Which alone spreadeth out the heavens,
Job 9:8
Schweitzer is excited about the discovery of what he calls "Earth 2.0," an extrasolar planet otherwise known as Kepler 452-B. If you believe what the Huffington Post tells you, it's probably a rocky earthlike planet thought to orbit its star within the region where liquid water is possible. He calls it "possibly habitable." In reality, many parameters beyond the mere existence of water are necessary for a planet to be habitable, so it has not been established that Kepler 452-B is habitable, or even "possibly habitable," like Earth. Schweitzer wants people to believe that this suggests habitable earthlike planets are extremely common in the universe. A quick check of the technical scientific literature shows he is mistaken.
According to an April 2015 paper in Proceedings of the National Academy of Sciences, "Jupiter's decisive role in the inner Solar System's early evolution," a review of the sizes and orbital radii of known extrasolar planets shows how exceptional our solar system is:
The statistics of extrasolar planetary systems indicate that the default mode of planet formation generates planets with orbital periods shorter than 100 days and masses substantially exceeding that of the Earth. When viewed in this context, the Solar System is unusual. ... The Solar System is an unusual member of the galactic planetary census in that it lacks planets that reside in close proximity to the Sun. [emphasis added]The problem for Schweitzer, essentially, is that the vast majority of extrasolar planets we've discovered orbit their stars much closer than even our earth orbits the sun -- and, these extrasolar planets are much larger than earth. Both of these properties make these planets uninhabitable. Moreover, large planets like Jupiter -- which in our solar system help keep earth habitable by sweeping up comets and asteroids -- almost never exist far out in the solar system, as Jupiter does.
Phys.org describes these findings as follows:
There's something about our solar system that appears to be unusual. For some reason, most of our bigger planets are far away from our host star, while closer in are smaller, rocky worlds, including Earth itself.What this means is that our solar system stands out dramatically compared to other solar systems we've discovered and that getting rocky planets orbiting near their star as Earth does, in the circumstellar habitable zone, requires a very exceptional set of circumstances." EN&V
This is not the case for many extrasolar systems that have been discovered. So-called "hot Jupiters" -- huge gas giant planets that nestle close to their star -- have been found in a few examples. In other instances, planets slightly bigger than Earth are so close to their stars as to be uninhabitable.
