The Closest Star to Us Also Has an Earth-Sized Planet Orbiting It

This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our solar system. ESO/M. Kornmesser

Researchers have confirmed that our sun's nearest celestial neighbor — Proxima Centauri — has a planet in tow. And from here, it looks a lot like Earth.

The planet, according to research published this week in the journal Astronomy & Astrophysics, boasts a mass of 1.17 Earth masses and orbits its stars in a brisk 11.2 days. It's also in the so-called "Goldilocks zone" — meaning it holds to an orbit that’s neither too hot nor too cold for the possibility of liquid water.

And liquid water, of course, is something of a holy grail in the search for life beyond our planet. Not only that, but at 4.2 light- years away, it's relatively close. That proximity is why the existence of the planet, Proxima b, was already suspected back in 2013, according to The Independent.

Its confirmation came courtesy of ESPRESSO, a new-generation spectrograph that’s mounted on the aptly named Very Large Telescope in Chile. Short for Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, ESPRESSO is considered the most precise planet-hunting sensor in operation. It's the successor to HARPS, a similar, but much more limited instrument.

"We were already very happy with the performance of HARPS, which has been responsible for discovering hundreds of exoplanets over the last 17 years," Francesco Pepe, the University of Geneva astrophysicist who heads the ESPRESSO program, explains in a press release.

"We're really pleased that ESPRESSO can produce even better measurements, and it's gratifying and just reward for the teamwork lasting nearly 10 years."

ESPRESSO can measure the radial velocity of stars like Proxima Centauri with an accuracy of 11.8 inches per second — sensitive enough to determine if a star has any rocky planets in its entourage.

And sure enough, when trained on Proxima Centauri, ESPRESSO sniffed out a promising planet. Although it's a lot closer to its host star than Earth is our own sun, it basks in about the same amount of energy. That means its surface temperature could be comparable, which in turn, raises the possibility that water flows there.

But there's a catch. Proxima Centauri isn't like the sun we know. As a red dwarf, it's constantly radiating X-rays — several hundred times more than what we receive here on Earth.

If there's life on Proxima b, it has found a way to overcome that steady bombardment. Or, as the researchers, suggest, the planet itself may have developed its own X-ray shielding atmosphere.

"Is there an atmosphere that protects the planet from these deadly rays?" study co-author Christophe Lovis muses in the release. "And if this atmosphere exists, does it contain the chemical elements that promote the development of life (oxygen, for example)? How long have these favourable conditions existed?"

While Earth-like planets are being discovered with increasing frequency — thanks to new, more powerful telescopes and sensory equipment — the confirmation of Proxima b is a particularly exciting development.

Mostly because it's so close — just a hop, skip and a 4.2 light-year rocket ride away. And also because it points to even more exciting discoveries in the future, thanks to ESPRESSO's planet-hunting prowess.

"ESPRESSO has made it possible to measure the mass of the planet with a precision of over one-tenth of the mass of Earth," Nobel-Prize-winning physicist Michel Mayor notes in the release. "It's completely unheard of."