But some images get more attention than others, stopping people midstride, midsentence, and eliciting an awed silence. It's the photographs of the spacecraft itself that draw such reactions, plunging even the most hardened scientist into a misty-eyed moment of reflection.
It's ironic, really: Curiosity is the thing we know best on Mars. Thousands of scientists and engineers have spent years, even decades of their lives characterizing every switch, valve, and pump. The 2000-pound rover might be one of the most intentionally constructed, thoroughly tested pieces of machinery in history.And yet, each new image of the spacecraft provokes spine-tingling reactions. First it was the mid-descent photograph of Curiosity with its unfurled parachute; then came the underbelly and mast self-portraits. Members of the science team and general public alike have expressed interest in driving over to the wrecked sky crane, their enthusiasm incommensurate with the scientific value of such an investigation.
Why are we so drawn to these pictures? Why are our favorite images those of the rover acting like a teenager on spring break, mugging for its own cameras?
On an otherwise barren and alien planet, the rover serves as a reference point, a scale bar in both spatial and philosophical terms. Just as it is difficult to understand rock dimensions or hill heights without a more familiar reference frame - a tree, or a car, for example - it's similarly challenging to comprehend our exploratory status without evidence of human presence. Telescopes can return beautiful, data-rich images from the far reaches of the universe, but the immediacy of manmade hardware on Mars makes our exploration more tangible. We can imagine running our hands over the rough tire treads and the smooth metal mast: these are textures, scales, and materials we're familiar with, and they just happen to be on top of the red-tinged dirt of another planet.
With the rover as our proxy - scientifically and emotionally - we imbue Curiosity with anthropic identity through anatomical shorthand (the rover's "arm" and "wrist") and tweets ("Yes, I've got a laser beam attached to my head. I'm not ill tempered; I zapped a rock for science").
We also use first person pronouns, a grammatical Freudian slip. Immediately after landing, incredulous scientists and engineers exclaimed, "We're on Mars!" while exchanging high fives beneath a Pasadena sunrise. Daily reactions note that "we're driving," or "we're powered on" as mission enthusiasts and the Curiosity rover merge identities.
Mars Science Lab may be a robotic mission, but it's also very much a human mission. Curiosity holds our collective aspirations as an interplanetary species on its chassis, and its self-portraits evoke memories of NASA astronauts on the Moon. Gazing across the dusty plains of new worlds is always a remarkable privilege of our Space Age civilization, but there's something indescribably different when a terrestrial emissary is looking back at you.