New calculations in a study published Wednesday in Monthly Notices of the Royal Astronomical Society indicate that billions of the Milky Way's stars have one to three planets in the habitable zone, meaning that they potentially have liquid water as well.
The calculations, which were produced by a group of researchers from the Australian National University and the Niels Bohr Institute at the University of Copenhagen, are based on a method called the Titius-Bode law. This law, which was created around 1770, predicts how planets in a solar system will be spaced out. The researchers applied the law to the 1,000 exoplanets (and 3,000 possible exoplanets) found by NASA's Kepler satellite. They looked at 151 planetary systems — ones where Kepler had detected between three and six planets — and found that the Titius-Bode law fit well with the way 124 of them were spaced out.
"Using T-B's law, we tried to predict where there could be more planets further out in the planetary systems. But we only made calculations for planets where there is a good chance that you can see them with the Kepler satellite," Steffen Kjær Jacobsen, PhD student in the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen, said in a statement. In the planetary systems where ratios were off, they were able to estimate where "missing" planets might be.
Once those planets were added, all 151 systems showed one to three planets in their habitable zone. The researchers believe this indicates that most systems do have planets orbiting at the proper distance to hold liquid water.
To help confirm their theory, they've flagged a number of supposed Goldilocks planets that Kepler should be able to see at some point. They hope that other scientists will spot them, adding weight to the "missing planets" they've calculated.
Unfortunately, being in the habitable zone doesn't mean that liquid water is present — and the presence of liquid water doesn't necessarily mean that life ever can, will, or did exist. But here's to hoping.