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Proxima b may have ocean that could sustain life

Artist's impression of the planet Proxima b orbiting Proxima Centauri.

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 the Solar System. The double star Alpha Centauri AB also appears in the image. 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. (Click for annotated full view) Image & Caption Credit: ESO / M. Kornmesser

Proxima Centauri b (Proxima b), the exoplanet closest to the Solar System, may be covered by an ocean of liquid water capable of sustaining life.

Located 4.25 light-years from Earth, Proxima b was discovered in August of this year orbiting the small red dwarf star Proxima Centauri, one of three stars that make up the Alpha Centauri system. The planet is located in the habitable zone of its low mass star, which has just 12 percent the mass of our Sun and 0.1 percent of its brightness.

Because Proxima Centauri is so much fainter than the Sun, its habitable zone is 25 times closer than that of our host star.

Proxima b orbits its star at a distance of 4.6 million miles (7.4 million km), just one-tenth of the distance at which Mercury orbits the Sun. This means that like Mercury and other planets in very close orbits around their stars, Proxima b is likely tidally locked, with one side always facing the star and the other always facing away from it.

On Mercury, tidal locking produces huge temperature extremes, with the Sun-facing side reaching temperatures of 801 degrees Fahrenheit (427 degrees Celsius) and the other side being extremely cold, with temperatures as low as –279 degrees Fahrenheit (–173 degrees Celsius), making the planet unlikely to be capable of hosting liquid water on its surface.

Artist's impression of the planet Proxima b orbiting Proxima Centauri

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Image & Caption Credit: ESO / M. Kornmesser

However, this is not the case for Proxima b, which scientists suspect is a rocky world.

A group of researchers, led by scientists at Marseille Astrophysics Laboratory in France, calculated the size and surface properties for Proxima b. Their results indicate that in spite of being tidally locked, the planet could be completely covered in liquid water capable of hosting microbial life, much like the icy moons orbiting Jupiter and Saturn in our own solar system.

The results of their study will be published in an upcoming issue of The Astrophysical Journal Letters.

“[T]he planet could be an ‘ocean planet’, with an ocean covering its entire surface, and similar water to some icy moons around Jupiter or Saturn,” the researchers said in a statement. “Contrary to what one might expect, such proximity does not necessarily mean that Proxima b’s surface is too hot for water to exist in liquid form.”

Unlike Proxima b, our solar system’s icy moons have their oceans underground rather than on the surface.

Two separate computer simulations carried out by the research team show Proxima b having a thin atmosphere along with temperatures that stay cool enough for liquid water to exist on the surface.

An atmosphere can circulate warmth from the hot side of the planet to the cold side as well as prevent water from boiling away into space.

The computer models simulated Proxima b’s composition based on an estimate of its apparent size, with a possible radius ranging between 0.94 to 1.4 that of Earth.

At 0.94 Earth radii, the planet’s radius would be 3,722 miles (5,590 kilometers), resulting in the planet being very dense, with a metallic core comprising two-thirds of its mass, surrounded by a rocky mantle.

Under those circumstances, any water on the surface would make up just 0.05 percent of the planet’s total mass, a situation similar to that of Earth, whose surface water comprises 0.02 percent of its mass.

In contrast, a radius 1.4 times that of Earth or 5,543 miles (8,920 kilometers) would result in Proxima b having a rocky core that comprises 50 percent of its mass surrounded by an ocean that makes up the other 50 percent.

“In this case, Proxima b would be covered by a single, liquid ocean 200 km (124 miles) deep,” the researchers stated.

Before the discovery of Proxima b, the closest known habitable exoplanet was Wolf 1061c, located 14 light-years from Earth. Scientists hope to learn more about Proxima b’s atmosphere with the James Webb Space Telescope, scheduled for launch in 2018. The telescope will analyze light coming from the star system.

Russian billionaire Yuri Milner recently announced plans to use lasers to propel tiny satellites or nanocraft to Proxima Centauri at a significant fraction of the speed of light, a trip that he estimates would take just 20 years.

Video Courtesy of Breakthrough



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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