Based on data from the Kepler space telescope and the Gaia mission, a team of scientists has deduced that there could be more than 300 million habitable planets in our galaxy.
Written in 1961 by Dr. Frank Drake, the equation of the same name is the most famous formula in the search for technological civilizations that could potentially communicate with the Earth via radio signals.
The calculation is based on a number of factors, including the rate of star formation, the fraction of stars that have planets, how many habitable planets a star has, the number of worlds capable of developing life, the number that will produce intelligent and later technological life, and the life expectancy of a civilization.
The problem lies in the fact that none of the above factors are certain. Some are mere estimates and others pure speculation. The result is that the Drake equation estimates that there are between 1 and 100 million technological civilizations in our galaxy — a range that is not very helpful.
In an effort to refine things a bit, researchers from the SETI institute and NASA used data from the Kepler mission to produce a more reliable estimate of one of the factors: how many habitable planets are there in the galaxy. To answer this, the study focused on exoplanets that are similar in size to Earth, orbit stars similar to the Sun in age and temperature, and are in the habitable zone where they can have liquid water on the surface.
Unlike previous studies, the new research has polished the habitable zone factor by including not only the distance to the star, but also the amount of light the planet receives. This was accomplished by combining data from the exoplanet hunter Kepler with those from the Gaia mission, which measure the amount of energy a host star emits.
As a result, a number of more than 300 million potentially habitable planets were found in the Milky Way – some of these being only 30 light years from Earth. However, this number may be further refined in the coming years, as we gain a better understanding of how a world’s atmosphere can affect its ability to hold liquid water. The scientists say they used conservative estimates for this type of atmospheric impact in their analyzes, which could contribute to future efforts in this regard.
“Knowing how common different types of planets are is extremely valuable for the design of future exoplanet hunting missions,” explained the study co-author Michelle Kunimoto. “”Surveys aimed at small, potentially habitable worlds around stars like the Sun will depend on results like these to maximize their chances of success.””
The research has been published in The Astronomical Journal.