The existence of a race of sentient alien robots might be not just possible, but inevitable. In fact, we might be living in a "postbiological universe" right now, in which intelligent extraterrestrials somewhere have exchanged organic brains for artificial ones.

The driving factor is a pragmatic desire to improve mental capacity. Alien beings may have already reached a point in their evolution where, having exhausted the potential of their biological brains, they have taken the next logical step and opted for robotic brains equipped with artificial intelligence.

Although it's only one part of the answer, we have come another step closer to solving the question of how life originated. Two necessary molecular ingredients of DNA and RNA have been confirmed to have originated from outer space. They join the handful of amino acids we have discovered to have been delivered to Earth on the backs of asteroids and comets.

When we catch up with the robot, it is poking along in a herky-jerky and rather flummoxed fashion through the Atacama Desert, which covers much of far northern Chile. The Atacama is reputedly the driest place on Earth, with rainfall measured in millimeters per decade. It is a rough place for man or robot, a tawny maze of high plateaus and shaley foothills under constant sun and an enormous cobalt-blue sky.