Newly Discovered Closest Planet to Solar System Is Potentially Habitable

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An analysis of previously obtained observations and new Doppler data gathered with instruments from the European Southern Observatory (ESO)’s Pale Red Dot collaboration, confirmed that this exoplanet not only exists, but resides within the zone where its surface temperature could allow liquid water, a key ingredient for life on Earth. Many of the discovery observations were made using the ESO’s 3.6-meter telescope at La Silla Observatory in La Silla, Chile. The image on the right shows the southern skies over the ESO telescope with images of the stars Proxima Centauri (lower right) and the double star Alpha Centauri AB (lower left).

Proxima b is a rocky, terrestrial planet with a surface (not a ball of gas, like Jupiter), a minimum mass of 1.3 Earth masses, and in a close orbit of approximately 11.2 days with Proxima Centauri, the nearest star to the Sun. The proximity of its orbit is only 5% of the distance between the Earth and the sun, even closer than Mercury and the sun. However, because Proxima Centauri is much cooler and fainter than our sun, Proxima b would have a temperature suitable for liquid water to exist on the surface without evaporating.

Proxima Centauri coexists with a binary star in Alpha Centauri, a well-observed star system that serves as a close neighbor to our sun. Though Proxima Centauri is a redder and cooler star than our Sun, one of the other two stars in the Alpha Centauri star system is very similar to it.

Proxima b is a mere 4.25 light-years away from our solar system, or 266,000 times the distance between the Earth and the sun, which are 92.96 million miles apart. Although seemingly unlikely at this point, if intelligent life does exist on Proxima b, it is close enough to Earth for two-way communication. The record for “solar system’s closest exoplanet” was previously held by rocky exoplanets discovered orbiting TRAPPIST-1, an ultra-cool red dwarf star 40 light-years away from the solar system.

“It’s not only the closest terrestrial planet found, it’s probably the closest planet outside our solar system that will ever be found because there is no star closer to the solar system than this one,” said lead study author Guillem Anglada-Escudé.

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There is some debate over whether this planet is like Earth, which comes with some connotations. Depending on its formation, perhaps it could be like Venus.

Researchers estimate that if Proxima b has an atmosphere, which could be assumed but isn’t yet known, the temperature on the surface may be between 86º to 104º Fahrenheit (31º to 40º Celsius). Without an atmosphere, it could be between -22ºF to -40ºF (-30ºC to -40ºC). To put that in perspective, Earth would be -4ºF  (-20ºC) if it didn’t have an atmosphere, according to study author Ansgar Reiners.

The researchers are also unsure whether, like Earth, Proxima b has a magnetic field protecting its surface by deflecting charged particles of stellar winds and cosmic rays, and other harmful radiation. The habitability of a planet like Proxima b is “a matter of intense debate,” according to the study. There are numerous arguments against it, such as: tidal locking, strong stellar magnetic fields, strong flares, and high ultraviolet and X-ray fluxes. However, none of those factors have been proven to be definitive.

Learning the answers to these questions about formation are possible with research. Researchers have long looked to Alpha Centauri for study, and more recently, to visit. Programs like Mission Centaur seek to design and build a space mission with a small telescope to point at the Alpha Centauri star system. It would look for exoplanets by imaging or other techniques that could find more of them around these three stars. Many researchers hope to someday be able to actually image these exoplanets, gathering an idea of their atmospheric makeup and surface composition.

“We know that there are terrestrial planets around stars. The excitement is because it’s the nearest one, and we expect to characterize it and maybe visit in a couple of centuries,” Anglada-Escudé said.

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