Can Earth-like Exoplanets Actually Support Life?

As of July 4^th, the NASA Exoplanet Archive (https://exoplanetarchive.ipac.caltech.edu/) lists 4,183 confirmed exoplanets, planets orbiting other stars, with another 2089 candidate planets awaiting confirmation. NASA and other institutions have only studied a tiny percent of all the stars in our Milky Way. Based on the sample so far, astronomers estimate that planets outnumber stars in our galaxy. That means the Milky Way contains several hundred billion planets.

These exoplanets come in a bewildering variety. Some are Jupiter-sized planets so close to their parent star that the heat from the star evaporates them. Some Earth-sized planets get so hot, they rain liquid metal from their clouds. Most confirmed planets are significantly larger than Earth, but that’s because larger planets are easier to discover than smaller planets. Astronomer estimate that Earth-sized planets number in the billions.

   Most Earth-like Exoplanets, credit NASA

Being the size of Earth doesn’t mean such a planet has life on it. Many factors play into planet habitability. Distance to its parent star determines surface temperature. Too hot or too cold and habitability becomes unlikely. The type of parent star plays a crucial role. Stars smaller than our sun often produce large, dangerous stellar flares.

If Earth is a good example of what conditions necessary for a planet to support life, water is an absolute must. On our planet, where there’s water, life exists, even at the bottom of the ocean, with near-freezing temperatures, in boiling hot springs, or three miles underground in cracks in the rock.

Scientist Lynnae Quick along with several other NASA scientists looked at the likelihood of finding other life-bearing planets. This initial study contained a small sample of only 53 Earth-sized planets. They specifically looked to see if the planets could support surface or subsurface oceans, as is the case with several moons in our own solar system. Of those, they calculated that 30 likely possess such bodies of water, more than half of the planets they analyzed. With a few billion Earth-sized planets in our galaxy alone, that means there might be a lot of life-bearing planets out there. "Forthcoming missions will give us a chance to see whether ocean moons in our solar system could support life,” said Quick.

The study didn’t address the presence of intelligent aliens. There isn’t enough data to decide that. But at least we have some idea of the possibilities now.

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.

 This is reprinted by permission from the Oklahoman and www.newsok.com.