Small, rocky planets can coalesce around a wide variety of stars, suggesting that Earth-like alien worlds may have formed early and often throughout our Milky Way galaxy’s history, a new study reveals.
Astronomers had previously noticed that huge, Jupiter-like exoplanets tend to be found around stars with high concentrations of so-called “metals” — elements heavier than hydrogen and helium. But smaller, terrestrial alien planets show no such loyalty to metal-rich stars, the new study found.
“Small planets could be widespread in our galaxy, because they do not require a high content of heavy elements to form,” said study lead author Lars Buchhave, of the University of Copenhagen in Denmark.
A Diversity of Stars
Buchhave and his colleagues analyzed data from NASA’s planet-hunting Kepler space telescope, which has been continuously observing more than 150,000 stars since its launch in March 2009.
Kepler watches those stars for tiny brightness dips, some of which are caused by alien planets that cross the stars’ faces from the telescope’s perspective. To date, Kepler has flagged more than 2,300 exoplanet candidates. While just a small fraction have been confirmed, Kepler scientists estimate that at least 80 percent will end up being the real deal.
In the new study, the researchers looked at Kepler observations of 226 planet candidates circling 152 different stars. More than three-quarters of these potential planets are smaller than Neptune — i.e., their diameters are less than four times that of Earth — and some of them are as diminutive as our own planet, researchers said.
The astronomers studied the stars’ spectra and found that small, rocky worlds circle stars with a much broader range of metal content than do giant planets.