On Wednesday, an international team of scientists in the Pale Red Dot campaign announced that the closest star to our solar system might just be our best bet at finding alien life.
The star, called Proxima Centauri, is a cool, dim red dwarf just four light years away.
It’s a thousand times fainter than the sun, and impossible to see with the naked eye.
Using data from ESO observatories and other telescopes, the scientists, led by Guillem Anglada-Escudé at Queen Mary University, picked up a small, potentially rocky planet, called Proxima b, that’s slightly more massive than Earth.
The team had been looking for looking for a “tiny back-and-forth wobble in the star caused by the gravitational pull of an orbiting planet,” according to a press release. The findings were published in Nature on Wednesday.
Smack in the middle of the habitable zone
Proxima b is about 4 million miles away from the star (just 5% of the distance between the Earth and the Sun) and completes its orbit every 11 days. That’s much closer than Mercury’s distance from the sun, but because Proxima Centauri is so cool and dim, the planet’s location puts it smack in the middle of its habitable zone, which means it has a temperature that might allow for liquid water.
Because the system is located so close, upcoming generations of large, ground-based telescopes and dedicated space missions will be able to directly image the planet and glean things like atmospheric composition and possibly even signs of life from the little light they detect.
“It’s extremely important that we found a small planet orbiting in the habitable zone of the closest star to the sun,” said Michael Endl from the University of Texas at Austin. “It opens up a whole array of exciting possibilities.”
Although Endl is not directly involved in the study, he had a personal stake in the star system. From 2000 until 2008, Endl and a team of other astronomers investigated Proxima Centauri. It was this research that helped scientists confirm the existence of Proxima b.
Mean red dwarfs
Proxima Centauri, like other red dwarfs, is an active star, and the scientists had to be careful because its ever changing brightness could fake the existence of a planet.
“These stars are kind of mean,” Endl said. “They can fake very tiny signals based on magnetic activity like sunspots and solar cycles.”
But the signal, Endl said, is like clockwork — it should always be there. So a huge component of this discovery was to show that the planetary signal is constant and present in all of Proxima Centauri’s data, because the planet and orbit of the planet don’t change.
When the scientists combined data collected from the Pale Red Dot campaign with earlier observations, they found a clear signal of the intriguing planet.
“I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign,”Anglada-Escudé said in an ESO press release. “The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper.”
Day and night
The planet is likely tidally locked to the star, which means the same side is always facing the star. That means that one side is in eternal darkness and one side is in eternal daylight.
Originally, systems like this were not considered good places to look for Earth-like planets because scientists thought their atmospheres would be heated up so much that any water on the day-side surface would boil off, and the night side would be so cold that the atmosphere would freeze out.
But, according to Endl, modern 3D climate models have shown that this is not the case. That’s because heat can be transported between the two sides.
Earth-like or not?
The planet’s mass, equal to about 1.3 Earths, suggests that the planet is terrestrial, which means it’s rocky and has a surface. That’s good news for the hunt for alien life. But scientists can’t really say whether or not the planet is Earth-like just yet. That’s because they don’t know if it has an atmosphere or liquid water.
The planet would also be more vulnerable to ultraviolet and X-ray flares from the star, and scientists still don’t know if it has a magnetic field to protect it from these high-energy charged particles.
According to Ansgar Reiners, a Pale Red Dot collaborator at the Institute of Astrophysics, these factors depend entirely on the formation and early history of the planet, which scientists don’t know much about just yet.
Scientists have a lot of work to do before they can say for sure if this planet is Earth-like, and it will be even trickier to find out if it’s home to alien life — something we’ve yet to confirm on any planet other than our own.
“Until we find signs of life on another planet we still have a very long steep road ahead,” said Sara Seager, a planetary scientist at MIT who has thoroughly studied exoplanet habitability.
The ‘long steep road ahead’
Scientists are already pushing forward to the next steps, trying to find out if the planet transits directly in front of the star. If this is the case, scientists will be able to measure starlight passing through the atmosphere and measure the chemical fingerprints of the atmosphere.
But according to Endl, there’s only a 1.5% probability that the planet is passing directly in front of the star. This means scientists will have to try to directly detect the planet and take images with enormous telescopes that will be built in the next decade or so.
Proxima Centauri is in the same cosmic neighbourhood as the sun-like Alpha Centauri system that, earlier this year, Stephen Hawking and Yuri Milner announced they were targeting with the Breakthrough Starshot project. And, according to Endl, this new finding could spur them to redirect some of their tiny, laser-powered spacecrafts to Proxima b.
If Breakthrough Starshot achieves its goal of propelling its spacecrafts to 20% the speed of light, it would take just 20 years to travel to the system. To put that into perspective, that’s how long it took NASA’s Voyager to reach Neptune, about 3 billion miles away.
“Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us,” Anglada-Escudé said. “Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next.”
Check Business Insider’s video about this awesome planetary discovery below: