Astronomers at the University of British Columbia (UBC) examined data from NASA’s Kepler project and came to a startling conclusion. From 2009 to 2018, the Kepler planet-hunting satellite collected data on 200,000 stars.
The scientists’ criterion for picking such a planet included that it had to be rocky, around the same size as Earth, and orbiting a star like our Sun. This planet had to be in the habitable zone of its star, where the conditions would be ideal for the presence of water and life.
Michelle Kunimoto, a UBC researcher who previously identified 17 new planets (“exoplanets”) outside our Solar System, stated that their calculations “set an upper limit of 0.18 Earth-like planets per G-type star.” In other words, there are approximately 5 planets for every Sun.
Artist’s illustration of the habitable zone around different types of stars. Credit: NASA
Kunimoto used a technique known as ‘forward modelling’ to undertake the study, which allowed her to overcome the problem that Earth-like planets are difficult to detect due to their tiny size and orbital distance from their star.
“I started by simulating the full population of exoplanets around the stars Kepler searched,” expounded the researcher in UBC’s press release. “I marked each planet as ‘detected’ or ‘missed’ depending on how likely it was my planet search algorithm would have found them. Then, I compared the detected planets to my actual catalogue of planets. If the simulation produced a close match, then the initial population was likely a good representation of the actual population of planets orbiting those stars.”
Sizes of verified planets just after a release of 715 confirmed planets from Kepler data in February 2014. Kepler’s results aren’t a true representation of exoplanet populations because it can find larger planets easier than it can find smaller ones. Credit: NASA
While the scientists came up with an astounding number of hypothetical Earths, this does not necessarily imply the number of such planets exists or whether they have life similar to ours. However, this new estimate increases the likelihood that comparable worlds exist.