Over the past ten years, the various robotic rovers crawling across the surface of Mars have confirmed one fact beyond any doubt: A long time ago, Mars was a warm, wet planet with a thick atmosphere that could easily have supported life. Yet today it is a frozen, barren, dry world with an atmosphere so thin that the any human explorers will need to wear pressurised space suits. So where did all the air go? NASA’s new MAVEN mission was launched in November last year to answer that question.“MAVEN joins our orbiters and rovers already at Mars to explore yet another facet of the Red Planet and prepare for human missions there by the 2030s,” NASA Administrator Charles Bolden said. “This mission is part of an integrated and strategic exploration program that is uncovering the mysteries of the solar system and enabling us to reach farther destinations.”
The presence of water on Mars is not a new discovery. Astronomers have known for a very long time that water ice can be found in Mars’s ice caps, along with large quantities of frozen carbon dioxide. But it was only once we were able to place powerful cameras in orbit around Mars, and send robotic laboratories to drive around the martian surface that we found evidence of liquid water. Images of what appeared to be dew on rover surfaces and the presence of fresh-looking gullies suggested that even in its frozen rarified state, the martian atmosphere is still able to condense out some moisture.
Orbiting spacecraft mapping the surface of mars had found winding gullies and canyons that looked suspiciously like ancient river beds. And when the Mars Science Laboratory (MSL), popularly known as Curiosity, confirmed that the minerals in a depression beneath the mountain Aeolis Mons could only have been formed underwater, planetary scientists knew that Mars must once have had an atmosphere as thick and warm as Earth’s. After all, lakes and rivers can only appear when you’ve got very large amounts of liquid water lying free on the surface of a world, and water can only be liquid within a specific range of temperature and pressure.
Of course, those conditions no longer exist on Mars, which is why liquid water is now so elusive. We know where the water went: It froze into ice, and is lying at the poles, and beneath the ground. But the question remains: What happened to the atmosphere? Scientists believe that it was stripped away by the solar wind – a constant stream of high energy particles blowing out from the Sun in all directions which gradually eroded away Mars’s atmosphere, one molecule at a time, over billions of years. This doesn’t happen to Earth because we have a powerful magnetic field which shields our atmosphere, deflecting the solar wind away. But Mars is only half the size of Earth, with no liquid core, so its magnetic field is very weak and offers no protection.
This theory makes a lot of sense to planetary scientists and it fits what we already know with Mars. But science requires that theory must be tested, and MAVEN will be collecting data to do exactly that. MAVEN carries instruments to examine Mars’s upper atmosphere, ionosphere and magnetic field, but will also be measuring the amount of solar energy received, and the rate at which ionised atmospheric molecules are escaping into space. Each of these parameters will be combined into current models and compared with the theory’s predictions. Depending on how well it matches up, the theory could be proven correct, but most likely it will diverge somewhat, and the mission scientists will need to modify it to better match reality as measured by MAVEN.
Since launch, the entire instrument package has been powered up and tested, to ensure that they survived the rigours of launch without suffering any damage. MAVEN will arrive at Mars on 21 September, where it will spend five weeks waking up and initialising all its components. The science mission is scheduled to last one year, but if previous missions are anything to go by, MAVEN should continue providing useful data for much longer than that.
“The performance of the spacecraft and instruments to date bears out all the hard work the team put into testing the system while it was on the ground,” said David Mitchell, MAVEN project manager at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The way that the operations team has performed while flying the system has been nothing short of outstanding. We have big events ahead of us before we can claim success but I am very pleased with how things have gone thus far.”