Maryland scientists vie for NASA missions

One mission would parachute a floating science lab into a lake on Saturn's largest moon, Titan. The other would send a spacecraft to hop on and off a comet as it races toward the sun.

Both outer-space adventures would be led by Maryland scientists — two women who attended Brown University together, and once shared a room at a scientific conference. And both ventures would be managed by Maryland institutions.

But only one (or neither) will win the $425 million in NASA funding needed to get off the ground.

Competing for the money are the Titan Mare Explorer (TiME) mission, led by planetary geologist Ellen Stofan, of Proxemy Research in Gaithersburg; and Comet Hopper, led by geologist Jessica Sunshine, at the University of Maryland.

The spoiler in the race, the one that could elbow both Maryland bidders aside, is a third mission, designed to study Mars' interior geology. Called Geophysical Monitoring Station, or GEMS, it's led by Bruce Banerdt at the NASA Jet Propulsion Laboratory in California.

Each of the three was awarded $3 million last month by NASA to conduct design and feasibility studies. Next year, one of them will be selected for launch. The losers can regroup and apply in 2013 for the next round of funding under NASA's Discovery program.

"When I found out that Comet Hopper was competing against Ellen and TiME, we exchanged emails, and I noted this was competition in the best sense of the word," Sunshine said.

It's going to be a tough choice for the space agency, but the two Marylanders in the race both make fascinating pitches for their proposals.

For Stofan, the idea of exploring a lake on a frigid, alien world is irresistible.

"Imagine the first image," she said. "A grayish day and a bleak seascape, with some waves and clouds on the horizon. … And yet it's not Earth, but another planet on the other side of the solar system."

"That kind of exploration is something that appeals to me romantically," she confessed. "But our reasons for going there are scientific and so fundamental."

Stofan, 50, worked at NASA's Jet Propulsion Laboratory in California for 10 years, studying geological processes on Earth, Venus and Mars. She was also a member of the radar team on NASA's Cassini mission to Saturn, which dropped a probe called Huygens onto Titan's surface in 2005. This is her first time leading a mission as principal investigator.

She now works for Proxemy Research Inc. in Gaithersburg, a small firm that competes for NASA research grants. But planetary exploration is a rather exclusive club.

"I love Jessica; she's definitely a friend of mine," Stofan said. "And I am friends with Bruce Banerdt, who had an office down the hall at JPL."

In fact, she knows most of the 28 team leaders who competed for this round of NASA funding. It's a smart, competitive bunch. "You have to step up your game," she said. "Obviously, I hope to win, and that's my aim."

The competition began in 2007, when NASA issued a request for innovative missions that could make use of the space agency's new Advanced Stirling Radioisotope Generators. The devices could provide electrical power and heat on missions far from the sun, where solar panels can't do the job.

Stofan was approached by Lockheed Martin in 2007 to help write a proposal. The Johns Hopkins University's Applied Physics Lab, near Laurel, was enlisted later to manage the mission.

Sometime in 2023, if NASA selects it for funding, the TiME spacecraft, after a voyage of 71/2 years, would drop by parachute through Titan's dense atmosphere and splash into a frigid lake of liquid methane and ethane.

"Titan is a very benign place for descent and landing," said the mission's project scientist, Ralph Lorenz of APL. Titan's atmosphere is four times denser than Earth's, and it extends much higher above the surface — lots of cushion for a gentle splashdown.

TiME's target is the second-largest of Titan's known lakes, called Ligeia. About 150 miles by 250 miles, it's roughly the size of Lake Superior. That's big enough to be forgiving if NASA's aim is a bit off.

"Titan's lakes, to me, are … at once incredibly familiar, and at the same time incredibly alien," Stofan said.

Titan's lakes are filled with liquid hydrocarbons — methane and ethane. Even at minus-297 degrees Fahrenheit, Lorenz, said they remain liquid, behaving much like gasoline at room temperature. They evaporate, condense, fall as "rain," wash down off the land and collect in rivers and lakes, an analog of the water cycle on Earth.

There is water on Titan. But it is perpetually frozen, so cold it behaves like solid rock.

For now, Titan's lakes look "smooth as a millpond" to the orbiting Cassini spacecraft, he said. But there is evidence of wave action on the shores.

Once TiME splashes down, Stofan said, it will drift with the breeze. An onboard chemistry lab will analyze the liquid; a weather station will record the winds, pressure and temperature changes; a sonar device will probe and map the lake's bottom; and radio gear will send the findings back to Earth.

TiME will help scientists determine how the cycle of wind, evaporation, condensation and precipitation works on Titan, and how that compares with Earth's familiar water cycle. "If it works the same in this very different environment, then you can be much more secure in your understanding of the process" on Earth, Lorenz said. If not, scientists will get to figure out why.

They are also eager to learn how Titan's organic chemistry compares with what is thought to have existed on a young Earth, and which led to the formation of amino acids, pyrimidines and other complex chemical precursors for life.

"We know the atmosphere of Titan can make surprisingly complicated molecules, and we suspect there are more complicated steps that can occur on the surface," Lorenz said. "By seeing how complicated things can get on Titan, we can appreciate how far past that things went on the early Earth."

"This really will be a trip of discovery," he said.

If TiME is not chosen, the project will likely be grounded for the rest of Stofan's career. In the late 2020s, she explained, Titan's northern hemisphere enters a decade-long winter in which the sun and the Earth drop below the horizon. Both the daylight needed for many observations and direct communication with Earth will be lost.

Lakes in Titan's southern hemisphere would be in summer, but they're too small for a safe landing.

So, "for all of us who are Titan scientists, this is it," at least until the 2040s, Stofan said. If NASA says no, "this will not happen, given my age."

Riding with a comet

Down the road at College Park, Jessica Sunshine is imagining a much different mission.

It's the first she's led as principal investigator. But she is a veteran of the UM-led Deep Impact mission, which in 2005 dropped a projectile onto Comet 9P/Tempel 1 to study the dust and frozen gases of its nucleus and its structure. And she stayed with it when it was renamed EPOXI for a flyby of Comet Hartley 2 last November.

It's been "fascinating," Sunshine, 44, said, "but also very frustrating."

As Deep Impact approached 9P/Tempel 1, "we were watching this thing going from a dot to an incredibly complex world before our eyes. Ever since, I have been asking, 'How and why?'"

The flybys provided only "one snapshot in time of a very dynamic environment. The advantage with Chopper is that we stay with it, up close" as it changes with increasing warmth and sunlight.

Comet Hopper, or "Chopper" as it's been nicknamed, would launch in late 2016. The mission would be managed by the NASA Goddard Space Flight Center in Greenbelt.

After a swing around Earth in November 2017 to gather more speed, it would sail out to the orbit of Jupiter and, in June 2022, pull alongside a comet called 46P/Wirtanen.

Discovered by Karl Wirtanen at the Lick Observatory in 1948, it is a small (656 yards long) but very active comet, Sunshine said. It circles the sun once every 5.5 years, from out near the orbit of Jupiter to as near to the sun as Earth's orbit.

"Comets are the most primitive bodies we know of" in the solar system, Sunshine said. "We used to think they were all the same," but visits in recent years have revealed them to be far more varied, both from one comet to another, and even across a single comet nucleus.

Understanding that diversity, scientists believe, should reveal clues to the conditions across the solar system as it formed, and the primitive organic chemistry of the early Earth.

With NASA's radioisotope generator for heat and electricity, she said, Chopper can join the comet at the farthest reaches of its orbit, and stay with it for 21/2 years, watching and probing as it nears the sun, warms up and starts to vent gases.

"We have no idea how the details work," Sunshine said. "How does subliming [the conversion of ices into gas] lead to the surface structures we see?"

Without cumbersome solar panels, she said, "we can land anywhere on the comet's orbit." Chopper could photograph, probe, analyze Wirtanen's surface material with an onboard mass spectrometer. It could even heat up the surface artificially along the way to learn more about it.

Thanks to the comet's weak gravity, Chopper could take off again at will, using thrusters to hop from place to place. The spacecraft will weigh a metric ton on Earth, but on the comet it would weigh "the equivalent of between a gnat and a paper clip," Sunshine said. "We couldn't possibly crash; we'll be going too slowly."

Of course, both Chopper and TiME could "crash" if the JPL Mars mission wins the NASA funding next year, eliminating both Stofan and Sunshine. But Sunshine is looking forward to the matchup against her old friend.

"Knowing we're competing will make us both stronger," she said.

NASA contenders

TiME (Titan Mare Explorer)

Principal investigator: Ellen Stofan, Proxemy Research Inc., Gaithersburg

Manager: Johns Hopkins Applied Physics Lab, Laurel

Goal: Splash down in Ligeia Mare, a liquid hydrocarbon lake on Titan, largest moon of Saturn, for 96 days of scientific study.

Launch: 2016

Arrival at Titan: 2023

Power: NASA's Advanced Stirling Radioisotope Generator

Comet Hopper

PI: Jessica Sunshine, University of Maryland, College Park

Manager: Goddard Space Flight Center, Greenbelt

Goal: Fly spacecraft to join Comet 46P/Wirtanen near orbit of Jupiter, and study it, hopping on and off as it races toward the sun.

Launch: Late 2016

Arrival on comet: November 2017

Power: NASA's Advanced Stirling Radioisotope Generator

Geophysical Monitoring Station (GEMS)

PI: Bruce Banerdt, NASA Jet Propulsion Laboratory, Pasadena, Calif.

Manager: JPL

Goal: Land a spacecraft on Mars with thermal probe, seismometer and orbital tracking gear to study inner composition of the planet.

Launch: Late 2016

Arrival at Mars: 2017

Power: NASA's Advanced Stirling Radioisotope Generator

Maryland weather blog: Frank Roylance on meteorology

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