Scientists have recently discovered an exoplanet with the longest known orbit. It takes 704 days to circle its host star.
Exoplanets are planets in solar systems outside of our own. So far, most of the exoplanets that scientists have discovered -- more than 1,800 total -- have been large planets that orbit close to their parent stars. Since one of the methods that scientists use to discover exoplanets is studying the star's light to check for orbiting bodies, these close-orbiting planets are much easier for scientists to discover. This planet is a huge step forward in cataloguing and discovering all the planetary bodies in the known universe.
The study will be published in the Astrophysical Journal.
The planet has been named Kepler-421b in honor of Johannes Kepler, a German astronomer who was instrumental in designing the current telescope. The planet orbits a star that is dimmer than the sun, and cooler. The planet orbits the sun from 177 million kilometers away (110 million miles).
In contrast, the Earth orbits the sun at 150 million kilometers. Mars orbits the sun at a distance of 228 million kilometers. Mars takes 780 days to orbit the sun, even longer than this new exoplanet.
Scientists estimate that Kepler has an average temperature of -93 degrees Celsius (-135 degrees Fahrenheit). The planet is about 1,040 light-years away from the Earth.
The study's lead author David Kippin said, "Finding Kepler-421b was a stroke of luck." Kipping works at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. He said, "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 Kepler telescope uses the transit method to find exoplanets, watching the same area of sky for four years and tracking when objects cut in front of light from stars. The observatory where Kepler-421b was found only recorded two orbits of the star during this four-year period because it has such a long orbital period.
This new planet is a gas giant. Most gas giants orbit extremely close to their star. However, the planet's orbit falls outside of the "snow line." Previously, it was thought that many gas giants migrate inward to their star soon after they are formed. This planetary migration may not be necessary though, as shown by Kepler-421 b.
The more exoplanets we discover that exist at a distance, and orbit dimmer and cooler suns, the more we can learn about the universe and the way that it works.
