|
||||
|
|
||||
|
|
||||
|
Radar shows no evidence of thick ice at lunar poles CORNELL UNIVERSITY NEWS RELEASE Posted: November 14, 2003 Despite evidence from two space probes in the 1990s, radar astronomers say they can find no signs of thick ice at the moon's poles. If there is water at the lunar poles, the researchers say, it is widely scattered and permanently frozen inside the dust layers, something akin to terrestrial permafrost. Using the 70-centimeter (cm)-wavelength radar system at the National Science Foundation's (NSF) Arecibo Observatory, Puerto Rico, the research group sent signals deeper into the lunar polar surface -- more than five meters (about 5.5 yards) -- than ever before at this spatial resolution. "If there is ice at the poles, the only way left to test it is to go there directly and melt a small volume around the dust and look for water with a mass spectrometer," says Bruce Campbell of the Center for Earth and Planetary Studies at the Smithsonian Institution.
Suggestions of lunar ice first came in 1996 when radio data from the Clementine spacecraft gave some indications of the presence of ice on the wall of a crater at the moon's south pole. Then, neutron spectrometer data from the Lunar Prospector spacecraft, launched in 1998, indicated the presence of hydrogen, and by inference, water, at a depth of about a meter at the lunar poles. But radar probes by the 12-cm-wavelength radar at Arecibo showed no evidence of thick ice at depths of up to a meter. "Lunar Prospector had found significant concentrations of hydrogen at the lunar poles equivalent to water ice at concentrations of a few percent of the lunar soil," says Donald Campbell. "There have been suggestions that it may be in the form of thick deposits of ice at some depth, but this new data from Arecibo makes that unlikely." Says Bruce Campbell, "There are no places that we have looked at with any of these wavelengths where you see that kind of signature." The Nature paper notes that if ice does exist at the lunar poles it would be considerably different from "the thick, coherent layers of ice observed in shadowed craters on Mercury," found in Arecibo radar imaging. "On Mercury what you see are quite thick deposits on the order of a meter or more buried by, at most, a shallow layer of dust. That's the scenario we were trying to nail down for the moon," says Bruce Campbell. The difference between Mercury and the moon, the researchers say, could be due to the lower average rate of comets striking the lunar surface, to recent comet impacts on Mercury or to a more rapid loss of ice on the moon. What makes the lunar poles good cold traps for water is a temperature of minus 173 degrees Celsius (minus 280 degrees Fahrenheit). The limb of the sun rises only about two degrees above the horizon at the lunar poles so that sunlight never penetrates into deep craters, and a person standing on the crater floor would never see the sun. The Arecibo radar probed the floors of two craters in permanent shadow at the lunar south pole, Shoemaker and Faustini, and, at the north pole, the floors of Hermite and several small craters within the large crater Peary. In contrast, Clementine focused on the sloping walls of Shackleton crater, whose floor can't be "seen" from Earth. "There is a debate on how to interpret data from a rough, tilted surface," says Bruce Campbell. The Arecibo radar probe is a particularly good detector of thick ice
because it takes advantage of a phenomenon known as "coherent
backscatter." Radar waves can travel long distances without being
absorbed in ice at temperatures well below freezing. Reflections from
irregularities inside the ice produce a very strong radar echo. In
contrast, lunar soil is much more absorptive and does not give as
strong a radar echo.
|
Apollo 11 special patch Special collectors' patch marking the 35th anniversary of the historic Apollo 11 moon landing is now available.U.S. - U.K. - E.U. - Worldwide Inside Apollo mission control
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.U.S. The ultimate Apollo 11 DVD This exceptional chronicle of the historic Apollo 11 lunar landing mission features new digital transfers of film and television coverage unmatched by any other.U.S. - U.K. - E.U. - Worldwide Next ISS crew
Own a little piece of history with this official patch for the International Space Station's Expedition 11 crew. We'll ship yours today!U.S. Viking patch Available now from the Astronomy Now Store: the embroidered mission patch for NASA's Viking Project which reached the Red Planet in 1976.U.S. - U.K. - E.U. - Worldwide Mars Rover mission patch A mission patch featuring NASA's Mars Exploration Rover is now available from the Astronomy Now Store.U.S. - U.K. - E.U. - Worldwide Apollo 12 tribute DVD set ![]() New! Featuring the jovial crew of Pete Conrad, Dick Gordon and Alan Bean, the Apollo 12 mission was struck by lightning shortly after liftoff but proceeded on the second successful exploration voyage to the lunar surface. This three-disc DVD brings the mission to life with extraordinary detail. U.S. - U.K. - E.U. - Worldwide Fallen Heroes special patch This special 12-inch embroidered patch commemorates the U.S. astronauts who made the ultimate sacrifice, honoring the crews of Apollo 1, Challenger and Columbia.U.S. - U.K. - E.U. - Worldwide Women in Space Women of Space: Cool Careers on the Final Frontier is for girls, young women, and anyone else interested in learning about exciting careers in space exploration. Includes CD-ROM.U.S. - U.K. - E.U. - Worldwide Mars rover poster This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.U.S. Apollo Collage This beautiful one piece set features the Apollo program emblem surrounded by the individual mission logos.STS-127 Patch The official embroidered patch for shuttle Endeavour's flight to finish building Japanese section of the space station.![]() Hubble Patch The official embroidered patch for mission STS-125, the space shuttle's last planned service call to the Hubble Space Telescope, is available for purchase.Project Orion The Orion crew exploration vehicle is NASA's first new human spacecraft developed since the space shuttle a quarter-century earlier. The capsule is one of the key elements of returning astronauts to the Moon.Fallen Heroes Patch Collection The official patches from Apollo 1, the shuttle Challenger and Columbia crews are available in the store.
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.U.S. Apollo 11 special patch Special collectors' patch marking the 35th anniversary of the historic Apollo 11 moon landing is now available.U.S. - U.K. - E.U. - Worldwide Inside Apollo mission control
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.U.S. The ultimate Apollo 11 DVD This exceptional chronicle of the historic Apollo 11 lunar landing mission features new digital transfers of film and television coverage unmatched by any other.U.S. - U.K. - E.U. - Worldwide Next ISS crew
Own a little piece of history with this official patch for the International Space Station's Expedition 11 crew. We'll ship yours today!U.S. Get e-mail updates Sign up for our NewsAlert service and have the latest news in astronomy and space e-mailed direct to your desktop (privacy note: your e-mail address will not be used for any other purpose). |
||||
|
INDEX | PLUS | NEWS ARCHIVE | LAUNCH SCHEDULE ASTRONOMY NOW | STORE ADVERTISE © 2009 Spaceflight Now Inc. |
|||||