Astronomers have identified an exoplanet that orbits Barnard’s star, which is the nearest lone star to our Sun. This newly found exoplanet has a mass of at least half that of Venus, and a year on this planet lasts just over three Earth days. Additionally, the research team has detected signs suggesting there are three more potential exoplanets orbiting the same star.
Barnard’s star, located merely six light-years away, is the second-closest star system after the three-star Alpha Centauri group and is the closest individual star to Earth. Its closeness makes it a prime candidate for the quest for Earth-like exoplanets. Although a promising detection occurred in 2018, no planets around Barnard’s star had been verified until now.
The announcement of this exoplanet discovery, detailed in a paper released today in the journal Astronomy & Astrophysics, is based on five years of observations using ESO’s VLT at the Paranal Observatory in Chile. “It took a while, but we always believed we would uncover something,” declared Jonay González Hernández, a researcher at the Instituto de AstrofÃsica de Canarias in Spain and the study’s lead author. The team searched for signs of exoplanets within Barnard’s star’s habitable or temperate zone, the area where liquid water might exist on a planet’s surface. Astronomers often focus on red dwarfs like Barnard’s star because detecting low-mass rocky planets is easier around these smaller stars than around larger, Sun-like stars. [1]
The planet, designated Barnard b [2], orbits its star at a distance twenty times shorter than Mercury’s distance from the Sun. It completes an orbit in just 3.15 Earth days and has a surface temperature of approximately 125 °C. “Barnard b is among the lowest-mass exoplanets known and is one of the few with a mass less than that of Earth. However, it is too close to its host star, situated inside the habitable zone,” mentioned González Hernández. “Although the star is about 2500 degrees cooler than our Sun, the conditions there are too hot to support liquid water on the surface.”
The research team utilized ESPRESSO, a highly sensitive instrument designed to detect the wobble of stars caused by the gravitational influence of orbiting planets. Their findings were backed up by data from other exoplanet-detecting instruments, including HARPS at ESO’s La Silla Observatory, HARPS-N, and CARMENES. However, the new findings do not corroborate the existence of the exoplanet suggested back in 2018.
Alongside the confirmed exoplanet, the international team also found potential indications of three additional exoplanet candidates orbiting Barnard’s star. Yet, further observations with ESPRESSO will be necessary to confirm their existence. “We need to continue monitoring this star to validate other candidate signals,” commented Alejandro Suárez Mascareño, a researcher at the Instituto de AstrofÃsica de Canarias and a co-author of the study. “Nonetheless, the discovery of this planet, along with earlier findings like Proxima b and d, illustrates that our cosmic neighborhood is rich with low-mass planets.”
The Extremely Large Telescope (ELT) of the European Southern Observatory, currently under construction, is poised to revolutionize exoplanet research. The ELT’s ANDES instrument will enable scientists to identify more of these small, rocky planets in the temperate zones surrounding nearby stars, extending beyond the capabilities of current telescopes, and facilitate studies of their atmospheric compositions.
Notes
[1] Astronomers often concentrate on cooler stars, like red dwarfs, because their temperate zones are located much closer to the star compared to hotter stars like the Sun. This proximity enables planets within the temperate zones to have shorter orbital durations, which allows astronomers to track them over several days or weeks, rather than years. Additionally, since red dwarfs are significantly less massive than the Sun, they experience stronger gravitational shifts caused by their orbiting planets, leading to more pronounced wobbles.
[2] In scientific practice, exoplanets are typically named after their hosting star with a lowercase letter appended, where ‘b’ indicates the first discovered planet, ‘c’ the next one, and so forth. Thus, the name Barnard b was also assigned to a previously suspected planet candidate around Barnard’s star that could not be confirmed by scientists.
