When the launch of the James Webb Space Telescope comes a few years from now, we will have then opportunity to probe deeper into the cosmos than ever before, to see things we had only dreamed of seeing previously. Among the prime targets for this modern marvel of human ingenuity are potentially habitable exoplanets, where future humans could live, provided there isn’t already life occupying the real estate. To help astronomers assign importance to the growing number of exoplanets, researchers at the University of Washington’s Virtual Planetary Laboratory have devised an index to represent the habitability of worlds, near and far. The most surprising fact is that Earth doesn’t top the list.
The top two prospects are the unconfirmed exoplanet known as KOI 3456.02, and Kepler 442-b, with indices of 0.955 and 0.836 respectively, while Earth comes in third with an index of 0.829. Beyond our solar system there are 1,000 confirmed exoplanets, with 5,000 candidates waiting to be confirmed. More than 100 have been flagged as potentially habitable, and statistically speaking, this would mean there are Millions of potentially habitable exoplanets within the Milky Way.
“Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said University of Washington astronomer Rory Barnes. “So that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”
In general, the habitability of a planet is considered favorable if it lies within the goldilocks zone, the range of distances from a star where the temperature would be suitable for liquid water, a necessary requirement for life. It’s also a good sign if the planet is similar in size and mass to the Earth, though the researchers’ model takes other factors into account, such as eccentricity of orbit and ‘rockiness’ of the planet.
Methods of prioritization will become much more important in the future as we will be increasing the number of discovered exoplanets into the tens and eventually hundreds of thousands. We will need to know which ones to spend the money on and which ones to move to the back burner. Ultimately it’s all about giving humanity the best chance at finding the answers to the greatest questions concerning life and seeding the cosmos with humanity.