Researchers have concluded that each star in the Milky Way galaxy likely has at least one planet orbiting it, meaning that our galaxy has at least 100 billion planets to its name.
Given that it's news every time Kepler discovers a new exoplanet (a planet orbiting a star other than our sun), how did astronomers come to this conclusion?
Using a technique called microlensing, and statistical analysis applied to six years' worth of observations from the PLANET (Probing Lensing Anomalies NETwork), MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment) surveys, researchers were able to determine that statistically speaking, every star in the Milky Way should have at least one orbiting planet, if not more. Moreover, these planets are likelier to have low masses, similar to Earth, than Jupiter-like masses.
"We used to think that the Earth might be unique in our galaxy. But now it seems that there are literally billions of planets with masses similar to Earth orbiting stars in the Milky Way," says Daniel Kubas, co-author of a paper on the subject released in the journal Nature, in a statement.
The microlensing technique uses the motion of stars and their gravity: when one star moves in front of another, it acts like a lens, magnifying the light from the background star. If there's a planet in orbit around the foreground star, it can further magnify the light. It's that extra boost that reveals the planet itself, which would otherwise be too faint to see through a telescope.
Microlensing also reveals the mass of the planet, but doesn't really indicate what the world is composed of.
These findings, reported by an international team of astronomers, are supported by data from two other planet-finding techniques, that is, detection of a planet's gravitational pull, or the dimming of a star as a planet passes in front of it. Taken together, the three techniques indicate that planets are pretty common in the Milky Way, and that there are more small planets than massive ones.
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