Astronomers have discovered an exoplanet roughly the size of Earth orbiting Alpha Centauri B, the star nearest our sun.
The Alpha Centauri system — composed of three stars orbiting one another — is only 4.4 light-years away, a cosmic stone’s throw from us. Though the newly discovered planet has about the same mass as our own, its orbit is 25 times smaller, so a year on this planet passes in just 3.2 days. This means the planet is sitting up against its star, roasting at perhaps 2,200 degrees Fahrenheit with a surface likely composed of molten lava.
While the new planet is probably devoid of life, many scientists see the discovery as a hopeful sign. It proves that at least one planet formed in the system, and perhaps other small planets exist there at the right distance to host life.
“Finding in our closest neighbor a one-Earth-mass planet really opens up the prospect for finding planets there in the habitable zone,” said astronomer Stephane Udry of the University of Geneva, one of the co-authors of the paper, which will appear in Nature on Oct. 17.
Because it is so close, the Alpha Centauri system has been a fertile place in authors’ imaginations, serving as the setting for the Transformer’s homeworld of Cybertron as well as the blue-skinned Na’vi’s homeworld of Pandora in Avatar. Though these science-fiction creations are, well, fiction, the system also has long drawn scientists searching for exoplanets. This one evaded detection because it is so small and its effect is so slight.
The team watched the Alpha Centauri system very carefully, looking for a characteristic wobble that indicated a planet was gravitationally tugging on one of the stars. The planet’s tiny perturbation caused the star to wobble at roughly one mile per hour. You walk faster than that.
Training their telescope at Alpha Centauri B, the team logged more than 450 days of observation. Their data was so precise, they could see sunspots on the star as well as the effects from giant solar flares. They had to rule out all these other possibilities and look for a repeated pattern indicating the existence of a planet.
“The amount of effort they’ve devoted to this star is pretty much unprecedented,” said astronomer Greg Laughlin of the University of California, Santa Cruz, who was not involved with the work. The team was lucky since Alpha Centauri B is a relatively quiet star and they eventually found a tiny signal in all the noise.
That Alpha Centauri B is so close is exciting to astronomers, said Laughlin. It means they can make follow-up observations to determine further characteristics of the new exoplanet. Though it would take 40,000 years to travel to the Alpha Centauri system using modern-day rockets, future means of propulsion might one day take probes to the distant world.
Luiz Buscapé Firmino Spencer Fisher Jon Fitch Kenny Florian Jesse Forbes
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