Billions of planets in our galaxy

Astronomers now estimate that there are billions of planets in our galaxy alone.Credit: NASA / JPL-Caltech
Astronomers now estimate that there are billions of planets in our galaxy alone.
Credit: NASA / JPL-Caltech

The new year has barely begun, and already it has been a good one for exoplanets. In a previous update, it was reported that the Kepler space telescope has added hundreds of exoplanet candidates to its rapidly growing list. That is exciting enough, but another new study now, similar to other ones, estimates that there are billions of other planets in our galaxy alone.

According to John Johnson, assistant professor of planetary astronomy at Caltech and coauthor of the study, “There are at least 100 billion planets in the galaxy, just our galaxy. That’s mind-boggling.”

The study suggests that planets are a normal part of star formation. In terms of numbers, there is at least one planet per star.

The study was conducted by astronomers at the California Institute of Technology, who analyzed the five known planets orbiting the star Kepler-32 which are thought to be representative of the vast majority of exoplanets.

The Kepler-32 system is a type known as an M-dwarf system, the most common in the galaxy. The stars in those systems are smaller and cooler than our Sun and the planets in those systems tend to orbit closer in to their stars, like a smaller, scaled-down version of our own solar system.

In that sense, our solar system is kind of an oddball, but when both the stars’ size and planetary orbits are smaller, that means many of those planets could still orbit within their stars’ habitable zones, where liquid water could exist on their surfaces.

All of the five known planets orbiting Kepler-32 are smaller worlds, ranging from 0.8 to 2.7 times the radii of Earth.

The new study has been accepted for publication in the Astrophysical Journal.

Carl Sagan would be proud…

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