The new candidate planet, Barnard's Star b, is thought to have a mass between those of Earth and Neptune in the Solar system.
Barnard's star b, as the new planet is called, was excruciatingly hard to pin down, and the team is referring to it as a "candidate planet" though it is confident it's there.
In the coming decade, the next generation of astronomical observatory will revolutionise our ability to peer into the space close to the nearest stars, looking for the dim glow of their planets, reflecting the light of their host stars. Although the planet orbits its star much closer than Earth does to the sun, Barnard's star, a red dwarf, is so dim that its planet gets only 2% of the energy that Earth does.
But it wasn't until the first exoplanet discovery was confirmed in 1995 that the search for a world around Barnard's Star began in earnest.
It's so damn close to us. "The thing is that the candidate planet we found is so small and so far from its host star that its effect on the star is really, really tiny".
"We knew we would have to be patient".
The Super-earth, which orbits Barnard's Star in about 233 days, is inhospitable to humans. This red dwarf, smaller and older than our Sun, is among the least active red dwarfs known, so it represents an ideal target to search for exoplanets.
Patterns in those spectral variations can point to the gravitational wobbles induced by a planet orbiting an alien star.
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The planet, designated Barnard's Star b, now steps in as the second-closest known exoplanet to Earth. While the star itself is ancient - probably twice the age of our Sun - and relatively inactive, it also has the fastest apparent motion of any star in the night sky. The timing of the signal indicates that the planet orbits at about the same distance as Mercury orbits our Sun. The farther a planet is, the less its gravity pulls at the star and the less light it blocks out when it passes between that star and Earth. Redoubling their efforts, Vogt's team added 45 more radial velocity measurements from the newly commissioned Automated Planet Finder (APF) telescope at UC's Lick Observatory, 39 velocities from the Carnegie Institution for Science's Planet Finder Spectrograph (PFS) on the Magellan II Telescope at Las Campanas Observatory in Chile, and more data that became publicly available in recent years from HARPS.
Martin Kurster an astronomer at the Max Planck Institute for Astronomy who worked on the new study, said it is possible that the detection of the new planet could one day be disproved.
The radial velocity method used in exoplanet hunting requires precise observations of a star's spectrum.
And the researchers also found something else in the data: faint evidence of another planet, which would be known as Barnard's Star c.
"After a very careful analysis, we are 99% confident that the planet is there", the team's lead scientist, Ignasi Ribas, said in a statement. "We combined archival data from other teams with new, overlapping, measurements of Barnard's star from different facilities", commented Guillem Anglada Escudé (Queen Mary University of London), co-lead scientist of the team behind this result.
Yet much about the planet around Barnard's Star remains uncertain.
Now that this planet appears to be a real world, Teske says that there are many unanswered questions she hopes to resolve quickly, such as what the surface is made of, or if it has an atmosphere.
"The new planet is impossible for Peter van de Kamp to have detected".