A Frozen Super-Earth Has Been Found in a Neighboring Star System

Olive Hawkins
November 15, 2018

The newly detected planet orbiting Barnard's Star may not be so hospitable, with surface temperatures of perhaps minus 274 degrees Fahrenheit (minus 170 degrees Celsius).

Graphic representation of the relative distances to the nearest stars from the sun.

Although it is about as close to its own star as Mercury is to our sun, scientists say it is probably as cold as Saturn.

The red dwarf star itself emits only about 0.4% of our sun's radiance, so the planet receives about 2% of the intensity that Earth receives from its sun.

But the new discovery is exciting for other reasons.

Nearby planets like this are likely to be prime targets in the search for signatures of life, using the next generation of telescopes. As they report today in Nature, they found that the star's light oscillated every 322 days, implying a planet orbiting with a 322-day year. (There was one approach that suggested the signal wasn't real, but that analysis is known to produce false negative results.) The strength of the signal also increased as new observations were added, reinforcing indications that it's real. "It is only by combining data and working collaboratively that this very challenging detection was possible". Most exoplanets, including the thousands identified by NASA's recently retired Kepler space telescope, were found using the "transit" technique: looking for a periodic dip in starlight as a planet passes in front. That means its "habitable zone" is extremely compact, and the exoplanet orbits beyond the star's "snow line".

It´s thought that Barnard´s Star is tearing through space at around 500,000 km/h, making it the fastest-moving known object in the universe.

Now, this cold Super-Earth is the second-closest known exoplanet to Earth, after Proxima Centaur b. In the 1960s, the Dutch astronomer Peter van de Kamp, working in the U.S., published his evidence for a planetary companion, based on perturbations in the motion of the star. 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.

However, as astrometry measurement techniques became more precise, scientists found that the supposed signals of Van de Kamp's two planets did not exist after all.

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A potentially rocky super-Earth orbits one of our closest stellar neighbors, Barnard's star, only 6 light-years away.

The magnitude of the wobble reveals the minimum mass of the planet that is responsible for the motion.

"With the radial velocity method, precision spectrometers are used to measure the Doppler effect".

This discovery pushes the bounds of what we can do with our best current astronomical instrumentation, so the authors are understandably cautious in claiming a "planet candidate", rather than a confirmed discovery.

This particular discovery was possible only because the research team was able to examine hundreds of measurements that had been made over 20 years, he said. But that method detects only the small fraction of planets that cross their star's face when viewed from Earth.

The subtle wobble of the star has caught the attention of astronomers for some time.

In the 1930s, Dutch-American astronomer Peter van de Kamp began a quest to study Barnard's star that lasted for most of his 93 years.

The European Space Agency's Gaia Space Observatory may be able to make detections that would further confirm the presence of a planet around Barnard's Star, he said, but those data aren't expected to be released until the 2020s.

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