Since NASA’s skateboard-sized Sojourner rover bounced to a landing on Mars in 1997, we have been co-explorers via to a succession of rovers, culminating in the fiery touchdown of the Volkswagen-sized Curiosity last summer.

We’ve spent a lot of time and effort exploring the arid “red rock” country of Mars. But Mars is frozen in geological time. Its water is locked away as ice. The last rainfall was billions of years ago.

Curiosity’s biggest excitement recently was when it came across an ancient dried streambed. It’s reminiscent of the Neil Youg song, "A Horse With No Name:"

“I was looking at a river bed.
And the story it told, of a river that flowed,
Made me sad to think it was dead.”

But imagine visiting a dynamic world of lakes and rivers; imagine navigating an extraterrestrial sea sprinkled with methane rain under hazy orange skies, looming anvil-shaped clouds.

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