Astronomers Discover a Transiting Exoplanet with the Longest Known Year

Astronomers have made a new discovery when it comes to a transiting exoplanet. They've found that the planet as the longest known year seen to date.

The new exoplanet is called Kepler 421b. It actually circles its star just once every 704 days. In comparison, Mars orbits our sun once every 780 days. That said, most of the 1,800-plus exoplanets that have been discovered are much closer to their stars and have shorter orbital periods.

The exoplanet orbits an orange, type K star that is both cooler and dimmer than our own sun. It circles its star at a distance of about 110 million miles. This means that the planet is a frozen world at a chilling -135 degrees Fahrenheit.

"Finding Kepler-421b was a stroke of luck," said David Kipping, the lead author of the new study, in a news release. "The farther a planet is from its star, the less likely it is to transit the star from Earth's point of view. It has to line up just right."

The planet's orbit actually places it behind the "snow line," which is the dividing line between rocky and gas planets. Outside of this line, water condenses into ice grains that stick together to build gas giant planets. What's interesting is that since gas giant planets can be found extremely close to their stars, in orbits lasting days or even hours, astronomers believe that many exoplanets migrate inward early in their history. Yet Kepler-421b shows that this migration isn't necessary.

"This is the first example of a potentially non-migrating gas giant in a transiting system that we've found," said Kipping.

The findings are published in The Astrophysical Journal.