Kepler finds planets by noticing the dip in light as they pass in front of their star, known as a transit. Three dips, or orbits, and you can confirm the planet exists.
For planets with longer orbits, however, this can be a bit tricky. This is because Kepler only looked at one portion of the sky for four years before moving on to its K2 mission. Finding planets on Earth-like orbits is therefore quite tough.
“The currently operating K2 mission is finding small planets orbiting close-by bright stars similar to our Sun, but only stares at them for 85 days – a far cry from the many years needed for true analogs of Earth to be found,” NASA's Steve Howell, a co-author on the study, told IFLScience.
That’s where this latest research comes in. The scientists used a method that’s called BLENDER. This involves looking at information contained in the initial transit light curve of the planet. Doing this means that false positives, like a passing star, can be ruled out.
Many of the candidates had already been validated by other methods. However, those methods failed to take into account the possibility that these planets orbited a different star on the same line of sight. If that were the case, these seemingly rocky planets would actually be much larger.
It also serves as a bit of a useful test of the BLENDER technique, which could be used to confirm other candidate planets in future too. And when it comes to finding worlds like our own, every tool is going to be key.