Confirmed! Sun's Nearest Neighbor Has 'Earth-Like' World
The discovery of a small rocky exoplanet at Proxima Centauri brings the search for life beyond the solar system into our home turf.
The star closest to the sun is home to an Earth-sized planet with temperatures suitable for water -- if any exists -- to pool on its surface, a scenario that is believed to be favorable for life, research published Wednesday shows.
But don't pack your bags for Proxima b quiet yet. Although the 25 trillion-mile journey is a stone's throw by celestial yardsticks, it would take more than 112,000 years to get there traveling at 25,000 mph, the speed of the Apollo moon rockets.
Zipping along at 20 percent of the speed of light, however, which is the goal of Russian billionaire Yuri Milner's Project Starshot, the journey would take 20 years.
Upon arrival, you might not be able to breathe. Scientists do not know if Proxima b has an atmosphere, though computer models suggest it is possible. They also have no evidence that Proxima b, which is believed to be at least 1.3 times the mass of Earth, has any water.
WATCH VIDEO: What You Need To Know About Proxima b
"The biggest question mark for whether this is an Earth-like planet or not is whether there is water. That entirely depends on the formation, on the history of the planet," said astronomer Ansgar Reiners, with the University of Gottingen in Germany.
"You can come up with formation scenarios that end up with an Earth-like atmosphere, that end up with a Venus-like atmosphere, that end up with no atmosphere at all," he said.
Proxima b also is probably tidally locked to its mother star, with half its surface in permanent darkness and the other half in constant daylight. Outbursts from its parent star probably blast the planet with a barrage of high-energy X-ray and ultraviolet radiation, which might make life a challenge.
Even so, red dwarf stars like Proxima Centauri, the parent star to the newly found Proxima b, have become popular targets in the hunt for habitable worlds beyond the solar system. That is because a planet about the size of Earth in orbit around one of these small stars is proportionally larger and easier to find than similarly sized planets circling stars as big as the sun.
Proxima Centauri, for example, is less than 20 percent the mass of the sun.
Its planet, Proxima b, was discovered after painstaking efforts to understand a slight but regular shift in the wavelengths of light coming from Proxima Centauri, one of a trio of stars in the Alpha Centauri system.
Astronomers discovered that light from Proxima Centauri shifted every 11.2 days, as measured by the HARPS spectrograph on the European Southern Observatory's 3.6-meter telescope in La Silla, Chile, and simultaneously by other telescopes.
As early as 2013, an international team of scientists began to suspect that Proxima Centauri was being regularly tugged by the gravity of an orbiting planet, but since it is an active star they had to rule out other options, such as stellar flares.
In a paper published in Nature on Wednesday, the team confirmed that the star closest to the sun is indeed home to a potential cousin Earth. It also may have siblings, scientists said.
"We have found a terrestrial planet orbiting Proxima Centauri," said lead author Guillem Anglada-Escude, with Queen Mary University of London.
The discovery gives scientists the closest possible extrasolar planet to try to directly image, though current instruments are not yet good enough yet to separate out light reflecting off Proxima b from light radiating from the parent star.
With even a pixel of light from the planet, scientists can attempt to ferret out whether Proxima b has an atmosphere, water or other chemicals tied to life, such as methane.
As the closest star to Earth, Proxima Centauri already has received a lot of telescope time, including a cursory scan by astronomers looking for radio signals from potential extraterrestrial civilizations.
The star is only visible from Earth's southern hemisphere, so the SETI Institute has not been able to use its current array of telescopes in California to look for ET on Proxima Centauri, astronomer Seth Shostak told Seeker.com.
A decade ago, the SETI Institute used Australia's Parkes Observatory for a search for extraterrestrials, beginning with a quick look at the sun's nearest neighbors.
"We didn't hear anything, but maybe the Alpha Centaurians were being coy that day," Shostak said.
GALLERY: Meet Proxima b, Our Nearest 'Earth-Like' Neighbor
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