When Galileo discovered moons in orbit around Jupiter it was rather a big deal. In 1610 the Earth was assumed by all except a few radical Copernicans to be the unique center of the universe, expressly created by God as a stage for the human drama of sin and salvation. In 1600 Giordano Bruno was burned at the stake for, among other things, teaching that the other stars were other Suns and that the universe contained a multiplicity of inhabited worlds. Galileo was lucky to have escaped the same fate.
When a few weeks ago we saw the first photographs of extrasolar planets, it created hardly a stir. For one thing, the existence of over 300 massive planets had already been indirectly deduced by their gravitational influence on their host star or by their periodic eclipsing of their host star's light. Further, we have long known that the stars are other Suns -- in virtually uncountable numbers -- and that the physics of star formation spins off planets as a matter of course. Now we have actual images of three large planets orbiting the Sunlike star HR 8799, and another large planet orbiting the somewhat bigger star Fomalhaut. We have every reason to believe that there are a trillion billion planet systems -- at least! -- in the universe.
To expect that our star system is the only one with life, or even intelligent life, would seem to be something of a stretch. If astronomers detected an intelligent extrasolar signal tomorrow, it would be a news sensation, but hardly a surprise.
Still, I think it is fair to say that psychologically most of us still live in the anthropocentric cosmos of Dante.
It is interesting to watch forward-thinking theologians grapple with the implications of multiple inhabited worlds. The problem, within a Christian perspective, has to do with the supposed uniqueness of Adam's fall into sin and the redemption of Christ. If there are other sentient beings in the universe, did they share in Adam's sin, and did they require separate acts of atonement on the part of the Redeemer? It may seem strange to many of us, but these obtuse questions have exercised theologians from Origen in the 3rd century to Karl Rahner in the 20th. A quick trip to the web turns up contemporary speculation, here and here, for example, and I remember reading a learned article on the subject by the eminent Catholic theologian Thomas O'Meara a decade or so ago.
It all seems rather a tempest in a teapot -- doing handstands and body twists to make first millennium theology mesh with third millennium science. This is the sort of intellectual acrobatics that results from committing oneself to dogmatic truth systems.
Meanwhile, we see the newly imaged planet of Fomalhaut moving along its orbit, three times more massive that Jupiter and 23 times further from its star than Jupiter is from the Sun. It is almost certainly a Jupiterlike gassy planet and unlikely to be a home for Earthlike life. But why should we expect Earthlike life? And closer to Fomalhaut there are very likely smaller, more Earthlike planets. The whole point of science is to apply our curiosity to the world and accept whatever we find. What we have found is infinitely more breathtaking than the tiny Danteesque cosmos that set the imaginative limits for the early codifiers of traditional theology.
(Photo credit: NASA, ESA, P. Kalas, J. Graham, E. Chiang, E. Kite (Univ. California, Berkeley), M. Clampin (NASA/Goddard), M. Fitzgerald (Lawrence Livermore NL), K. Stapelfeldt, J. Krist (NASA/JPL))