This Newly Discovered Super-Earth Might Be Our Second-Closest Exoplanet

It’s always inspiring to learn about objects we’ve discovered in the farthest reaches of the universe, but when it comes to practicality, it’s often the closest ones that are the most useful. That’s why a discovery announced today is so exciting: astronomers have detected a “super-Earth” orbiting the closest single star to our own. But don’t pack your bags for an interstellar vacation just yet — from all appearances, it looks like a pretty harsh place to visit.

Hello Out There!

Astronomers detected the planet around Barnard’s Star, an ancient and solitary red dwarf located only 6 light years from our Sun. While the three stars of Alpha Centauri take the cake for closest star at a little more than 4 light years away, Barnard’s Star is our closest single-star neighbor. It’s small, cool, and probably twice as old as our sun, and one of the least-active red dwarf stars we know about.

That’s why even though this new planet, known as Barnard’s Star b, is much closer to its home star than Earth is to the Sun — orbiting at less than half Earth’s distance, with a year of roughly 233 days — astronomers believe it could be very, very cold. In fact, it orbits close to what’s known as the “snow line.” Just as a mountain’s tree line delineates where it’s too cold for trees to grow, a solar system’s snow line delineates where it’s too cold for water and other volatile compounds to avoid freezing into solid ice. Barnard’s Star only feeds this world 2 percent of the energy Earth gets from the sun, resulting in what scientists estimate to be a surface temperature of minus 150 degrees Celsius.

Astronomers estimate that this new planet is at least 3.2 times as massive as Earth, which makes it what’s known as a super-Earth. Low-mass stars like Barnard’s Star tend to be home to planets like these, which are defined as worlds with a radius up to four times and a mass up to 20 times as large as Earth’s — in other words, they’re planets that are bigger than Earth, but smaller than Uranus or Neptune.

Artistic impression of a sunset from Barnard’s star b.

A Team Effort

The discovery of Barnard’s Star b was unlike anything that’s been done before. We’ve looked for planets around this elderly star before to no avail. But this time, teams on the Red Dots and CARMENES exoplanet-hunting projects joined forces and combined 20 years of measurements from nearly a dozen high-precision instruments mounted on telescopes all over the world. In all, they used a whopping 771 measurements to find this planet.

They needed them, too. That’s because they used what’s known as the radial velocity method, which relies on the gravitational tug a planet gives to its home star. That tug causes the star to wobble ever so slightly, enough to cause a redshift, or lengthening, in the wavelengths of light that reach our instruments on Earth. At such a large distance from its star, Barnard’s Star b wouldn’t have given that strong of a tug, but an ESO instrument known as HARPS was still sensitive enough to detect it.

While this discovery still needs confirmation, the team is pretty sure it’s a done deal. “After a very careful analysis, we are 99% confident that the planet is there,” said Ignasi Ribas, the team’s lead scientist from the Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain, said in a statement. “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”

If all goes well, we may have a neighbor we never knew about. Somebody buy a housewarming gift!

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