Today marks the fourth anniversary of NASA's rover Curiosity landing on the Red Planet and beginning its work to investigate Mars' history of habitability.
The last four years have been ones of great exploration, scientific and engineering achievements, and... well.... curiosity.
"Recently, NASA gave Curiosity the best anniversary gift it could hope for -- an extension of its mission for at least two more years," said Ashwin Vasavada, Curiosity project scientist for NASA, in a posted video. "We'll use it to reach progressively higher and younger rocks on Mount Sharp, including rock types we've not yet explored. We can't wait to see how the story of the ancient habitability of Mars continues to unfold."
Curiosity, NASA's nuclear-powered, SUV-sized super rover with the widest array of scientific instruments to yet work on another planet, landed on Mars during the evening (Pacific Time) of Aug. 5, 2012.
That landing, which had scientists around the world holding their collective breath, was the beginning of a great voyage for this robotic machine.
Curiosity has been tasked with finding evidence that Mars was ever -- in its history -- able to support life, even in microbial form.
Less than two months into the beginning of its mission, Curiosity found a piece of key evidence -- water .
The rover sent back evidence that there had been what scientists call "vigorous" ancient water flows on the surface of Mars.
That was just the beginning.
The next year, Curiosity found evidence that there is water in the Martian soil. That's encouraging both from a historical perspective and for the fact that it might one day help humans to live and work on Mars.
Astronauts would not be able to carry all the water they would need with them on the journey from Earth, so they would need to be able to source water right there on Mars. Finding water in the soil would help them do just that.
Just last year, Curiosity discovered that Mars holds another key element for life -- nitrogen.
Scientists said the nitrogen could have found its way to Mars by being carried on meteorites or lightning.
With the data being sent back from Curiosity, scientists now know that at least some Martian rocks contain sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon -- all key chemical ingredients for life, be it microbial or bacterial or another form.
Of course, the robotic rover has had its challenges as well.
Just this summer, for instance, Curiosity put itself into safe mode because it suffered a software glitch. NASA engineers, though, quickly resumed communications with Curiosity and got the rover back to work by sidestepping use of the glitchy software.
"Our rover operations team has hit its stride," Vasavada said in the video. "It used to take a month to drill and analyze a rock sample. Now it takes just a week."
He added that despite "expected wear and tear" on Curiosity's wheels, they continue to function and are expected, with careful driving, to enable the rover to cover all the ground it needs to during its mission.
Just last month, NASA announced that Curiosity now is using an artificial intelligence system that allows the machine to pick out targets -- without human intervention -- to photograph and hit with its laser.
Curiosity now is "frequently" choosing multiple targets every week on its own.
With Curiosity's long-term success already assured, NASA engineers now are working on building their next robotic Mars rover.
The next rover, scheduled to launch in the summer of 2020 and land on Mars in February 2021, has the goal of going the next step. While Curiosity is searching for proof that Mars could have supported life in its history, the next rover will search for evidence of that ancient life.