Purchasing new hardware? Read our latest product comparisons

Astronomers discover exoplanet with longest known year


July 23, 2014

Artists impression of the Uranus-sized exoplanet Kepler-421b (Image: Daid A. Aguilar)

Artists impression of the Uranus-sized exoplanet Kepler-421b (Image: Daid A. Aguilar)

Image Gallery (2 images)

With the aid of NASA's Kepler spacecraft a team of astronomers, including members from the Harvard-Smithsonian Center for Astrophysics, has discovered an exoplanet with the longest yearly cycle ever recorded. The planet, imaginatively named Kepler-421b, takes an impressive 704 days to orbit its parent, a dim type K star.

The discovery was made by analyzing data from the Kepler spacecraft, which accrued the information over the course of a four year continuous vigil of the patch of sky containing Kepler-421b. The planet was detected using a technique which measures the dip in light as the exoplanet transits over the face of its parent star. Due to the impressive length of Kepler-421b's orbit, only two transits were detected over the entire four year period in which Kepler stood watch.

"Finding Kepler-421b was a stroke of luck," states David Kipping of the Harvard-Smithsonian Center for Astrophysics, and lead author on the paper detailing the discovery. "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 newly-discovered exoplanet sits around 1,000 light years from Earth. It orbits outside its own star's snow line, a hypothetical point of demarcation at which exoplanets cease to be rocky in composition and instead shift towards a predominantly ice-like make-up. The discovery of Keplar-421b holding an apparently stable orbit beyond the snow line may force astronomers to revise the current theories on the early behavior of gas giants that are thought to form in this area.

It is currently believed under the standard model of behavior for these bodies, that soon after formation a gas giant will drift back towards its parent star as Jupiter has done in our own solar system. The discovery of a planet remaining in orbit beyond the snow line means that this is not necessarily the norm, and that current theories will have to be altered to account for the behavior of planets such as Kepler-421b.

The explanation for Kepler-421b's lengthy orbit relates to its surprising distance from its parent star, which it orbits at a range of around 110 million miles, granting the planet a frigid surface temperature of -135º F (-57º C). Most other exoplanets discovered by the Kepler space telescope were found to be much closer to the focus of their orbit, making the length of their year more similar to that of our own.

A paper detailing the findings is due to be published in The Astrophysical Journal.

Source: Harvard-Smithsonian Center for Astrophysics

About the Author
Anthony Wood Anthony is a recent law school graduate who also has a degree in Ancient History, for some reason or another. Residing in the UK, Anthony has had a passion about anything space orientated from a young age and finds it baffling that we have yet to colonize the moon. When not writing he can be found watching American football and growing out his magnificent beard. All articles by Anthony Wood

The number of days depends on the rotational speed of the particular planet. 704 days can't apply to that planet. It may rotate faster or slower than Earth. It's possible - albeit highly unlikely - that planet orbits its star the same number of days Earth orbits the Sun.


It takes Pluto 248 YEARS to orbit the sun. Oh, yeah - not a planet any more.

Fairly Reasoner

@Fairly Reasoner Right! And if we dismiss Pluto, Uranus has an 84 Earth-years year... Maybe the article focuses on the fact that this EXOplanet is the one with the longest year recorded so far, but 704 days are a bit short of being "impressive".

Giolli Joker

"It takes Saturn 10,832 Earth days to complete one orbit around the Sun.

Is it possible that an error has occurred , and what the writer meant to say was 704 Years? not days?

Exoplanets are planets outside our solar system, so Saturn doesn't qualify - Ed. James Donohue

So would that effect a presidents term ?

Jay Finke

Yeah something about this article isn't quite right... A distance of 110 million miles from its star puts it just beyond the distance of Earth from the sun (Earth is 92 million miles from the sun)and Mars at 141 million miles from the sun has a year of 686 Earth days.


The 704 days is correct but the "longest year" isn't.

Many exoplanets have longer years.

Gizmag even reported one a couple of months ago as having an orbit of 80,000 years:



The article ends by saying "Most other exoplanets discovered by the Kepler space telescope were found to be much closer to the focus of their orbit, making the length of their year more similar to that of our own."

Orbits that take only a few weeks, days or even hours are not more similar to our own.


Another interesting planet is GU Piscium b.

Post a Comment

Login with your Gizmag account:

Related Articles
Looking for something? Search our articles