comScore Kepler-421b Has Longest Orbit of Any Transiting Exoplanet | The Mary Sue

Newly Discovered Kepler-421b Has Longest-Known Year of Any Transiting Exoplanet

One-million, thirteen-thousand, seven-hundred sixty minutes, how do you measure, measure a year?


Kepler-421b orbits its star at a leisurely pace of making one trip around every 704 Earth days, or nearly half the speed the Earth moves around the Sun. That’s not the slowest orbit we’ve found, but it’s significant because Kepler-421b is beyond its star’s “Snow Line,” and it’s a transiting exoplanet. Together those things mean we were incredibly lucky to find it at all.

David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA) said, “Finding Kepler-421b was a stroke of luck.”

An exoplanet is transiting when it passes between its star and the Earth. It’s one of the ways we are able to detect the presence of an exoplanet around a star. This great video from MinutePhysics explains that and some other ways we can hunt for exoplanets here on Earth:

What’s unique about Kepler-421b and its orbit is that the farther a body orbits from its star, the less likely it is to line up with the Earth and transit between us and that star. Being beyond the snow line means 421b is too far from its star to form into a rocky planet like Earth. Instead, it’s a gas giant similar in size to Uranus. That distance is what makes it hard to find.

Imagine a grape orbiting a watermelon on the other side of the room. The closer the grape is to the watermelon, the more likely it is that the grape will fall between your eye and the watermelon. The farther it moves out, the less likely it is that the orbit will put it between you and the melon. 421b’s slow orbit also made it hard to find because it goes nearly two years between passes. We have better luck finding planets with shorter orbits just because they transit more often.

(via, image via David A. Aguilar, CfA)

Previously in exoplanets

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Glen is a comedian, writer, husband, and father. He won his third-grade science fair and is a former preschool science teacher, which is a real job.