Frozen super-Earth discovered just six light-years away
Staff Writer |
Astronomers have found a frozen exoplanet more than three times the mass of Earth, orbiting a star that's only six light-years away.
Article continues below
The exoplanet is orbiting Barnard's star, the closest solitary star to our sun.
This makes it the second closest known exoplanet to us. Previously, an exoplanet was found orbiting in the three-star Proxima Centauri system.
The exoplanet was found after stitching together 20 years of data, including 771 individual measurements, from seven instruments. The analysis that led to the discovery is detailed in a study published Wednesday in the journal Nature.
For years, astronomers thought they would find a planet around the nearby star, but it eluded them.
"The biggest 'kick' about this discovery is the host star," Paul Butler, study co-author and astronomer at the Carnegie Institution for Science, wrote in an email. "Barnard's star is the 'great white whale' of planet hunting."
The planet, known as Barnard's star b, is probably dimly lit by its star and slightly colder than Saturn. The researchers believe that it is an icy desert with no liquid water, a hostile environment where the average surface temperature is around minus-274 degrees Fahrenheit.
The red dwarf star itself emits only about 0.4% of our sun's radiance, so the planet receives about 2% of the intensity that Earth receives from its sun. This is because Barnard's star is in the class of M dwarf stars, cooler and less massive than our sun. It's also an old star that predates our own solar system.
And to look at it through a telescope, the star appears to be moving the fastest among the other stars in the night sky. This is because it's moving quickly in relation to the sun, and it's the nearest single star in the sky to us, Butler said.
"The star is named in honor of the great American astronomer Edward Emerson Barnard, who was a pioneer of stellar photography and astrometry," Butler said. "He recognized that this star had the largest known proper motion a century ago."
The planet is about the same orbital distance from its star as Mercury is from our sun, making a full pass around the star every 233 days. This places it in the "snow line" of the star, where it's cold enough for water to freeze into solid ice. This region in a planetary system is where the building blocks of planets are thought to form, collecting material to become cores. As they migrate closer to their host stars, gathering more material, they become planets.
It's the first time a planet this small and distant from its star has been detected using the radial velocity technique, which Butler helped pioneer. This method is sensitive to the mass of the exoplanet and measures changes in the host star's velocity. Instruments can be used to detect tiny wobbles in the star's orbit that are caused by the planet's gravity. ■