[Sherman Logan]

Discouraging results from the search for life on Mars cause us to put our faith in life on exoplanets -- lest Earth be seen as unusual (the Copernican Principle).

Generally good article. But this part doesn't make much sense.

I don't know anyone who expected to find evidence of life on Mars and has therefore been forced to drop back to expecting life to be present on exoplanets.

It's been pretty thoroughly known for upwards of 50 years that we are unlikely to find evidence of life in this solar system away from Earth.

Recent evidence is that planets and solar systems are common if not ubiquitous. It is likely that the basic conditions for life are also fairly common, which of course does not necessarily mean that life itself is.

[circlecity]

"It is likely that the basic conditions for life are also fairly common,"

This is not necessarily true. There have been physicists who claiml they have been able to identify at least 25 finely tuned variables (ie, temperature, gravitational force, radiation level, etc. etc.) which must all be present for life as we know it to exist. The probabiliity against all or even half of these finely tuned variables to be present on any given planet is off the charts. Something like 10 to the negative 250th power or, in other words, impossible.

[MHGinTN]

So the ruins on Mars got there how?