Nov 29 2012

From The Space Library

RELEASE: 12-409 ICE SHEET LOSS AT BOTH POLES INCREASING, MAJOR STUDY FINDS

WASHINGTON -- An international team of experts supported by NASA and the European Space Agency (ESA) has combined data from multiple satellites and aircraft to produce the most comprehensive and accurate assessment to date of ice sheet losses in Greenland and Antarctica and their contributions to sea level rise. In a landmark study published Thursday in the journal Science, 47 researchers from 26 laboratories report the combined rate of melting for the ice sheets covering Greenland and Antarctica has increased during the last 20 years. Together, these ice sheets are losing more than three times as much ice each year (equivalent to sea level rise of 0.04 inches or 0.95 millimeters) as they were in the 1990s (equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of the loss is coming from Greenland, with the rest from Antarctica. This rate of ice sheet losses falls within the range reported in 2007 by the Intergovernmental Panel on Climate Change (IPCC). The spread of estimates in the 2007 IPCC report was so broad, however, it was not clear whether Antarctica was growing or shrinking. The new estimates, which are more than twice as accurate because of the inclusion of more satellite data, confirm both Antarctica and Greenland are losing ice. Combined, melting of these ice sheets contributed 0.44 inches (11.1 millimeters) to global sea levels since 1992. This accounts for one-fifth of all sea level rise over the 20-year survey period. The remainder is caused by the thermal expansion of the warming ocean, melting of mountain glaciers and small Arctic ice caps, and groundwater mining. The study was produced by an international collaboration -- the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) -- that combined observations from 10 satellite missions to develop the first consistent measurement of polar ice sheet changes. The researchers reconciled differences among dozens of earlier ice sheet studies by carefully matching observation periods and survey areas. They also combined measurements collected by different types of satellite sensors, such as ESA's radar missions, NASA's Ice, Cloud and land Elevation Satellite (ICESat) and the NASA/German Aerospace Center's Gravity Recovery and Climate Experiment (GRACE). "What is unique about this effort is that it brought together the key scientists and all of the different methods to estimate ice loss," said Tom Wagner, NASA's cryosphere program manager in Washington. "It's a major challenge they undertook, involving cutting-edge, difficult research to produce the most rigorous and detailed estimates of ice loss from Greenland and Antarctica to date. The results of this study will be invaluable in informing the IPCC as it completes the writing of its Fifth Assessment Report over the next year." Professor Andrew Shepherd of the University of Leeds in the United Kingdom coordinated the study, along with research scientist Erik Ivins of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Shepherd said the venture's success is because of the cooperation of the international scientific community and the precision of various satellite sensors from multiple space agencies. "Without these efforts, we would not be in a position to tell people with confidence how Earth's ice sheets have changed, and to end the uncertainty that has existed for many years," Shepherd said. The study found variations in the pace of ice sheet change in Antarctica and Greenland. "Both ice sheets appear to be losing more ice now than 20 years ago, but the pace of ice loss from Greenland is extraordinary, with nearly a five-fold increase since the mid-1990s," Ivins said. "In contrast, the overall loss of ice in Antarctica has remained fairly constant with the data suggesting a 50-percent increase in Antarctic ice loss during the last decade."

RELEASE: 12-411 NASA SPACECRAFT FINDS NEW EVIDENCE FOR WATER ICE ON MERCURY

WASHINGTON -- A NASA spacecraft studying Mercury has provided compelling support for the long-held hypothesis the planet harbors abundant water ice and other frozen volatile materials within its permanently shadowed polar craters. The new information comes from NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Its onboard instruments have been studying Mercury in unprecedented detail since its historic arrival there in March 2011. Scientists are seeing clearly for the first time a chapter in the story of how the inner planets, including Earth, acquired their water and some of the chemical building blocks for life. "The new data indicate the water ice in Mercury's polar regions, if spread over an area the size of Washington, D.C., would be more than 2 miles thick," said David Lawrence, a MESSENGER participating scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of three papers describing the findings. The papers were published online in Thursday's edition of Science Express. Spacecraft instruments completed the first measurements of excess hydrogen at Mercury's north pole, made the first measurements of the reflectivity of Mercury's polar deposits at near-infrared wavelengths, and enabled the first detailed models of the surface and near-surface temperatures of Mercury's north polar regions. Given its proximity to the sun, Mercury would seem to be an unlikely place to find ice. However, the tilt of Mercury's rotational axis is less than 1 degree, and as a result, there are pockets at the planet's poles that never see sunlight. Scientists suggested decades ago there might be water ice and other frozen volatiles trapped at Mercury's poles. The idea received a boost in 1991 when the Arecibo radio telescope in Puerto Rico detected radar-bright patches at Mercury's poles. Many of these patches corresponded to the locations of large impact craters mapped by NASA's Mariner 10 spacecraft in the 1970s. However, because Mariner saw less than 50 percent of the planet, planetary scientists lacked a complete diagram of the poles to compare with the radar images. Images from the spacecraft taken in 2011 and earlier this year confirmed all radar-bright features at Mercury's north and south poles lie within shadowed regions on the planet's surface. These findings are consistent with the water ice hypothesis. The new observations from MESSENGER support the idea that ice is the major constituent of Mercury's north polar deposits. These measurements also reveal ice is exposed at the surface in the coldest of those deposits, but buried beneath unusually dark material across most of the deposits. In the areas where ice is buried, temperatures at the surface are slightly too warm for ice to be stable. MESSENGER's neutron spectrometer provides a measure of average hydrogen concentrations within Mercury's radar-bright regions. Water ice concentrations are derived from the hydrogen measurements. "We estimate from our neutron measurements the water ice lies beneath a layer that has much less hydrogen. The surface layer is between 10 and 20 centimeters [4-8 inches] thick," Lawrence said. Additional data from detailed topography maps compiled by the spacecraft corroborate the radar results and neutron measurements of Mercury's polar region. In a second paper by Gregory Neumann of NASA's Goddard Flight Center in Greenbelt, Md., measurements of the shadowed north polar regions reveal irregular dark and bright deposits at near-infrared wavelength near Mercury's north pole. "Nobody had seen these dark regions on Mercury before, so they were mysterious at first," Neumann said. The spacecraft recorded dark patches with diminished reflectance, consistent with the theory that ice in those areas is covered by a thermally insulating layer. Neumann suggests impacts of comets or volatile-rich asteroids could have provided both the dark and bright deposits, a finding corroborated in a third paper led by David Paige of the University of California at Los Angeles. "The dark material is likely a mix of complex organic compounds delivered to Mercury by the impacts of comets and volatile-rich asteroids, the same objects that likely delivered water to the innermost planet," Paige said. This dark insulating material is a new wrinkle to the story, according to MESSENGER principal investigator Sean Solomon of Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y. "For more than 20 years, the jury has been deliberating whether the planet closest to the sun hosts abundant water ice in its permanently shadowed polar regions," Solomon said. "MESSENGER now has supplied a unanimous affirmative verdict." MESSENGER was designed and built by APL. The lab manages and operates the mission for NASA's Science Mission Directorate in Washington. The mission is part of NASA's Discovery Program, managed for the directorate by the agency's Marshall Space Flight Center in Huntsville, Ala.

MEDIA ADVISORY: M12-222 WILDFIRES, MARS AND EARTH'S RADIATION BELTS AMONG NASA NEWS HIGHLIGHTS AT AMERICAN GEOPHYSICAL UNION MEETING

WASHINGTON -- NASA researchers will present new findings on a wide range of Earth and space science topics next week at the annual meeting of the American Geophysical Union (AGU). The meeting takes place Dec. 3-7 at the Moscone Convention Center, 747 Howard St., in San Francisco. Media registration for the event is open. None of the briefings will be carried on NASA Television, but all will be webstreamed for registered journalists on AGU's website. NASA's media briefings during the meeting will feature topics such as the latest discoveries on Mars by NASA's Curiosity and Opportunity rovers, the impact of climate change on future U.S. wildfires, and new features discovered inside Earth's radiation belts by the agency's Van Allen Probes. In addition, NASA scientists and their colleagues who use NASA research capabilities will present noteworthy findings during scientific sessions that are open to registered journalists.