Scientists from the Kepler mission have just announced that they’ve potentially found more that 1,200 new planets orbiting other stars. That’s incredible!
Here’s a brief rundown: out of the potential 1,235 planets, 68 are approximately Earth-size, 288 are super-Earth-size (i.e. rocky planets that are several times the mass of Earth), 662 are Neptune-size, 165 are the size of Jupiter and 19 are larger than Jupiter.
Furthermore, they’ve found that 54 of these planets orbit within their star’s habitable zone, and that of these 5 are roughly Earth-sized.
Now, the Kepler survey covers roughly 156,000 stars, and detects planets by watching them transit across the face of their star, measuring the small dip in the star’s brightness. Naturally, the odds of an orbiting planet actually passing in front of its star is very low. Still, I estimate that, assuming there is a planet orbiting within its habitable zone, there is 0.3% it will be lined up correctly, which translates into about 450 stars.
Think about that, out of 450 candidate stars, 5 have Earth-sized planets in Earth-like orbits, or 1 out of every 90. That would imply that there are a few billion potentially Earth-like planets in the galaxy, the closest likely being no more than 20 light-years away.
Even considering other planets, 54 out of 450 equates to 1 out of 9. Which means that there’s likely some Jovian planet (possibly with habitable moons) within 10 light-years.
Note, however that I say Earth-sized, not Earth-like. The survey can’t measure the atmosphere or anything like that, so they could all actually be uninhabitable. Venus would count along one of the five if it were in the survey. But still, given what it implies about the abundance of Earth-like planets, this is a HUGE discovery.