The Milky Way is home to far more planets than previously thought, boosting the odds that at least one of them may harbor life, according to a study released on Wednesday.
Not long ago, astronomers counted the number of “exoplanets” detected outside our own solar system in the teens, then in the hundreds. Today the tally stands at just more than 700.
However, the new study, published in Nature, provides evidence that there are more planets than stars in our own stellar neighborhood.
“We used to think that Earth might be unique in our galaxy,” said Daniel Kubas, a professor at the Institute of Astrophysics in Paris, and co-leader of the study.
An international team of astronomers led by Kubas and colleague Arnaud Cassan used a different method called gravitational microlensing, which looks at how the combined gravitational fields of a host star and the planet itself act like a lens, magnifying the light of another star in the background.
If the star that acts as a lens has a planet, the orbiting sphere will appear to slightly brighten the background star. The survey picked up on planets between 75 million and 1.5 billion kilometers from their stars — a range equivalent in the solar system to Venus at one end and Saturn at the other — and with masses at least five times greater than Earth.
Over six years, the team surveyed millions of stars with a round-the-world network of telescopes located in the southern hemisphere, from Australia to South Africa to Chile.
Besides finding three new exoplanets themselves — no minor feat — they calculated that there are, on average, 1.6 planets in the Milky Way for every star, Cassan said.
Whether this may be true in other galaxies is unknown.
“Remarkably, these data show that planets are more common than stars in our galaxy — they are the rule rather than the exception,” Cassan said. “We also found lighter planets ... would be more common than heavier ones.”
One in six of the stars studied was calculated to host a planet similar in mass to Jupiter, half had planets closer in mass to Neptune, and nearly two-thirds had so-called super-Earths up to 10 times the mass of the rock we call home.