Scientists have discovered that a super-Earth could be orbiting a red dwarf called Barnard’s star, located just 6 light-years away, making this the second closest planet known to our Solar System.
Called Barnard’s star b, the planet is thought to be 3.2 times the mass of Earth, completing an orbit once every 233 days. It was discovered by a team led by Ignasi Ribas from the Institute of Space Sciences in Spain, with the findings published in Nature.
“We know of almost 4,000 planets today, so what matters one more?” Ribas told IFLScience. “The thing is that this is an effort to find planets in our immediate solar neighborhood. The goal is to understand the planet population in our immediate surroundings.”
Barnard’s star b is hugely exciting for its proximity. The star itself is the closest single star to our Sun – only the Alpha Centauri system is closer, which comprises three stars. One of these is Proxima Centauri, 4.2 light-years away, around which we think there is a planet called Proxima b.
The discovery of Barnard’s star b was made by noticing wobbles in its host star, known as the radial velocity method. The team used over 700 observations of the star from 20 years of data, highlighting just how tricky it is to find planets in this way.
Barnard’s star itself (also known as GJ 699) has a very low mass, about one-seventh that of our Sun, and only about 2 percent of our Sun’s energy. But it was one of the targets in the Red Dots campaign, of which this research is a part, which is trying to find planets around the closest stars to Earth.
This planet sits five times further than the star’s habitable zone, although only about 0.4 times as far as Earth orbits our Sun, meaning the chances of liquid water are slim. But if the planet is rocky, then it is “very likely to be a frozen planet,” noted Ribas, with an average temperature of about -170°C (-270°F).
There is also a small chance the planet does not exist – the method used to detect it can be fooled by changes in the star itself. But the team noted they were about 99.2 percent confident in their detection, with this planet being a prime target for future observations.
As far as we know the planet does not transit its star, meaning it doesn’t pass in front of it from our point of view. That will make further studies somewhat tricky, but the Hubble telescope or future James Webb Space Telescope (JWST) could take a closer look.
Interestingly, back in the 1960s, a Dutch astronomer called Peter van de Kamp claimed to have found two Jupiter-mass planets around Barnard’s star. Those were later found to be an error with his instruments, but the claims did encourage more detailed observations of the star – which led to this discovery thanks to the large swathe of data available.
The data also allows us to put some constraints on this Solar System. The researchers believe it's unlikely Barnard’s star has any Earth-mass planets in its habitable zone; if it does have habitable planets, they must be smaller than Earth.
There are still many unknowns about Barnard’s star b. We only know its mass, not its size, and 3.2 Earth masses is a minimum estimate. It’s also unclear what the planet’s inclination is to its star, or if it has any companion planets.
But what is clear is that this is one of the most exciting exoplanet discoveries ever made. To know there is a super-Earth sitting on our cosmic doorstep is hugely exciting, and suggests there are many more fascinating nearby worlds waiting to be found.
We now know of four planetary systems within 10 light-years of our Sun, and 14 within 15 light-years. Barnard’s star b may well be an uninhabitable frozen rock, but for now, it’s the second closest friend we’ve got in this vast universe.