Posthuman Blues

Take a look at this massively eroded tomb. By the time-scales used to date possible artificial structures on Mars, this thing is downright recent, and already it's begun receding into the desert landscape.

In addition to its obvious state of disrepair, it doesn't particularly look like anything. Yet critics of planetary SETI lambaste sincere efforts to study candidate artifacts on Mars precisely because they look old and degraded -- which is, of course, wholly consistent with the hypothesis that Mars is home to archaeological sites.

We tend to expect ET artifacts to be immediately recognizable, and we do so at our own cognitive risk.