Satellite News

NASA selected Orbital Sciences Corp.'s, Technical Services Division in Greenbelt, Md., for the agency's Sounding Rockets Operations contract. The total value of this indefinite-delivery, indefinite-quantity cost-plus incentive fee contract is $310 million. The period of performance is five years.

Orbital Sciences will coordinate and implement NASA's overall Sounding Rockets Program and provide services and supplies as necessary to complete individual missions and projects. Services include designing, fabricating, integrating, and performing flight qualification testing of sub-orbital payloads; providing launch vehicles and associated hardware; and conducting various activities associated with subsequent mission launch operations.

Additional services to be provided under the contract may also include special engineering and technical support, education and outreach activities, and environmental studies.

The majority of the work will be done at NASA's Wallops Flight Facility in Virginia, which manages the agency's sounding rocket program.

NASA is inviting the public to choose an area in the northern Arizona where explorers will conduct part of annual Desert Research and Technology Studies, known as Desert RATS.




"Desert RATS 2010 is an annual test where NASA takes equipment and crews into the field to simulate the future planetary exploration missions," said Joe Kosmo, Desert RATS manager at NASA's Johnson Space Center in Houston. "We want the public to be take part of this."

From July 27th through August 8th, space enthusiasts can vote where to send the Desert RATS team, which includes led of engineers, scientists and astronauts.

Scientists are using the arid, rocky environment of the Haughton Crater on Devon Island, Canada to simulate conditions that might be encountered by explorers on other planetary bodies. The latest edition of the HMP-2010 began July 19 and includes three weeks of crew and mission control activities and robotic testing.

"Explorers, such as geologists, often find themselves with a set of observations they would have liked to make, or samples they would have liked to take, if only they had been able to stay longer at a site," said Terry Fong, director of the Intelligent Robotics Group at NASA's Ames Research Center in Moffett Field, Calif. "Our work this year is to study how remotely -operated robots, perhaps even vehicles previously used for crew transport, can be used to perform follow-up work."

Using robots for such follow-up work could save astronauts from performing tedious, repetitive or time-consuming activities. Surveying a site could take hundreds to thousands of readings using ground-penetrating radar, spectrometers, or geotechnical instruments. Additionally, robots could make measurements and take pictures that complement or supplement those initially taken by humans.

Mission planners speculate that in the future, there could be substantial amounts of time between crewed missions for robots to perform research work at a range of destinations.

During HMP-2010, NASA will deploy robots developed by the Intelligent Robotics Group at Ames. The robots, known as K10s, are equipped with a variety of instruments including 3-D scanning lidar, color imagers, spectrometers and ground-penetrating radar. The K10s will map systematically above and below ground structures and characterize rocks, soil and landscape of key areas at Haughton Crater.

NASA also will conduct a series of experiments designed to examine how future surface systems, such as crew rovers, might be repositioned robotically from one location to a new rendezvous location with astronauts.

"Poor lighting and low resolution of satellite imagery can make a planned route look very simple from above," said Matt Leonard, deputy manager of the Lunar Surface Systems Project (LSS) at NASA's Johnson Space Center in Houston. "But once we are on the ground, we can see obstacles we couldn't before that make the route unexpectedly challenging. We will study how to use ground robots to scout alternative safe routes, categorize hard-to-detect obstacles and examine how best to prepare for venturing into unknown terrain."

In addition to working around unexpected roadblocks during future planetary convoys, the LSS experiment team will study how a robot on a set route with a fixed schedule can conduct science tasks, such as taking samples or gathering images. The team will work with a K10 robot and HMP's MARS-1 Humvee Rover field exploration vehicle to simulate a large planetary crew rover equipped with science instruments.

What if work performed in space could improve the treatment of household and nuclear waste on Earth? That's what investigators are hoping to do with the results of a fluid physics study in progress on the International Space Station.

The experiment, called DECLIC-HTI, is studying supercritical water that could lead to spin-offs in the field of clean technologies for treating waste here on Earth.

A supercritical fluid is any substance at a temperature and pressure above its critical point -- the point at which the fluid is one homogeneous phase and exhibits properties of both liquids and gases. In this form, the substance can flow through solids like a gas and dissolve materials like a liquid. Water and carbon dioxide are the most commonly used supercritical fluids. Using extremely high temperatures, supercritical water can completely break down waste into benign forms.

DECLIC, or DEvice for the study of Critical LIquids and Crystallization, is a miniaturized, automatic thermo-optical laboratory that studies transparent fluids by finely tuning the temperature of a sample and sending images and video to the ground. The HTI, or high temperature insert, can measure fluid temperatures up to 400 degrees Celsius.

For the experiment, astronauts plug an insert, containing the water sample cell, into the DECLIC payload. The sample is precisely heated and observed in real time by investigators on the ground.

"These phenomena will be of interest to understand the behavior of supercritical fluids in space, but also to improve industrial processes on the ground," said Gabriel Pont, DECLIC mission manager with the CNES, or Centre National d'Etudes Spatiales, in Toulouse, France.

"A typical example is burning completely organic or industrial waste in supercritical water at a much lower temperature than in conventional systems, thus saving energy and being cleaner. Microgravity will provide the ideal environment to understand how to do that."

The supercritical water temperature is very sensitive to gravity and has never been measured in microgravity conditions. "We expect HTI to give us the best measurement of this temperature ever found," added Pont.

The experiment began in October 2009 when the High Temperature Insert commissioning was performed. Since then, four experimental sequences have been performed, leading to more than 80 running days. "We are very excited about what we've seen thus far, and cannot wait to see the potential benefits of our work on Earth," added Pont.

During NASA's ICESCAPE voyage to the Arctic, scientists have been looking at the phytoplankton in the Arctic's Chukchi Sea - how many, how big and at what depths they are found. But there are other ways of looking at these small life forms.

"We measure phytoplankton in terms of their pigments and light absorption properties," said Stan Hooker of NASA's Ocean Biology and Biogeochemistry Calibration and Validation Office at Goddard Space Flight Center, Greenbelt, Md. Hooker, Joaquin Chaves and Aimee Neeley, also of NASA, measure the color of the water. Anything in the water, plankton or not, can influence that color.

On July 2, a crane maneuvered a small boat halfway down the side of the U.S. Coast Guard Cutter Healy – the platform for the five-week ICESCAPE mission, NASA's first dedicated oceanographic field campaign, which is studying the physics, chemistry and biology of the ocean and sea ice within a changing Arctic.

Hooker, Chaves and Coast Guard crew boarded the small boat and readied for an expedition away from the stirred water and shadow of the 420-foot Healy. Lowered to the ocean surface, Hooker's team powered away, entering uncharted waters. Maneuvering over smooth water and around chunks of sea ice, the small boat slowed to a stop near the edge of an ice floe.

"This is new for us because we usually haven't been able to work this close to the ice before," Hooker said. "Satellites can't measure near the ice, so we do this to help specify the next generation of equipment, and to contribute to the science objectives."

First over the side was a small red instrument that the crew dropped on a line into the ocean and then reeled by hand, as if wrangling a fish. Sensors on the instrument measured the wavelengths of sunlight at different depths - both what's coming into the ocean and what's reflected back out which is similar to what is "seen" by satellites.

Last, the crew collected water samples to be returned to the Healy for analysis in the lab. "We can measure the changes in the color to find out what's happening with the ecology," said Greg Mitchell, a research biologist at Scripps Institution of Oceanography in San Diego, who analyzes the water samples. "We can relate color back to how much chlorophyll is in the ocean, how much algae biomass there is, and processes such as the rate of photosynthesis."

Similar, more frequent measurements are made from the Healy, which marked its one-hundredth ocean station of the mission on July 8. The small boat deploys less often -- almost daily -- but reaches more targeted regions. "We do the measurements at sea in order to relate what's going on in the ocean with the optics," Mitchell said. "Then we apply those relationships to the optical data from the ocean color satellites and we can make estimates of processes and distributions globally."

Onboard the Healy to help scientists figure out where to sample is Bob Pickart, a physical oceanographer from Woods Hole Oceanographic Institution. Pickart can decipher water type and circulation to guide where to make measurements. A great unknown, for example, is a picture of what's feeding the evolution of a "hotspot" in Barrow Canyon. Right now, winter water -- rich with nutrients -- has been carried across the shallow shelf where the Healy is surveying.

"This is a really interesting, important time of year," Pickart said. "As the ice recedes, productivity is starting and things are getting cranked up."

But for how long will these hotspots thrive? While this is dictated by light and nutrients, the circulation near Barrow and Herald canyons -- two fissures that channel water off the shelf -- plays a vitally important role as well. On July 12, after a night of cutting through sea ice, ICESCAPE scientists caught a glimpse of the hotspot. As an instrument lowered from the Healy descended through the water, real-time fluorescence information showed low levels of chlorophyll.

Scientists on the Healy will analyze the hotspot data and water samples, but whether a plankton bloom has come and gone, the region remains a hotspot for ground-dwelling communities, according to Karen Frey of Clark University. Feeding off plankton that sink to the seafloor, species here are diverse and large. A single sample retrieved from the ocean floor turned up a large crab, sponges and a sea star.

Meanwhile, samples returned from the near-ice survey July 2 on the small boat are turning up mixed results – sometimes indicating the presence of phytoplankton communities and sometimes not, according to Atsushi Matsuoka, of Laboratoire d'Oceanographie de Villefranche. To find out why, his group will look at trends after returning home from ICESCAPE.

Engineers at NASA's John C. Stennis Space Center recently installed an Aerojet AJ26 rocket engine for qualification testing as part of a partnership that highlights the space agency's commitment to work with commercial companies to provide space transportation.

Stennis has partnered with Orbital Sciences Corporation to test the AJ26 engines that will power the first stage of the company's Taurus® II space launch vehicle. Orbital is working in partnership with NASA under the agency's Commercial Orbital Transportation Services (COTS) joint research and development project. The company is under contract with NASA through the Commercial Resupply Services program to provide eight cargo missions to the International Space Station through 2015.

Stennis operators have been modifying their E-1 test facility since April 2009 to test the AJ26 engines for Orbital. Work has included construction of a 27-foot-deep flame deflector trench.




The latest step in the project involved delivery and installation of an AJ26 engine for testing. In upcoming days, operators will perform a series of "chilldown" test, which involves running sub-cooled rocket propellants through the engine, just as will occur during an actual "hotfire" ignition test.

The chilldown tests are used to verify proper temperature conditioning of the engine systems and elapse time required to properly chill the engine, and to measure the quantity of liquid oxygen required to perform the operation.

Once the installed engine passes the chilldown and other qualification tests, it will be removed from the Stennis E-1 test facility. The first actual flight engine then will be delivered and installed for hotfire testing.

NASA's Wide-field Infrared Survey Explorer, or WISE, will complete its first survey of the entire sky on July 17, 2010. The mission has generated more than one million images so far, of everything from asteroids to distant galaxies. "Like a globe-trotting shutterbug, WISE has completed a world tour with 1.3 million slides covering the whole sky," said Edward Wright, the principal investigator of the mission at the University of California, Los Angeles.

Some of these images have been processed and stitched together into a new picture being released today. It shows the Pleiades cluster of stars, also known as the Seven Sisters, resting in a tangled bed of wispy dust. The pictured region covers seven square degrees, or an area equivalent to 35 full moons, highlighting the telescope's ability to take wide shots of vast regions of space.

The new picture was taken in February. It shows infrared light from WISE's four detectors in a range of wavelengths. This infrared view highlights the region's expansive dust cloud, through which the Seven Sisters and other stars in the cluster are passing. Infrared light also reveals the smaller and cooler stars of the family.

"The WISE all-sky survey is helping us sift through the immense and diverse population of celestial objects," said Hashima Hasan, WISE Program scientist at NASA Headquarters in Washington. "It's a great example of the high impact science that's possible from NASA's Explorer Program."



The first release of WISE data, covering about 80 percent of the sky, will be delivered to the astronomical community in May of next year. The mission scanned strips of the sky as it orbited around the Earth's poles since its launch last December. WISE always stays over the Earth's day-night line. As the Earth moves around the sun, new slices of sky come into the telescope's field of view. It has taken six months, or the amount of time for Earth to travel halfway around the sun, for the mission to complete one full scan of the entire sky.

For the next three months, the mission will map half of the sky again. This will enhance the telescope's data, revealing more hidden asteroids, stars and galaxies. The mapping will give astronomers a look at what's changed in the sky. The mission will end when the instrument's block of solid hydrogen coolant, needed to chill its infrared detectors, runs out.

"The eyes of WISE have not blinked since launch," said William Irace, the mission's project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Both our telescope and spacecraft have performed flawlessly and have imaged every corner of our universe, just as we planned."

So far, WISE has observed more than 100,000 asteroids, both known and previously unseen. Most of these space rocks are in the main belt between Mars and Jupiter. However, some are near-Earth objects, asteroids and comets with orbits that pass relatively close to Earth. WISE has discovered more than 90 of these new near-Earth objects. The infrared telescope is also good at spotting comets that orbit far from Earth and has discovered more than a dozen of these so far.

WISE's infrared vision also gives it a unique ability to pick up the glow of cool stars, called brown dwarfs, in addition to distant galaxies bursting with light and energy. These galaxies are called ultra-luminous infrared galaxies. WISE can see the brightest of them.

"WISE is filling in the blanks on the infrared properties of everything in the universe from nearby asteroids to distant quasars," said Peter Eisenhardt of JPL, project scientist for WISE. "But the most exciting discoveries may well be objects we haven't yet imagined exist."

Ontario Lacus, the largest lake in the southern hemisphere of Saturn's moon Titan, turns out to be a perfect exotic vacation spot, provided you can handle the frosty, subzero temperatures and enjoy soaking in liquid hydrocarbon.

Several recent papers by scientists working with NASA's Cassini spacecraft describe evidence of beaches for sunbathing in Titan's low light, sheltered bays for mooring boats, and pretty deltas for wading out in the shallows. They also describe seasonal changes in the lake's size and depth, giving vacationers an opportunity to visit over and over without seeing the same lake twice. (Travel agents, of course, will have to help you figure out how to breathe in an atmosphere devoid of oxygen.)

"With such frigid temperatures and meager sunlight, you wouldn't think Titan has a lot in common with our own Earth," said Steve Wall, deputy team lead for the Cassini radar team, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "But Titan continues to surprise us with activity and seasonal processes that look marvelously, eerily familiar."

Cassini arrived at Saturn in 2004 when the southern hemisphere of the planet and its moons were experiencing summer. The seasons have started to change toward autumn, with winter solstice darkening the southern hemisphere of Titan in 2017. A year on Titan is the equivalent of about 29 Earth years.




Titan is the only other world in our solar system known to have standing bodies of liquid on its surface. Because surface temperatures at the poles average a chilly 90 Kelvin (about minus 300 degrees Fahrenheit), the liquid is a combination of methane, ethane and propane, rather than water. Ontario Lacus has a surface area of about 15,000 square kilometers (6,000 square miles), slightly smaller than its terrestrial namesake Lake Ontario.

Cassini first obtained an image of Ontario Lacus with its imaging camera in 2004. A paper submitted to the journal Icarus by Alex Hayes, a Cassini radar team associate at the California Institute of Technology in Pasadena, and colleagues finds that the lake's shoreline has receded by about 10 kilometers (6 miles). This has resulted in a liquid level reduction of about 1 meter (3 feet) per year over a four–year period.

The shoreline appears to be receding because of liquid methane evaporating from the lake, with a total amount of evaporation that would significantly exceed the yearly methane gas output of all the cows on Earth, Hayes said. Some of the liquid could also seep into porous ground material. Hayes said the changes in the lake are likely occurring as part of Titan's seasonal methane cycle, and would be expected to reverse during southern winter.

This seasonal filling and receding is similar to what occurs at the shallow lakebed known as Racetrack Playa in Death Valley National Park, Hayes said. In fact, from the air, the topography and shape of Racetrack Playa and Ontario Lacus are quite similar, although Ontario Lacus is about 60 times larger.

"We are very excited about these results, because we did not expect Cassini to be able to detect changes of this magnitude in Titan's lakes," Hayes said. "It is only through the continued monitoring of seasonal variation during Cassini's extended mission that these discoveries have been made possible."

Other parts of the Ontario Lacus' shoreline, as described in the paper published in Geophysical Research Letters in March 2010 by Wall, Hayes and other colleagues, show flooded valleys and coasts, further proof that the lake level has changed.
The delta revealed by Cassini radar data on the western shore of Ontario Lacus is also the first well-developed delta observed on Titan, Wall said. He explained that the shape of the land there shows liquid flowing down from higher plain switching channels on its way into the lake, forming at least two lobes.

Examples of this kind of channel switching and wave-modified deltas can be found on Earth at the southern end of Lake Albert between Uganda and the Democratic Republic of Congo in Africa, and the remains of an ancient lake known as Megachad in the African country Chad, Wall said.

The radar data also show a smooth beach on the northwestern shore of Ontario Lacus. Smooth lines parallel to the current shoreline could be formed by low waves over time, which were likely driven by winds sweeping in from the west or southwest. The pattern at Ontario Lacus resembles what might be seen on the southeastern side of Lake Michigan, where waves sculpt the shoreline in a similar fashion.

This work represents the first time network engineers have redesigned and replaced the hydrostatic bearing assembly, which enables the antenna to rotate horizontally. To accomplish this, they lifted the entire rotating structure of the giant antenna for the first time. The hydrostatic bearing assembly puts the weight of the antenna on three pads, which glide on a film of oil around a large steel ring. The ring measures about 24 meters (79 feet) in diameter and must be flat to work efficiently. After 44 years of near-constant use, the Mars antenna needed a kind of joint replacement, since the bearing assembly had become uneven.


Engineers and managers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., which manages the Deep Space Network for NASA, drew up plans for new runner segments, new sole plates below the runner segments, and an epoxy grout that is more impervious to oil. The thicker segments deform less when the antenna's pads pass over them, and allow for more tightly sealed joints.

Since beginning work in March, engineers and technicians have carefully lifted several million pounds of delicate scientific instruments about five millimeters (0.2 inches) and transferred the weight of the antenna to temporary supporting legs. They have removed the old steel runner and cement-based grout. They have also installed sole plates, which cover the grout and anchor the new runner. Over the past week, JPL engineers checked to make sure the sole plates were level, and workers poured the new epoxy grout underneath to hold them in place. Mixing and pouring the new grout occurred at night to ensure the work was completed within the tight temperature tolerances required to handle this material.

Over the next few weeks, the new, thicker steel runner segments will be installed.

Scientists working for NASA's Geostationary Operational Environmental Satellite (GOES) Project at NASA's Goddard Space Flight Center, Greenbelt, Md. have developed continually updating "movies" of satellite imagery that allows on-line, iPhone and iPad viewing of any cyclone's movement in the Hurricane Alleys of the Atlantic Ocean or Eastern Pacific Ocean.

The National Oceanic and Atmospheric Administration's (NOAA) GOES-13 satellite captures visible and infrared images of the weather over the U.S. East coast. These images are overlaid on a true-color background map, and fed into small and medium-sized videos of the Gulf of Mexico and the nearby Atlantic Ocean for the last 3 days. The GOES-11 satellite provides similar coverage of the U.S. west coast and Eastern Pacific.

The GOES satellites scan further into the oceans twice per hour, offering the opportunity to watch storm development in the swath called "Hurricane Alley," from Atlantic to Pacific. The bigger scans are used to make large-scale Hurricane Alley movies for the last three to five days, illustrating the life-cycle of subtropical storms, as some of them spin up to become hurricanes.

The GOES satellites also scan the entire disk of the Earth every three hours. These are used to produce "full disk movies" from the last five days of satellite imagery data from GOES-13 in the Atlantic and GOES-11 in the eastern Pacific. With just eight frames per day, time flies by quickly as weather circulates across the Western Hemisphere.

"We have recently changed the code for the up-to-date GOES movies, including the "Hurricane Alley" movies, that have links on the page goes.gsfc.nasa.gov," said Dr. Dennis Chesters of the NASA GOES Project at Goddard. "They are now all encoded with H264, the digital compression standard used by the cable TV industry."

Dr. Chesters said that the NASA GOES Project also slightly resized the GOES movies, so that all of the movies have at least one dimension that is a sub-multiple of a standard HDTV dimension (720/1080). "This makes it easy for software that automatically fits movies to a screen to resize them without complicated interpolation," Dennis said. "So, the movies appear sharp and have snappy playback on small-screen devices. For instance, they work nicely on the popular iPads."

As a hidden bonus, each of the four frames at the top of the page is linked to a "reference movie" that downloads a movie that is the right size for your device. This is a Quicktime-only feature that will work on all Apple computers and Windows PCs that have Quicktime installed. The "reference movie" will accommodate iPhones and iPads as well as Macs and PCs. It sends a highly compressed version if the device is using a slow G3 phone link, but sends a larger, less compressed version to bigger screens with faster connections.

For decades, X-ray astronomers have studied the complex behavior of binary systems pairing a normal star with a black hole. In these systems, gas from the normal star streams toward the black hole and forms a disk around it. Friction within the disk heats the gas to millions of degrees -- hot enough to produce X-rays. At the disk's inner edge, near the black hole, strong magnetic fields eject some of the gas into dual, oppositely directed jets that blast outward at about half the speed of light.

That's the big picture, but the details have been elusive. For example, do most of the X-rays arise from the jets? The disk? Or from a high-energy region on the threshold of the black hole?

Now, astronomers using NASA's Rossi X-ray Timing Explorer (RXTE) satellite, together with optical, infrared and radio data, find that, at times, most of the X-rays come from the jets.

"Theoretical models have suggested this possibility for several years, but this is the first time we've confirmed it through multiwavelength analysis," said David Russell, lead author of the study and a post-doctoral researcher at the University of Amsterdam.

Russell and his colleagues looked at a well-studied outburst of the black-hole binary XTE J1550-564. The system lies 17,000 light-years away in the southern constellation of Norma and contains a black hole with about 10 times the sun's mass. The usually inconspicuous binary was discovered by RXTE in 1998, when the system briefly became one of the brightest X-ray sources in the sky.

Between April and July 2000, the system underwent another outburst. RXTE monitored the event in X-rays, with some additional help from NASA's Chandra X-ray Observatory. Optical and infrared observations covering the outburst came from the YALO 1-meter telescope at Cerro Tololo Inter-American Observatory in Chile, while radio observations were collected by the Australia Telescope Compact Array.

Drawing on these data, Russell and his team reconstructed a detailed picture of X-ray emission during the outburst. The study appears in the July 1 edition of Monthly Notices of the Royal Astronomical Society.

"We suspect that these outbursts are tied to increases in the amount of mass falling onto the black hole," explained Russell. "Where and how the emission occurs are the only clues we have to what's going on."

As the outburst began in mid-April 2000, the system's brightest X-ray emission was dominated by higher-energy ("hard") X-rays from a region very close to the black hole.

"We think the source of these X-rays is a region of very energetic electrons that form a corona around the innermost part of the disk," Russell said. When these electrons run into photons of visible light, the collision boosts the photons to hard X-ray energies, a process known as inverse Compton scattering. The jets were present, but only minor players.

Over the next couple of weeks, the peak X-ray emission moved to lower ("softer") energies and seems to have come from the dense gas in the accretion disk. At the same time, the hot disk quenched whatever process powers the jets and shut them down.

By late May 2000, XTE J1550-564's accretion disk was cool enough that the jets switched on again. Most of the X-rays, which were fainter but higher in energy, again came from scattering off of energetic electrons close to the black hole.

In early June, as the system faded and its peak emission gradually softened, the jets emerged as the main X-ray source. In the jet, electrons and positrons moving at a substantial fraction of light speed emit the radiation as they encounter magnetic fields, a process called synchrotron emission.

The jets require a continuous supply of particles with energies of a trillion electron volts -- billions of times the energy of visible light. "The total energy bound up in the jet is enormous, much larger than previously thought," Russell said.

As summer wore on, the jets gradually faded and their X-ray emission softened. By September, the system's brightest X-rays came from high-speed blobs of matter that the jets had hurled into space during previous eruptions.

"We're really beginning to get a handle on the 'ecology' of these extreme systems, thanks in large part to RXTE," Russell added. "We can apply what we've learned in nearby binaries like XTE J1550 to the supersized black holes and jets found at the centers of galaxies."

Launched in 1995, RXTE is still going strong. "Of currently operating NASA missions, only Hubble has been working longer," said Tod Strohmayer, the mission's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. RXTE's unique capabilities provide insight into accreting black holes and neutron stars and allow it to detect short, faint outbursts that are easily missed by other current missions exploring the X-ray regime.

Complex interactions between Saturn and its satellites have led scientists using NASA's Cassini spacecraft to a comprehensive model that could explain how oxygen may end up on the surface of Saturn's icy moon Titan. The presence of these oxygen atoms could potentially provide the basis for pre-biological chemistry.

The interactions are captured in two papers, one led by John Cooper and another led by Edward Sittler, published in the journal Planetary and Space Science in late 2009. Cooper and Sittler are Cassini plasma spectrometer team scientists at NASA's Goddard Space Flight Center in Greenbelt, Md.

"Titan and Enceladus, another icy moon of Saturn, are chemically connected by the flow of material through the Saturn system," Cooper said. In one paper, Cooper and colleagues provide an explanation for forces that could generate the Enceladus geysers that spew water vapor into space. In the other, published in the same issue, Sittler and colleagues describe a unique new process in which oxygen that circulates in the upper atmosphere of Titan can be carried all the way to the surface without further chemical contamination by being encased in carbon cages called fullerenes.
The work draws upon previous work by Sittler and others that model the dynamics of how particles, including water molecules, travel from Enceladus to Titan. At Enceladus the flow process begins with what they call the "Old Faithful" model, after the Old Faithful geyser in Yellowstone National Park. In this model, gas pressure slowly builds up inside Enceladus, then gets released occasionally in geyser-like eruptions.

Unlike terrestrial geysers, or even geyser-like forces on Jupiter's moon Io, the model proposed by Cooper shows that charged particle radiation raining down from Saturn’s magnetosphere can create the forces from below the surface that are required to eject gaseous jets.

Energetic particles raining down from Saturn's magnetosphere – at Enceladus, mostly electrons from Saturn's radiation belts - can break up molecules within the surface. This process is called radiolysis. Like a process called photolysis, in which sunlight can break apart molecules in the atmosphere, energetic radiation from charged particles that hit an icy surface, like that of Enceladus, can cause damage to molecules within the ice. These damaged molecules can get buried deeper and deeper under the surface by the perpetual churning forces that can repave the icy surface. Meteorites constantly crashing into the surface and splashing out material might also be burying the molecules.

When chemically altered icy grains come into contact beneath the surface with icy contaminants such as ammonia, methane and other hydrocarbons, they can produce volatile gases that can explode outward. Such gases can create plumes of the size seen by Cassini. Cooper and colleagues call such icy volatile mechanics "cryovolcanism."

What's unique about the "Old Faithful" model is that it "is a model for cryovolcanism that is based on not only liquid water, but also requires the production of gases by the radiolytic chemistry observed at Enceladus," said Sittler.

The plumes that emanate from Enceladus' south polar region consist of water, ammonia and other compounds. Scientists have known since the 1980s that Saturn's magnetosphere is inexplicably filled with neutral particles. In the intervening decades, particularly since the discovery of plumes jetting out from the south pole of Enceladus, work has shown how some of the water molecules that escape from Enceladus get split up into neutral and charged particles and are transported throughout Saturn's magnetosphere.

Sittler's new model indicates that as these broken water molecules enter Titan's atmosphere, they may be captured by fullerenes—hollow, soccer-ball shaped shells made of carbon atoms. Although the heavy molecules Cassini has detected in the upper atmosphere of Titan may be other molecules, Sittler suggests they are likely fullerenes.

In Sittler's model, the fullerenes then condense into larger clusters that can attach to polycyclic aromatic hydrocarbons—chemical compounds also found on Earth in oil, coal and tar deposits, and as the byproducts of burning fossil fuels. The fullerene clusters form even larger aerosols that travel down to Titan's surface.

This process protects the trapped oxygen from Titan's atmosphere, which is saturated with hydrogen atoms and compounds that are capable of breaking down other molecules. Otherwise, the oxygen would combine with methane in Titan's atmosphere and form carbon monoxide or carbon dioxide. Until now, scientists have not been able to explain how oxygen fits into the picture of the dynamics and chemistry of Saturn and its moons.

As the oxygen-rich aerosols fall to Titan's surface, they are further bombarded by products of galactic cosmic ray interactions with Titan's atmosphere. Cosmic rays bombarding the oxygen-stuffed fullerenes could produce more complex organic materials, such as amino acids, in the carbon-rich and oxygen-loaded fullerenes. Amino acids are considered important for pre-biological chemistry.

Scientists have been able to couple the new models that describe the generation of plumes at Enceladus and oxygen ion capture in fullerenes near the top of Titan's atmosphere to existing theories of the transport of oxygen across the magnetosphere. Taken together, Sittler and Cooper suggest a chemical pathway that allows the oxygen to be introduced to Titan's surface chemistry.

"Cooper and Sittler's work helps us understand more about the potential for chemical interactions among Saturn's moons," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The Saturn system is indeed a dynamic place, with the Enceladus plumes creating the E ring and loading the magnetosphere with water which interacts with Titan and the other moons," Spilker said.

The Cassini mission is a joint effort of NASA, the European Space Agency, and the Italian space agency Agenzia Spaziale Italiana. The mission is managed for NASA by the Jet Propulsion Laboratory, a division of the California Institute of Technology. Partners include the U.S. Air Force, Department of Energy, and academic and industrial participants from 19 countries.