Astronomers Discover Transiting Exoplanet with Longest Known Year, Kepler-421b

Kepler-421b Transiting Exoplanet with the Longest Known Year

This artist’s conception shows the Uranus-sized exoplanet Kepler-421b, which orbits an orange, type K star about 1,000 light-years from Earth. Kepler-421b is the transiting exoplanet with the longest known year, circling its star once every 704 days. It is located beyond the “snow line” – the dividing line between rocky and gaseous planets – and might have formed in place rather than migrating from a different orbit. Credit: David A. Aguilar (CfA)

Astronomers from the Harvard-Smithsonian Center for Astrophysics have discovered a transiting exoplanet with the longest known year, circling its star once every 704 days.

Astronomers have discovered a transiting exoplanet with the longest known year. Kepler-421b circles its star once every 704 days. In comparison, Mars orbits our Sun once every 780 days. Most of the 1,800-plus exoplanets discovered to date are much closer to their stars and have much shorter orbital periods.

“Finding Kepler-421b was a stroke of luck,” says lead author David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA). “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 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 (180 million kilometers). As a result, this Uranus-sized planet is chilled to a temperature of -135° Fahrenheit (-93° Celsius).

As the name implies, Kepler-421b was discovered using data from NASA’s Kepler spacecraft. Kepler was uniquely suited to make this discovery. The spacecraft stared at the same patch of sky for 4 years, watching for stars that dim as planets cross in front of them. No other existing or planned mission shows such long-term, dedicated focus. Despite its patience, Kepler only detected two transits of Kepler-421b due to that world’s extremely long orbital period.

The planet’s orbit places it beyond the “snow line” — the dividing line between rocky and gas planets. Outside of the snow line, water condenses into ice grains that stick together to build gas giant planets.

“The snow line is a crucial distance in planet formation theory. We think all gas giants must have formed beyond this distance,” explains Kipping.

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 host star, Kepler-421, is located about 1,000 light-years from Earth in the direction of the constellation Lyra.

This research has been accepted for publication in The Astrophysical Journal.

Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution, and ultimate fate of the universe.

Reference: Discovery of a Transiting Planet Near the Snow-Line” by David M. Kipping, Guillermo Torres, Lars A. Buchhave, Scott J. Kenyon, Christopher E. Henze, Howard Isaacson, Rea Kolbl, Geoff W. Marcy, Stephen T. Bryson, Keivan G. Stassun and Fabienne A. Bastien, 9 October 2014,  The Astrophysical Journal.
DOI: 10.1088/0004-637X/795/1/25
arXiv: 1407.4807

2 Comments on "Astronomers Discover Transiting Exoplanet with Longest Known Year, Kepler-421b"

  1. Would have been nice if you’d given the distance of the planet that is actually the farthest from its star as well. I know there’s a few that have been discovered by methods other than transiting that are much further out, like beyond the distance of Neptune and Pluto’s orbits in our solar system, and even giant planets straddling the brown dwarf definition that are several times the Pluto distance away.

    This article gives the impression that this planet in a Mars-like orbit is the furthest exoplanet found, which isn’t true at all, its just the furthest one that’s been discovered using the transit method of detection.

  2. Madanagopal.V.C. | July 29, 2014 at 12:49 am | Reply

    Most of the exoplanets discovered could be from a closer range as against this exoplanet which is about our Mars distance from the star but still beyond the snowline, which in our case is the asteroid belt. The theory is that it is not migrated but formed there itself is interesting. All our gas planets, like Jupiter, Saturn, Uranus, Neptune do have a ring around them pulling large number of planets and planetoids, which can migrate that orbit closer towards the Sun. In Kepler421b a massive planet is formed just beyond the snow line.Thank You.

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