Atmospheric Sciences Professor Part of Mars Rover Team

By Amelia Williamson 

Although many people’s jobs take them only a short distance from home, Mark Lemmon’s job takes him out of this world – to Mars. Lemmon, part of NASA’s Mars Exploration Rover Mission team and an associate professor in the atmospheric sciences department at Texas A&M University, has spent many days living on Mars time and communicating with the rovers Spirit and Opportunity as they explore the surface of Mars.

“[When] we look at Mars, we see a planet that’s had rivers flow on its surface in the past. We see a place where there have been catastrophic floods… where there might have been a global ocean – and [yet], for billions of years, it’s been a dry, cold, arid desert with no obvious signs of life,” Lemmon says. He says it is important to understand what Mars was like in the past and why its climate changed so dramatically in order to better understand Earth’s climate and “what sorts of things can happen to Earth without dramatically changing its climate.” He adds, “It’s just kind of scary when you think of how Earth-like Mars might have been and how non-Earth-like it is now.”

Although Lemmon currently spends most of his time studying Mars, his interest in planetary science began with Titan, one of Saturn’s moons.

Mysterious Titan

As a planetary science graduate student at the University of Arizona in the early 1990s, Lemmon worked on what became a NASA project for studying Titan’s atmosphere. Lemmon says Titan is interesting because in many ways it is very Earth-like, but still very alien. Titan is an incredibly cold world, with “ice as hard as rock,” he says. And although Titan is covered in thick smog, its lower atmosphere resembles Earth’s, with wind, clouds, and rain – but instead of water, it’s methane. “It’s got a lot of the same stuff going on that Earth has, with just some kind of alien twists,” Lemmon says. 

Lemmon says that at the time, scientists did not think it was possible to see Titan’s surface because of its thick atmosphere, which is about four times as dense as Earth’s. In 1992, Lemmon had used ground-based telescopes to show there were brighter and darker parts of Titan’s surface, but Titan was too small for the telescopes to make out any details. In 1994, however, Lemmon and others in his research group at the University of Arizona used Hubble Space Telescope images mostly at near-infrared wavelengths to get through the haze and piece together the first map of Titan’s surface.                                              

After earning his doctorate in 1994, Lemmon did some work with the Galileo probe, which had been launched in 1989 to study Jupiter and its moons. In 1997, he joined the imaging team for Mars Pathfinder, and then in 1999, he worked on plans for the Mars Polar Lander mission until the lander was lost during its entry into Mars’ atmosphere in December 1999.

In August 2000, Lemmon moved to A&M, where his wife, Maria Escobar-Lemmon, had been offered a job in the political science department. Lemmon started working at A&M as a visiting assistant professor in the physics department. In June 2002, he moved to the atmospheric sciences department as an associate research scientist, and in September 2005, he became an associate professor. He has taught basic astronomy, survey of astronomy, and introduction to atmospheric sciences classes and a graduate course in planetary atmospheres.

In 2002, Lemmon joined the science team for the Mars Exploration Rover Mission, which is still in progress. He is also now involved with the Phoenix mission, which is scheduled to send a lander to Mars’ polar region in August 2007, and the Mars Science Laboratory, which is set to launch in fall 2009.

Exploring Mars

At first, NASA intended to send only one rover to Mars and had chosen 25 people for the science team. It later decided to send two rovers and needed more people, so in December 2001, proposals were solicited. Lemmon submitted a proposal in which he explained the atmospheric science he could do with the rover cameras if he was selected.

In May 2002, NASA announced its selections, which included Lemmon. In December 2003, Lemmon and his wife moved to Pasadena, California, where the mission was being run from the Jet Propulsion Laboratory.

Spirit landed on Mars on January 4, 2004, and Opportunity landed on January 25. “The main purpose [of the mission] was to look for signs of water being involved in Mars’ climate in the past,” Lemmon says, “and it has been successful beyond the wildest dreams of anyone ever involved in it.”

Lemmon was at JPL when each of the two rovers landed on Mars. “It was very exhilarating going through the whole experience,” Lemmon says. “For both of them I was there at JPL, just watching all of the events as they happened, listening to the people who were on console who were monitoring the different signals.”

Lemmon says the team had expected to lose the signal while the landers, which carried the rovers, passed through the Martian atmosphere and bounced onto the surface of Mars. But surprisingly, for Spirit, the signal remained detectable the whole way through. “The way it happened was that we could listen to every step in the descent all the way down and just get the callout – ‘now the heat shield is deployed… now the parachute’s deployed, it’s swinging on its parachute, the thrusters fire to slow it down, it’s bouncing,’” Lemmon says. “And we got the signal after it had done the first bounce, and everyone started cheering. And then the signal went away. And someone said, ‘Now remember, it has to survive all the bounces.’” For the next five minutes, the team heard nothing. Then, all of a sudden, the signal returned. Lemmon says that it was a long five minutes in the mission room at JPL. Opportunity’s signal also remained detectable throughout its descent.

Mars Time

For the first four months of the mission, the team lived and worked on “Mars time” (a Mars day is 40 minutes longer than an Earth day). Lemmon had a Mars-time alarm clock and wristwatch that helped him keep track of what time it was on Mars. “I gave up Earth time completely,” Lemmon says. “I did everything in Mars time and really had no track of what time it was in the outside world. We were in a building, and we had covered up all the windows so that we wouldn’t get signals from the outside saying day or night.” 

The mission no longer runs on Mars time, however, because it has lasted so much longer than the originally planned 90 days. Lemmon moved back to College Station in April 2004 and now works on the mission mainly from his office at A&M.

Martian Weather

During the mission, Lemmon has been deeply involved in using the rovers to make movies of dust devils moving across the surface of Mars. When Spirit arrived at the Cascade Hills on Mars, it had a clear view of the Martian plains and captured many images of dust devils. “When it’s summertime on Mars, at least where Spirit was, you couldn’t wake up and look out onto the plains without seeing dust devils racing across the surface,” Lemmon says. “I think [the movies] really helped bring Mars home for a lot of people, even on the team. It’s not just something static that you look at pictures of – we actually see dynamic things happening.”

Lemmon says the large amount of dust in Mars’ atmosphere affects its climate, and by studying the dust devils, scientists can learn more about how Mars’ climate works. Lemmon also used the rovers, especially Opportunity, to take pictures of clouds in the Martian sky.

Mike Wolff, one of the atmospheric scientists on the team with Lemmon, says he has enjoyed working with Lemmon. “It’s fabulous,” Wolff says. “He’s a good team player and he’s very entertaining. We call him Mr. Sunshine.” Wolff says Lemmon is a “very careful, focused scientist” and brings much to the team with his extensive experience with Mars Pathfinder.

Wolff says Lemmon’s work with the rovers is important because it’s “all part of understanding how the weather works.” To figure out what Mars’ climate was like in the past, scientists must understand the weather in the present. Wolf says, “The sort of observations and analyses that Mark does characterize the state of the atmosphere now and provide important information for people who are attempting to model the weather [on Mars].”

Stephanie Grounds, a Texas A&M atmospheric sciences graduate student, is working on atmospheric research for the Mars Exploration Rovers mission with Lemmon. “The best way for me to describe Dr. Lemmon is brilliant,” she says. “When I first met him, I was a little intimidated… [but] he is so nice – he’s a wonderful person.” Grounds says Lemmon is always willing to stop and explain things and that he “always gives you little tidbits of information that keep you really excited.”

When Grounds watches the rovers driving around on Mars via the live feed on Lemmon's computer, she is awestruck. “It’s unbelievable,” she says. “You stop and think, this really can’t be happening – I can’t be sitting here in his office and looking at live feed from another planet – it’s so cool!”

Lemmon says he plans to continue exploring other worlds and that he “certainly expects to be involved with Mars for years down the road.” Although Mars is important to study, Lemmon says it should not be scientists’ only focus. He says it is also important to study other planets and moons in our solar system to try to understand their history and learn how they are similar and different from Earth. “These are all places where we’re trying to figure out how things work under different conditions. It helps us understand how we got where we are here on Earth.”

Amelia Williamson is a Science and Technology Journalism graduate student at Texas A&M University.