Mars orbiter set for launch on atmospheric research mission
BY STEPHEN CLARK
Posted: November 17, 2013
An Atlas 5 rocket is geared up for launch from Cape Canaveral on Monday with a NASA spacecraft dreamed up a decade ago to help solve the puzzle of how Mars cooled off and dried up sometime long ago, likely killing off any life that may have existed there.
Scientists do not know how Mars transformed from a world with lakes, rivers and potential life into a barren planet without any sign of life today.
"We're trying to understand why the climate changed on Mars - why Mars appears to have gone from an environment that was habitable, to microorganisms at least, to one that is the cold, dry, uninhabitable environment we see today," said Bruce Jakosky, MAVEN's principal investigator from the University of Colorado at Boulder's Laboratory for Atmospheric and Space Physics.
Data from ongoing Mars missions, including NASA's Curiosity rover, have convinced scientists Mars once had ample moisture and harbored warmer temperatures, giving it all the ingredients necessary to support life at some point in its 4.6-billion-year history.
"We don't just launch missions to Mars one at a time," said John Grunsfeld, head of NASA's science division. "We have an integrated program of Mars exploration. We've been following a path of looking for water on Mars, looking for current water and past water. We've now confirmed that ... We're transitioning into the search for biosignatures, past evidence that life could have started on Mars. And we don't have that answer yet. That's part of the quest trying to answer, are we alone in the universe, in a broader sense."
Despite an onslaught of missions over the past decade-and-a-half, including four rovers, a stationary lander, and four orbiters, there is scant evidence for how and when Mars lost its thick atmosphere, leaving a thin blanket of gas just above the surface.
Scientists posed that question when developing the proposal for the $671 million MAVEN mission in 2003, Jakosky said.
"One of the big questions has been what happened to the climate? Why did it change? What we're trying to do is answer that question of where did the water go? Where did the [carbon dioxide] from the early thick atmosphere go? There are two places it can go," Jakosky said. "It can go down into the crust and be locked up there, or it can go up and be lost to space. We have evidence that both of those happened, but we don't see reservoirs of [carbon dioxide] in the crust that could explain what happened to the early thick atmosphere. We're trying to explain the role of loss to space."
Asked if he felt anxious, nervous or excited on the eve of launch, Jakosky replied: "All of the above."
MAVEN is the first mission dedicated to surveying the Martian upper atmosphere, and the probe also hosts an Electra radio to join NASA and European orbiters providing communications relay between Earth and the rovers on the surface.
"By looking at the nature of the upper atmosphere today, we learn about the processes that control the atmopshere, and we're going to have a good understanding of what the history of the atmosphere has been," Jakosky said.
Fitted with eight instruments, MAVEN is set to blast off from Cape Canaveral, Fla., at 1:28 p.m. EST (1828 GMT) Monday aboard a United Launch Alliance Atlas 5 rocket.
Powered by a Russian-built RD-180 engine, the Atlas 5 will ascend from the Florida coastline, break the sound barrier about 78 seconds into flight and rocket into the upper atmosphere in four minutes before releasing its kerosene-fueled first stage to fall back into the Atlantic Ocean.
MAVEN is programmed to radio its status to a pair of ground stations in Australia moments later, and its two wings of power-generating solar panels should be unfurled within 15 minutes of spacecraft separation, according to David Mitchell, MAVEN's project manager at NASA's Goddard Space Flight Center in Maryland.
The solar arrays stretch 37.5 feet tip-to-tip, about the length of a school bus. Filled with propellant, MAVEN weighs about the same as a fully-loaded SUV, according to NASA.
The trip to Mars will take 10 months, and MAVEN is due to put itself into orbit there with a make-or-break 38-minute braking burn scheduled for Sept. 22, 2014, assuming the launch occurs as planned Monday. "There's quite an interest in this mission," said Omar Baez, NASA's launch director for the MAVEN mission. "You wouldn't think so in that it's not as sexy as the rovers going over the planet, but this is kind of like a weather satellite for mars, and it's providing relay. It's real science."
Several more engine firings next fall will put MAVEN into its operational orbit, which will take the probe as close as 93 miles to Mars and as far as 3,860 miles, completing lap of the planet every four-and-a-half hours.
"Every orbit, we're dipping down below the altitude from which gas is lost, so we sample that column directly on every orbit," Jakosky said.
The probe has to extend several instrument booms once it arrives at Mars, allowing MAVEN's sensors to be far enough away from the spacecraft to avoid interference and collect pristine measurements. One of the deployable platforms holds three instruments, allowing those sensors to pivot and point toward Mars while the craft's solar arrays are aimed the sun to charge its batteries.
By early November 2014, MAVEN should be ready to begin its science campaign, which will last at least one Earth year. MAVEN's science instruments come from institutions across the United States and France. Some of the payloads will track the sun's influence on Mars.
Unlike other Mars missions, MAVEN does not carry a camera. As a cost-saving measure, Jakosky said he decided to limit MAVEN's expenditures to those focused on its prime science mission.
Other sensors will identify the gases, ions and elements making up the tenuous outer reaches of the Martian atmosphere.
"This will allow us to estimate over long time periods, on the order of billions of years ... how long Mars has been exposed to this loss process and, therefore, how much atmosphere has been removed in this way," Luhmann said.
One way MAVEN will try to quantify how much of the atmosphere was lost to space is measuring concentrations of heavy and lighter isotopes of gases. Scientists think Mars should hold a greater number of heavy isotopes because lighter atoms would have been easier to strip away with the solar wind, a stream of charged particles coming from the sun.
"Over billions and billions of years, you leave more of the heavy stuff in the atmosphere," said Paul Mahaffy, lead scientist for one of MAVEN's instruments.
"What got me into this were the measurements of isotopes of the noble gases in the atmosphere," Jakosky said. "The key one that got me excited about this was the ratio of argon-38 to argon-36 because on Mars, it's been measured through Martian meteorites and now confirmed with [the Curiosity rover], that the ratio of argon-38 to argon-36 is about 20-to-30 percent greater than on Earth, and the only thing that can explain that is loss to space, so to me that's a direct measurement proving that atmospheric loss to space was an important process."
Earth's strong magnetic field makes it more resistant to atmospheric decay from the solar wind, but Mars does not have the global magnetism required to hold on to air over billions of years.
"We think that escape to space has been responsible for removing a lot of gas from the atmosphere, and we designed this mission to try to understand how those processes work, and see if we can measure things that will tell us how much gas has escaped over time," Jakosky said.
MAVEN will get to Mars just after the peak of the sun's 11-year solar cycle, so scientists hope to get a front-row seat on how a strong solar wind impacts the planet's atmosphere.
"What we're really getting at is understanding the history of the climate, the history of the volatile inventory, and I think the understanding of the history of the habitability of Mars by microbes," Jakosky said. "I see it as a geology mission, or an astrobiology mission, because that's what we're getting at by studying the top of the atmosphere and its interactions with the sun."
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