Monday, September 10, 2012

NASA Mars Rover Curiosity Begins Arm-Work Phase

PASADENA, Calif. -- After driving more than a football field's length since landing, NASA's Mars rover Curiosity is spending several days preparing for full use of the tools on its arm.

Curiosity extended its robotic arm Wednesday in the first of six to 10 consecutive days of planned activities to test the 7-foot (2.1-meter) arm and the tools it manipulates.

"We will be putting the arm through a range of motions and placing it at important 'teach points' that were established during Earth testing, such as the positions for putting sample material into the inlet ports for analytical instruments," said Daniel Limonadi of NASA's Jet Propulsion Laboratory in Pasadena, Calif., lead systems engineer for Curiosity's surface sampling and science system. "These activities are important to get a better understanding for how the arm functions after the long cruise to Mars and in the different temperature and gravity of Mars, compared to earlier testing on Earth."

Since the Mars Science Laboratory spacecraft placed Curiosity inside Mars' Gale Crater on Aug. 5 PDT (Aug. 6 EDT), the rover has driven a total of 358 feet (109 meters). The drives have brought it about one-fourth of the way from the landing site, named Bradbury Landing, to a location selected as the mission's first major science destination, Glenelg.

"We knew at some point we were going to need to stop and take a week or so for these characterization activities," said JPL's Michael Watkins, Curiosity mission manager. "For these checkouts, we need to turn to a particular angle in relation to the sun and on flat ground. We could see before the latest drive that this looked like a perfect spot to start these activities."

The work at the current location will prepare Curiosity and the team for using the arm to place two of the science instruments onto rock and soil targets. In addition, the activities represent the first steps in preparing to scoop soil, drill into rocks, process collected samples and deliver samples into analytical instruments.

Checkouts in the next several days will include using the turret's Mars Hand Lens Imager to observe its calibration target and the Canadian-built Alpha Particle X-Ray Spectrometer to read what chemical elements are present in the instrument's calibration target.

"We're still learning how to use the rover. It's such a complex machine -- the learning curve is steep," said JPL's Joy Crisp, deputy project scientist for the Mars Science Laboratory Project, which built and operates Curiosity.

After the arm characterization activities at the current site, Curiosity will proceed for a few weeks eastward toward Glenelg. The science team selected that area as likely to offer a good target for Curiosity's first analysis of powder collected by drilling into a rock.

"We're getting through a big set of characterization activities that will allow us to give more decision-making authority to the science team," said Richard Cook, Mars Science Laboratory project manager at JPL.

Curiosity is one month into a two-year prime mission on Mars. It will use 10 science instruments to assess whether the selected study area ever has offered environmental conditions favorable for microbial life. JPL manages the mission for NASA's Science Mission Directorate in Washington.

Monday, September 03, 2012

NASA Mars rover Curiosity begins trek to new destination

The Mars rover Curiosity is hitting the road. It headed east Tuesday, driving 52 feet toward a spot where it will use its robotic arm for the first time to drill into bedrock. It'll take weeks for the six-wheel NASA rover to reach the site called Glenelg about a quarter mile away.

"It's nice to see some Martian soil on our wheels," mission manager Arthur Amador said in a statement Wednesday.

The drive was the third and longest one yet since the car-size rover touched down in an ancient crater Aug. 5 to study whether the Martian environment could have been favorable for life. The early drives have been deliberately short, allowing Curiosity to identify any hazards on the road and so that engineers can gain practice driving on the Martian terrain.

Scientists have said they eventually expect the rover to travel about the length of a football field a day. Curiosity spent Wednesday at its new locale, snapping pictures of a distant mountain that is its ultimate destination. Intriguing layers of rocks have been spotted at the base and most of its two-year mission will be spent examining the lower slopes.

Since landing, Curiosity has been busy checking out its instruments and it's not done yet. Next week, it will make a longer stop along the way to Glenelg to continue its health checkups.

Wednesday, August 08, 2012

Launch Director Hails Curiosity Landing

Omar Baez completed his eighth trip to Mars on Monday when NASA's Curiosity rover touched down perfectly inside the Gale Crater to begin a two-year geologic survey of the mysterious red planet. As with everyone else on Earth, Baez can only go to Mars remotely, but that doesn't diminish his excitement.

Nine months ago, Baez was carefully going over the details of Curiosity ahead of its launch on a United Launch Alliance Atlas V rocket. As launch director for NASA's Launch Services Program, it was up to Baez to confirm that the one-ton robotic rover was ready to make a months-long voyage through space to a planet 14 million miles away.

On Nov. 26, 2011, Baez gave his "go" to start the mission, offering his confidence that everything he had seen showed that the rover was ready. Not to mention the rocket pack that would fly through the Martian atmosphere and lower Curiosity onto the surface in a landing maneuver that had never been tried before.

Although he checked out everything several times in a processing hangar on Earth and worked closely with the rover's builders and operators from the Jet Propulsion Laboratory in Pasadena, Calif., he still had an anxious night watching the landing on TV.

"I think there's been roughly 7,000 people who have worked on this," Baez said Monday morning. "There's a personal sense of ownership and some skin that went into making this happen. So I am overjoyed. I was so ecstatic to see them succeed and see this thing on the surface."

Before the mission was launched, and knowing how difficult the entry and landing would be, Baez said he would call the flight a success if the rover landed and returned some video and photos of the barren Martian landscape. That goal has been met, but Baez said he is on to the next level of expectations from Curiosity.

"I think I'm still numb, I'm still waiting for more pictures," Baez said. "I want to see the thing roll around and rove. I'm not ready to pop the champagne corks yet." The landing buoyed the whole launch team. "Everyone's walking with a spring in their step, just having a good time," Baez said. "Overall, it's a great feeling."

Even after launching eight spacecraft to Mars, Baez' work with the red planet is not finished. The Launch Services Program is working toward the launch of the MAVEN mission, a spacecraft that will study Mars from orbit. MAVEN, short for Mars Atmosphere and Volatiles EvolutioN, is to look for clues as to why the Martian atmosphere changed and why its surface water was lost to space. It is to launch in late 2013.

Friday, August 03, 2012

Dust Dominates Foreign Aerosol Imports to North America

NASA and university scientists have made the first measurement-based estimate of the amount and composition of tiny airborne particles that arrive in the air over North America each year. With a 3-D view of the atmosphere now possible from satellites, the scientists calculated that dust, not pollution, is the main ingredient of these imports.

According to a new analysis of NASA satellite data, 64 million tons of dust, pollution and other particles that have potential climate and human health effects survive a trans-ocean journey to arrive over North America each year. This is nearly as much as the estimated 69 million tons of aerosols produced domestically from natural processes, transportation and industrial sources. The results were published Aug. 2 in the journal Science.

"This first-of-a-kind assessment is a crucial step toward better understanding how these tiny but abundant materials move around the planet and impact climate change and air quality," says Hongbin Yu, lead author and an atmospheric scientist at the University of Maryland, College Park, and NASA's Goddard Space Flight Center in Greenbelt, Md.

Observing these microscopic airborne particles and quantifying their global impact on warming or cooling Earth remains one of the most difficult challenges of climate science. Dust and pollution particles rise into the atmosphere and can travel for days across numerous national boundaries before settling to Earth.

Data from several research satellites flying advanced observing technology developed and launched by NASA enabled the scientists to distinguish particle types and determine their heights in the atmosphere. They combined that information with wind speed data to estimate the amount of pollution and dust arriving over North America. The scientists used data from instruments on NASA's Terra satellite and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, a joint effort between NASA and the French space agency, Centre National d'Etudes Spatiales.

Yu and colleagues estimated that dust crossing the Pacific Ocean accounts for 88 percent, or 56 milliontons, of the total particle import to North America every year. Dust movement is particularly active in spring, when the rise of cyclones and strong mid-latitude westerlies boost particle transport across the Pacific. Global aerosol transport models revealed Asia was a primary source of the dust reaching North America. About 60 to 70 percent comes from Asia, and the remaining 30 to 40 percent comes from Africa and the Middle East.

Dust particles are fine pieces of minerals that primarily come from dry, desert-like regions. Winds lift these lightweight particles high into the atmosphere where they meet even faster-moving winds capable of transporting them around the planet. Pollution particles, in contrast, come from combustion sources such as wildfires or agricultural fires and fossil fuel burning for power and industry. These particles are emitted close to the ground, making them of prime interest to air quality researchers and managers. High-altitude dust particles are less a concern for human health, but their impact on climate can be significant.

One such impact on climate is a cooling effect, brought about by dust and some pollution particles that reflect sunlight back to space. The team calculated that the imported particles account for one third of the reduction in solar radiation, or solar dimming, over North America. "Globally this can mask some of the warming we expect from greenhouse gases," says Lorraine Remer, an atmospheric scientist at University of Maryland, Baltimore County, and co-author on the study.

Friday, July 27, 2012

NASA launches hypersonic inflatable heat shield prototype

NASA launched a novel new heat shield prototype on a successful test flight Monday (July 23), a mission that sent a high-tech space balloon streaking through Earth's atmosphere at hypersonic speeds of up to Mach 10.

The test flight blasted off atop a suborbital rocket at 7:01 a.m. EDT (1101 GMT) from NASA's Wallops Flight Facility on Wallops Island, Va. It sent a small capsule, called the Inflatable Re-entry Vehicle Experiment 3 (IRVE-3) into suborbital space, which deployed the inflatable heat shield and then plunged back down through Earth's atmosphere to splash down in the Atlantic Ocean.

The mission, according to NASA, was an unqualified success and will help shape new re-entry systems for future spacecraft.

"We had a really great flight today," James Reuther, deputy director of NASA's Space Technology Program, told reporters in a news briefing Monday (July 23). "Initial indications are we got good data. Everything performed as well, or better, than expected."

The IRVE-3 flight was designed to demonstrate how the technology could be used for heat shields during atmospheric entries on future space missions.

The successful test flight is, "a first step for how we explore other worlds," said Steve Jurczyk, deputy director of NASA's Langley Research Center in Hampton, Va.

"As far as the applicability of the technology, [we were] originally motivated to do this to allow us to potentially land more masses at Mars," said Neil Cheatwood, IRVE-3 principal investigator at Langley Research Center. "Mars is a very challenging destination. It has a very thin atmosphere — too much of an atmosphere to ignore, but not enough for us to do the things we would at other planets. That was our motivation about nine years ago when we started doing this stuff."

With inflatable heat shields, scientists may be able to land at higher altitudes on Mars, or use the IRVE-3 technology to one day carry larger payloads, including humans, to the surface of the Red Planet, Cheatwood added. 

Friday, July 20, 2012

NASA builds menu for planned Mars mission in 2030s

HOUSTON (AP) ― Through a labyrinth of hallways deep inside a 1950s-era building that has housed research that dates back to the origins of U.S. space travel, a group of scientists in white coats is stirring, mixing, measuring, brushing and, most important, tasting the end result of their cooking.

Their mission: Build a menu for a planned journey to Mars in the 2030s.

The menu must sustain a group of six to eight astronauts, keep them healthy and happy and offer a broad array of food. That’s no simple feat considering it will likely take six months to get to the Red Planet, astronauts will have to stay there 18 months and then it will take another six months to return to Earth. Imagine having to shop for a family’s three-year supply of groceries all at once and having enough meals planned in advance for that length of time.

“Mars is different just because it’s so far away,” said Maya Cooper, senior research scientist with Lockheed Martin who is leading the efforts to build the menu. “We don’t have the option to send a vehicle every six months and send more food as we do for International Space Station.”

Astronauts who travel to the space station have a wide variety of food available to them, some 100 or so different options, in fact. But it is all pre-prepared and freeze-dried with a shelf life of at least two years. And while astronauts make up a panel that tastes the food and gives it a final OK on Earth before it blasts off, the lack of gravity means smell ― and taste ― is impaired. So the food is bland.

On Mars though, there is a little gravity, allowing NASA to consider significant changes to the current space menu. That’s where Cooper’s team comes in. Travel to Mars opens the possibility that astronauts can do things like chop vegetables and do a little cooking of their own. Even though pressure levels are different than on Earth, scientists think it will be possible to boil water with a pressure cooker too.

One option Cooper and her staff are considering is having the astronauts care for a “Martian greenhouse.” They would have a variety of fruits and vegetables ― from carrots to bell peppers ― in a hydroponic solution, meaning they would be planted in mineral-laced water instead of soil. The astronauts would care for their garden and then use those ingredients, combined with others, such as nuts and spices brought from Earth, to prepare their meals.

“That menu is favorable because it allows the astronauts to actually have live plants that are growing, you have optimum nutrient delivery with fresh fruits and vegetables, and it actually allows them to have freedom of choice when they’re actually cooking the menus because the food isn’t already pre-prepared into a particular recipe,” Cooper said.

The top priority is to ensure that the astronauts get the proper amount of nutrients, calories and minerals to maintain their physical health and performance for the life of the mission, Cooper said.

The menu must also ensure the psychological health of the astronauts, Cooper explained, noting studies have shown that eating certain foods ― such as meatloaf and mashed potatoes or turkey on Thanksgiving ― improve people’s mood and give them satisfaction. That “link to home” will be key to astronauts on the Mars mission, and there are currently two academic studies looking further into the connection between mood and food. Lacking certain vitamins or minerals can also harm the brain, she said.

Jerry Linenger, a retired astronaut who spent 132 days on the Russian space station in 1997, said food is important for morale, and the monotony of eating the same thing day after day is difficult.

“You just wanted something different. I didn’t care if it was something I wouldn’t eat in a million years on Earth. If it was different, I would eat it,” Linenger said, recalling with a laugh how he would even drink up a Russian sour milk-like concoction for breakfast or drink up some borscht because it offered variety.

Already, Cooper’s team of three has come up with about 100 recipes, all vegetarian because the astronauts will not have dairy or meat products available. It isn’t possible to preserve those products long enough to take to Mars ― and bringing a cow on the mission is not an option, Cooper jokes.

To ensure the vegetarian diet packs the right amount of protein, the researchers are designing a variety of dishes that include tofu and nuts, including a Thai pizza that has no cheese but is covered with carrots, red peppers, mushrooms, scallions, peanuts and a homemade sauce that has a spicy kick.

To keep this menu going, and get the most out of any research about food sustainability on Mars, Cooper says it’s possible NASA will choose to have one astronaut solely dedicated to preparing the food ― the Emeril of the Mars mission.

Tuesday, July 17, 2012

NASA's Car-Sized Rover Nears Daring Landing on Mars

PASADENA, Calif. -- NASA's most advanced planetary rover is on a precise course for an early August landing beside a Martian mountain to begin two years of unprecedented scientific detective work. However, getting the Curiosity rover to the surface of Mars will not be easy.

"The Curiosity landing is the hardest NASA mission ever attempted in the history of robotic planetary exploration," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate, at NASA Headquarters in Washington. "While the challenge is great, the team's skill and determination give me high confidence in a successful landing."

The Mars Science Laboratory mission is a precursor for future human missions to Mars. President Obama has set a challenge to reach the Red Planet in the 2030s.

To achieve the precision needed for landing safely inside Gale Crater, the spacecraft will fly like a wing in the upper atmosphere instead of dropping like a rock. To land the 1-ton rover, an airbag method used on previous Mars rovers will not work. Mission engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., designed a "sky crane" method for the final several seconds of the flight. A backpack with retro-rockets controlling descent speed will lower the rover on three nylon cords just before touchdown.

During a critical period lasting only about seven minutes, the Mars Science Laboratory spacecraft carrying Curiosity must decelerate from about 13,200 mph (about 5,900 meters per second) to allow the rover to land on the surface at about 1.7 mph (three-fourths of a meter per second). Curiosity is scheduled to land at approximately 10:31 p.m. PDT on Aug. 5 (1:31 a.m. EDT on Aug. 6).

"Those seven minutes are the most challenging part of this entire mission," said Pete Theisinger, the mission's project manager at JPL. "For the landing to succeed, hundreds of events will need to go right, many with split-second timing and all controlled autonomously by the spacecraft. We've done all we can think of to succeed. We expect to get Curiosity safely onto the ground, but there is no guarantee. The risks are real."

During the initial weeks after the actual landing, JPL mission controllers will put the rover through a series of checkouts and activities to characterize its performance on Mars, while gradually ramping up scientific investigations. Curiosity then will begin investigating whether an area with a wet history inside Mars' Gale Crater ever has offered an environment favorable for microbial life.

"Earlier missions have found that ancient Mars had wet environments," said Michael Meyer, lead scientist for NASA's Mars Program at NASA Headquarters. "Curiosity takes us the next logical step in understanding the potential for life on Mars."

Curiosity will use tools on a robotic arm to deliver samples from Martian rocks and soils into laboratory instruments inside the rover that can reveal chemical and mineral composition. A laser instrument will use its beam to induce a spark on a target and read the spark's spectrum of light to identify chemical elements in the target.

Other instruments on the car-sized rover will examine the surrounding environment from a distance or by direct touch with the arm. The rover will check for the basic chemical ingredients for life and for evidence about energy available for life. It also will assess factors that could be hazardous for life, such as the radiation environment.

"For its ambitious goals, this mission needs a great landing site and a big payload," said Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters. "During the descent through the atmosphere, the mission will rely on bold techniques enabling use of a smaller target area and a heavier robot on the ground than were possible for any previous Mars mission. Those techniques also advance us toward human-crew Mars missions, which will need even more precise targeting and heavier landers."

The chosen landing site is beside a mountain informally called Mount Sharp. The mission's prime destination lies on the slope of the mountain. Driving there from the landing site may take many months.

"Be patient about the drive. It will be well worth the wait and we are apt to find some targets of interest on the way," said John Grotzinger, MSL project scientist at the California Institute of Technology in Pasadena. "When we get to the lower layers in Mount Sharp, we'll read them like chapters in a book about changing environmental conditions when Mars was wetter than it is today."

In collaboration with Microsoft Corp., a new outreach game was unveiled Monday to give the public a sense of the challenge and adventure of landing in a precise location on the surface. Called "Mars Rover Landing," the game is an immersive experience for the Xbox 360 home entertainment console that allows users to take control of their own spacecraft and face the extreme challenges of landing a rover on Mars.

"Technology is making it possible for the public to participate in exploration as it never has before," said Michelle Viotti, JPL's Mars public engagement manager. "Because Mars exploration is fundamentally a shared human endeavor, we want everyone around the globe to have the most immersive experience possible." 

Tuesday, July 10, 2012

NASA hopes are riding on Mars rover's tricky descent

It is the last 78 miles of a NASA rover's 154 million-mile journey to Mars that concerns Ravi Prakash the most.

That's because this is the first time that NASA - or anyone else - has ever tried to land something nearly so big as the 1-ton Curiosity rover on Mars, and because so much is riding on this particular mission.

"We've got to go from five times as fast as a speeding bullet - 13,000 mph - all the way to a screeching halt in seven minutes," said Prakash, a Texas City native who now works at NASA's Jet Propulsion Laboratory on the rover's lander team.

Five times the size of the Spirit and Opportunity rovers already on Mars, Curiosity is packed with scientific equipment: HD-resolution cameras that can also capture video; a laser than can ignite a spark on rocks 20 feet away to determine what they're made of; and other high-tech tools including an X-ray diffraction setup, a mass spectrometer, and a gas chromatograph.

With these devices the six-wheeled rover will be able to sample hundreds of layers of sedimentary rock, allowing scientists to understand how the surface of Mars changed over time, and providing a detailed history of the Red Planet and clues to whether life could have flourished there.

But it's got to get there safely at first.Adding to the pressure is that NASA is not currently planning or building a next generation rover to go to Mars. More than 200 scientists attended a NASA meeting earlier this year in Houston to discuss plans for follow-up missions, but none has been chosen.

Nail-biting time
So Curiosity, itself a decade in the works, is it for a long time."With no sense of how or when we will follow this up, and without knowing which direction our tools and techniques are evolving - yes, landing successfully is a big deal," said Mark Lemmon, a Texas A&M University planetary scientist who will help operate the rover on Mars.

Launched in November, the $2.5 billion rover will reach the upper limit of the Martian atmosphere at 12:30 a.m. CDT on Aug. 6. Almost out of rocket fuel, it will proceed directly to the planet's surface.

Then the nail-biting will begin. The capsule carrying the rover will slow as it falls through the thin Martian atmosphere, and at seven miles above the Red Planet a parachute will deploy. One mile above the surface, and at a speed of 180 mph, the parachute will separate, and thrusters will further slow the descent.

Thursday, July 05, 2012

NASA Unveils Orion During Ceremony

The Orion capsule that will make the first flight test into space was celebrated Monday morning as the cornerstone of a new era of exploration for America's space program.

The spacecraft's aluminum-alloy crew pressure module arrived at NASA's Kennedy Space Center in Florida on Friday, June 29, where it will be built up into a fully functioning spacecraft ahead of a test flight slated for 2014.

"This starts a new, exciting chapter in this nation's great space exploration story," said Lori Garver, NASA deputy administrator. "Today we are lifting our spirits to new heights."

Orion will be the most advanced spacecraft ever designed. It will provide emergency abort capability, sustain astronauts during space travel and provide safe re-entry from deep space.

The 2014 uncrewed flight, called Exploration Flight Test-1 or EFT-1, will be loaded with a wide variety of instruments to evaluate how the spacecraft behaves during launch, in space and the through the searing heat of reentry.

Later Orion spacecraft will take astronauts on missions to destinations far beyond Earth, such as to an asteroid and Mars.

"Ladies and gentlemen, we're going to Mars," proclaimed U.S. Sen. Bill Nelson, D-Fla., who joined Garver and other officials to welcome the Orion spacecraft. "We know the Orion capsule is a critical part of the system that's going to take us there."

Designed with astronauts in mind, Orion will take crews beyond low-Earth orbit for the first time since 1972, when Apollo 17 completed the last moon landing. The Space Launch System, or SLS -- a gigantic rocket akin to the Saturn V that launched the Apollo spacecraft -- is being developed to launch future Orion missions to deep space. The first launch of the SLS, with Orion atop, is scheduled for 2017.

Astronaut Rex Walheim, who flew on the final space shuttle mission and has had a leading role in the development of Orion, said the capsule can be the principal spacecraft for 30 years of human exploration of the solar system.

"It's the first in a line of vehicles that can take us where we've never gone before," Walheim said. "It'll be a building block approach, we'll have to have a lander and a habitation module, but we can get there."

Although the design is reminiscent of the landmark Apollo capsule that took men to the moon, the interior of the spacecraft if significantly more advanced. Its guidance, navigation and life support equipment have seen significant improvements in size and capabilities.

"The systems on this spacecraft, it's bigger than Apollo and it has to stay in space longer than Apollo, so it has to be better than Apollo," said Bob Cabana, director of Kennedy and a former shuttle commander.

For now, the focus for NASA and Lockheed Martin, the spacecraft's builder, is on preparing this capsule for space in 2014. During the EFT-1 mission, a Delta IV-Heavy rocket from United Launch Alliance will lift the spacecraft into orbit. Its second stage will remain attached to the capsule and will be fired to raise the Orion's orbit to 3,600 miles, about 15 times higher than the International Space Station. The mission will last only a few hours, long enough to make two orbits before being sent plunging back into the atmosphere to test it at deep-space reentry speeds.

Friday, June 29, 2012

Cassini Finds Likely Subsurface Ocean on Saturn Moon

PASADENA, Calif. -- Data from NASA's Cassini spacecraft have revealed Saturn's moon Titan likely harbors a layer of liquid water under its ice shell.

Researchers saw a large amount of squeezing and stretching as the moon orbited Saturn. They deduced that if Titan were composed entirely of stiff rock, the gravitational attraction of Saturn would cause bulges, or solid "tides," on the moon only 3 feet (1 meter) in height. Spacecraft data show Saturn creates solid tides approximately 30 feet (10 meters) in height, which suggests Titan is not made entirely of solid rocky material. The finding appears in today's edition of the journal Science.

"Cassini's detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth," said Luciano Iess, the paper's lead author and a Cassini team member at the Sapienza University of Rome, Italy. "The search for water is an important goal in solar system exploration, and now we've spotted another place where it is abundant."

Titan takes only 16 days to orbit Saturn, and scientists were able to study the moon's shape at different parts of its orbit. Because Titan is not spherical, but slightly elongated like a football, its long axis grew when it was closer to Saturn. Eight days later, when Titan was farther from Saturn, it became less elongated and more nearly round. Cassini measured the gravitational effect of that squeeze and pull.

Scientists were not sure Cassini would be able to detect the bulges caused by Saturn's pull on Titan. By studying six close flybys of Titan from Feb. 27, 2006, to Feb. 18, 2011, researchers were able to determine the moon's internal structure by measuring variations in the gravitational pull of Titan using data returned to NASA's Deep Space Network (DSN).

"We were making ultrasensitive measurements, and thankfully Cassini and the DSN were able to maintain a very stable link," said Sami Asmar, a Cassini team member at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The tides on Titan pulled up by Saturn aren't huge compared to the pull the biggest planet, Jupiter, has on some of its moons. But, short of being able to drill on Titan's surface, the gravity measurements provide the best data we have of Titan's internal structure."

An ocean layer does not have to be huge or deep to create these tides. A liquid layer between the external, deformable shell and a solid mantle would enable Titan to bulge and compress as it orbits Saturn. Because Titan's surface is mostly made of water ice, which is abundant in moons of the outer solar system, scientists infer Titan's ocean is likely mostly liquid water.

On Earth, tides result from the gravitational attraction of the moon and sun pulling on our surface oceans. In the open oceans, those can be as high as two feet (60 centimeters). While water is easier to move, the gravitational pulling by the sun and moon also causes Earth's crust to bulge in solid tides of about 20 inches (50 centimeters).

The presence of a subsurface layer of liquid water at Titan is not itself an indicator for life. Scientists think life is more likely to arise when liquid water is in contact with rock, and these measurements cannot tell whether the ocean bottom is made up of rock or ice. The results have a bigger implication for the mystery of methane replenishment on Titan.

"The presence of a liquid water layer in Titan is important because we want to understand how methane is stored in Titan's interior and how it may outgas to the surface," said Jonathan Lunine, a Cassini team member at Cornell University, Ithaca, N.Y. "This is important because everything that is unique about Titan derives from the presence of abundant methane, yet the methane in the atmosphere is unstable and will be destroyed on geologically short timescales."

A liquid water ocean, "salted" with ammonia, could produce buoyant ammonia-water liquids that bubble up through the crust and liberate methane from the ice. Such an ocean could serve also as a deep reservoir for storing methane.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by JPL for NASA's Science Mission Directorate in Washington. DSN, also managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. Cassini's radio science team is based at Wellesley College in Massachusetts. JPL is a division of the California Institute of Technology in Pasadena.