Kepler Space Telescope Finds Exoplanet With Longest-Known Year

NASA’s Kepler Space Telescope has found an exo-planet with the longest-known year. Kepler-421b, which transits its host star from Earth’s perspective, takes an incredible 704 Earth days to complete one orbit.

For comparison, Earth orbits its sun once every 365 days and Mars completes one lap every 780 days. The exoplanet has the longest year known for any transiting alien world, reports Space.com.

Study lead author David Kipping, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, stated of the discovery, “Finding Kepler-421b was a stroke of luck. 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.”

Kepler-421b doesn’t have the longest year of any known planet, as many nontransiting worlds have farther orbits, including gas giant GU Piscium b, which takes roughly 160,000 years to complete one lap round its host star. Rather, it has the longest known orbit for any transiting exoplanet.

Kepler-421b is about the size of Uranus and is located in the constellation Lyra, about 1,000 light-years from Earth. The orbiting rock was spotted by Kepler, which launched in March 2009 to hunt tor transiting exoplanets by observing the tiny brightness dips caused when the planets cross in front of their stars.

BBC notes that Kepler was uniquely suited to make the discovery, since it stared at the same patch of sky for four years. Kepler suffered a glitch in May 2013 that ended its first mission, but NASA recently signed off on a new mission, called K2, which will keep the space telescope hunting for exoplanets, along with other cosmic bodies and phenomena.

While the mission has ended, scientists are still pouring over the massive amounts of data Kepler provided, including roughly 1,800 new exoplanets the telescope found during its operation. Most of the finds so far are worlds that orbit close to their parent stars. These worlds transit relatively frequently, making them easier for the telescope to detect.

Researchers explained that the instrument generally requires three transits to definitively identify an exoplanet, but Kepler-421b was discovered after two transits. The planet orbits its cooler and dimmer sun at an average distance of 100 million miles, placing it beyond the solar system’s “snow line,” or the boundary between rocky and gaseous planets.

Planets like Saturn and Jupiter are created beyond the snow line, where ice grains clump together to form gas giants. These planets don’t often remain beyond the snow line, as astronomers have discovered numerous “hot Jupiters” in their stargazing. So, Kepler-421b’s lack of movement makes it remarkable.

Kipping noted, “This is the first example of a potentially nonmigrating gas giant in a transiting system that we’ve found.” The new study about Kepler-421b will be published in The Astrophysical Journal.

[Image by NASA/Troy Cryder]