Corey S. Powell writes:

One of the greatest debates in the long history of astronomy has been that of exceptionalism versus mediocrity—and one of the great satisfactions of modern times has been watching the arguments for mediocrity emerge triumphant. Far more than just a high-minded clash of abstract ideas, this debate has shaped the way we humans evaluate our place in the universe. It has defined, in important ways, how we measure the very value of our existence.

In the scientific context, exceptional means something very different than it does in the everyday language of, say, football commentary or restaurant reviews. To be exceptional is to be unique and solitary. To be mediocre is to be one of many, to be a part of a community. If Earth is exceptional, then we might be profoundly alone. There might not be any other intelligent beings like ourselves in the universe. Perhaps no other habitable planets like ours. Perhaps no other planets at all, beyond the neighboring worlds of our own solar system.

If Earth is mediocre, the logic runs the other way. We might live in a galaxy teeming with planets, many of them potentially habitable, some of them actually harboring life. In the mediocre case, we bipedal little humans might not be the only sentient creatures peering out into the depths of space, wondering if anyone else is peering back.

Today, the broadest version of exceptionalism has been thoroughly disproven, as astronomers have discovered 4,150 confirmed exoplanets, a tally that increases almost daily. The roster of alien worlds includes a remarkable variety of forms, many of which have no equivalent in our solar system. And that is just a limited sampling from the stars in our local corner of the galaxy.

We do not yet have the technology needed to find a close analog of Earth orbiting a close analog of the sun, so we still know little about how common or rare such worlds may be. The question of alien life is still wide open. What we do know is that the Milky Way is home to a tremendous number of other planets. In that sense, at least, we are certainly not exceptional, and Earth is certainly not alone. [Continue reading…]