Up to 300 million planets in the Milky Way may be habitable
Based on data from the Kepler Space Telescope and the Gaia mission, there may be up to 300 million habitable planets in the Milky Way galaxy, according to a team of scientists from the SETI Institute, NASA, and other international organizations. The research not only gives a measurement of how many potentially life-bearing planets there are, it also provides a key factor in the Drake equation that estimates how many extraterrestrial civilizations may exist.
Written in 1961 by Dr. Frank Drake, the Drake equation is the most famous formula in the search for extraterrestrial technological civilizations that could potentially communicate with Earth using 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 planets that develop life, the number that produce intelligent life, the number that produce a technological civilization, and the life span of that civilization.
The problem is that none of these factors are known for certain. Some are only rough estimates and some are pure guess work. The result is that the Drake equation estimates that there are anywhere between one and 100 million technological civilizations in our galaxy – a range that isn't very helpful.
In an effort to refine things a bit, researchers used data from the Kepler exoplanet hunting mission to produce a more reliable estimate of one factor in the equation – how many habitable planets are there in the galaxy. To answer this, the study looked at exoplanets that are roughly the same size as the Earth, revolve around Sun-like stars of the same approximate age and temperature, and are in the habitable zone of their star where liquid water could exist.
This is similar to previous studies, but according to the SETI Institute, the new research refined the habitable zone factor by including not only the distance from the star, but also the amount of light the planet receives. This was achieved by combining the Kepler data with that of the Gaia mission, which measures the amount of energy the host star emits.
The result is an estimate that there may be up to 300 million potentially habitable planets in our galaxy, with some as close as 30 light years from Earth. However, this number may be further refined down or up as we gain a greater understanding of how the atmosphere of a planet can affect its ability to support liquid water. The researchers say they used a conservative estimate of this atmospheric impact for their analysis, which should help inform future exoplanet-hunting efforts.
"Knowing how common different kinds of planets are is extremely valuable for the design of upcoming exoplanet-finding missions," says study co-author Michelle Kunimoto. "Surveys aimed at small, potentially habitable planets around Sun-like stars will depend on results like these to maximize their chance of success."
The research was published in the Astronomical Journal.
Source: SETI Institute