Updated 5:15 p.m. ET
A new NASA Mars probe began a 10-month voyage to the red planet Monday, blasting off on a $671 million mission to study the thin martian atmosphere in a bid to find out what triggered a dramatic case of climate change that turned a once-hospitable environment into a cold, presumably barren desert.
"Something clearly happened," said Principal Investigator Bruce Jakosky. "Water was abundant on early Mars, the environment was something that was capable of supporting liquid water yet today we see a cold, dry planet that is not able to support water. What we want to do is to understand what are the reasons for that change in the climate."Taking off just ahead of approaching clouds, NASA's Mars Atmosphere and Volatile Evolution -- MAVEN -- spacecraft, mounted inside a protective nose cone atop a United Launch Alliance Atlas 5 rocket, blasted off on time from the Cape Canaveral Air Force Station at 1:28 p.m. EST (GMT-5).
Generating 860,000 pounds of thrust, the first stage majestically boosted the rocket out of the dense lower atmosphere and fell away just over four minutes after liftoff. The rocket's hydrogen-fueled Centaur second stage then ignited for the first of two planned "burns," firing for nine-and-a-half minutes to complete the initial phase of ascent.After a 27-and-a-half-minute coast, the Centaur re-ignited an additional five-and-a-half-minute burn, boosting the spacecraft to a velocity of more than 27,000 mph, fast enough to escape Earth's gravity and begin the long trip to Mars.
A few minutes after that, MAVEN was released from the Centaur stage to fly on its own, followed by deployment of the orbiter's two solar arrays. Flight controllers plan to activate and check out MAVEN's instruments over the next few weeks.
"What a Monday
at the office," project manager David Mitchell told reporters during a
post-launch briefing. "You build something to fly to Mars, and we're now
flying to Mars! Maybe I'm not showing it, but I'm euphoric! It's been
great, guys. What an effort by this team to get to this point."
Jakosky said that after 10 years of planning and development, "I don't
have the words to describe what I'm feeling. It's every possible
emotion, but they're all positive. This is about the most exciting thing
I can imagine happening. This day has been picture perfect from
beginning to end."
Flight controllers plan to carry out the first of four trajectory correction maneuvers Dec. 3. After that, they will begin activating and checking out MAVEN's scientific instruments.
If all goes well, the 2.5-ton spacecraft will reach Mars on Sept. 22, 2014, braking into an elliptical orbit with an eventual high point of around 3,860 miles and a low point of just 93 miles. That will allow the spacecraft to repeatedly fly through the upper reaches of the martian atmosphere to directly sample its constituents and map out its structure.
In addition, MAVEN will carry out five "deep dip" sessions lasting about five days each, dropping to a low point of around 78 miles to study the atmosphere in "well mixed" regions where it is 30 times denser than the much thinner "air" the spacecraft normally samples.
The mission is expected to last a full year. But if the spacecraft stays healthy, managers say it could remain in operation for up to a decade, carrying out extended observations while serving as a backup communications relay satellite for rovers on the surface of the planet.
The goal is to characterize the atmosphere as it exists today, along with the processes that affect it, gathering the data needed to help researchers understand how the martian atmosphere has changed over time.
Scientists believe Mars once enjoyed a warmer, thicker atmosphere that allowed liquid water to flow and pool on the surface, resulting in a global environment that was hospitable to life as it is known on Earth.
"With Mars having had liquid water early on, we think there must have been a thicker atmosphere that would have produced greenhouse warming so that the planet was warmer early on," said Jakosky, MAVEN principal investigator at the University of Colorado's Laboratory for Atmospheric and Space Physics. "And something happened. What we want to do is understand where did the water go, where did the carbon dioxide from an early thick atmosphere go?"
A major factor is Mars' magnetic field and current lack thereof. Around 3 billion years ago, scientists believe, Mars apparently lost its global magnetic field and along with it, an effective shield against the effects of the solar wind and high energy radiation.
A major question is whether the sun's influence, in the absence of an active magnetic field, could have stripped away a significant portion of the atmosphere, slowly but surely changing the climate via lower temperatures and pressures to the point where liquid water could no longer exist on the surface.
Another possibility is that significant amounts of CO2 and water ended up trapped in the martian crust. "But we don't see the evidence for widespread, abundant carbon-bearing minerals in the abundance necessary to be a reservoir for that thick early atmosphere," Jakosky said.
"The other place these could have gone is up to the top of the atmosphere where they could be stripped away and lost to space. The removal process would have involved forcing by the sun, from solar wind, from solar extreme ultraviolet photons, from solar storms that might strip away gas from the top of the atmosphere.
"MAVEN is all about trying to understand these loss processes, understand what could have happened at the top of the atmosphere and how gas could have been removed from it."
MAVEN measures 37.5 feet across its two solar panels, which generate between 1,150 and 1,700 watts of power. The spacecraft is equipped with eight scientific instruments and a UHF communications package that can relay data back to Earth from rovers on the martian surface.
The instruments will measure a wide variety of factors to determine how fast the current atmosphere is leaking away into space to help scientists figure out what the rates might have been in the past when the sun was more active.
"The most intense loss is thought to have occurred early in the history (of the solar system) when the sun and the solar wind were more intense," Jakosky said. "The loss rates today are low enough that we're probably not going to see the loss of the entire atmosphere.
"The reason we're studying it today, even though the loss rates are so much lower, is that we can understand the specific processes that are going on and learn how to extrapolate them backwards in time."
Six of MAVEN's instruments will characterize particles and fields, measure the interaction of the atmosphere with electrically charged particles from the sun and the effects of high-energy solar radiation. Other instrument packages will carry out remote sensing and chemical analysis of particles in the martian atmosphere.
Nick Schneider, leader of MAVEN's imaging ultraviolet spectrograph team, said "the reason we're studying the composition and structure of the atmosphere is that it reveals to us how much energy the atmosphere is receiving from the sun and the times when there's excess energy input in the form of those harsh ultraviolet photons or particles from the solar wind."
High levels of solar radiation can cause the atmosphere to warm and expand slightly, triggering chemical reactions that can break molecules apart and strip away electrons.
"We can measure all of that," Schneider said. "The excess energy in all these forms also causes extra atmospheric escape. As we're making these measurements, studying the properties of the atmosphere, we're very sensitive to how the input conditions are leading to atmospheric escape."
Of particular interest is what happens to the atmosphere during periods of high solar activity, "because those are the times most representative of the early sun," Schneider said.
"So when we're measuring the escape rates during periods of high solar activity, that's our best guess about how much atmospheric escape was occurring billions of years ago. If we add up that level of atmospheric escape over time, we'll have a good sense of just how much atmosphere Mars lost through escape to space."
While the history of climate change on Mars is the primary focus of the MAVEN mission, Jakosky said the the results could help scientists get a better understanding of planetary evolution in general.
"If we think more broadly, we're understanding processes by which a planetary environment can change through time," Jakosky said. "We don't know the whole range of processes yet, but as we're starting to discover more and more planets outside our solar system and see Earth-like planets and ask about whether there could be life on those, we want to understand what makes a planet habitable, and what makes a planet go from being habitable to not being habitable.
"So I see this as a much broader mission than just exploring the Mars upper atmosphere today and the history of the climate. But that's where we start."