An international team of astronomers has detected evidence of a cold planet at least three times the size of Earth orbiting an ancient red dwarf star, right in our stellar neighborhood.
If you were traveling at the speed of light, it would take you just six years to reach it. In the context of the universe, that’s basically right next door.
The newly discovered world, described in Nature, is associated with a small, dim star known as Barnard’s star that is older than our solar system. It takes the planet 233 days to complete a single orbit around its cool red sun.
It is now the second-closest known planet to our solar system. The only closer known planet is an Earth-sized body that orbits the small red star Proxima Centauri in the Alpha Centauri triple star system. That planet was discovered in 2016 and lies just four light-years from Earth. The planet around Barnard’s star is probably too cold to host life, researchers said.
Although it is about as close to its own star as Mercury is to the sun, scientists say it is probably as cold as Saturn. That’s because Barnard’s Star emits only 0.4 percent of the sun’s radiant power.
But the new discovery is exciting for other reasons.
The proximity of the newly found planet to Earth makes it an excellent target for future observations. It is so close that the next generation of telescopes may be able to image it directly, the researchers said.
In addition, the new find provides further evidence that planets are nearly ubiquitous around red dwarf stars, said Ignasi Ribas, an astronomer and director of the Institute of Space Studies of Catalonia in Spain. “The chances of finding new ones is quite high.”
The new detection was made by a team of scientists working on an astronomy collaboration called Red Dots. Together, they are scanning the night sky for planets orbiting nearby dim red dwarf stars. Ultimately they hope to find a world in the habitable zone of these stars, where liquid water could pool on its surface.
This is not the first time that astronomers thought they had found a planet around Barnard’s star. In the 1960s Peter van de Kamp, a Dutch astronomer based in the U.S., reported the discovery of two planets roughly the size of Jupiter. Based on his observations, he believed one of the planets completed a full orbit around the dim star in 12 years, while the other completed its orbit in 20 years. However, as measurement techniques became more precise, scientists found that the supposed signals of Van de Kamp’s two planets did not exist after all.
The discovery of a single, much smaller planet orbiting Barnard’s star is based on a technique called radial velocity. Scientists use spectrometers to look for a small wobble in the light from the star that would indicate it has a planet orbiting around it. The magnitude of the wobble reveals the minimum mass of the planet that is responsible for the motion.
The radial velocity method was developed in the 1990s and has been improving ever since, Ribas said. Even so, the size of the newly found planet is just on the edge of what current instruments can detect.
This discovery was possible only because the research team was able to examine hundreds of measurements that had been made over 20 years, he said. That gave them enough data to detect the small signal of the planet.