In the constellation Cygnus, which appears to us as a great swan in the sky, about 500 light-years away, there is a star about half the size of our sun. And around that star orbits a planet that has a high probability of looking like our own. It's called Kepler-186f, depicted above in an artist's rendering. Today, NASA is announcing that it is the most Earth-like planet it has ever found.
That's because it's around the size of the Earth, is likely to be rocky, and, most important, it lies in the habitable zone of its star system. That's the range of distances from the star in which liquid water could exist.
The NASA press release reads:
"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," said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames, and coauthor of the paper. "Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth."
The Kepler planet circles a star that is much smaller than the sun, as can be seen in the comparison chart below. In the coming decades, researchers will be looking for a true Earth twin, circling a star the size of the sun. Such planets would be the most likely to harbor life similar to ours. Right now, we just don't have the technology to find such a planet. Stars like the sun are just too bright. (Putting it crudely, NASA finds new planets by measuring the change in light from the star as the planet crosses it. Kind of like looking for solar eclipses, just ones light-years away.)
"It's like looking for a firefly next to a search light," Sara Seager, an MIT astrophysicist, said at a lecture at the National Academy of Science last month. NASA researchers are currently working on a new telescope system, equipped with what's called star shade, that will make it easier to see Earth-like planets orbiting around bright, sun-like stars. And that's our best chance of finding life in the universe.