After more than 15 years of research, astronomers have confirmed the existence of a planet orbiting Proxima Centauri, the small red dwarf star located some 4.2 light years, or 25 trillion miles away, from Earth. This may seem far, but it’s extremely close in cosmic terms; other exoplanets (planets outside our solar system) considered “close” to Earth are some 40 light years away. The newly discovered planet is located in the habitable zone around Proxima Centauri, meaning that liquid water could potentially flow on its surface, raising the possibility for life.

It’s being called one of the biggest astronomical discoveries of the century: a potentially habitable Earth-like planet is orbiting the closest neighbor to our sun, a red dwarf star known as Proxima Centauri. Scientists with the European Southern Observatory (ESO) confirmed the planet’s existence yesterday in a new study published in the journal Nature, on the heels of rumors reported earlier this month in the German weekly magazine Der Spiegel.

This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in color like the Sun. (Credit:Digitized Sky Survey 2)
This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in color like the Sun. (Credit:Digitized Sky Survey 2)

Proxima Centauri, a small red dwarf star, has only about 12 percent the mass of the sun and about 1/600th the luminosity. It is so dim that it cannot be seen from Earth with the naked eye. Proxima Centauri is located in the star system Alpha Centauri, which also includes the larger but more distant binary star pair known as Alpha Centauri AB.

Some of the researchers involved in the new study began searching for hints of an exoplanet orbiting Proxima Centauri back in 2000. During the first half of this year, telescopes around the world were trained on the star, looking for the slight movement in the colors of the starlight, called a “Doppler wobble,” that would be caused by a gravitational planet in orbit. These observations, combined with the earlier research, data and published studies, enabled the astronomers to confirm the existence of a planet at least 1.3 times the mass of Earth that orbits Proxima Centauri every 11.2 days.

The newly discovered planet, dubbed Proxima b, is only about 5 million miles away from Proxima Centauri. By contrast, some 93 million miles separate Earth from the sun. Because Proxima Centauri is so much cooler and fainter than the sun, however, the temperature on Proxima b is low enough that water could potentially exist on its surface without evaporating, a vital condition for life.

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. (Credit: ESO / M. Kornmesser)
This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. (Credit: ESO / M. Kornmesser)

Scientists still can only speculate about whether liquid water does in fact flow on Proxima b, or whether the planet has an atmosphere. They also want to explore whether, like Earth, the planet has a magnetic field around it protecting it from some of the radiation it receives from its star. Some of the biggest questions they have are around how the planet formed: How close to the star was it at the time of formation? Did it initially have water, or did it form dry? Could its atmosphere have been destroyed by powerful radiation during formation?

Answers to these questions could determine if Proxima b has conditions similar to those of Earth, or if its conditions more closely resemble those of other planets, such as Venus (extremely hot) or Mars (cold and dry). As the astronomer Guillem Anglada-Escudé of Queen Mary University of London, who led the team that made the new discovery, said in a news conference: “There are viable models and stories that lead to a viable Earth-like planet today.”

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope. (Credit: Y. Beletsky / ESO / ESA / NASA/M. Zamani)
This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope. (Credit: Y. Beletsky / ESO / ESA / NASA/M. Zamani)

Despite its proximity to Earth, astronomers cannot view Proxima b with a telescope because it is lost in the glare of Proxima Centauri, but they hope the next generation of technology will change this in a decade or so. The researchers said the planet is a potential target for robotic exploration, a possibility that is already being explored by the Breakthrough Starshot Initiative, the privately funded effort led by Russian entrepreneur Yuri Milner, famed theoretical physicist Stephen Hawking and Facebook founder Mark Zuckerberg, among others. The project aims to create and send ultra-fast light-driven nanocraft (iPhone-sized spacecraft) to Alpha Centauri within two or three decades.

At the same time, programs such as Mission Centaur are also focusing on Alpha Centauri, seeking other potentially Earth-like exoplanets that may be orbiting the three stars in the system. The authors of the new study did encounter extra signals in some of their observations of Proxima Centauri, suggesting hints of other possible planets yet to be discovered.