An icy exoplanet & from the super-earth & # 39; glimpsed around the nearby Barnard star

The single star closest to the sun is apparently hosting a large icy planet.

Astronomers have found solid evidence of an icy extraterrestrial world about 3.2 times more massive than the Barnard star surrounding Earth, a pale red dwarf located just 6 light years from the sun. The Barnard star is the nearest neighbor to our sun, apart from the Alpha Centauri three-star system, located about 4.3 light-years away.

The newly detected world, known as Barnard's Star B, remains for the moment a candidate for the planet. But the researchers who have spotted it are convinced that the extraterrestrial planet will finally be confirmed. [Gallery: The Strangest Alien Planets]

"After a very thorough analysis, we are 99% convinced that the planet is there," said Ignasi Ribas, of the Institute for Space Studies of Catalonia and the Institute of Sciences of Catalonia. Space in Spain, in a statement.

"However, we will continue to observe this moving star to rule out possible, but unlikely, natural variations of stellar brightness that could pose as a planet," added Ribas, lead author of a new study announcing the detection of Barnard's disease. Star b. This study was published online today (14 November) in the journal Nature.

Barnard's star b, if confirmed, will not be the closest exoplanet to the Earth. This designation is owned by Proxima b, a world about the size of the Earth, which revolves around Proxima Centauri, one of the Alpha Centauri trios.

NASA's Kepler Space Telescope has shown that small planets are common in the Milky Way galaxy. Together, Proxima B and Barnard's Star B strongly suggest that such "worlds" are also common in our neighborhood, "said Johanna Teske, co-author of the study, Department of Magnetism at Space.com. of the Carnegie Institution for Science in Washington, DC. "And it's super exciting."

An almost solar neighbor

Barnard's Star owes its name to the American astronomer E. E. Barnard, who discovered in 1916 the speed mentioned by Ribas. No other star moves faster in the Earth's sky than Barnard's star, which travels about the width of the full moon every 180 years.

This unprecedented apparent movement is a consequence of the proximity of Barnard's star and its high speed (without reaching a record) of 310,000 km / h (500,000 km / h) compared to the sun.

And Barnard & # 39; s Star is getting closer to us every day: in about 10,000 years, the Red Dwarf will take over the Alpha Centauri system. At this time, only 3.8 light-years apart will separate Barnard's star from the sun.

The Barnard star is about twice as old as the Earth's sun, with one sixth of mass and 3% of light. As Barnard's star is so dark, its "habitable zone" – the range of distances where liquid water may be possible at the surface of the world – is extremely close. Indeed, the researchers estimate that this zone is a brightness located between 0,06 AU and 0,10 AU of the star. (An astronomical unit, or astronomical unit, is the Earth-Sun distance – about 93 million miles, or 150 million kilometers).

The concept of habitable zone is of course delicate. To measure the true livability of a world, one must, among other characteristics, be familiar with its atmospheric composition and thickness. And such information is difficult to obtain for exoplanets.

A long search

Barnard's Star has long been a target of exoplanet hunters, but their searches have always remained empty – until now.

And the new detection was not easy: Ribas and his team analyzed huge amounts of data, both archival and newly collected, before finally unearthing Barnard's Star b.

They used the "radial velocity" method, which searches for changes in starlight caused by the gravitational tug of a planet in orbit. Such tugs are slightly swinging a star, shifting its light towards the red wavelengths at times and towards the blue end of the spectrum in others, as seen from the Earth. [7 Ways to Discovery Alien Planets]

"We used observations from seven different instruments, spanning 20 years of measurements, making it one of the largest and most comprehensive data sets ever used for accurate radial velocity studies," he said. Ribas in the same release. "The combination of all the data has led to a total of 771 measurements – a huge amount of information!"

Never before has the method of radial velocity been used to find such a small planet in such a distant orbit, said members of the study team. (Large, closely spaced planets drive their host stars more powerfully and therefore cause more dramatic and easily detectable light offsets.)

These seven instruments were the high-precision Search Radial Velocity Planet Searcher (HARPS) at the La Silla Observatory of the European Southern Observatory (ESO) in Chile; Ultraviolet and visual scale spectrograph on the very large telescope, at the Paranal observatory of ESO in Chile; HARPS-North at Galileo National Telescope in the Canary Islands; the High Resolution Scale spectrometer at the 10-meter Keck telescope in Hawaii; the Carnegie Institute's Planet Finder Spectrograph, at the 6.5-meter Magellan Telescope at the Las Campanas Observatory in Chile; the automatic planet finder at the 2.4 m telescope of the Lick Observatory of the University of California; and & CARMENES, at the observatory of Calar Alto in Spain.

The researchers also detected allusions to another possible planet in the system, orbiting farther away than the more distant Barnard star, with an orbital period of 6,600 terrestrial days. But this second signal is too weak to be considered a candidate for the planet, said Teske.

"There is not enough data," she told Space.com.

An icy super-land

Barnard's star b is at least 3.2 times more massive than our own planet, making it a "super-Earth" – the class of worlds considerably larger than Earth but smaller than "giants" ice "such as Neptune and Uranus.

The new study indicates that the new candidate planet is 0.4 UA from its host star and orbits every 233 days on Earth.

This orbital distance is similar to that of radiation-treated mercury in our own solar system. But since Barnard's star is so dark, the potential planet is all around the system's "snow line" – the area where volatile materials such as water can condense into solid ice.

"Until now, only giant planets had been detected at a distance as far removed from their stars," said Rodrigo Diaz, of the Institute of Astronomy and Space Physics of the National Council of Scientific and Technical Research and the University of Buenos Aires in Argentina. an accompanying article "News and Views" which was also published today in Nature.

"The discovery by the authors of a low-mass planet near the snow line is severely undermining the training patterns of this type of planet," added Diaz, who did not participate in the new study.

Barnard & # 39; s Star B, if it does exist, is not a very promising home for life as we know it, at least not on the surface. The potential planet is probably very cold, with an estimated surface temperature of minus 275 degrees Fahrenheit (minus 170 degrees Fahrenheit), the study team members said.

It is unlikely that the confirmation of Barnard's star b will come from additional radial velocity measurements, wrote Diaz. But very precise measurements of the position of the stars, such as those currently carried out by the Gaia spacecraft of the European Space Agency, could do well in the coming years, he added.

"Even more exciting, the next generation of ground-based instruments, which will also come into service in the 2020s, should be able to directly image the reported planet and measure its light spectrum," wrote Diaz. .

"Using this spectrum, the characteristics of the planet's atmosphere – such as its winds and speed of rotation – could be deduced," he added. "This remarkable planet is therefore a key element in the puzzle of the formation and evolution of planets, and could be among the first small-scale exoplanets whose atmospheres are explored in detail."

Mike Wall's book on extraterrestrial life research, "Out There" (Grand Central Publishing, 2018, illustrated by Karl Tate) has just been published. Follow him on Twitter @michaeldwall. follow us @Spacedotcom or Facebook. Originally posted on Space.com.