Welcome to Proxima b, Our Nearest 'Earth-like' Neighbor

The historic discovery of a small rocky world orbiting our sun's nearest stellar neighbor could transform humanity's interstellar future -- but what does this alien world look like?

Astronomers of the Pale Red Dot campaign -- a project searching for hints of an alien world around our sun's nearest stellar neighbor -- have done it. They've not only discovered an exoplanet orbiting Proxima Centauri, they've discovered a world orbitingwithin the star's habitable zone. The habitable zone is the distance from any star at which it's not too hot and not too cold for liquid water to exist on a hypothetically rocky world.

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Now we know there's a rocky world inside Proxima's habitable zone, raising the question as to whether alien life may thrive there or if it could be our future interstellar target. But what does Proxima b look like? Here are some ideas:

This artist's impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our solar system -- "only" 4.25 light-years away. Included in view is the more distant Alpha Centauri AB binary star system that Proxima orbits from afar. Now that an alien world has been confirmed to be orbiting within Proxima Centauri's "habitable zone" and is most likely a small, rocky world slightly larger than Earth, speculation rumbles as to its "Earth-like" potential. However, we currently have no idea whether Proxima b has an atmosphere and, though liquid water could exist on its surface, we have no idea if water is even there. But it's a start.

Credit: ESO/M. Kornmesser

This artist's impression is an imagining of Proxima b's hypothetical rocky surface with a hazy atmosphere. From observations made by the ESO's La Silla Observatory, we know Proxima b is around 30% more massive than Earth, most likely making it a rocky exoplanet. But as it orbits so close to its star, the world would be ravaged by the small star's X-ray emissions and frequent flares, likely damaging its habitable potential. Interestingly, as Proxima b has a very compact orbit, it's likely tidally-locked (one hemisphere will always be facing the star).

Credit: ESO/M. Kornmesser

In this Digital Sky Survey 2 observation of the space surrounding Alpha Centauri AB, our closest stellar neighbor Proxima Centauri can be seen glowing red. Proxima Centauri is a small red dwarf star approximately 15% the diameter of our sun. This diminutive stellar object also has a "surface" temperature of 3,042 Kelvin (2,769C/5,016F), which is around half that of our sun. Its lower temperature means Proxima Centauri's habitable zone is much more compact than the sun's.

Credit: Digitized Sky Survey 2 Acknowledgement: Davide De Martin/Mahdi Zamani

As can be seen in this diagram, a comparison is made between the orbit of Mercury, the closest planet to the sun in our solar system, and Proxima b around Proxima Centauri. Proxima b is so close to its parent star that it completes one orbit every 11.2 days. As a comparison, Mercury takes 88 days to complete one orbit about the sun.

Credit: ESO/M. Kornmesser/G. Coleman

The ESO's 3.6-metre telescope at the La Silla Observatory in Chile is shown here with the locations of Alpha Centauri and Proxima Centauri in the night sky. The 3.6-meter telescope, and High Accuracy Radial velocity Planet Searcher (HARPS) instrument, studied the light from Proxima Centauri to detect the slight wobble the star experiences as Proxima b completes its orbit. From this signal, the exoplanet's orbital period and mass could be determined.

Credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani

Using the HARPS instrument, astronomers of the Pale Red Dot campaign watched these spectroscopic variations of Proxima Centauri as Proxima b orbited the star. This technique is so sensitive that it could detect the very slight motion of the star approach and recede from the Earth at a speed of only 5 kilometers per hour, around walking pace. From the Doppler shifting of the recorded light from January 1 for 90 days, an oscillating signal became clear, which represents the 11.2 day orbit of an exoplanet, 1.3 times the mass of Earth.

These Hubble Space Telescope observations show the binary system of Alpha Centauri (left) and their distant third sibling, Proxima Centauri. Although we currently know precious little about Proxima's newly-discovered world, we do know it orbits in the star's habitable zone and that it's most likely rocky -- two characteristics it shares with Earth. But for us to find out whether Proxima b is truly Earth-like, we need a dedicated astronomical campaign with advanced observatories so we can directly image it and decipher what its atmosphere is made of (if indeed it does have an atmosphere). But the mere fact that we have a possible "Earth 2.0" on our galactic doorstep is momentous and could invigorate an exciting interstellar future for humanity.

Credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani