One year after a nail-biting descent to the surface of Mars, NASA's $2.5 billion Curiosity rover, fresh from confirming the red planet was habitable in the distant past, is making its way to the base of a towering mound of rocky terrain where it will climb through the geologic history of a once-wet world.
"One year ago today, believe it or not, began one of the most daring adventures yet in planetary exploration, certainly the most daring of our exploration steps for Mars," Dan McCleese, chief scientist at the Jet Propulsion Laboratory, told scientists, engineers and managers marking the anniversary.
"The thrill of the Curiosity rover and its science payload hurtling toward the planet to a soft touchdown on six wheels remains with us today, and we're reminded just what an incredible science and engineering feat this is."
Curiosity's thrilling entry, descent and landing using a rocket-powered "sky crane" that lowered the car-size rover to the surface on a long bridle captured the public's imagination, both for the sheer drama of the untried technique and its flawless execution.
The successful landing set the tone for the high-stakes mission and Curiosity quickly demonstrated its ability to act as a robotic geologist, chalking up a near-flawless performance on the way to becoming one of NASA's most productive planetary explorers.
"I'm impressed by the work that's been done since those initial moments on the surface where everything worked perfectly, I'm impressed by the work that's been done in the first year of exploration," McCleese said. "The rover's performance has been in excess of what the most optimistic of us imagined it might be."
Since landing on the floor of Gale Crater on Aug. 6, 2012, Curiosity has beamed back more than 190 gigabits of data, more than 70,000 photographs and fired more than 75,000 laser shots at targeted rocks and soil, searching for evidence of past habitability.
During its voyage to Mars and its first year on the surface, Curiosity also measured the radiation environment in unprecedented detail -- data needed for any eventual manned missions -- and served as a weather station, charting shifting winds and temperature swings.
Using a high-tech impact drill and a suite of compact but sophisticated laboratory instruments to study collected samples, the rover met its primary mission objective eight months into its mission, confirming a once-habitable past in a region where ancient stream beds show water once flowed freely.
Curiosity's discoveries came during what amounts to a side trip on the way from the landing site to Mount Sharp, a mound of sedimentary rocks rising more than 3 miles above the floor of Gale Crater. The rover landed about four-and-a-half miles from an area at the base of the mound where orbital photos indicate a safe path through surrounding sand dunes.
Reaching Mount Sharp and sampling its layered terrain will give scientists a long-awaited opportunity for close-range observations across a significant slice of its history.
Climbing through layers of older rocks and clays that were deposited when the planet was warmer and wetter and possibly through a transition zone to younger strata deposited in a dramatically drier environment, scientists hope to learn more about how Mars evolved what impact environmental changes had on habitability.
"We went there thinking that every layer is a page in a history book and we can go there and see not only are there habitable environments recorded in there, but how did the environments change over time?" said principal investigator Ken Edgett. "As you go up the mountain you will see the time getting closer and closer to now, it will get younger and younger."
But instead of heading directly to Mount Sharp, mission managers opted to divert the rover to a nearby area where three different types of terrain came together, looking for interesting science and an opportunity to thoroughly test Curiosity's instruments.
The trip paid off with dramatic results, culminating in the discovery of an ancient stream bed and chemical analysis of rock samples that confirmed conditions favorable to life as it's known on Earth in the red planet's distant past.
"We drove, literally, through a stream bed on Mars that flowed ankle deep two billion years ago," said Ashwin Vasavada, deputy project scientist. "I'm getting goosebumps just telling you about it!"
John Grotzinger, the Mars Science Laboratory project scientist, said the data collected at a site dubbed Yellowknife Bay "all added up to understanding this environment as being chemically one that was favorable for life, not in a harsh way but actually quite a benign environment that's very much like Earth."
Reflecting on Curiosity's first year on Mars, Grotzinger said "I think the most extraordinary thing, really, is we found (confirmation of habitability) so quickly. That decision to drive 500 meters in the opposite direction obviously paid off very well."
The rover now is finally making its way to Mount Sharp, covering about 764 yards in the past month. Depending on the terrain, Curiosity can travel up to about a football field per day -- "pedal to the metal," Grotzinger jokes -- on a trek expected to take another several months to complete.
"We selected Gale out of the four finalists for one simple reason, because it's so diverse," he said. "So by driving now to Mount Sharp, we will return to our initial objective, which is to explore these foothills.... We know from orbit that they have clays, we know there's hematite, we know there are sulfates. So we hope to be able to sample a number of what could be different habitable environments."
Unlike earlier rovers that relied on solar panels for power, Curiosity is equipped with a radioisotope thermoelectric generator, or RTG, that converts the heat of decaying plutonium dioxide into electricity.
The mission design life is two Earth years -- one year on Mars -- but barring major problems, the rover should be able to operate for years beyond the official target.
"What we have today is an astonishingly powerful tool for science," McCleese said. "We've been observing, we've been measuring, we've been sampling and in the background, throughout laboratories across the globe, there've been scientists working to help interpret the measurements that have been made.
"The questions we ask address some of the most important questions in science and for Mars, one of the great mysteries. And that is, was this planet ever habitable? Our celebration of the success of Curiosity's first year includes the anticipation of even more exciting years of discoveries to come."