First Earth-Sized Planet Confirmed in the Habitable Zone

  • Apr 18, 2014 7:19am GMT

Yesterday, scientists announced the first confirmed Earth-sized planet located in the habitable zone of its host star.

For a few months now I have been compelled to write a blog post about really taking in what it is like to live in the time before the first Earth-like planet has been found.

To savor this amazing moment in history when humankind really didn't know if we were alone, if we were unique. What else was out there? I wanted us to really notice and appreciate, the calm, quaint quiet before Columbus discovers a whole new continent is out there.

With yesterday’s announcement though our time for contemplating our life before other Earth-like planets are found is going to be very short!

The planet, Kepler-186f, was found by the Kepler Space Telescope. Kepler is pointed at a few hundred thousand stars just in a small patch of sky near the constellation Cygnus (part of the Summer Triangle) to see how many planets it can see there and extrapolate from that how many there might be across the whole sky. The host star Kepler-186 (because the star had no name before Kepler started looking at it) is 500 light years from Earth and has four other planets in closer orbits, too hot to support liquid water on their surfaces (think Mercury).

Although Kepler-186 (the star) is cooler than our sun, Kepler-186f (the designation of its 5th planet out) is at the right distance to be in its habitable zone. It is 1.1 times the size of Earth, though its mass and composition are 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," said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames, and co-author of the paper.

When I was in school there were nine planets and I loved them. In my aunt’s National Geographic 'Our Universe' book I would read about each of them marvel at the depictions of the Roman gods who were their namesakes. That was our universe.

Then in 1992, we discovered the first exoplanet, or planet orbiting another star. Before that time we did not have the capability to detect planets orbiting other stars. Now we can detect them by looking for dips in the light output of the host star as the planets “transit” in front of them [Note this only works if they are orbiting in the plane we are looking, like looking at a DVD edge on! If the planet’s orbit is not edge- on to us (the DVD is turned so we are looking at the label) we will miss those.]

We can also detect planets by the wobble their gravity induces in the star as they orbit around, tugging just a little on their host star. This method is useful for catching planets that are not “edge on” since we can see the wobble they induce in their host stars from other angles as well.

In February 2014, Kepler announced 715 confirmed exoplanets jumping the number from around 1,000 to now nearly 1,800 confirmed extrasolar planets out there in a bizarre array of shapes, sizes and planetary system combinations. But because it's easier to detect the larger ones we still had not found many that could be our twin. That is why yesterday’s announcement, which accompanied a paper being published with the findings in the journal Science, is so exciting.