Kepler's planet candidates by size.
Image source: NASA/Wendy Stenzel.

The Kepler Space Telescope has discovered 461 new planetary candidates. This brings the 22-month-old telescope’s total planetary find to a staggering 2,740. It is important to note that only 105 of these candidates have been confirmed as being alien worlds, but with further study, scientists are confident that most of these candidates (about 90%) will receive confirmation and get added to our exponentially-expanding list of known planets. About 50 of these planets orbit within their star’s habitable zone, and about five of them are super-Earths, one of which is an Earth-like world about 1.5 times the size of our own blue orb.

In addition, Kepler discovered more than 100 stars with multiple planets, bringing that number from 365 to 467. According to Jack Lissauer, a planetary scientist for NASA, “[t]he large number of multi-candidate systems being found by Kepler implies that a substantial fraction of exoplanets reside in flat multiple-planet systems. This is consistent with what we know about our own planetary neighborhood.”

Kepler uses the transit method to detect new planets. I’m sure you all remember the Venus transit that happened in June of 2012. As Venus transited the Sun, it blocked sunlight and the Sun got a little dimmer. That dimming is what Kepler looks for. This means the orbital plane of the system needs to be perfectly aligned with Earth so that we can actually see the transit. Kepler was observing some 156,000 stars, only a small fraction of which have orbital planes perpendicular to Earth.

When a planet makes a transit, we can learn a lot about it. We can learn its size by how much sunlight is blocked, various things about its composition by analyzing the star’s light as it shines through the planet, and its orbital period by how often we see the same dip in starlight. From that, we can use Kepler’s laws of planetary motion to figure out its mass and the planet’s orbital distance… all from a little dip in starlight (now, that is bloody awesome)!

Kepler is revolutionizing our knowledge of exoplanets and teaching us about the wide variety of systems that exist in the cosmos. Because Kepler’s detection system is so limited—if the orbital plane of a system is anything but perpendicular to ours, we won’t see a transit—it is only able to show us a fraction of the planets that are out there. And, in 22 months, that fraction has been shown to contain nearly 3,000 worlds in a tiny section of our night sky. Needless to say, Kepler will probably discover thousands or tens of thousands of new planetary candidates before its time is up. That is very exciting indeed.

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