparse existence of water all over the surface of the Moon? One of the speculations was that the water formed as protons, which are basically hydrogen atoms without electrons, combine with the oxygen in lunar rock. And it seems that this is indeed the case as the ESA's SARA instrument on the same spacecraft had collected data showing that a substantial number of protons in the solar wind are being absorbed by the lunar regolith.

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LCROSS crashes into the Moon

The Moon as LCROSS closes in
The Moon as LCROSS closes in

LCROSS has just crashed into Cabeus crater on the Moon four minutes after the Centaur upper stage crashed, too. During the four minutes, LCROSS observed the plume that the upper stage kicked up and hopefully getting data that confirms the existence of water. The spacecraft had separated from the Centaur upper stage almost ten hours previously, after which they traveled almost 10,000 kilometers before reaching the Moon. NASA TV had just broadcast the impact live, and it's impressive how much media attention the LCROSS impact has grabbed. I had thought only space enthusiasts such as myself would have paid any attention to it.

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LCROSS changes its target

LCROSS was going to crash into crater Cabeus A. But after analyzing data from spacecraft such as the LRO, the Lunar Prospector, Chandrayaan-1, and Kaguya, the impact site for LCROSS has been changed to Cabeus (proper), a bigger crater close to Cabeus A. This determination was made because the hydrogen content and terrain suggests that crashing into Cabeus rather than into its satellite crater would give the best chance of observing water in the resulting plume.

Cabeus and other craters
Cabeus and other craters

Confirmation of water on the Moon

The Moon
The Moon

The Clementine and Lunar Prospector spacecraft had detected lots of hydrogen on the Moon, which strongly argued for the existence of water. Traces of water was also found in moon rocks brought back by the Apollo mission. However, the detected hydrogen might have been from sources other than water or could just be unattached protons from the solar wind that somehow managed to stick to the Moon, and the water in the moon rocks might have been from contamination when they were brought back to Earth, so the existence of water on the Moon has continued to be in question.

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