Apr 25 2012
From The Space Library
RELEASE: 12-126 WARM OCEAN CURRENTS CAUSE MAJORITY OF ICE LOSS FROM ANTARCTICA
WASHINGTON -- Warm ocean currents attacking the underside of ice shelves are the dominant cause of recent ice loss from Antarctica, a new study using measurements from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) revealed. An international team of scientists used a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves: warm ocean currents thawing the underbelly of the floating extensions of ice sheets and warm air melting them from above. The finding, published today in the journal Nature, brings scientists a step closer to providing reliable projections of future sea level rise. The researchers concluded 20 of the 54 ice shelves studied are being melted by warm ocean currents. Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise. This ocean-driven thinning is responsible for the most widespread and rapid ice losses in West Antarctica and the majority of Antarctic ice sheet loss during the period studied. "We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt," said the study's lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom. "The oceans can do all the work from below." To map the changing thickness of almost all the floating ice shelves around Antarctica, the team used a time series of 4.5 million surface height measurements taken by a laser instrument mounted on ICESat from October 2003 to October 2008. They measured how the ice shelf height changed over time and ran computer models to discard changes in ice thickness because of natural snow accumulation and compaction. The researchers also used a tide model that eliminated height changes caused by tides raising and lowering the ice shelves. "This study demonstrates the power of space-based, laser altimetry for understanding Earth processes," said Tom Wagner, cryosphere program scientist at NASA Headquarters in Washington." Coupled with NASA's portfolio of other ice sheet research using data from our GRACE mission, satellite radars and aircraft, we get a comprehensive view of ice sheet change that improves estimates of sea level rise." Previous studies used satellite radar data to measure the evolution of ice shelves and glaciers, but laser measurements are more precise in detecting changes in ice shelf thickness through time. This is especially true in coastal areas. Steeper slopes at the grounding line, where floating ice shelves connect with the landmass, cause problems for lower-resolution radar altimeters. ICESat was the first satellite specifically designed to use laser altimetry to study the Earth's polar regions. It operated from 2003 to 2009. Its successor, ICESat-2, is scheduled for launch in 2016. "This study demonstrates the urgent need for ICESat-2 to get into space," said Jay Zwally, ICESat project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "We have limited information on the changes in polar regions caused by climate change. Nothing can look at these changes like satellite measurements do." The new research also links the observed increase in melting that occurs on the underside of a glacier or ice shelf, called basal melt, and glacier acceleration with changes in wind patterns. "Studies have shown Antarctic winds have changed because of changes in climate," Pritchard said. "This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica's glaciers are responding rapidly to a changing climate." A different picture is seen on the Antarctic Peninsula, the long stretch of land pointing towards South America. The study found thinning of the largest ice shelf on the peninsula can be explained by warm summer winds directly melting the snow on the ice shelf surfaces. The patterns of widespread ocean-driven melting and summer melting on the Antarctic Peninsula can be attributed to changing wind patterns. The study was carried out by an international team from the British Antarctic Survey, Utrecht University in Utrecht, Netherlands, the University of California in San Diego and the non-profit research institute Earth and Space Research in Corvallis, Ore.
RELEASE: 12-134 NASA DAWN SPACECRAFT REVEALS SECRETS OF GIANT ASTEROID VESTA
WASHINGTON -- Findings from NASA's Dawn spacecraft reveal new details about the giant asteroid Vesta, including its varied surface composition, sharp temperature changes and clues to its internal structure. The findings were presented today at the European Geosciences Union meeting in Vienna, Austria and will help scientists better understand the early solar system and processes that dominated its formation. Spacecraft images, taken 420 miles (680 kilometers) and 130 miles (210 kilometers) above the surface of the asteroid, show a variety of surface mineral and rock patterns. Coded false-color images help scientists better understand Vesta's composition and enable them to identify material that was once molten below the asteroid's surface. Researchers also see breccias, which are rocks fused during impacts from space debris. Many of the materials seen by Dawn are composed of iron- and magnesium-rich minerals, which often are found in Earth's volcanic rocks. Images also reveal smooth pond-like deposits, which might have formed as fine dust created during impacts settled into low regions. "Dawn now enables us to study the variety of rock mixtures making up Vesta's surface in great detail," said Harald Hiesinger, a Dawn participating scientist at M?nster University in Germany. "The images suggest an amazing variety of processes that paint Vesta's surface." At the Tarpeia crater near the south pole of the asteroid, Dawn revealed bands of minerals that appear as brilliant layers on the crater's steep slopes. The exposed layering allows scientists to see farther back into the geological history of the giant asteroid. The layers closer to the surface bear evidence of contamination from space rocks bombarding Vesta's surface. Layers below preserve more of their original characteristics. Frequent landslides on the slopes of the craters also have revealed other hidden mineral patterns. "These results from Dawn suggest Vesta's 'skin' is constantly renewing," said Maria Cristina De Sanctis, lead of the visible and infrared mapping spectrometer team based at Italy's National Institute for Astrophysics in Rome. Dawn has given scientists a near 3-D view into Vesta's internal structure. By making ultrasensitive measurements of the asteroid's gravitational tug on the spacecraft, Dawn can detect unusual densities within its outer layers. Data now show an anomalous area near Vesta's south pole, suggesting denser material from a lower layer of Vesta has been exposed by the impact that created a feature called the Rheasilvia basin. The lighter, younger layers coating other parts of Vesta's surface have been blasted away in the basin. Dawn obtained the highest-resolution surface temperature maps of any asteroid visited by a spacecraft. Data reveal temperatures can vary from as warm as -10 degrees Fahrenheit (-23 degrees Celsius) in the sunniest spots to as cold as -150 degrees Fahrenheit (-100 degrees Celsius) in the shadows. This is the lowest temperature measurable by Dawn. These findings show the surface responds quickly to illumination with no mitigating effect of an atmosphere. "After more than nine months at Vesta, Dawn's suite of instruments has enabled us to peel back the layers of mystery that have surrounded this giant asteroid since humankind first saw it as just a bright spot in the night sky," said Carol Raymond, Dawn deputy principal investigator at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "We are closing in on the giant asteroid's secrets." Launched in 2007, Dawn began its exploration of the approximately 330-mile- (530-kilometer-) wide asteroid in mid-2011. The spacecraft's next assignment will be to study the dwarf planet Ceres in 2015. These two icons of the asteroid belt have been witness to much of our solar system's history. Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team.
RELEASE: 12-135 NASA SCIENTISTS FIND HISTORY OF ASTEROID IMPACTS IN EARTH ROCKS
WASHINGTON -- Research by NASA and international scientists concludes giant asteroids, similar or larger than the one believed to have killed the dinosaurs, hit Earth billions of years ago with more frequency than previously thought. To cause the dinosaur extinction, the killer asteroid that impacted Earth 65 million years ago would have been almost 6 miles (10 kilometers) in diameter. By studying ancient rocks in Australia and using computer models, researchers estimate that approximately 70 asteroids the same size or larger impacted Earth 1.8 to 3.8 billion years ago. During the same period, approximately four similarly-sized objects hit the moon. "This work demonstrates the power of combining sophisticated computer models with physical evidence from the past, further opening an important window to Earth's history," said Yvonne Pendleton, director of NASA's Lunar Science Institute (NLSI) at NASA's Ames Research Center at Moffett Field, Calif. Evidence for these impacts on Earth comes from thin rock layers that contain debris of nearly spherical, sand-sized droplets called spherules. These millimeter-scale clues were formerly molten droplets ejected into space within the huge plumes created by mega-impacts on Earth. The hardened droplets then fell back to Earth, creating thin but widespread sedimentary layers known as spherule beds. The new findings are published today in the journal Nature. "The beds speak to an intense period of bombardment of Earth," said William Bottke principal investigator of the impact study team at the Southwest Research Institute (SwRI) in Boulder, Colo. "Their source long has been a mystery." The team's findings support the theory Jupiter, Saturn, Uranus and Neptune formed in different orbits nearly 4.5 billion years ago, migrating to their current orbits about 4 billion years ago from the interplay of gravitational forces in the young solar system. This event triggered a solar system-wide bombardment of comets and asteroids called the "Late Heavy Bombardment." In the paper, the team created a model of the ancient main asteroid belt and tracked what would have happened when the orbits of the giant planets changed. They discovered the innermost portion of the belt became destabilized and could have delivered numerous big impacts to Earth and the moon over long time periods. At least 12 mega-impacts produced spherule beds during the so-called Archean period 2.5 to 3.7 billion years ago, a formative time for life on Earth. Ancient spherule beds are rare finds, rarer than rocks of any other age. Most of the beds have been preserved amid mud deposited on the sea floor below the reach of waves. The impact believed to have killed the dinosaurs was the only known collision over the past half-billion years that made a spherule layer as deep as those of the Archean period. The relative abundance of the beds supports the hypothesis for many giant asteroid impacts during Earth's early history. The frequency of the impacts indicated in the computer models matches the number of spherule beds found in terrains with ages that are well understood. The data also hint at the possibility that the last impacts of the Late Heavy Bombardment on Earth made South Africa's Vredefort crater and Canada's Sudbury crater, both of which formed about 2 billion years ago. "The Archean beds contain enough extraterrestrial material to rule out alternative sources for the spherules, such as volcanoes," said Bruce Simonson, a geologist from Oberlin College in Oberlin, Ohio. The research was funded by NLSI and conducted by members or associates of NLSI's Center of Lunar Origin and Evolution, based at SwRI. The impact study team also includes scientists from Purdue University in West Lafayette, Ind.; Charles University in Prague, Czech Republic; Observatorie de la Cote d'Azur in Nice, France; and Academia Sinica in Taipei, Taiwan.
RELEASE: 12-137 NASA RELEASES CALL FOR PHASE II VISIONARY ADVANCED CONCEPTS
WASHINGTON -- The NASA Innovative Advanced Concepts (NIAC) Program is seeking proposals to continue promising studies for which it has supported the first phase. These cutting-edge concepts have the potential to transform future exploration missions, enable new capabilities, or significantly alter current approaches to launching, building, and operating aerospace systems. "These transformative concepts have the potential to mature into the new capabilities NASA needs for the challenging space missions in its future," said Michael Gazarik, director of NASA's Space Technology Program at NASA Headquarters in Washington. NIAC projects are chosen based on their character as innovative and visionary, technically substantiated, and very early in development -- 10 years or more from use in a mission. NIAC's current diverse portfolio represents multiple technology areas, including power, propulsion, structures, and avionics. "We are thrilled to be launching Phase II, so the 2012 NIAC portfolio can feature the most exciting combination of new ideas and continued development," said Jay Falker, NIAC program executive at NASA Headquarters. The call for proposals follows last summer's inaugural selection of Phase I concepts, which are now under study. NIAC will be accepting proposals of no more than 20 pages until June 6. NASA expects to fund between five and nine Phase II studies this year. The number of awards will depend on the strength of proposals and availability of appropriated funds. Awardees will receive up to $500,000 over two years to further analyze and develop their innovative concepts and help create new avenues for future NASA missions. Selection announcements are expected in August. This limited solicitation is only for continuing NIAC Phase I concepts. Phase II proposals are eligible based on any current Phase I studies, or any prior Phase I studies from the original NASA Institute for Advanced Concepts that did not complete Phase II. NASA's early investment and partnership with creative scientists, engineers and citizen inventors from across the nation will pay huge technological dividends and help maintain America's leadership in the global technology economy. NIAC is part of NASA's Space Technology Program, managed by the Office of the Chief Technologist.
