Discovered: Frozen Super-Earth orbiting closest single star to our own

Greg Lawrence
November 17, 2018

Astronomers discovered a frozen exoplanet, sometimes larger than Earth, orbiting around a star only 6 light-years away.

Artist's impression of Barnard's Star b under the orange-tinted light from its red dwarf host.

At almost 6 light-years away, the star is the next closest star to the Sun after the Alpha Centauri triple stellar system.

"Barnard's star has a rather bad reputation among astronomers - in the past, many people have repeatedly talked about the discovery of planets around her, and all these statements were later refuted". Known as a "super-Earth", the planet (designated Barnard's Star b, or GJ 699 b) is thought to be at least 3.3 times the mass of Earth and orbits its star once every 233 days.

The planet's surface temperature is estimated to be around minus 170 degrees Celsius, meaning it is likely to be a frozen world which is uninviting to Earth-like life, they said. "If this planet had an atmosphere, maybe that could keep the surface temperature warmer", Teske added. This type of analysis, known as the radial velocity method, led to the very first detections of extrasolar planets in the mid-1990s. But, despite being so close to its star, light from Barnard's Star provides the exoplanet with only 2 percent of the energy that the sun provides Earth. When the planet moves closer to the star, the starlight is shifted toward shorter, blue wavelengths (called blueshift) and when the planet moves farther away from the star, the starlight shifts toward longer, red wavelengths (called redshift). This makes Barnard's Star b a prime candidate for us to use powerful spectroscopic techniques to, one day, peer into its atmosphere (if it has one) and understand what it's really made of. This breakthrough - announced in a paper published today in the journal Nature - is a result of the Red Dots and CARMENES projects, whose search for local rocky planets has already uncovered a new world orbiting our nearest neighbour, Proxima Centauri.

That seemed to be the case when a team of researchers started checking archival data for Barnard's star images. As it orbits one of the Solar system's closest neighbours, it presents a flawless target for future observations. The idea is that the gravity of a planet orbiting that star would cause the star to shift its position ever so slightly compared with more distant background stars.

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For now, the planet is called Barnard star b, it is the second nearest planet to the Earth outside our solar system.

"Tantalisingly, super-Earths like Barnard's Star b probably sustain geothermal activity for longer than their lower mass counterparts". Furthermore, current theories of planetary formation predict that the snow line is the ideal location for such planets to form. Since that time we've found thousands, and they exist around many different kinds of stars. More recently, most exoplanets have been detected using a different technique known as the transit method. It is so close that the next generation of telescopes may be able to image it directly, the researchers said.

Rodrigo Diaz, an astronomer at the University of Buenos Aires who was not involved in the new work, said that, while the findings are promising, he'd still like to see more evidence of the new planet's existence.

The dimness of Barnard's Star also explains the difficulty and the slight uncertainty surrounding the detection.

"The star is named in honor of the great American astronomer Edward Emerson Barnard, who was a pioneer of stellar photography and astrometry", Butler said.

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