The search for extraterrestrial life zeroed in a bit today as NASA announced that its unmanned Kepler Space Telescope detected the most Earth-like planet yet found beyond the Solar System. Named Kepler-186f, the new planet orbits a red dwarf star about 500 light years away from Earth in the constellation of Cygnus, is only 10 percent larger than our planet, and could have liquid water, which is essential for life as we know it.
Kepler-186f isn't the first Earth-like planet found, nor is it the first to be found in a habitable or “Goldilocks” zone – that is, the region around a star where the temperature of a planet could be within the range where liquid water could exist. However, the Earth-like planets found so far inside the zone have all been much larger than the Earth, with the previous most Earth-like planet, Kepler-62f, coming in at 40 percent larger than our planet.
The new planet is only 1.11 times the size of Earth, and with a year of 130 days, this puts it inside the habitable zone of the dwarf star called, unimaginatively, Kepler-186. According to NASA, Kepler-186f only gets one-third the energy from Kepler-186 as the Earth does from the Sun, so its noon is as bright as an hour before sunset on Earth.
Though the size of the planet is known, its composition is still a mystery, though NASA points out that previous research suggests that a planet the size of Kepler-186f is likely to be rocky. As to the actual presence of life or even water, that, too, is unknown,
"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," says Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames. "Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth."
Though small, red or M dwarf stars like Kepler-186 make up 70 percent of the stars in the Milky Way galaxy. Kepler-186 is only half the size of the Sun, and Kepler-186f is one of five planets in the system with the others, Kepler-186b, Kepler-186c, Kepler-186d, and Kepler-186e, orbiting the star once every 4, 7, 13 and 22 days. They are, however, too large and too hot to be considered candidates for life.
Kepler-186f is one of almost a thousand planets detected by the unmanned Kepler probe, from the time it was launched in 2009 until its at-least-temporary decommissioning last year. It surveyed about 150,000 stars and was able to detect possible planets orbiting around them, as the planets cut off part of the starlight when passing in front of the star. Using this technique, Kepler detected thousands more planetary candidates that are still being assessed.
NASA says that with the detection of such Earth-like planets, the next step is to narrow the search to true Earth twins and learning more about their chemical composition.
The findings of the NASA team were published in Science.
The video below describes Kepler-186f.