Meet the new planet next door

The planet Proxima Centauri b is awash in pale light from a red dwarf star, as seen in an artist's illustration.
 

Meet the New Planet Next Door:

Since 1988, scientists have found more than 3,000 planets orbiting stars other than our sun. The newest addition is Proxima Centauri b, a small, rocky world just 4.24 light-years away, which may be in a habitable orbit.  The data suggest Proxima b is 1.3 times Earth's mass and takes 11.2 days to orbit its star, putting it in the region where the star’s feeble light is warm enough to keep any surface  water flowing. This is often called the Goldilocks region.                                                         

Small planets sometimes generate gargantuan buzz. For weeks, eager media outlets have been reporting rumors that a potentially habitable planet is circling the star closest to our sun, a red dwarf called Proxima Centauri.

Now, finally, astronomers are ready to unveil this alien world. Observations made with a telescope in Chile have indeed revealed a planet about as massive as Earth that orbits Proxima Centauri, which is a cosmic walk to the corner store at just 4.24 light-years away. And if conditions are right, the planet is in an orbit that’s warm enough for liquid water to survive on its surface.

Illuminated by a pale reddish light, the world orbits the smallest star in a triple system known as Alpha Centauri, which shines in the southern constellation Centaurus.

The Alpha Centauri system, long a wonderland for science fiction authors, is often considered a destination for humanity’s first leap into interstellar space—as well as a potential haven for future civilizations fleeing the inevitable destruction of Earth as we know it.

“A habitable, rocky planet around Proxima would be the most natural location to where our civilization could aspire to move after the sun will die, five billion years from now,” says Avi Loeb of the Harvard-Smithsonian Center for Astrophysics and an adviser to the Breakthrough Starshot project.

Even before today’s announcement, Breakthrough Starshot had announced its plan to send tiny spacecraft to the Alpha Centauri system later this century. But don’t expect any postcards from the new planet anytime soon: It will take more than 20 years for a spacecraft traveling at a monstrous 20 percent of the speed of light to reach Proxima Centauri, and another 4.24 years for any data to arrive back on Earth.

 

Based on data collected over 54 nights, the signature of the planet is strong, popping out even when the data are inspected by eye and not a computer algorithm.

“It’s pretty unambiguous,” says Yale University’s Greg Laughlin. “This isn’t a case where you kind of have to resort to black arts to pull the signal out.”

Finding Proxima

Known as Proxima b, the planet was discovered by a team of scientists working on the Pale Red Dot project—a twist on Carl Sagan’s description of Earth, which looks like a pale blue dot from afar.

Scientifically, the discovery is not exactly a surprise. The last decade of exoplanet discoveries has revealed that red dwarf stars like Proxima are very likely to host planets, and a large fraction of those worlds should be somewhat like this new one: small, rocky, and warm enough for water to flow on its surface.

While earlier searches for planets around Proxima had officially turned up empty, there were tantalizing signs that at least one planet could be there, waiting to be detected with a more comprehensive search.

As a planet goes about its orbital business, its gravity tugs ever so slightly on its star, causing the star to wobble. Larger planets naturally produce bigger wobbles. Smaller, Earth-mass planets tug almost imperceptibly on their stars, requiring long observing campaigns with extremely sensitive instruments to detect.

Observations taken sporadically between 2000 and 2014 had hinted at the presence of a planet in an 11-day orbit around Proxima, but its shaky signature wasn’t clear enough to be anything more than a tease. Determined to see if a planetary hand really was the source of Proxima’s wobbles, the Pale Red Dot team aimed Earth’s sharpest wobbly-star watcher, the High Accuracy Radial velocity Planet Searcher (HARPS), at the red
dwarf earlier this year.


There are even signs that Proxima b could have siblings: One additional signature in the data could be the work of a super-Earth on a 200-day orbit, Anglada-Escudé says, but the team will need to do more work to determine the signal’s origin.


When Worlds Align

In addition to ruling out false alarms, one of the most popular ways of validating a planet is to find it using a different detection method. Already, scientists are aiming Canada’s MOST space telescope at Proxima and looking to see if its planet transits, or crosses the face of its star as seen from Earth.

“If it does transit, that would be an extraordinary home run. I don’t think it gets any better than a transiting, Earth-size planet in the habitable zone orbiting the nearest star—unless there’s a radio broadcast emanating from it,” Laughlin says.