On October 9, 2009, a piece of launch rocket still attached to an orbiting spacecraft will finally let go so it can take a dive into the moon.
The event is the end goal of NASA's LCROSS mission, which aims to study material kicked up by the impact to find out whether the lunar surface has water ice.
Today NASA announced that Cabeus A, a 25-mile-wide (40-kilometer-wide) crater on the moon's south pole, will be the site in the mission's crosshairs.
[LCROSS's Candidate Impact Craters -- That's Cabeus A Marked as "SP C"]
—Picture courtesy NASA/Ames Research Center
Not too much is known about this crater, which is part of the reason it was selected. Cabeus A sits on a region of the moon that's almost always in shadow, making it more likely that any water ice could exist there, since it wouldn't have been effectively vaporized by direct sunlight.
The crater is also among the sites on the moon known to have a mysterious quantity of hydrogen, which your grade-school chemistry teacher would remind you is a major component of good old H2O. Cabeus A in particular has a high concentration of hydrogen clustered in what NASA scientists call a "sweet spot" near its rim.
Finally, Cabeus A rests along an edge of the moon that is easily visible from Earth, making it an ideal place to send up a plume for people to see.
The plume will be bright but short lived, lasting only about 30 seconds before it starts to fade, LCROSS scientist Tony Colaprete said today at a news briefing.
To get the most out of this "flash in the pan," the LCROSS team has coordinated a vast army of stargazers on the ground and in space to watch the event and collect as much information as they can about the plume.
Top of the list will be the LCROSS craft itself, which will be speeding toward the impact site just after it sends the leftover rocket hurtling toward the moon.
Instruments aboard LCROSS will collect data about the plume and the newly minted impact crater until the probe looses contact with Earth about 15.5 miles (25 kilometers) above the lunar surface. Four minutes after the first impact, LCROSS itself will then slam into the moon.
The duty roster also includes massive telescopes in Hawaii and the U.S. Southwest as well as orbiters such as the Hubble Space Telescope and the GeoEye imaging satellite.
In addition, NASA has put out the call for amateur astronomers with backyard telescopes to train their instruments on Cabeus A and report back via a "citizen science" web site.
The data entry page isn't up and running just yet, but if you'd like to take part LCROSS does have a page full of tips for when and where to look, what equipment to use, and how to take pictures.
The impact will happen at 4:30 a.m. Pacific time, which should allow enough darkness for the plume to be visible to people in the Western Hemisphere. Us folks on the East Coast will have our view blocked by dawn skies, but we can watch live streaming video of the moon crash on NASA TV.
For an idea of what you might see, go out and look at the moon tonight, LCROSS experts suggest: The moon is in the same phase right now as it will be on impact day.
As for what we might find, water is the goal but it's not the only option. Hydrogen could also mean the moon's pockets are full of methane, hydrocarbons, or whatever else the body has collected over the last 3.5 billion years, Colaprete noted.
Water or no, the plume's contents, he said, will be "a window into the past of the entire inner solar system."
