NASA launched its Maven orbiter on Monday to begin a journey that could unravel the mysteries surrounding Mars' past and current atmosphere — and perhaps reveal how the planet lost its life-friendly environment.
A United Launch Alliance Atlas 5 rocket rose from Cape Canaveral Air Force Station's Launch Complex 41 in Florida at 1:28 p.m. ET, carrying the probe into space to kick off its $671 million mission.
If all goes according to schedule, the bus-sized, 2.7-ton spacecraft will enter Martian orbit next September to study the Red Planet's upper atmosphere over the course of at least one Earth year.
What happened on Mars?
"Maven" is an acronym that stands for Mars Atmophere and Volatile EvolutioN. The mission's objective is to help scientists figure out how the Red Planet's environment changed from a warm, moist place into the chilly wasteland it is today.
Previous missions — including NASA's Curiosity rover, which has been working on Red Planet's surface for more than a year — have found ample geological evidence that Marshad enough liquid water on its surface to be hospitable to life billions of years ago. That's not the case anymore.
"Something clearly happened," said Bruce Jakosky, a planetary scientist at the University of Colorado who serves as Maven's principal investigator.
The leading hypothesis is that Mars was too small to hang onto its global magnetic field over the long term. As a result, the planet lost the kind of magnetic shield that protects Earth's atmosphere from the damaging effects of solar radiation. In this scenario, electrically charged particles from the sun stripped away Mars' air from the top, leaving behind a carbon dioxide atmosphere that's only 1 percent as dense as Earth's. That kind of atmosphere can't retain heat, shield the surface from radiation or sustain liquid water.
There are also hints that some of Mars' atmospheric CO2 was locked up as carbonates in the Red Planet's rocks. How much was stripped away from above, and how much was locked up below?
"We can't go back and study what happened over 4 billion years," Jakosky told reporters, "but we can go and look at how these processes are operating today, and how the processes have changed over time."
Maven's array of nine sensors, built into eight scientific instruments, can monitor the solar radiation hitting the top of Mars' atmosphere, gauge the current rate of atmospheric loss, and map the planet's localized, jumbled-up magnetic "umbrellas." Scientists plan to factor in all those readings to produce better models for the global climate shift that swept over Mars — and changed the odds for life in the process.
A team player
Maven won't be working in isolation: It will be joining three other orbiters and two surface rovers that are already on the job at Mars. Yet another orbiter — India's Mars Orbiter Mission, also known as the Mangalyaan probe — was launched earlier this month and is due to reach Martian orbit just after Maven's arrival.
The teams for Maven and Mangalyaan plan to collaborate in their studies of the Red Planet's atmosphere. For instance, there's been some evidence that methane is being released into the Martian atmosphere, which could hint at biological activity. Curiosityhasn't detected any methane at the surface, and Maven won't be measuring methane because that doesn't mesh with the mission's scientific goals. But Mangalyaan can take a closer look at the methane question, and its results could add to Maven's models.
Maven is destined to be a team player in another sense: NASA's current Mars orbiters are well into their extended missions, and if one of them fails, Maven can help with the task of relaying data between the rovers on the Martian surface and radio antennas back on Earth. That relay function was considered so essential that the Maven team was exempted from the effects of last month's government shutdown.
If the spacecraft launches on time and all goes well, the science team might give it yet another task. Maven could use its Imaging Ultraviolet Spectrograph to observe Comet ISON as it approaches the sun, said the University of Colorado's Nick Schneider, who is the lead scientist for that instrument. "We should, if we have the time, get some really great observations," he said.
A key part of Maven's payload won't be used for observations at all, but will instead bring messages to Mars. The spacecraft carries a decorated DVD that contains the digital code for about 100,000 names, 377 student artworks and more than 1,100 haiku poems — all of which were submitted in response to the Maven team's public outreach campaign. One of the 17-syllable poems puts Maven's climate-centric mission into cosmic perspective:
Amidst sand and stars
We scan a lifeless planet
To escape its fate
More about Maven and Mars:
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.