Mar 31 2011
From The Space Library
RELEASE: 11-094 SALT-SEEKING SPACECRAFT ARRIVES AT LAUNCH SITE NASA INSTRUMENT WILL MEASURE OCEAN SURFACE SALINITY
WASHINGTON -- An international spacecraft that will take NASA's first space-based measurements of ocean surface salinity has arrived at its launch site at Vandenberg Air Force Base in California. The Aquarius/SAC-D mission will provide scientists with a key missing variable in satellite observations of Earth that links ocean circulation, the global balance of freshwater, and climate. The Aquarius/SAC-D spacecraft left Sao Jose dos Campos, Brazil on March 29. Following final tests, the spacecraft will be attached to a Delta II rocket for a June 9 launch. The mission is a collaboration between NASA and Argentina's space agency, Comision Nacional de Actividades Espaciales (CONAE), with participation from Brazil, Canada, France and Italy. Aquarius, the NASA-built primary instrument on CONAE's SAC-D spacecraft, will map global changes in the concentration of dissolved salt at the ocean surface. Measuring salinity is important to understanding how changes in rainfall, evaporation and the melting or freezing of ice influence ocean circulation and are linked to climate changes. The three-year mission will provide new insights into how variations in ocean surface salinity relate to these fundamental climate processes. "Just as salt is essential to life as we know it, salinity is crucial to Earth's climate system," said Aquarius principal investigator Gary Lagerloef of Earth and Space Research in Seattle. "Very small changes in salinity can have large-scale effects on ocean circulation and the way the ocean moderates our climate. These changes are linked to the movement of water between the ocean, atmosphere and cryosphere." Aquarius will greatly enhance the quantity of ocean salinity measurements that have been collected from ships, buoys and floats. "When combined with data from other sensors that measure sea level, ocean color, temperature, winds, rainfall and evaporation, Aquarius' continuous, global salinity data will give scientists a much clearer picture of how the ocean works, how it is linked to climate and how it may respond to climate change," Lagerloef said. Precise salinity measurements from Aquarius will reveal changes in patterns of global precipitation and evaporation, and show how these affect ocean circulation. Studies from Aquarius eventually will improve computer models used to forecast future climate conditions, including short-term climate events such as El Nino and La Nina. "The mission continues a long and successful partnership between NASA and CONAE, and it will provide a new type of ocean observation for ocean and climate studies," said Amit Sen, Aquarius project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Aquarius will measure ocean surface salinity by sensing thermal microwave emissions from the water's surface with a radiometer. When other environmental factors are equal, these emissions indicate how salty the surface water is. Because salinity levels in the open ocean vary by only about five parts per thousand, Aquarius employs new technologies to detect changes in salinity as small as about two parts per 10,000, equivalent to about one-eighth of a teaspoon of salt in a gallon of water. Flying in a 408-mile high, polar orbit, Aquarius/SAC-D will map the global ocean once every seven days. Its measurements will be merged to yield monthly estimates of ocean surface salinity with a spatial resolution of 93 miles. The data will reveal how salinity changes over time and from one part of the ocean to another. Aquarius is a NASA Earth System Science Pathfinder Program mission. The Aquarius instrument was jointly built by JPL and NASA's Goddard Space Flight Center in Greenbelt, Md. NASA's Launch Services Program at the Kennedy Space Center in Florida is managing the launch. JPL will manage Aquarius through the mission's commissioning phase and archive mission data. Goddard will manage the mission's operations phase and process Aquarius science data. CONAE is providing the SAC-D spacecraft, an optical camera, a thermal camera in collaboration with Canada, a microwave radiometer, sensors developed by various Argentine institutions, and the mission operations center in Argentina. France and Italy also are contributing instruments.
RELEASE: 11-095 NASA SPACECRAFT REVEAL MYSTERIES OF JUPITER AND SATURN RINGS PASADENA, Calif. --
In a celestial forensic exercise, scientists analyzing data from NASA's Cassini, Galileo and New Horizons missions have traced telltale ripples in Saturn and Jupiter's rings to specific collisions with cometary fragments that occurred decades, not millions of years, ago. Jupiter's ripple-producing culprit was comet Shoemaker-Levy 9. The comet's debris cloud hurtled through the thin Jupiter ring system on a collision course into the planet in July 1994. Scientists attribute Saturn's ripples to a similar object - likely another cloud of comet debris - plunging through the inner rings in 1983. The findings are detailed in two papers published Thursday in the journal Science. "We're finding evidence that a planet's rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago," said Matthew Hedman, a Cassini imaging team associate, lead author on one of the papers, and a research associate at Cornell University in Ithaca, N.Y. "The solar system is a much more dynamic place than we gave it credit for." Scientists learned about the patchy patterns in Jupiter's rings in the late 1990s from Galileo's visit to Jupiter. Unfortunately, the images from that mission were fuzzy, and scientists didn't understand why such patterns would occur. Not until Cassini entered orbit around Saturn in 2004 and started sending back thousands of images did scientists have a better picture of the activity. A 2007 science paper by Hedman and colleagues first noted corrugations in Saturn's innermost ring, dubbed the D ring. A group including Hedman and Mark Showalter, a Cassini co-investigator based at the SETI Institute in Mountain View, Calif., saw that the grooves in the D ring appeared to wind together more tightly over time. Playing the process backward, Hedman demonstrated the pattern originated when something tilted the D ring off its axis by about 300 feet (100 meters) in late 1983. The scientists found Saturn's gravity on the tilted area warped the ring into a tightening spiral. Cassini imaging scientists received another clue around August 2009 when the sun shone directly along Saturn's equator and lit the rings edge-on. The unique lighting conditions highlighted ripples not previously seen in another part of the ring system. Whatever happened in 1983 was big - not a small, localized event. The collision tilted a region more than 12,000 miles (19,000 kilometers) wide, covering part of the D ring and the next outermost ring, called the C ring. Unfortunately, spacecraft were not visiting Saturn at that time, and the planet was on the far side of the sun out of sight from ground or space-based telescopes. Hedman and Showalter, the lead author on the second paper, wondered whether the long-forgotten pattern in Jupiter's ring system might illuminate the mystery. Using Galileo images from 1996 and 2000, Showalter confirmed a similar winding spiral pattern by applying the same math they had applied to Saturn and factoring in Jupiter's gravitational influence. Galileo was launched on a space shuttle in 1989 and studied Jupiter until 2003. Unwinding the spiral pinpointed the date when Jupiter's ring was tilted off its axis between June and September 1994. Shoemaker-Levy plunged into the Jovian atmosphere in late July. The Galileo images also revealed a second spiral, which was calculated to have originated in 1990. Images taken by New Horizons in 2007, when the spacecraft flew by Jupiter on its way to Pluto, showed two newer ripple patterns, in addition to the fading echo of the Shoemaker-Levy impact. "We now know that collisions into the rings are very common - a few times per decade for Jupiter and a few times per century for Saturn," Showalter said. "Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later." Launched in Oct. 15, 1997, Cassini began orbiting Saturn in 2004 and sends back data daily. "Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system," said Linda Spilker, Cassini project scientist, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Cassini's long sojourn around Saturn has helped us tease out subtle clues that tell us about the history of our origins." The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate in Washington. The imaging team is based at the Space Science Institute in Boulder, Colo.
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