Posted on by Fraser Cain

NASA Orbiter Arrives at Mars

NASA’s Mars orbiter approaching Mars. Image credit: NASA/JPL Click to enlarge
Mars added a new satellite today, when NASA’s Mars Reconnaissance Orbiter arrived at the Red Planet. The spacecraft fired its engines for 27 minutes shortly before arrival to slow it down a little, just enough so that Mars could capture it with its gravity. Over the next seven months, the spacecraft will pass through Mars’ atmosphere 550 times, slowing itself down further through a process called aerobraking. After having settled into its final orbit, it will search for signs of water and scout out future landing locations.

NASA’s Mars Reconnaissance Orbiter has begun its final approach to the red planet after activating a sequence of commands designed to get the spacecraft successfully into orbit.

The sequence began Tuesday and will culminate with firing the craft’s main thrusters for about 27 minutes on Friday — a foot on the brakes to reduce velocity by about 20 percent as the spacecraft swings around Mars at about 5,000 meters per second (about 11,000 miles per hour). Mission controllers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and Lockheed Martin Space Systems, Denver, are monitoring the events closely.

“We have been preparing for years for the critical events the spacecraft must execute on Friday,” said JPL’s Jim Graf, project manager. “By all indications, we’re in great shape to succeed, but Mars has taught us never to get overconfident. Two of the last four orbiters NASA sent to Mars did not survive final approach.”

Mars Reconnaissance Orbiter will build upon discoveries by five successful robots currently active at Mars: NASA rovers Spirit and Opportunity, NASA orbiters Mars Global Surveyor and Mars Odyssey, and the European Space Agency’s Mars Express orbiter. It will examine Mars’ surface, atmosphere and underground layers in great detail from a low orbit. It will aid future missions by scouting possible landing sites and relaying communications. It will send home up to 10 times as much data per minute as any previous Mars mission.

First, it must get into orbit. The necessary thruster burn will begin shortly after 1:24 p.m. Pacific Time on Friday. Engineers designed the burn to slow the spacecraft just enough for Mars’ gravity to capture it into a very elongated elliptical orbit. A half-year period of more than 500 carefully calculated dips into Mars’ atmosphere — a process called aerobraking — will use friction with the atmosphere to gradually shrink the orbit to the size and nearly-circular shape chosen for most advantageous use of the six onboard science instruments.

“Our primary science phase won’t begin until November, but we’ll actually be studying the changeable structure of Mars’ atmosphere by sensing the density of the atmosphere at different altitudes each time we fly through it during aerobraking,” said JPL’s Dr. Richard Zurek, project scientist for the mission.

Additional information about Mars Reconnaissance Orbiter is available online at: http://www.nasa.gov/mro

The mission is managed by JPL, a division of the California Institute of Technology, Pasadena, for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft.

Original Source: NASA News Release

Posted on by Fraser Cain

GIOVE A Transmits Loud and Clear

Chilbolton Observatory. Image credit: ESA Click to enlarge
After a successful launch on 28 December 2005, GIOVE A began transmitting navigation signals on 12 January 2006. Work is currently being performed to check the quality of these signals.

In space, the success of a mission relies on the achievement of a series of milestones. This is especially true for a pioneering mission such as GIOVE A, the first Galileo satellite, launched late last year under the European Space Agency’s responsibility.

Manufacture, launch, reaching final orbit and transmission of first signals: all these key steps were met by the satellite, which is now going to achieve its first goal, the filing for the frequencies allocated to Galileo by the International Telecommunication Union (ITU).

After launch and platform commissioning, GIOVE A started signal transmission on 12 January and the quality of these signals is now being checked. This checking process is employing several facilities, including the Navigation Laboratory at ESA’s European Space Research and Technology Centre (ESTEC), in the Netherlands, the ESA ground station at Redu, in Belgium, and the Rutherford Appleton Laboratory (RAL) Chilbolton Observatory in the United Kingdom.

Chilbolton’s 25 metre antenna makes it possible to acquire the signals from GIOVE A and verify they conform to the Galileo system’s design specification. Each time the satellite is visible from Chilbolton, the large antenna is activated and tracks the satellite. GIOVE A orbits at an altitude of 23 260 kilometres, making a complete journey around the Earth in 14 hours and 22 minutes.

Every orbital pass provides an opportunity to analyse the signals from the satellite. The quality of the signals transmitted by GIOVE A will have an important influence on the accuracy of the positioning information that will be provided by the user receivers on the ground, so a detailed check-out of the signal properties is mandatory. The signal quality can be affected by the environment of the satellite in its orbit and by the propagation path of the signals travelling from space to ground. Additionally, the satellite signals must not create interference with services operating in adjacent frequency bands, and this is also being checked.

The engineers at Chilbolton have means to observe and record in real time the spectrum of the signals transmitted by GIOVE A. Several measurements are performed relating to transmitted signal power, centre frequency and bandwidth, as well as the format of the navigation messages generated on-board. This allows the analysis of the satellite transmissions in the three frequency bands which are reserved for it and confirmation that GIOVE A is transmitting that which is expected of it.

The GIOVE A mission also represents an opportunity for the testing of a key element of the future Galileo system, the user receivers. The first Galileo experimental receivers, manufactured by Septentrio of Belgium, were installed at the Redu and Chilbolton In Orbit Test Stations and at the Guildford, United Kingdom, premises of Surrey Satellite Technology Limited (SSTL), the manufacturer of the satellite and now in charge of its control in orbit.

A meticulous task, sometimes tedious, but essential for the progress of the project, ensuring that Galileo, the joint civilian navigation initiative from the European Space Agency and the European Commission, can offer the value added services which will fundamentally depend on the quality of the transmitted signals.

Original Source: ESA Portal

Posted on by Fraser Cain

Merging White Dwarfs Create Helium Stars

Harlan J. Smith Telescope. Image credit: Marty Harris/McDonald Observatory. Click to enlarge
An international group of astronomers has used the Hubble Space Telescope to determine the origin of an unusual class of objects called extreme helium stars. These objects are formed when two white dwarf stars merge together. Since they were first discovered more than 60 years ago, less than two dozen have found. They contain almost no hydrogen, and are dominated by helium and other heavier elements. When two white dwarf stars merge together, the resulting star swells up to become a supergiant star rich in helium.

An international group of astronomers including Dr. David L. Lambert, director of The University of Texas at Austin McDonald Observatory, has used Hubble Space Telescope to determine the origin of a very unusual and rare type of star. The group’s studies indicate that the so-called “extreme helium stars” are formed by the merger of two white dwarf stars. The work has been published in the February 10 issue of The Astrophysical Journal.

The team was led by Dr. Gajendra Pandey of the Indian Institute of Astrophysics (IIA) in Bangalore, and also includes Dr. C. Simon Jeffery of Armagh Observatory in Northern Ireland, and Professor N. Kameswara Rao, also of IIA.

“It’s taken more than 60 years after the first discovery at McDonald to get some idea of how these formed,” Rao said. He has been studying these types of stars for more than 30 years. “We are now getting a consistent picture.”

The nature of the first extreme helium star, HD 124448, was discovered at McDonald Observatory in 1942 by Daniel M. Popper of The University of Chicago. Since then, fewer than two dozen of these stars have been identified. They are supergiant stars – less massive than the Sun but many times larger and hotter – and remarkable for their strange compositions. They contain almost no hydrogen, the most abundant chemical element in the universe, and the most basic component of all stars. Instead, they are dominated by helium, with significant amounts of carbon, nitrogen, and oxygen, and traces of all other stable elements.

The origin of extreme helium stars cannot be traced back to formation in a cloud of helium gas, since no such clouds exist in our Milky Way galaxy. Nuclear reactions in a star like the Sun convert hydrogen to helium to provide sunlight or starlight. Since the helium is confined the hot core of a star, the star must lose vast amounts of gas before the helium is at the star’s surface – and thus detectable by telescopes. No known mechanism inside the star can drive off the overlying layers to expose the helium.

Two decades ago, astronomers Ronald Webbink and Icko Iben of the University of Illinois introduced the theory that extreme helium stars formed from the merger of two white dwarfs.

White dwarfs are the end product of the evolution of stars like the Sun. They don’t contain much hydrogen. Some are rich in helium, and others in carbon and oxygen. A pair of white dwarfs can result from the evolution of a normal binary star (two normal stars in orbit around each other).

Webbink and Iben supposed that, in some cases, one star in the binary may evolve as a helium-rich white dwarf, and the other as a carbon-oxygen-rich white dwarf. Over billions of years of orbiting each other, the two stars lose energy and move steadily closer to each other. Eventually, the helium white dwarf is consumed by the more massive carbon-oxygen white dwarf. The resultant single star swells up to become a helium-rich supergiant star.

To test this theory, astronomers needed to uncover the exact chemical composition of extreme helium stars. This is what Pandey, Lambert, and their colleagues set out to do. They obtained crucial observations with NASA’s Hubble Space Telescope, and made supporting observations from the 2.7-meter Harlan J. Smith Telescope at McDonald Observatory and the 2.3-meter Vainu Bappu Telescope in India.

“As an aside,” Lambert said, “it’s interesting to note that the namesakes of these two telescopes, Harlan J. Smith and Vainu Bappu, were the very best of friends in graduate school at Harvard.” Later, Smith served as director of McDonald Observatory from 1963 to 1989. Vainu Bappu founded the Indian Institute of Astrophysics. “Today, with collaborations like this project,” Lambert said, “we’re maintaining the important international and personal ties that astronomy thrives upon.”

The group made detailed studies of the ultraviolet light coming from seven extreme helium stars with Hubble Space Telescope’s STIS instrument (the Space Telescope Imaging Spectrograph) and of the optical light from the telescopes in Texas and India. This data provided them with the specific amounts of at least two dozen different chemical elements present in each star they studied.

According to Rao, it is the advance in technology of being able to observe the spectra of these stars in ultraviolet light with Hubble that made this breakthrough study possible more than 60 years after extreme helium stars were discovered.

The Hubble results match up well with predicted compositions from models of the composition of a star formed through the merger of two white dwarf stars in which the helium-core white dwarf is torn apart, and forms a thick disk around the carbon-oxygen white dwarf. Then, in a process taking only a few minutes, the disk is gravitationally pulled into the carbon-oxygen white dwarf.

What happens next depends of the mass of the new, resulting star. If it is above a certain mass, called the Chandrasekar limit, it will explode (specifically, it will explode as a Type Ia supernova). However, if the mass is below this limit, the new merged star will balloon up into a supergiant, eventually becoming an extreme helium star.

Pandey, Lambert, Jeffery, and Rao plan to continue their research on extreme helium stars, using both the Smith and Hobby-Eberly Telescopes at McDonald Observatory. They hope to identify more extreme helium stars, and discover even more chemical elements in these stars.

This research was supported by grants from the Robert A. Welch Foundation of Houston, Texas and the Space Telescope Science Institute in Baltimore, Maryland.

Original Source: University of Texas at Austin

Posted on by Fraser Cain

Cometary Globule CG4

Cometary globule CG4. Image credit: NOAO. Click to enlarge
This object looks like a comet, but it’s actually a star forming region called CG4. Cometary globules like this are relatively small clouds of gas and dust in the Milky Way. CG4 is about 1,300 light years from Earth; its head is about 1.5 light-years across, and its tail is about 8 light-years long. The head of the nebula is opaque, but it’s illuminated by the light from the hot newly forming stars.

A dramatic new image of cometary globule CG4 marks the one-thousandth image posted to the online gallery hosted by the National Optical Astronomy Observatory.

The flower-like image of this star-forming region in Earth’s southern skies was taken by Travis Rector and Tim Abbott using a 64-megapixel Mosaic imaging camera on the National Science Foundation’s Victor M. Blanco telescope at Cerro Tololo Inter-American Observatory.

Cometary globules are isolated, relatively small clouds of gas and dust within the Milky Way. This example, called CG4, is about 1,300 light years from Earth. Its head is some 1.5 light-years in diameter, and its tail is about 8 light-years long. The dusty cloud contains enough material to make several Sun-sized stars. CG4 is located in the constellation of Puppis.

The head of the nebula is opaque, but glows because it is illuminated by light from nearby hot stars. Their energy is gradually destroying the dusty head of the globule, sweeping away the tiny particles which scatter the starlight. This particular globule shows a faint red glow from electrically charged hydrogen, and it seems about to devour an edge-on spiral galaxy (ESO 257-19) in the upper left. In reality, this galaxy is more than a hundred million light-years further away, far beyond CG4.

The image from the 4-meter telescope was taken in four filters, three of which are for blue, green and near-infrared light. The fourth is designed to isolate a specific color of red, known as hydrogen-alpha, which is produced by warm hydrogen gas.

The National Optical Astronomy Observatory (NOAO) consists of Kitt Peak National Observatory near Tucson, AZ; Cerro Tololo Inter-American Observatory near La Serena, Chile; and, the NOAO Gemini Science Center, the route for U.S. astronomers to observe with the Gemini North telescope in Hawaii and the Gemini South telescope in Chile. NOAO is operated by the Association of Universities for Research in Astronomy Inc. (AURA), under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

Posted on by Fraser Cain

SOHO Can See Right Through the Sun

The Sun. Image credit: NASA/ESA Click to enlarge
NASA researchers have developed a technique that allows them to look right through the Sun to see what’s happening on the other side. The Solar and Heliospheric Observatory (SOHO) can trace the sound waves caused by active regions on the opposite side of the Sun. This technique allows the researchers to be more prepared when large sunspots rotate around to face the Earth, and better predict active space weather.

NASA researchers using the Solar and Heliospheric Observatory (SOHO) spacecraft have developed a method of seeing through the sun to the star’s far side. The sun’s far side faces away from the Earth, so it is not directly observable by traditional techniques.

“This new method allows more reliable advance warning of magnetic storms brewing on the far side that could rotate with the sun and threaten the Earth,” said NASA-supported scientist Phil Scherrer of Stanford University, Stanford, Calif.

Magnetic storms resulting from violent solar activity disrupt satellites, radio communications, power grids and other technological systems on Earth. Advance warning can help planners prepare for operational disruptions. The sun rotates once every 27 days, as seen from Earth, and this means the evolution of active regions on the far side of the sun previously has not been detectable.

Many of these storms originate in groups of sunspots, or active regions – areas with high concentration of magnetic fields. Active regions situated on the near side of the sun, the one facing the Earth, can be observed directly. However, traditional methods provided no information about active regions developing on the other side of the sun. Knowing whether there are large active regions on the opposite side of the sun may greatly improve forecast of potential magnetic storms.

The new observation method uses SOHO’s Michelson Doppler Imager (MDI) instrument to trace sound waves reverberating through the sun to build a picture of the far side.

The sun is filled with many kinds of sound waves caused by the convective (boiling) motion of gas in its surface layers. The far side imaging method compares the sound waves that emanate from each small region on the far side with what was expected to arrive at that small region from waves that originated on the front side. An active region reveals itself because its strong magnetic fields speed up the sound waves. The difference becomes evident when sound waves originating from the front side and from the back side get out of step with one another.

“The original far-side imaging method only allowed us to see the central regions, about one-quarter to one-third of its total area,” Scherrer said. “The new method allows us to see the entire far side, including the poles.” Scherrer started an effort to use the new method to create full far-side images from archived MDI data collected since 1996. The project was completed in December 2005.

Douglas Biesecker of the National Oceanic and Atmospheric Administration’s Space Environment Center, Boulder, Colo., said, “With the new far side photo album going back to 1996, we can discover identifying characteristics of active regions. This will improve our ability to distinguish real active regions.”

SOHO is a cooperative project between the European Space Agency and NASA. For SOHO information and images on the Web, visit:
www.nasa.gov/vision/universe/solarsystem/soho_xray.html

Original Source: NASA News Release

Posted on by Fraser Cain

Liquid Water Might Be On Enceladus

Plumes of icy material extend above the polar region of Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
Scientists have discovered geysers of liquid water streaming off Enceladus, one of Saturn’s moons, like a colder version of Yellowstone Hot Springs. Enceladus is one of the few objects in the Solar System that has volcanoes, joining the Earth, Io and possibly Neptune’s moon Triton. This occurrence of liquid water, right near the surface, raises the hopes that there could be life, like the ecosystems on Earth which exist around deep sea vents, using geothermal heat for energy.

NASA’s Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geysers on Saturn’s moon Enceladus. The rare occurrence of liquid water so near the surface raises many new questions about the mysterious moon.

“We realize that this is a radical conclusion — that we may have evidence for liquid water within a body so small and so cold,” said Dr. Carolyn Porco, Cassini imaging team leader at Space Science Institute, Boulder, Colo. “However, if we are right, we have significantly broadened the diversity of solar system environments where we might possibly have conditions suitable for living organisms.”

High-resolution Cassini images show icy jets and towering plumes ejecting large quantities of particles at high speed. Scientists examined several models to explain the process. They ruled out the idea that the particles are produced by or blown off the moon’s surface by vapor created when warm water ice converts to a gas. Instead, scientists have found evidence for a much more exciting possibility — the jets might be erupting from near-surface pockets of liquid water above 0 degrees Celsius (32 degrees Fahrenheit), like cold versions of the Old Faithful geyser in Yellowstone.

Mission scientists report these and other Enceladus findings in this week’s issue of Science.

“We previously knew of at most three places where active volcanism exists: Jupiter’s moon Io, Earth, and possibly Neptune’s moon Triton. Cassini changed all that, making Enceladus the latest member of this very exclusive club, and one of the most exciting places in the solar system,” said Dr. John Spencer, Cassini scientist, Southwest Research Institute, Boulder, Colo.

“Other moons in the solar system have liquid-water oceans covered by kilometers of icy crust,” said Dr. Andrew Ingersoll, imaging team member and atmospheric scientist at the California Institute of Technology, Pasadena, Calif. “What’s different here is that pockets of liquid water may be no more than tens of meters below the surface.”

Other unexplained oddities now make sense. “As Cassini approached Saturn, we discovered that the Saturnian system is filled with oxygen atoms. At the time we had no idea where the oxygen was coming from,” said Dr. Candy Hansen, Cassini scientist at NASA’s Jet Propulsion Laboratory in Pasadena. “Now we know that Enceladus is spewing out water molecules, which break down into oxygen and hydrogen.”

Scientists are also seeing variability at Enceladus. “Even when Cassini is not flying close to Enceladus, we can detect that the plume’s activity has been changing through its varying effects on the soup of electrically-charged particles that flow past the moon,” said Dr. Geraint H. Jones, Cassini scientist, magnetospheric imaging instrument, Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany.

Scientists still have many questions. Why is Enceladus currently so active? Are other sites on Enceladus active? Might this activity have been continuous enough over the moon’s history for life to have had a chance to take hold in the moon’s interior?

“Our search for liquid water has taken a new turn. The type of evidence for liquid water on Enceladus is very different from what we’ve seen at Jupiter’s moon Europa. On Europa the evidence from surface geological features points to an internal ocean. On Enceladus the evidence is direct observation of water vapor venting from sources close to the surface,” said Dr. Peter Thomas, Cassini imaging scientist, Cornell University, Ithaca, N.Y.

In the spring of 2008, scientists will get another chance to look at Enceladus when Cassini flies within 350 kilometers (approximately 220 miles), but much work remains after Cassini’s four-year prime mission is over.

“There’s no question that, along with the moon Titan, Enceladus should be a very high priority for us. Saturn has given us two exciting worlds to explore,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist, University of Arizona, Tucson, Ariz.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the Caltech, manages the mission for NASA’s Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and more information, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Original Source: NASA News Release

Posted on by Fraser Cain

Gigantic Eruptions Helped in the Dinosaur’s Demise

Earth factors may be the most probable scenario for past mass extinctions. Image credit: NASA Click to enlarge
Most scientists agree that a large meteor probably wiped out the dinosaurs 65 million years ago, but two geologists from the University of Leicester think that some homegrown cataclysms might have done the trick for previous extinctions. There just isn’t enough evidence that an impact caused the mass extinction that happened 250 million years ago. But one of the largest flood basalt eruptions did occur at that time, and released enough greenhouse gasses to dramatically change the Earth’s climate – killing the dinosaurs off in the process.

Earth history has been punctuated by several mass extinctions rapidly wiping out nearly all life forms on our planet. What causes these catastrophic events? Are they really due to meteorite impacts? Current research suggests that the cause may come from within our own planet – the eruption of vast amounts of lava that brings a cocktail of gases from deep inside the Earth and vents them into the atmosphere.

University of Leicester geologists, Professor Andy Saunders and Dr Marc Reichow, are taking a fresh look at what may actually have wiped out the dinosaurs 65 million years ago and caused other similarly cataclysmic events, aware they may end up exploding a few popular myths.

The idea that meteorite impacts caused mass extinctions has been in vogue over the last 25 years, since Louis Alverez’s research team in Berkeley, California published their work about an extraterrestrial iridium anomaly found in 65-million-year-old layers at the Cretaceous-Tertiary boundary. This anomaly only could be explained by an extraterrestrial source, a large meteorite, hitting the Earth and ultimately wiping the dinosaurs – and many other organisms – off the Earth’s surface.

Professor Saunders commented: “Impacts are suitably apocalyptic. They are the stuff of Hollywood. It seems that every kid’s dinosaur book ends with a bang. But are they the real killers and are they solely responsible for every mass extinction on earth? There is scant evidence of impacts at the time of other major extinctions e.g., at the end of the Permian, 250 million years ago, and at the end of the Triassic, 200 million years ago. The evidence that has been found does not seem large enough to have triggered an extinction at these times.”

Flood basalt eruptions are – he says – an alternative kill mechanism. These do correspond with all main mass extinctions, within error of the techniques used to determine the age of the volcanism. Furthermore, they may have released enough greenhouse gases (SO2 and CO2) to dramatically change the climate. The largest flood basalts on Earth (Siberian Traps and Deccan Traps) coincide with the largest extinctions (end-Permian, and end-Cretaceous). “Pure coincidence?”, ask Saunders and Reichow.

While this is unlikely to be pure chance, the Leicester researchers are interested in precisely what the kill mechanism may be. One possibility is that the gases released by volcanic activity lead to a prolonged volcanic winter induced by sulphur-rich aerosols, followed by a period of CO2-induced warming.

Professor Andy Saunders and Dr. Marc Reichow at Leicester, in collaboration with Anthony Cohen, Steve Self, and Mike Widdowson at the Open University, have recently been awarded a NERC (Natural Environment Research Council) grant to study the Siberian Traps and their environmental impact.

The Siberian Traps are the largest known continental flood basalt province. Erupted about 250 million years ago at high latitude in the northern hemisphere, they are one of many known flood basalts provinces – vast outpourings of lava that covered large areas of the Earth’s surface. A major debate is underway concerning the origin of these provinces -including the Siberian Traps- and their environmental impact.

Using radiometric dating techniques, they hope to constrain the age and, combined with geochemical analysis, the extent, of the Siberian Traps. Measuring how much gas was released during these eruptions 250 million years ago is a considerable challenge. The researchers will study microscopic inclusions trapped in minerals of the Siberian Traps rocks to estimate the original gas contents. Using these data they hope to be able to assess the amount of SO2 and CO2 released into the atmosphere 250 million years ago, and whether or not this caused climatic havoc, wiping out nearly all life on earth. By studying the composition of sedimentary rocks laid down at the time of the mass extinction, they also hope to detect changes to seawater chemistry that resulted from major changes in climate.

From these data Professor Saunders and his team hope to link the volcanism to the extinction event. He explained: “If we can show, for example, that the full extent of the Siberian Traps was erupted at the same time, we can be confident that their environmental effects were powerful. Understanding the actual kill mechanism is the next stage. watch this space.”

Original Source: University of Leicester

Posted on by Fraser Cain

Say Goodbye to the Polar Ice Sheets

A RADARSAT map of Antarctica. Image credit: AMM/SVS/NASA/CSA Click to enlarge
NASA has completed the most comprehensive survey ever made of the Earth’s polar ice caps, and confirmed that they’re disappearing at increasing rates. These rates match computer climate models precisely, giving climate scientists greater confidence in their predictions about global warming. The survey combined data from airborne maps and measurements from two ESA satellites. NASA’s ICESat satellite is taking an even more comprehensive survey of ice levels, which should be available next year.

In the most comprehensive survey ever undertaken of the massive ice sheets covering both Greenland and Antarctica, NASA scientists confirm climate warming is changing how much water remains locked in Earth’s largest storehouse of ice and snow.

Other recent studies have shown increasing losses of ice in parts of these sheets. This new survey is the first to inventory the losses of ice and the addition of new snow on both in a consistent and comprehensive way throughout an entire decade.

The survey shows that there was a net loss of ice from the combined polar ice sheets between 1992 and 2002 and a corresponding rise in sea level. The survey documents for the first time extensive thinning of the West Antarctic ice shelves and an increase in snowfall in the interior of Greenland, as well as thinning at the edges. All are signs of a warming climate predicted by computer models.

The survey, published in the Journal of Glaciology, combines new satellite mapping of the height of the ice sheets from two European Space Agency satellites. It also used previous NASA airborne mapping of the edges of the Greenland ice sheets to determine how fast the thickness is changing.

In Greenland, the survey saw large ice losses along the southeastern coast and a large increase in ice thickness at higher elevations in the interior due to relatively high rates of snowfall. This study suggests there was a slight gain in the total mass of frozen water in the ice sheet over the decade studied, contrary to previous assessments.

This situation may have changed in just the past few years, according to lead author Jay Zwally of NASA’s Goddard Space Flight Center, Greenbelt, Md. Last month NASA scientists at the Jet Propulsion Laboratory, Pasadena, Calif., reported a speed up of ice flow into the sea from several Greenland glaciers. That study included observations through 2005; Zwally’s survey concluded with 2002 data.

When the scientists added up the overall gains and losses of ice from the Greenland and Antarctic ice sheets, there was a net loss of ice to the sea. The amount of water added to the oceans (20 billion tons) is equivalent to the total amount of freshwater used in homes, businesses and farming in New York, New Jersey and Virginia each year.

“The study indicates that the contribution of the ice sheets to recent sea-level rise during the decade studied was much smaller than expected, just two percent of the recent increase of nearly three millimeters a year,” says Zwally. “Continuing research using NASA satellites and other data will narrow the uncertainties in this important issue.”

NASA is continuing to monitor the polar ice sheets with the Ice, Cloud and land Elevation Satellite (ICESat), launched in January 2003. ICESat uses a laser beam to measure the elevation of ice sheets with unprecedented accuracy three times a year. The first comprehensive ice sheet survey conducted by ICESat is expected early next year, said Zwally, who is the mission’s project scientist.

Original Source: NASA News Release

Posted on by Fraser Cain

Enceladus in Front of Saturn

Enceladus hanging against Saturn’s rings. Image credit: NASA/JPL/SSI Click to enlarge
This beautiful natural colour image shows Enceladus hanging in front of Saturn and its rings. This view of Saturn shows the terminator; the line across the planet that separates day from night. Cassini took separate images with its red, green, and blue filters, and then controllers combined the images together on computer. Cassini took this photograph on January 17, 2006 when it was 200,000 kilometers (125,000 miles) from Enceladus.

Enceladus hangs like a single bright pearl against the golden-brown canvas of Saturn and its icy rings. Visible on Saturn is the region where daylight gives way to dusk. Above, the rings throw thin shadows onto the planet.

Icy Enceladus is 505 kilometers (314 miles) across.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken using the Cassini spacecraft wide-angle camera on Jan. 17, 2006 at a distance of approximately 200,000 kilometers (100,000 miles) from Enceladus. The image scale is 10 kilometers (6 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Iapetus’ Terminator

Saturn’s moon Iaptus. Image credit: NASA/JPL/SSI Click to enlarge
This view of Iapetus, one of Saturn’s moons, shows its terminator running from pole to pole. This is the line that separates night from day on the moon, and right along this line, the shadows are very long. This allows planetary geologists to see a tremendous amount of detail and measure the height of mountains and the depths of craters. Cassini took this photograph on January 22, 2006, when it was 1.3 million kilometers (800,000 miles) from Iapetus.

Sunlight strikes the terminator (the boundary between day and night) region on Saturn’s moon Iapetus at nearly horizontal angles, making visible the vertical relief of many features.

This view is centered on terrain in the southern hemisphere of Iapetus (1,468 kilometers, or 912 miles across). Lit terrain visible here is on the moon’s leading hemisphere. In this image, a large, central-peaked crater is notable at the boundary between the dark material in Cassini Regio and the brighter material on the trailing hemisphere.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 22, 2006, at a distance of approximately 1.3 million kilometers (800,000 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 67 degrees. Resolution in the original image was 8 kilometers (5 miles) per pixel. The image has been magnified by a factor of two and contrast-enhanced to aid visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release