Our planet is just the right distance from the sun to support liquid water. And, so are billions of other planets in the Milky Way galaxy according to new research.

NASA’s Kepler satellite has spotted about 1,000 planets orbiting stars in the Milky Way. Astronomers have spotted about 3,000 more potential planets. Many of these stars have planetary systems of 2-6 planets. That number is likely higher as the Kepler satellite works best when looking for large planets near their host star. The problem is these planets are often too close to their host star to support life.

Ok, so how can researchers figure out if a planetary system may have planets in the habitable zone? They used a new version of a law created 250 years ago. The Titius-Bode Law.

Around 1770, the Titius-Bode law was created and was able to accurately calculate the position of Uranus before it was discovered. According to the Titius-Bode law, a certain ratio exists between the orbital periods of planets in a solar system. The ration between the orbital period of the first and second planet is the same as the second and third planet, third and fourth planet and so on.

Once researchers knew the ration for discovered planets, they could calculate the position of planets not yet spotted by Kepler.

“We decided to use this method to calculate the potential planetary positions in 151 planetary systems, where the Kepler satellite had found between 3 and 6 planets. In 124 of the planetary systems, the Titius-Bode law fit with the position of the planets as good as or better than our own solar system. 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,” said Steffen Kjær Jacobsen, PhD student in the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen.

Jacobsen says the researchers then picked 77 planets in 40 planetary systems for closer study. These 77 planets were picked “because they have a high probability of making a transit, so you can see them with Kepler.”

Confirming these calculations should be easy. Take another look at these 40 planetary systems with the Kepler satellite. If these planets are found, it will confirm the theory.

If you take this data and extend it to the entire Milky Way galaxy, there could be billions of stars with planets in the habitable zone.

The Habitable Zone

The habitable zone is a region around a star where a planet, or moon could support liquid water. It’s also known as the Goldilocks zone. The habitable zone differs depending on the star.

Hotter stars have a habitable zone stretching further out. While cooler stars have habitable zones closer to the host star.

goldilocks zone

Plus, you can’t discount moons around larger planets. Take Europa or Titan. The gravitational pull of their planet may produce enough energy to heat the moons’ cores. This could lead to liquid water.

Billions of potentially habitable planets in the Milky Way? We will know soon enough. The calculations shouldn’t be difficult to test.