Astronomers have discovered the first Earth-size planet orbiting a star in the habitable zone. The planet – Kepler-186f – has been described as an ‘Earth-cousin’ and was found using the Kepler space telescope.
The Kepler-186 system is located 500 lightyears away in the Cygnus constellation and is home to four other inner planets and a host star that is half the size and mass of Earth’s sun.
The star is classified as a red dwarf, the most common type of star in the Milky Way galaxy.
The habitable zone refers to the distance from a star where liquid water might pool on the surface of an orbiting planet, which suggests the potential to support life.
Not quite twins, but bearing a family resemblance
Kepler-186f is located on the outer edge of the habitable zone in the Kepler-186 system. It orbits the red dwarf once every 130 days and receives one-third the energy from its star that Earth gets from the sun. At high noon on Kepler-186f, the surface is only as bright as it would be on Earth an hour before sunset.
“Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has,” explained Thomas Barclay, research scientist at the Bay Area Environmental Research Institute in California, and co-author of the paper, which appeared in the journal Science.
“Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth,” he added.
The search for Earth-like planets continues
The Kepler space telescope launched in 2009 with the goal of finding Earth-like planets that follow the gravitational pull of other stars.
Other planets have been found in the habitable zone, but all of those discovered are at least 40pc larger than the Earth and understanding their make-up is challenging.
While the size of Kepler-186f is known, its mass and composition is not, though previous research suggests it’s likely to be rocky. What this discovery confirms, however, is that other planets of Earth’s size exist in the habitable zone of stars other than our sun.
Kepler will continue searching for true Earth-twins and measure their chemical compositions.
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