Astronomers have identified a tiny exoplanet circling Barnard’s star, the closest solitary star to our solar system. This newly found exoplanet, called Barnard b, has a mass at least half that of Venus and completes its orbit around the star in just over three Earth days. This discovery suggests the potential existence of three additional exoplanets in varying orbits around Barnard’s star. The comprehensive findings are presented in a study published on October 1 in the journal Astronomy and Astrophysics.
Understanding Barnard’s Star
Barnard’s star is a red dwarf located about six light-years from both the sun and Earth, making it the nearest isolated star and the second closest star system, trailing behind the trio of stars in Alpha Centauri. Although it is relatively close, it is too faint to be seen with the naked eye and can only be observed using telescopes.
Red dwarf stars like Barnard’s are ideal targets in the quest for Earth-like exoplanets. Detecting low-mass rocky planets around these smaller stars is often more straightforward compared to larger stars like our sun due to their cooler temperatures. This results in a habitable zone much closer to the star’s surface than that of hotter stars like the sun. Consequently, any planets orbiting within this zone complete their orbits more quickly, allowing astronomers to monitor them over days or weeks, rather than years.
In 2018, there was an initial promising detection of an exoplanet called Barnard b, but scientists could not verify it. The European Southern Observatory (ESO) notes that it is standard practice in the scientific community to name exoplanets after their host stars, adding a lowercase letter to denote their order of discovery—‘b’ for the first, ‘c’ for the second, and so forth.
“Although it took a while, we always believed that we could make progress,” stated Jonay González Hernández, a co-author of the study and astrophysicist at the Instituto de Astrofísica de Canarias in Spain.
Detecting the Exoplanet with ESPRESSO
To identify this new exoplanet, researchers utilized the Very Large Telescope (VLT) in Chile. They conducted observations over the past five years, searching for signals from potential exoplanets existing in the habitable or temperate zone of Barnard’s star, which is the area where liquid water might be present on a planet’s surface.
Barnard b is situated 20 times closer to its star than Mercury is to the sun. With a surface temperature around 257° Fahrenheit, this exoplanet completes an orbit in just over three Earth days.
“Barnard b is among the lowest-mass exoplanets discovered and is one of the few known to have a mass less than Earth’s. However, it orbits too closely to its host star, falling outside the habitable zone,” explained González Hernández. “Even with the star being about 2,500 degrees cooler than our sun, it’s too hot to support liquid water on its surface.”
The research team also utilized an instrument known as ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) for their observations. This highly sensitive instrument aboard the VLT aids in detecting stellar wobble caused by the gravitational effects of orbiting planets.
To validate these wobbles, the team analyzed data from additional instruments specialized in exoplanet detection—specifically HARPS at ESO’s La Silla Observatory, along with HARPS-N and CARMENES. Unfortunately, this new data did not corroborate the existence of the exoplanet that was reported in 2018.
Is There More to Discover?
In addition to Barnard b, the research team detected signs of three additional exoplanet candidates orbiting the same star. However, further observations with ESPRESSO are necessary to confirm their existence.
“We need to continue observing this star to verify the other candidate signals,” stated Alejandro Suárez Mascareño, a co-author and astronomer at the Instituto de Astrofísica de Canarias. “The discovery of this planet, along with previous findings such as Proxima b and d, indicates that there are many low-mass planets in our cosmic neighborhood.”
The ESO’s Extremely Large Telescope (ELT) is currently under construction and expected to be completed by 2028. Astronomers are optimistic that this will significantly enhance the field of exoplanet research, particularly through its ANDES instrument, which will facilitate the detection and atmospheric study of more small, rocky planets in the temperate zones around nearby stars.
