Earth-size planet discovered around nearest stellar neighbor
An international team of scientists working with the European Southern Observatory (ESO) in Chile has published a paper in the journal Nature reporting a rocky planet approximately 1.3 times the size of Earth has been detected orbiting Proxima Centauri, a small red dwarf star 4.2 light-years from Earth.
Finding a planet over 25 trillion miles away may not seem like a big deal. However, in astronomical terms, that’s practically next door. Proxima b, the new world, is an important find for a number of reasons. It is close to Earth in stellar terms. Its composition is rocky, like Earth. Finally, it is at the right distance from the red dwarf star.
As Proxima Centauri is smaller and cooler than the Sun. Because of this, the habitable zone is much closer to the host star. This infographic compares the orbit of Proxima b with that of Mercury. (Click to Enlarge) Image Credit: ESO
The Goldilocks Zone
Earth is the only planet in the universe known to support life. As such, scientists have been searching for worlds with characteristics similar to it in the hopes of finding alien life. These characteristics include surface temperature, planetary size, and the presence of liquid water.
Proxima b orbits in a region around Proxima Centauri called the “Goldilocks zone”. This is a cute science term describing the right distance from the host star to allow liquid water on a planets’ surface, assuming it has an atmosphere similar to Earth’s.
Proxima Centauri is a much smaller, dimmer star compared with the Sun. It has a surface temperature of around 5,400 degrees Fahrenheit (3,000 degrees Celsius). The Sun’s surface temperature is nearly 11,900 degrees Fahrenheit (6,600 degrees Celsius). Additionally, the red dwarf star has a luminosity only 0.17 percent of the Sun’s.
As a result of all of this, Proxima’s Goldilocks zone is much closer than it is for the Sun’s. One consequence of this is a ‘year’ is much shorter. While Earth takes just over 365 days to circle the Sun, Proxima b zips around in its orbit in just 11.2 days.
How do you find a planet four light-years away?
Humanity has been able to detect planets around other stars since 1995. However, it is not possible to see them directly yet. Stars are just too bright and planets too dim for current instruments to see them. Instead, astronomers have found other methods for exoplanet hunting.
Proxima b was found using the radial velocity method, which studies a star’s movement around its center of mass, measuring Doppler shift changes its spectrum. As the star moves away from Earth, the spectrum of light it emits shifts toward the red end. Its spectrum shifts toward blue when it moves toward Earth.
Orbital telescopes, such as Kepler, and Earth-based telescope systems, like ESO, have located over 3,000 planets outside of the Solar System.
What happens next?
An infographic showing the size of the stars in the Alpha Centauri system compared to other stars, the Sun, and Jupiter. Image Credit: ESO
Guillem Anglada-Escudé, an astronomer at Queen Mary University of London and leader of the team that made the discovery, told Nature, “The search for life starts now.” Unfortunately, current technology is a long way off from being able to send a spacecraft to drop by Proxima b for a visit. So what can be done about this discovery right now?
Spaceflight Insider spoke with two authors who have extensive experience writing about interstellar travel. Paul Gilster, author of the Centauri Dreams blog, was enthusiastic about the Proxima b discovery.
“This is a really big deal,” Gilster said. “Finding a planet not much more massive than the Earth around Proxima Centauri, the nearest star, implies that a lot of red dwarfs have small planets.”
Gilster believes in the next 10 to 20 years, telescopes will be able to investigate the atmospheres of exoplanets and search for signs of life. He said the next logical step would be a fly-by mission of a nearby star because a spacecraft capable of slowing down near another star would have to carry too much fuel. Several organizations have done studies on interstellar probes, including the British Interplanetary Society and a donor-funded venture known as the Breakthrough Starshot initiative.
However, Gilster did not think Proxima b will be the first star human beings would send a probe to.
“Proxima b is probably tidally locked [always having one side facing the star] and Proxima Centauri is an active flare star, emitting a lot of X-rays,” Gilster said. “Alpha Centauri A and B are much more like our Sun.”
Still, Gilster did not discount the potential for life at Proxima b. He said the radiation from solar flares could serve as an evolutionary spur for life and it could have a magnetic field. This could protect life much like Earth’s Van Allen belts do.
Gilster sees the potential for sending multiple miniature space probes to Alpha Centauri A and B as well as Proxima Centauri. These probes would be attached to small microwave- or laser-powered sails and travel at speeds approaching 20 percent of the speed of light.
Gilster suggested the private sector, using private donations, could provide the sustained funding needed for a mission’s initial groundwork.
“However, if scientists find something really interesting,” Gilster said, “it could be a combination of governments and private organizations sending vehicles to the stars.”
Les Johnson is an aerospace engineer, author, a founding member of the Tennessee Valley Interstellar Workshop, and editor of Going Interstellar, an anthology of fiction and nonfiction stories about interstellar travel. Like Gilster, he thinks the Proxima discovery is very exciting. However, he was a bit more cautious.
“Just because it’s a rocky planet in the habitable zone doesn’t mean there’s anything (life-like) there,” Johnson said. “When I hear about this object being relatively close, I want to laugh. Even at ‘relatively close’, it’s almost impossibly far away. The Moon is around 250,000 miles away. Proxima Centauri is 250,000 astronomical units away. But it’s not impossible.”
For Johnson, the next important step would be to get more data. He favors developing bigger, better telescopes like the NASA starshade project, which would allow us to actually see exoplanets. Beyond that? He believes investments need to be made in advanced propulsion technologies that can send spacecraft there.
“Right now we’re decades or a century away from that,” Johnson said. “This is not something that’s going to happen next year. I don’t see how you make a business case for sending a probe to another star, but we should be doing it, and it’s exciting.”
Bart Leahy
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.
I am glad we are looking further afield for potential planets that may be habitats for us in the future. We need goals to speed us on in generating scientific plans to overcome current obstacles hindering completion of realistic goals that are being projected.