Rover Will Spend 7th Birthday at Stadium-Size Crater

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter captured a Dec. 31, 2010, view of the Mars Exploration Rover Opportunity on the southwestern rim of a football-field-size crater called "Santa Maria."

Opportunity arrived at the western edge of Santa Maria crater in mid-December and will spend about two months investigating rocks there. That investigation will take Opportunity into the beginning of its eighth year on Mars. Opportunity landed in the Meridiani Planum region of Mars on Jan. 25, 2004, Universal Time (Jan. 24, Pacific Time) for a mission originally planned to last for three months.

The new image is online at http://www.nasa.gov/mission_pages/mer/multimedia/gallery/pia13754-anno.html and http://hirise.lpl.arizona.edu/releases/oppy-santa-maria.php .

Opportunity and its twin, Spirit, which passed its seventh anniversary on Mars this week, both have made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter and Mars Exploration Rover projects for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the orbiter. The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo.

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Opportunity Studying a Football-Field Size Crater

NASA's Mars Exploration Rover Opportunity reached a crater about the size of a football field-some 90 meters (295 feet) in diameter. The rover team plans to use cameras and spectrometers during the next several weeks to examine rocks exposed at the crater, informally named "Santa Maria."

A mosaic of image frames taken by Opportunity's navigation camera on Dec. 16 shows the crater's sharp rim and rocks ejected from the impact that had excavated the crater.

Opportunity completed its three-month prime mission on Mars in April 2004 and has been working in bonus extended missions since then. After the investigations at Santa Maria, the rover team plans to resume a long-term trek by Opportunity to the rim of Endeavour Crater, which is about 22 kilometers (14 miles) in diameter.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the NASA Science Mission Directorate, Washington. For more information about the mission, see http://marsrovers.jpl.nasa.gov .

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Andromeda is So Hot 'n' Cold

This mosaic of the Andromeda spiral galaxy highlights explosive stars in its interior, and cooler, dusty stars forming in its many rings. The image is a combination of observations from the Herschel Space Observatory taken in infrared light (seen in orange hues), and the XMM-Newton telescope captured in X-rays (seen in blues). NASA plays a role in both of these European Space Agency-led missions.

Herschel provides a detailed look at the cool clouds of star birth that line the galaxy's five concentric rings. Massive young stars are heating blankets of dust that surround them, causing them to glow in the longer-wavelength infrared light, known as far-infrared, that Herschel sees.

In contrast, XMM-Newton is capturing what happens at the end of the lives of massive stars. It shows the high-energy X-rays that come from, among other objects, supernova explosions and massive dead stars rotating around companions. These X-ray sources are clustered in the center of the galaxy, where the most massive stars tend to form.

Andromeda is our Milky Way galaxy's nearest large neighbor. It is located about 2.5 million light-years away and holds up to an estimated trillion stars. Our Milky Way is thought to contain about 200 billion to 400 billion stars.

Read more at: http://www.esa.int/SPECIALS/Herschel/SEMY1K0SDIG_0.html .

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information about Herschel is online at http://www.herschel.caltech.edu , http://www.nasa.gov/herschel and http://www.esa.int/SPECIALS/Herschel/index.html .

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Contract Marks New Generation for Deep Space Network

NASA has taken the next step toward a new generation of Deep Space Network antennas. A $40.7 million contract with General Dynamics SATCOM Technologies, San Jose, Calif., covers implementation of two additional 34-meter (112-foot) antennas at Canberra, Australia. This is part of Phase I of a plan to eventually retire the network's aging 70-meter-wide (230-foot-wide) antennas.

The Deep Space Network (DSN) consists of three communications complexes: in Goldstone, Calif.; Madrid, Spain; and Canberra, Australia. The 70-meter antennas are more than 40 years old and are showing signs of surface deterioration from constant use. Additional 34-meter antennas are being installed in Canberra in the first phase; subsequent phases will install additional 34-meter antennas in Goldstone and Madrid.

The 34-meter beam waveguide antennas are essential to keep communications flowing smoothly as NASA's fleet of spacecraft continues to expand. In addition, the waveguide design of the antennas provides easier access for maintenance and future upgrades, because sensitive electronics are housed in a below-the-ground pedestal equipment room, instead of in the center of the dish.

"As a result of several studies, it was determined that arrays of 34-meter beam waveguide antennas were the best solution to long-term continuation of DSN 70-meter capabilities," said Miguel Marina, who manages the 70-meter replacement task force at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The new antennas are critical communication resources for all current and future NASA missions."

NASA expects to complete the building of the first two 34-meter antennas in Canberra by 2016. They will be named Deep Space Stations 35 and 36. Deep Space Station 35 is due to be online in 2014, and Deep Space Station 36 is expected to follow in 2016.

In 1958, NASA established the Deep Space Network as a separately managed and operated communications facility to accommodate all deep space missions. This avoided the need for each flight project to acquire its own specialized space communications network. During the Apollo period (1967-1972), these stations supported America's missions to the moon, including the historic first manned landing. The Goldstone antenna, in particular, captured Neil Armstrong's words and sent them on to American television sets while the images came through another antenna.

The Deep Space Network is now sending commands to numerous robotic spacecraft, such as NASA's Mars Exploration Rovers, the Spitzer Space Telescope, the Saturn explorer Cassini and the two Voyager spacecraft, which are near the edge of the solar system.

JPL, a division of the California Institute of Technology in Pasadena, manages the Deep Space Network for NASA Headquarters, Washington. More information about the Deep Space Network is online at: http://deepspace.jpl.nasa.gov . More information about NASA's Space Communications and Navigation program is at: https://www.spacecomm.nasa.gov .

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Cassini Celebrates 10 Years Since Jupiter Encounter

Ten years ago, on Dec. 30, 2000, NASA's Cassini spacecraft made its closest approach to Jupiter on its way to orbiting Saturn. The main purpose was to use the gravity of the largest planet in our solar system to slingshot Cassini towards Saturn, its ultimate destination.

But the encounter with Jupiter, Saturn's gas-giant big brother, also gave the Cassini project a perfect lab for testing its instruments and evaluating its operations plans for its tour of the ringed planet, which began in 2004.

"The Jupiter flyby allowed the Cassini spacecraft to stretch its wings, rehearsing for its prime time show, orbiting Saturn," said Linda Spilker, Cassini project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Ten years later, findings from the Jupiter flyby still continue to shape our understanding of similar processes in the Saturn system."

Cassini spent about six months - from October 2000 to March 2001 - exploring the Jupiter system. The closest approach brought Cassini to within about 9.7 million kilometers (6 million miles) of Jupiter's cloud tops at 2:05 a.m. Pacific Time, or 10:05 a.m. UTC, on Dec. 30, 2000.

Cassini captured some 26,000 images of Jupiter and its moons over six months of continual viewing, creating the most detailed global portrait of Jupiter yet.

While Cassini's images of Jupiter did not have higher resolution than the best from NASA's Voyager mission during its two 1979 flybys, Cassini's cameras had a wider color spectrum than those aboard Voyager, capturing wavelengths of radiation that could probe different heights in Jupiter's atmosphere.

The images enabled scientists to watch convective lightning storms evolve over time and helped them understand the heights and composition of these storms and the many clouds, hazes and other types of storms that blanket Jupiter.

The Cassini images also revealed a never-before-seen large, dark oval around 60 degrees north latitude that rivaled Jupiter's Great Red Spot in size. Like the Great Red Spot, the large oval was a giant storm on Jupiter.

But, unlike the Great Red Spot, which has been stable for hundreds of years, the large oval showed itself to be quite transient, growing, moving sideways, developing a bright inner core, rotating and thinning over six months. The oval was at high altitude and high latitude, so scientists think the oval may have been associated with Jupiter's powerful auroras.

The imaging team was also able to amass 70-day movies of storms forming, merging and moving near Jupiter's north pole. They showed how larger storms gained energy from swallowing smaller storms, the way big fish eat small fish. The movies also showed how the ordered flow of the eastward and westward jet streams in low latitudes gives way to a more disordered flow at high latitudes.

Meanwhile, Cassini's composite infrared spectrometer was able to do the first thorough mapping of Jupiter's temperature and atmospheric composition. The temperature maps enabled winds to be determined above the cloud tops, so scientists no longer had to rely on tracking features to measure winds.

The spectrometer data showed the unexpected presence of an intense equatorial eastward jet (roughly 140 meters per second, or 310 mph) high in the stratosphere, about 100 kilometers (60 miles) above the visible clouds. Data from this instrument also led to the highest-resolution map so far of acetylene on Jupiter and the first detection of organic methyl radical and diacetylene in the auroral hot spots near Jupiter's north and south poles. These molecules are important to understanding the chemical interactions between sunlight and molecules in Jupiter's stratosphere.

As Cassini approached Jupiter, its radio and plasma wave instrument also recorded naturally occurring chirps created by electrons coming from a cosmic sonic boom. The boom occurs when supersonic solar wind - charged particles that fly off the sun - is slowed and deflected around the magnetic bubble surrounding Jupiter.

Because Cassini arrived at Jupiter while NASA's Galileo spacecraft was still orbiting the planet, scientists were also able to take advantage of near-simultaneous measurements from two different spacecraft.

This coincidence enabled scientists to make giant strides in understanding the interaction of the solar wind with Jupiter. Cassini and Galileo provided the first two-point measurement of the boundary of Jupiter's magnetic bubble and showed that it was in the act of contracting as a region of higher solar wind pressure blew on it.

"The Jupiter flyby benefited us in two ways, one being the unique science data we collected and the other the knowledge we gained about how to effectively operate this complex machine," said Bob Mitchell, Cassini program manager based at JPL. "Today, 10 years later, our operations are still heavily influenced by that experience and it is serving us very well."

In celebrating the anniversary of Cassini's visit 10 years ago, scientists are also excited about the upcoming and proposed missions to the Jupiter system, including NASA's Juno spacecraft, to be launched next August, and the Europa Jupiter System Mission, which has been given a priority by NASA.

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Cassini Finishes Sleigh Ride by Icy Moons

On the heels of a successful close flyby of Saturn's moon Enceladus, NASA's Cassini spacecraft is returning images of Enceladus and the nearby moon Dione.

Several pictures show Enceladus backlit, with the dark outline of the moon crowned by glowing jets from the south polar region. The images show several separate jets, or sets of jets, emanating from the fissures known as "tiger stripes." Scientists will use the images to pinpoint the jet source locations on the surface and learn more about their shape and variability.

The Enceladus flyby took Cassini within about 48 kilometers (30 miles) of the moon's northern hemisphere. Cassini's fields and particles instruments worked on searching for particles that may form a tenuous atmosphere around Enceladus.

They also hope to learn whether those particles may be similar to the faint oxygen- and carbon-dioxide atmosphere detected recently around Rhea, another Saturnian moon. The scientists were particularly interested in the Enceladus environment away from the jets emanating from the south polar region. Scientists also hope this flyby will help them understand the rate of micrometeoroid bombardment in the Saturn system and get at the age of Saturn's main rings.

This flyby of Enceladus, the 13th in Cassini's mission, took a similar path to the last Enceladus flyby on Nov. 30.

About eight hours before the Enceladus flyby, Cassini also swung past Dione at a distance of about 100,000 kilometers (62,000 miles). During that flyby, the spacecraft snapped clear, intriguing images of the bright, fractured region known as the "wispy terrain." These features are tectonic ridges and faults formed by geologic activity on the moon sometime in the past. Scientists will now be able to measure the depth and extent of them more accurately.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's 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.

For more information about the Cassini-Huygens mission, visit
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

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NASA Railroad Keeps Shuttle's Boosters on the Right Track

For nearly three decades, the NASA Railroad at Kennedy Space Center in Florida has kept the space shuttle's solid rocket boosters on track.

The mighty boosters fly in pairs and generate a combined 5.3 million pounds of thrust at ignition, pushing the shuttle assembly past the grip of Earth's gravity during the critical first two minutes of flight. Stacked within each of the 15-story-tall, reusable boosters are four solid rocket motor segments packed with a hard, rubbery cocktail of propellants.

Getting the 12-foot-wide, 150-ton segments to the launch site is only possible by rail. The segments are loaded by manufacturer ATK at a plant in Promontory, Utah, then shipped in customized train cars on a seven-day trip to Kennedy.

Every single booster segment used in the Space Shuttle Program has arrived at Kennedy the same way.

"The railroad is a lifeline in and out of this center," said Chris Bryant, a locomotive engineer and mechanic with URS Corp. Bryant is one of 11 team members in the URS railroad shop who operate and maintain the railroad's cars, tracks and facilities.

At the Wilson's Corners junction at the northern end of the space center, the NASA Railroad splits into two nine-mile stretches of track. Kennedy's mainline runs south, past the Vehicle Assembly Building and other Launch Complex 39 facilities before reaching the center's Industrial Area. To the east, a second line of track extends to the Cape Canaveral Air Force Station.

Each incoming shuttle-booster segment rests on a cradle in a custom-built railcar. A clamshell-like cover, hinged at the top, protects the hardware throughout the journey. Fully loaded, a single segment car weighs 513,000 pounds.

The cross-country route involves commercial rail companies such as Union Pacific, Kansas City Southern, Norfolk Southern, CSX and Florida East Coast Railway (FEC). FEC handles the final leg of the trip, pulling the hazardous cargo into NASA's Jay Jay railroad yard north of Titusville, Fla.

That's when the Kennedy railroad crew takes charge, starting with a thorough inspection.

"When loads come in, you have to inspect every car," explains Will Eriksen, part of the URS team and a three-decade veteran of the Kennedy railroad operation. "You want to make sure you're not going to drag anything in that's going to cause a hazard to the commodity."

Although the train has to traverse a drawbridge spanning the Indian River, the bridge is not strong enough to hold a train with so many heavy cars. The solution: Empty "spacer" cars are added between the segments to distribute the weight over the individual spans of the bridge, so the weight on the bridge is manageable.

The NASA locomotive pulls the train across the river to Wilson Yard, just west of Wilson's Corners junction, where the spacer cars are removed.

"Once we're done and have (the segment cars) all gathered up, we bring them into Suspect Siding," Bryant says, referring to an isolated staging area on the northeast side of the Shuttle Landing Facility. The segments stay there until ATK technicians are ready for them in the booster Rotation, Processing and Surge Facility, where they are rotated to vertical and prepared for stacking.

Although the Kennedy rails are built to withstand mainline track speeds of 60 mph, when the booster segments arrive at Kennedy, the weight and the danger involved require more caution.

"Our track speed is 25 miles an hour -- and normally, we don't reach that," Bryant says. "Normally, our speed is no more than 10 to 15 miles an hour. When we come up to crossings, sometimes it's even slower than that."

"When we're hauling in, we're hauling 4 to 5 million pounds of explosives," Bryant points out. "Through the crossings, too. It's not something to sneeze about, you know."

Kennedy's rail system was activated in 1963 when FEC added a 7.5-mile connection from its mainline across the Indian River to the space center. At that time, the spaceport was in the midst of a construction boom as facilities were built for the Apollo program, and the railroad provided a means of hauling heavy building materials into the center.

"The railroad was built to accommodate the freight cars of that time, which were mostly 50 and 70 ton capacity. It was a very adequate railroad for the cars of the time," says David Hoffman, who managed the NASA Railroad at Kennedy for 13 years until his retirement in 1996.

But by the time the Space Shuttle Program was beginning, the railroad was in sad shape after years of exposure to the salt air and moist, tropical climate. The wood crossties were rotting, rust had eaten away at the hardware, and the rail itself needed to be strengthened. FEC was contracted to upgrade the system.

"We put in the heavy rail (with) welded joints, which are stronger than a bolted joint, and (requires) virtually no maintenance," Hoffman recalls. "And we went to the concrete crossties. You're looking at a 50 or 60 year life of the crosstie instead of 10 or 12 or so for wood in Kennedy's subtropical climate, which means we put it in place and basically walk away and forget it. A lot of that track out there has been in place now since the late 80s, and it has not been touched except for weed spray."

NASA bought that portion of the railroad line from FEC in 1983, two years after the shuttle began flying, and today the skilled Kennedy crew maintains the system.

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'There's the Orbiter, Go Put a Motor in It'

The first time anyone installed a main engine in a space shuttle in 1980, it took three days and prompted a series of changes that quickly became standard practice.

"The first one, it was, 'There's the orbiter, go put a motor in it,'" recalled Robert "Bob" Rysdyk, a lead engine technician for Pratt & Whitney Rocketdyne who helped install that first engine.

There were laser instruments galore marking off all sorts of measurements as technicians tried to set the first engine carefully inside shuttle Columbia's aft compartment.

Rysdyk credits engineer Roy Austin with working out a simple solution.

"He actually went down to the janitor's closet and cut two broomsticks the same length and used those to align the pump to the orbiter," Rysdyk said.

Thirty years and more than 130 missions later, Rysdyk was part of the team that installed what’s expected to be the last set of main engines in a shuttle, this time in Atlantis. It took less than four hours and the team used the same measurements that Austin came up with when he cut the broom handles.

Two years before that first installation, Rysdyk said he had no space program ambitions.

"I was working on four-cylinder airplane engines that would fit on a desk," Rysdyk said. "I got recruited from my next door neighbor who was an engineer out here in '79. Literally, my application was a sheet of notebook paper with my name and what I did on it. I got a job interview and hired within a week."

Michael Kerasotis, a quality inspector with Pratt & Whitney Rocketdyne, came to Kennedy in 1979 as part of a summer program. He started working on the shuttle's tiles but migrated to engine work within a couple years of Columbia's first launch.

"This has been the longest summer ever," Kerasotis joked. "We got a pass to come out here and see (the shuttle). I never thought I'd be working on it."

One of the most carefully choreographed aspects of preparing a shuttle for launch involves placing three 7,700 pound main engines into the back of the spacecraft.

It takes eight people and a lot of patience.

The machinery involved starts with a cone-shaped fitting specially made to handle a main engine. Because the engines face slightly up toward the rudder, they have to be installed at an angle. So the fitting is welded to a sliding rack. The rack and fitting are, in turn, positioned on the front of a huge forklift known as the "Hyster" for the engine installation.

The engine installer, forklift and the technicians who oversee an installation preach careful control anytime an engine is on the move.

The installer has seen very few changes since it was brought to Kennedy in the late 70s, Rysdyk said.

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NASA Scientists Theorize Final Growth Spurt for Planets

A team of NASA-funded researchers has unveiled a new theory that contends planets gained the final portions of their mass from a limited number of large comet or asteroid impacts more than 4.5 billion years ago. These impacts added less than one percent of the planets' mass.

Scientists hope the research not only will provide a better historical picture of the birth and evolution of Earth, the moon and Mars, but also allow researchers to better explore what happened in our solar system's beginning and middle stages of planet formation.

“No one has a model of precisely what happened at the end of planet formation—we’ve had a broad idea—but variables such as impactor size, the approximate timing of the impacts, and how they affect the evolution of the planets are unknown,” said William Bottke, principal investigator from the Southwest Research Institute (SWRI) in Boulder, Colo. “This research hopefully provides better insights into the early stages of planet formation.”

The team used numerical models, lunar samples returned by Apollo astronauts and meteorites believed to be from Mars to develop its findings. The scientists examined the abundances of elements such as gold and platinum in the mantles, or layers beneath the crust, of Earth, the moon and Mars. Consistent with previous studies, they concluded the elements were added by a process called late accretion during a planet's final growth spurt.

"These impactors probably represent the largest objects to hit Earth since the giant impact that formed our moon," Bottke said. “They also may be responsible for the accessible abundance of gold, platinum, palladium, and other important metals used by our society today in items ranging from jewelry to our cars’ catalytic convertors.”

The results indicate the largest Earth impactor was between 1,500 - 2,000 miles in diameter, roughly the size of Pluto. Because it is smaller than Earth, the moon avoided such enormous projectiles and was only hit by impactors 150 - 200 miles wide. These impacts may have played important roles in the evolution of both worlds. For example, the projectiles that struck Earth may have modified the orientation of its spin axis by 10 degrees, while those that hit the moon may have delivered water to its mantle.

"Keep in mind that while the idea the Earth-moon system owes its existence to a single, random event was initially viewed as radical, it is now believed that large impacts were commonplace during the final stages of planet formation,’ Bottke said. “Our new results provide additional evidence that the effects of large impacts did not end with the moon-forming event."

The paper, "Stochastic Late Accretion to the Earth, Moon, and Mars," was published in the Dec. 9 issue of Science. It was written by Bottke and David Nesvorny of SWRI; Richard J. Walker of the University of Maryland; James Day of the University of Maryland and Scripps Institution of Oceanography, University of California, San Diego; and Linda Elkins-Tanton of the Massachusetts Institute of Technology. The research is funded by the NASA Lunar Science Institute (NLSI) at the agency's Ames Research Center in Moffett Field, Calif.

The NLSI is a virtual organization that enables collaborative, interdisciplinary research in support of NASA lunar science programs. The institute uses technology to bring scientists together around the world and comprises competitively selected U.S. teams and several international partners. NASA's Science Mission Directorate and the Exploration Systems Mission Directorate at the agency's Headquarters in Washington, funds the institute, which is managed by a central office at Ames.

For more information on NLSI, visit:

http://lunarscience.nasa.gov

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Site List Narrows For NASA's Next Mars Landing

Four intriguing places on Mars have risen to the final round as NASA selects a landing site for its next Mars mission, the Mars Science Laboratory.

The agency had a wider range of possible landing sites to choose from than for any previous mission, thanks to the Mars Science Laboratory's advanced technologies, and the highly capable orbiters helping this mission identify scientifically compelling places to explore.

Mars Science Laboratory project leaders at NASA's Jet Propulsion Laboratory, Pasadena, Calif., chose the four this month, after seeking input from international Mars experts and from engineers working on the landing system and rover capabilities.

The sites, alphabetically, are: Eberswalde, where an ancient river deposited a delta in a possible lake; Gale, with a mountain of stacked layers including clays and sulfates; Holden, a crater containing alluvial fans, flood deposits, possible lake beds and clay-rich deposits; and Mawrth, which shows exposed layers containing at least two types of clay.

"All four of these sites would be great places to use our roving laboratory to study the processes and history of early Martian environments and whether any of these environments were capable of supporting microbial life and its preservation as biosignatures," said John Grotzinger of the California Institute of Technology, Pasadena. He is the project scientist for the Mars Science Laboratory.

The mission's capabilities for landing more precisely than ever before and for generating electricity without reliance on sunshine have made landing sites eligible that would not have been acceptable for past Mars missions. During the past two years, multiple observations of dozens of candidate sites by NASA's Mars Reconnaissance Orbiter have augmented data from earlier orbiters for evaluating sites' scientific attractions and engineering risks.

JPL is assembling and testing the Mars Science Laboratory spacecraft for launch in fall 2009. Paring the landing-site list to four finalists allows the team to focus further on evaluating the sites and planning the navigation. The mission plan calls for the rover to spend a full Mars year (23 months) examining the environment with a diverse payload of tools.

After evaluating additional Mars orbiter observations of the four sites, NASA will hold a fourth science workshop about the candidates in the spring and plans to choose a final site next summer. Three previous landing-site science workshops for Mars Science Laboratory, in 2006, 2007 and two months ago, drew participation of more than 100 Mars scientists and presentations about more than 30 sites. The four sites rated highest by participants in the latest workshop were the same ones chosen by mission leaders after a subsequent round of safety evaluations and analysis of terrain for rover driving. One site, Gale, had been a favorite of scientists considering 2004 landing sites for NASA's Spirit and Opportunity rovers, but was ruled out as too hazardous for the capabilities of those spacecraft.

"Landing on Mars always is a risky balance between science and engineering. The safest sites are flat, but the spectacular geology is generally where there are ups and downs, such as hills and canyons. That's why we have engineered this spacecraft to make more sites qualify as safe," said JPL's Michael Watkins, mission manager for the Mars Science Laboratory. "This will be the first spacecraft that can adjust its course as it descends through the Martian atmosphere, responding to variability in the atmosphere. This ability to land in much smaller areas than previous missions, plus capabilities to land at higher elevations and drive farther, allows us consider more places the scientists want to explore."

For their Mars landings in 2004, Spirit and Opportunity needed safe target areas about 70 kilometers (about 40 miles) long. Mars Science Laboratory is designed to hit a target area roughly 20 kilometers (12 miles) in diameter. Also, a new "skycrane" technology to lower the rover on a tether for the final touchdown can accommodate more slope than the airbag method used for Spirit and Opportunity. In addition, a radioisotope power supply, like that used by Mars Viking landers in the 1970s, will enable year-round operation farther from the equator than the solar power systems of more recent missions.

Gale is near the equator, Eberswalde and Holden are farther south, and Mawrth is in the north.

As a clay-bearing site where a river once flowed into a lake, Eberswalde Crater offers a chance to use knowledge that oil industry geologists have accumulated about locations of the most promising parts of a delta to look for any concentrations of carbon chemistry that is crucial to life.

The mountain inside Gale Crater could provide a route for the rover to drive up a 5-kilometer (3-mile) sequence of layers, studying a transition from environments that produced clay deposits near the bottom to later environments that produced sulfate deposits partway up.

Running water once carved gullies and deposited sediments as alluvial fans and catastrophic flood deposits in Holden Crater, a site that may also present the chance to evaluate layers deposited in a lake. Exploration of key features within this target area would require drives to the edge of a broad valley, and then down into the valley.

Mawrth Valley is an apparent flood channel near the edge of vast Martian highlands. It holds different types of clays in clearly layered context, offering an opportunity for studying the changes in wet conditions that produced or altered the clays. The clay signatures are stronger than at the other sites, and this is the only one of the four for which the science target is within the landing area, not nearby.

JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Science Laboratory for the NASA Science Mission Directorate, Washington. For additional information about the mission, see http://mars.jpl.nasa.gov/msl.

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