NASA’s Kepler Mission has discovered the first planet orbiting in the habitable zone of a star similar to the Sun. The planet, 600 light years away, is called Kepler 22-b.
EarthSky spoke with astronomer Alan Boss of the Carnegie Institution of Science. He’s on the team of researchers that discovered Kepler 22-b. He told us:
Today, we have for the first time something much closer to a true Earth analog, that is a planet orbiting with a period of roughly one year around a sun-like star.
It’s a bit bigger than the Earth. It’s about 2-2.5 times as large as our Earth is. And it certainly is orbiting at the right distance so that it could have liquid water on its surface, if it does indeed have a watery composition. The surface temperature is pretty much like a spring day on Earth, roughly 72 degrees Fahrenheit, which sounds wonderful for those of us who are rather frozen this time of the year.
We asked Dr. Boss what what it means that the first planet has been discovered to orbit another star’s habitable zone?
In particular it’s the habitable zone of a sun-like star. There have been previous discoveries of habitable zones, super-Earths, orbiting around M-dwarf stars. M-dwarfs are stars with masses one-tenth to one-half the mass of the sun. And that means that they’re much less luminous than the sun. That means you have to orbit much closer to the star in order to be warm enough to have liquid water.
Those planet that have been found previously are in at much shorter orbital periods. They’re inside, basically, the orbit of Mercury. And those are probably perfectly habitable planets, although there’s been a little bit of debate as to which ones might be habitable.
What’s different here is again, this is a super-Earth mass planet, but for the first time it’s out at a much greater distance form the star. It’s not orbiting every thirty days, or every forty days, or sixty days; it’s orbiting every 290 days, which is very close to 365, the orbital period of the Earth.
Planet Kepler 22-b is in our Milky Way galaxy, but far away. Light from its parent star takes 600 years to reach Earth. The evidence for Kepler 22-b are repeated observations of blinks in that star’s light, happening when the planet transits in front of the star. Dr. Boss talked about the next step in finding worlds like Earth out there.
The next step is to basically keep the Kepler Telescope up and running, unfortunately. It’s slated to stop functioning roughly one year from now. If it really does get that extended mission, four more years, then Kepler really will be able to measure, right down to Earth size, at Earth-like orbits. And that’s the key factor we need to understand how frequently Earth-like planets are there.
Boss remarked that just a little over 15 years ago, we had no proof that sun-like stars had any planets at all.
Now, 16 years later, we know that not only such planets exist, but they appear to be remarkably common. So that when you look up at the stars at night in the sky, you can basically imagine that one out of two stars up there probably have a habitable planet in orbit around them, something on order like that, which is truly an amazing thing to think of the next time up look up at a good, dark night sky.