Our home planet Earth is just one of the over 100 billion planets found in the entire Milky Way galaxy. Orbiting our Sun at literally the perfect distance to support life, it kinda makes you wonder: Of these billions of planets, just how many other habitable worlds are really out there?
Well, new research from NASA, the European Space Agency, and the SETI Institute estimates that there could be close to 300 MILLION potentially habitable planets in our galaxy alone! So, how did they settle on this number?
Well, first the researchers needed a set of great telescopes. Enter NASA’s Kepler space telescope and ESA’s Gaia space observatory. Two missions, launched separately, but with a shared goal of making a huge DISCOVERY! The aim of NASA’s Kepler mission was to literally stare into space searching for celestial bodies that varied in size, mass, and even orbit. By staring at one or even multiple patches of space, Kepler was able to identify a planet's characteristics through a process called the transit method, which when a planet breaks the line of sight between the observed star and the telescope. And to make this method as efficient as possible, scientists needed two major criteria met: an extremely dense field of view and a clear line of sight.
Basically, this meant that Kepler needed to continuously monitor the most star-rich patch of space possible without being blocked by the Sun or Earth. And what better place to look than the Cygnus and Lyra constellations, known for their vast array of northern stars.
Using the transit method, Kepler was able to collect data on over 530,000 stars during its nearly decade-long run before retiring.This is where the recent work comes in. Unlike previous studies, which mostly focused on findings from Kepler, teams from the SETI Institute, NASA, and ESA incorporated data gathered by Gaia. This mission, which has already observed and measured roughly 1 billion stars, is using a host of instruments to make a 3D map of the Milky Way.
Its goal is to observe the location and brightness of stars by measuring the distances, positions, motions, and changes in a star’s brightness. Using these data points along with Kepler's, scientists can now provide a more definite estimate of a planet’s temperature based on its distance from the host star. Which is absolutely critical when you consider what is necessary to host life on a planet. Too much heat and you get the scorching surface of Venus, while too little heat, and you get the freezing temperatures of Pluto. So, for the seemingly perfect distance from a star, scientists look to the Goldilocks Zone, otherwise known as the Habitable Zone.
This region contains exoplanets which could possibly have liquid water on their surface... and could in theory support life! So, let’s do the math! The team estimates that from the stars observed with similar characteristics to the Sun, anywhere from 30% to 90% have Earth-like planets in their habitable zone. And looking at the Milky Way specifically, NASA estimates that there could be 4 billion stars similar to our Sun. Estimating with an extremely conservative success rate of 7 percent, there could be close to 300 million habitable worlds in our solar system.
An estimation like this is exactly what scientists, like the ones that developed the Kepler mission, have been searching for. And while the team from this latest study has confirmed a few thousand exoplanets that fit the criteria for habitability, it would be extremely difficult to know if these planets actually do have life based on this data alone. The teams will still be gathering data from Gaia until at least 2022, and following Kepler is NASA’s TESS mission. But even now, I think it’s safe to say that we might not be so alone in this massive universe.