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LCROSS Update: Target Crater Selected for Lunar South Pole Impacts

LCROSS heads for Moon

The LCROSS impacts will be timed so that they can be observed with the large telescopes on Mauna Kea. Courtesy NASA.

NASA has selected a final destination for its Lunar Crater Observation and Sensing Satellite (LCROSS) after a journey of nearly 5.6 million miles that included several orbits around Earth and the Moon. The mission team announced September 9 that Cabeus A will be the target crater for the LCROSS dual impacts scheduled for 1:30 a.m. HST on October 9, 2009. After an extensive review, the crater was selected as the optimal location for the spacecraft's evaluation of whether water ice exists at the lunar south pole.

LCROSS will search for water ice by sending its spent upper-stage Centaur rocket to impact the permanently shadowed polar crater. The satellite will fly into the plume of dust left by the impact and measure the properties before also colliding with the lunar surface. The LCROSS team selected Cabeus A based on a set of conditions that include proper debris plume illumination for visibility from Earth, a high concentration of hydrogen, and mature crater features such as a flat floor, gentle slopes, and the absence of large boulders.

Professional astronomers will observe the impact with both ground-based telescopes and with telescopes in space, including the newly refurbished Hubble Space Telescope and the Lunar Reconnaissance Orbiter.

At Mauna Kea Observatories on the island of Hawaii, the NASA Infrared Telescope Facility, W. M. Keck Observatory, and the UH 2.2-meter telescope will be among those observing the impact.

On Maui, IfA scientists and staff have joined with staff at Las Cumbres Observatory, which operates the 2-meter Faulkes Telescope North on Haleakala, to conduct a unique experiment. They will use a technique called polarization modulation to virtually eliminate water in Earth's atmosphere from the observations, and then by looking at the resulting light through filters that limit the light to specific wavelengths, they hope to detect water (H2O) that has been photolyzed, that is broken up into hydrogen and hydroxyl ions (H and OH-) components by light. IfA scientists will also be observing the impact with the IfA-designed and -built HiVis spectropolarimeter on the 3.6-meter AEOS telescope. "With smaller telescopes, we may have greater sensitivity than larger ground-based observatories because of our use of novel polarimetry techniques," said Dr. Joe Ritter, director of the IfA Advanced Technology Research Center Laboratory.

Amateur astronomers will also play an important role in chronicling the impact and its aftermath. On Maui, at a site at the 9,955-foot (3,034-m) elevation, the Haleakala Amateur Astronomers (HAA) will observe the LCROSS impact both visually and using 14- and 18-inch telescopes with cameras attached. One of their cameras was obtained with the help of Ritter and IfA Education and Outreach Specialist Dr. J. D. Armstrong. They worked with Kalama Intermediate School Vice Principal Penrod Valdyka (an HAA member) to write a grant submitted to the state Department of Education. Students from that school will have the opportunity to learn by analyzing the images taken by the camera. IfA staff on Hawaii island are also working with amateur astronomers who will observe the impact.

The LCROSS mission was launched on June 18, along with the with the Lunar Reconnaissance Orbiter, from Cape Canaveral, Florida. For more information about the LCROSS mission and images of Cabeus A, visit