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Artist's impression of this newly-discovered planet orbiting lone star Barnard. ESO/M
Spanish researchers discover small planet orbiting lone star closest to the Sun
Astronomy

Spanish researchers discover small planet orbiting lone star closest to the Sun

Located six light years away, Barnard b is much smaller than Earth

Judith de Jorge

Madrid

Saturday, 5 October 2024, 11:46

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A team led by Spanish researchers has discovered a planet orbiting Barnard, the closest single star to our Sun, located only six light years away. Called Barnard b, this new exoplanet (planets beyond our solar system, also called extrasolar planets) is much smaller than planet Earth and one of the known planets with least mass. Situated very close to its star, its year lasts little more than three Earth days. Conditions on that planet are hellish, but it may not be the only one. The team's observations also point to the existence of three other candidates around the same lone star that could be classed as planets

Barnard's star is the second closest star system (after the three-star cluster of Alpha Centauri) and the closest single star to us. Because of its proximity it is a prime target in the search for Earth-like exoplanets. Despite a promising identification in 2018, so far no planets have been confirmed orbiting around it.

The discovery of this new exoplanet - announced in an article published on Tuesday in the journal Astronomy & Astrophysics - is the result of observations made over the past five years with the Very Large Telescope (VLT) at the European Southern Observatory (ESO Chile) located at the Paranal Observatory in Chile.

The team was looking for signs of possible exoplanets within the habitable or temperate zone of Barnard's star, the range where liquid water can exist on the planet's surface. Red dwarfs like Barnard's star are often targeted by astronomers as low-mass rocky planets are easier to detect there than around larger Sun-like stars.

Feeling hot, hot, hot...

Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of the Earth, but it is twenty times closer to its star than Mercury is to the Sun, which means that its tight orbit lasts only 3.15 Earth days. Because it is so close its average surface temperature reaches 125C. "We think that one side of the planet faces Barnard permanently, so it would be much hotter still, while the other side would be much cooler. These conditions make it much closer to Mercury than to Earth. There is no way we can talk about habitability," as Alejandro Suárez Mascareño, researcher at the Instituto de Astrofísica de Canarias (IAC) and co-author of the study, explained to this newspaper. Although the star is about 2,500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface.

Finding Barnard b "has been quite difficult because it is very small, much smaller than Earth," said the astrophysicist. For their observations the team used Espresso, a high-precision instrument designed to measure the wobble of a star (its motion) caused by the gravitational pull of one or more orbiting planets. This is called the radial velocity method. "The planet slightly moves its star as it revolves around it. We measure the change in the star's velocity, and if the signal repeats over and over again, there is a planet. In this case, there is a repeated signal of half a metre per second, less than two km per hour. By comparison, the speed of a person walking is five or six km per hour."

The results obtained from these observations were confirmed by data from other instruments also specialised in the search for exoplanets: HARPS at ESO's La Silla Observatory, HARPS-N , Roque de Los Muchachos Observatory (La Palma), and Carmenes , at Calar Alto Observatory in Almeria.

A quadruple system?

In addition to the confirmed planet of Barnard b, the international team of astronomers also found indications of three other exoplanet candidates orbiting the same lone star. These candidates, however, will require further observations with Espresso Star Wobble - to give it its full name - to be confirmed. "We now need to continue observing this star to confirm the other candidate signals. If we succeed, it would be a spectacular system," said Suárez Mascareño.

For this researcher, "the discovery of this planet, together with other previous discoveries - such as the Proxima b and d worlds,+ about four light years away - suggests that our solar system neighbourhood is very rich in planets and systems. We are now finding many Earth-like and even smaller planets." For this reason, "I am confident that we will soon find nearby Earth-like planets in Sun-like stars."

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