The much-celebrated Mars rover Curiosity is headed for Mount Sharp, where it will help scientists explore the question of life on Mars as it climbs up and up.
Meanwhile, however, NASA's budget for planetary exploration is slated to go down, down, down.
Scientists are basking in the success of Curiosity's stunning landing earlier this week, proving that a complicated system involving a parachute and a sky crane can safely deliver a 2,000-pound vehicle to Mars. The $2.6 billion Curiosity will spend years roaming the planet, snapping photos and gathering scientific data.
Given the budget constraints facing the space agency, however, there are limits on what the rover, and NASA, will be able to do on the surface of the Red Planet. Although astronauts brought back thousands of moon rocks during the Apollo Mission, there's never been a sample of Martian material returned to Earth. Such a mission is considered a priority, so scientists can do more detailed chemical analyses.
But it may not happen anytime soon.
"We're optimistic, given the success of our program, but we're anxious, too," said Richard Zurek, chief scientist for the Mars Program Office at NASA's Jet Propulsion Laboratory in Pasadena, California. "Like all of us, we're anxious about our country's ability to be able to support and do these kinds of things."
NASA's budget for Mars exploration is slated to take a huge hit in 2013, dropping from $587 million to $361 million. It will then further decline to $228 million in 2014 and $189 million in 2015, rising slightly in 2016 before sloping upward to $503 million in 2017.
Researchers landed Curiosity on Gale Crater, which is 96 miles across and may have once hosted a lake. Mount Sharp, in the middle of the crater, is composed of hundreds of rock layers accumulated over time. The rover will climb a small portion of the 3-mile-high mountain, testing different layers to search for organic molecules that could indicate the presence of life on the barren planet.
"We've demonstrated that we've got a landing system that worked. And it worked well," Zurek said, referring to Curiosity's dramatic touchdown. "The question now is: What will we use this for? Or will we have to step back from that because those kinds of missions -- of putting something that takes a metric ton down to the surface -- they're just too expensive for our future?"
The early days
Curiosity is the latest in a long trajectory of missions that have allowed humanity to study Mars more extensively than any other planet apart from our own. A series of visits from Earth-made spacecrafts has taught us that Mars used to be a warmer, wetter place, perhaps with liquid water and even life.
Decades of research have led scientists to understand Martian history and pinpoint places on the planet where liquid water may have once flowed -- targets for future investigation, if money allows.
But getting to Mars didn't happen on the first try.
The USSR initiated a number of failed attempts to go to Mars in the early 1960s, including Sputnik 24, a lander that never left Earth's orbit. The United States also started out with bad luck: a failed flyby attempt by Mariner 3 in 1964.
Earthlings' first successful landing on Mars happened in May 1971 with the Soviet Union's Mars 3 lander. It failed after sending 20 seconds of video data to the orbiter, however.
NASA claimed a big success the same year: Mariner 9 marked the first time a U.S. spacecraft had orbited a planet other than our own. This orbiter discovered river and channel-like features on Mars, and took the first high-resolution images of Mars' moons Phobos and Deimos.
Hopes were high for NASA's Viking mission, launched in 1975, which included two landers equipped to search for tiny organisms. The orbiters mapped the surface of the planet, while the landers monitored the weather and sent back color panoramic views of Mars.
"It was extraordinary engineering achievement. A huge amount of science came out," said Scott Hubbard, former head of NASA's Mars program and author of the book "Exploring Mars: Chronicles from a Decade of Discovery."
But the expectation of evidence of life -- namely, that the lander's arm would be able to put material into its chemistry kit and see organic molecules -- fell through. These molecules wouldn't prove that life existed, but they would be a signal that life was once possible there. There just wasn't conclusive evidence that Mars had these molecules.
Then came almost two decades of inactivity. NASA didn't send any other spacecraft to Mars until 1993 with the failed Mars Observer, followed by the successful orbiter Mars Global Surveyor in 1996.
Why the break? The space-shuttle program was one reason, said Zurek. NASA's priority at the time was manned vehicles, and budgets were tight. The Challenger disaster of 1986 also set NASA back.
Zurek believes we may be in a phase like that today, with not enough money to go around for all the programs NASA wants to develop. Also, the priority is once again in a new project: The Space Launch System, which will be the largest and most powerful rocket ever built.
Exploring Mars' surface
A game-changer was the discovery of a meteorite that appears to have come from Mars, found in Allan Hills, Antarctica, in 1984. Some scientists said they thought they saw evidence of tiny fossils that looked like dried-out life from Mars embedded in the meteorite.
No one knew where the meteorite came from, but it ignited a huge amount of interest in returning to Mars, Hubbard said. It also stressed the need to return samples from Mars to Earth, so they could be fully analyzed by multiple scientists.