Hiding just six light-years away from our solar system, an exoplanet has been revealed to be orbiting the closest single star to Earth.
The world—dubbed Barnard b—is thought to have about half of the mass of Venus and has such a tight orbit that its year only lasts three Earth days.
It is the first to be discovered around the red dwarf Barnard's Star, according to a study published today in the journal Astronomy and Astrophysics.
While the three stars in the triple star system Alpha Centauri are actually closer at only four light-years away, Barnard's Star is the closest lone star to our sun.
The star is named after the American astronomer Edward Emerson Barnard, who measured its motion relative to the Sun back in 1916.
The exoplanet was spotted by astronomers using the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert.
"We have detected a sub-Earth planet with a mass about half of the mass of Venus, or about three masses of Mars, in an orbit of 3.15 days—so the year in this planet lasts for about only 3 days," paper author and astrophysicist Jonay González Hernández of the Instituto de Astrofísica de Canarias, Spain, told Newsweek.
He added: "Barnard's star is an isolated cool (red) star in the second closest stellar system to our Sun, after alpha Centauri stellar system."
Finding the world required more than four years of observations, González Hernández explained, adding: "It took us quite long to detect this tiny planet since the planet signal is quite weak and very difficult to detect."
Astronomers have long suspected that Barnard's Star may have planets, so focussed on the habitable zone around the star.
This is the region around a star where conditions are "just right" for liquid water to exist on a planet's surface—hence its other name: the Goldilocks zone.
The zone is of particular interest because planets there with the right atmospheric conditions could potentially harbor life.
Unfortunately, as Barnard b orbits its star twenty times closer than Mercury orbits our own sun, the newly-discovered world is simply too hot for life as we know it.
"Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth. But the planet is too close to the host star, closer than the habitable zone," González Hernández said in a statement.
"Even if the star is about 2500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface."
The planet was detected using a special instrument named ESPRESSO, which can measure the tiny wobbles that stars makes due to the gravitational pull of planets orbiting them.
The researchers think that there may be more planets orbiting Barnard's Star, and hope to examine the solar system further to catch a glimpse of them.
"There are some additional candidates that we have identified in the new data taken with the ESPRESSO instrument that still require more observations to be confirmed. Let's see what happens in the next years," González Hernández said.
"These signals point to an additional three planets that are also less massive than the Earth. All of them are closer to the habitable zone."
Regardless of whether there are indeed more planets around Barnard's Star, the researchers are excited that we have discovered a new exoplanet so close to our home planet. Thus far, only the two planets around Proxima Centauri are closer to Earth, as no planets have been detected around Alpha Centauri A or B.
"But the discovery of this planet, along with other previous discoveries such as Proxima b and d, shows that our cosmic backyard is full of low-mass planets," Alejandro Suárez Mascareño, a researcher also at the Instituto de Astrofísica de Canarias and co-author of the study, said in the statement.
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Reference
González Hernández, J. I., Suárez Mascareño, A., Silva, A. M., Stefanov, A. K., Faria, J. P., Tabernero, H. M., Sozzetti, A., Rebolo, R., Pepe, F., Santos, N. C., Cristiani, S., Lovis, C., Dumusque, X., Figueira, P., Lillo-Box, J., Nari, N., Benatti, S., Hobson, M. J., Castro-González, A., Allart, R., Passegger, V. M., Zapatero Osorio, M.-R., Adibekyan, V., Alibert, Y., Allende Prieto, C., Bouchy, F., Damasso, M., D'Odorico, V., Di Marcantonio, P., Ehrenreich, D., Lo Curto, G., Génova Santos, R., Martins, C. J. A. P., Mehner, A., Micela, G., Molaro, P., Nunes, N., Palle, E., Sousa, S. G., & Udry, S. (2024). A sub-Earth-mass planet orbiting Barnard's star. Astronomy & Astrophysics. http://dx.doi.org/10.1051/0004-6361/202451311
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