Astronomers estimate 4.5 billion ‘Earth-like’ planets in our galaxy

There are now estimated to be about 4.5 billion "Earth-like" planets orbiting red dwarf stars in our galaxy. Credit: David A. Aguilar (CfA)
There are now estimated to be about 4.5 billion “Earth-like” planets orbiting red dwarf stars in our galaxy. Credit: David A. Aguilar (CfA)

There was more exciting exoplanet-related news this morning – a team of astronomers announced a new study today which estimates that there are likely about 4.5 billion “Earth-like” planets in our galaxy!

The results come from a survey of red dwarf stars, the most common in our galaxy, which are smaller and cooler than our own Sun. They number about 75 billion, or three-quarters of all of the stars in the galaxy.

From analysis of data from the Kepler space telescope, it turns out that approximately 60% of red dwarfs have planets smaller than Neptune. That’s good news for astronomers searching for smaller planets like Earth, but it gets better. About 6% of those stars have planets which are Earth-sized and orbiting in the habitable zone of their stars. That’s around 4.5 billion planets which are both about the same size of Earth and could have temperatures which would allow liquid water to exist on their surfaces.

It also means, according to the new calculations, that the closest of these planets might be only 13 light-years away, or “right next door” in galactic terms.

“We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted,” said Courtney Dressing, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA). She is also the lead author of the new paper, to be published in The Astrophysical Journal.

According to co-author David Charbonneau, “We now know the rate of occurrence of habitable planets around the most common stars in our galaxy. That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

It should be noted that “Earth-like” here means planets which are about the same size and temperature of Earth. It doesn’t necessarily imply an Earth “twin” although the overall conditions could still be suitable for life of some kind, at least as we know it, to exist.

Determining just how many of these planets are nearby and their actual characteristics will require follow-up studies from new, upcoming telescopes such as the ground-based Giant Magellan Telescope and the James Webb Space Telescope.

Red dwarf stars also tend to live a lot longer than Sun-like stars. If any of those planets support life, it could be much older than life on Earth.

Remember too, that this study focuses on red dwarf stars; there is also growing evidence for numerous “Earth-like” planets orbiting Sun-like and other stars as well. Not long ago we wondered if there any other planets similar to Earth out there at all, but now it seems that there are many such worlds, and some of them are very close to home…

This article was first published on

Thoughts? Leave a Reply!