Since its dramatic touchdown on Mars in 2012,
Before Curiosity departed for the Red Planet, scientists held spirited debates over the best landing site for the geology lab on wheels. Researchers focused on four possibilities that would allow the rover to search for signs of past environments that could have been hospitable to life.
Each of the candidates offered tantalizing hints of ancient water: Eberswalde Crater seemed to hold the remains of a river delta; Holden Crater's contents could have resembled a series of alpine lakes; and the Mawrth Vallis channel may have been carved by floods.
But it was Gale Crater that finally prevailed, thanks to the mountain in its middle. To a geologist, Mount Sharp's layers of rock can be read like the pages in a book, each describing a different chapter in Martian history. Some of the layers near the mountain's base were rich in clay, a sign that they may have formed when water was present on Mars.
Evidently, the planetary scientists chose well. Curiosity has explored only about 7 miles in the 96-mile-wide crater -- and yet the discoveries made in this tiny stretch of real estate have helped scientists rethink what Mars looked like more than 3.5 billion years ago. Evidence from Gale Crater suggests the planet was once warmer, wetter and friendly to microbial life.
In short, ancient Mars was a lot like Earth.
Curiosity's primary mission was to journey to the center of the crater in search of past watery environments where microbial life could have survived.
But shortly after landing, the rover's handlers at NASA's Jet Propulsion Laboratory in La Canada Flintridge took a gamble and steered the craft toward a spot called Yellowknife Bay. There, the rover drilled into rock and found an ancient environment that was once wet and brimming with the basic chemical ingredients for living things.
This probably wasn't an isolated Martian oasis. A recent study in the journal Science reported that Gale Crater used to be filled with a series of lakes that rose and fell over millions of years. This means the atmosphere must have been thick enough to allow liquid water to remain on the surface without quickly evaporating -- and that environment could have persisted long enough for life to emerge. NASA has envisioned just such a Mars, one
Gale Crater is revealing its secrets in surprising ways. A recent study in Nature Communications explained how pebbles lying near the rover's landing site must have been carried for about 30 miles by a sustained river.
Now that Curiosity has found clear signs of once-habitable environments, planetary scientists have moved on to more ambitious goals. NASA's Mars 2020 rover will search for direct evidence of past life.
But Curiosity's not yet done exploring Gale Crater -- and neither are you. To see what it's like to roam the crater today, take this virtual tour. It might put Curiosity's 7-mile journey in perspective.
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