Astronomers Discover Exoplanet Kepler-421b with Longest Known Year

A year on the newly discovered Uranus-sized exoplanet Kepler-421b lasts for 704.2 days, making it the longest orbital period exoplanet yet found. Its parent star, Kepler-421, is a G9/K0 dwarf star located in the constellation Lyra, about 1,000 light-years from Earth.

Most of the 1,800-plus exoplanets discovered to date are much closer to their stars and have much shorter orbital periods, astronomers claim.

‘Finding Kepler-421b was a stroke of luck,’ said lead author David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA) in Massachusetts.

‘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 orange, type K star that Kepler-421b orbits is cooler than our own Sun, as well as being dimmer. Kepler-421b, about the size of Uranus, is approximately 110 million miles from its star, making this planet a frosty -135 degrees Fahrenheit. Kepler-421, the host star, is approximately 1,000 light-years from Earth near the constellation Lyra.

 Dr David Kipping of the Harvard-Smithsonian Center for Astrophysics and his colleagues discovered the exoplanet by detecting the decrease in brightness of Kepler-421 as the exoplanet passed in front – a transit event. They detected only two transits of Kepler-421b due to that world’s extremely long orbital period.

The planet’s long year makes it more than merely a new record-holder, it makes it the first transiting planet discovered near the so-called frost-line – the dividing line between rocky and gas planets.

“When our Solar System was first forming, it was at this special distance that the temperature was cold enough for ice grains to form,” explained Dr Kipping, who is the lead author of a paper accepted for publication in the Astrophysical Journal.

Since gas giant planets can be found extremely close to their stars, in orbits lasting days or even hours, theorists believe that many exoplanets migrate inward early in their history. Kepler-421b shows that such migration isn’t necessary. It could have formed right where we see it now.

“This is the first example of a potentially non-migrating gas giant in a transiting system that we’ve found,” adds Kipping.

The Kepler probe was launched in 2009. To find the latest planet, spacecraft stared at the same patch of sky for four years, watching for stars that dim as planets cross in front of them

Kepler-421b Fast Facts

It takes Kepler-421b circles almost two Earth years to circle its star – or 704 days.

Kepler-421b orbits an orange type K star that is cooler and dimmer than our sun.

It circles the star at a distance of about 110 million miles.

The host star, Kepler-421, is located about 1,000 light-years from Earth in the direction of the constellation Lyra. As a result, this Uranus-sized planet is chilled to a temperature of -93°C (-135° F). It the first example of a potentially non-migrating gas giant in a transiting system that astronomers have found.
 

Image Source: https://goo.gl/DODGkp
Preprint paper: https://goo.gl/vL1MQf