Posthuman Blues

SETI.com has posted a short essay intended to precede the Phoenix Mars landing. Here's an excerpt:

While I predict we'll find extant life on Mars sooner or later, I'm not as certain if that life will be truly Martian. It's just as likely to have come from Earth in the remote past, only to adapt to Mars' harsh, arid climate. A cause for celebration, to be sure--but not quite the triumph of discovering a legitimately alien form of life.

If and when we do stumble across alien organisms in our own celestial backyard, we might hope to learn that they evolved independently of Earth's own biosphere. Such a discovery would add evidential force to the argument that the galaxy is bound to harbor at least a handful of technological civilizations.