Today, a little over two decades since the first confirmation that planets beyond our solar system actually exist, comes the biggest exoplanet announcement yet -- one that could change everything.
Researchers have discovered an Earth-like planet orbiting a red dwarf star at a range where conditions might be right for water, and maybe, just maybe, life. Proxima Centauri, at just over 4 light-years away, is the closest star to Earth besides our own sun.
"Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analog and succeeding has been the experience of a lifetime for all of us," Guillem Anglada-Escudé of Queen Mary University of London, said Wednesday in a statement.
Anglada-Escudé led the Pale Red Dot project, an outreach campaign that invited the public to follow along on the team's search for "another earth" around our nearest stellar neighbor. The project comes to a historic end with Wednesday's official announcement and publication of a paper detailing the discovery in the journal Nature, which also features the planet on the cover.
The confirmation of a potentially habitable planet so close to our stellar neighbor gives scientists around the globe a new target of study that's just around the corner, cosmically speaking. And that, in turn, could help answer a number of fundamental questions some of the rest of us like to chew on -- about how planets and life form, for example, not to mention that big one we're still chasing: Are we alone?
"I see this as one of the most important exoplanet discoveries in the last 15 years," Columbia University astronomer David Kipping said in an email.
Proxima b, the planet's nondescript name for the time being, was spotted using Doppler measurements, the same technique used to identify the very first exoplanet in 1995. As the below video from Nature explains, those measurements track slight shifts in the color of starlight coming from a distant star, which can be caused by a nearby planet's gravity tugging on its star.
Anglada-Escudé and the Pale Red Dot team analyzed Doppler data for Proxima Centauri from the European Southern Observatory collected between 2000 and 2014, as well as their new observations from the first three months of this year using the HARPS spectrograph on the ESO 3.6-meter telescope in Chile.
According to Anglada-Escudé, the first hints of a possible planet were spotted in 2013, but the detection was unconvincing. The Pale Red Dot campaign was launched to gather enough additional observations to confirm the existence of the closest possible exoplanet and it quickly yielded exciting results.
"I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign," he recalls. "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."
The team completed its observations before April and began working up a summary of their findings for publication. By the end of May, the paper had been submitted for peer review and the campaign essentially went into quiet mode.
From all the years of data, the team was able to deduce the presence of a planet orbiting at a distance of 7.5 million kilometers (4.7 million miles) and orbiting every 11.2 days.
Novice space nerds will note this planet is almost five times closer to its star than Mercury is to our star and wonder how that could possibly place it in the habitable zone. Keep in mind that Proxima Centauri is a red dwarf star that's closer in size to Jupiter than the sun, which also means that it is dimmer and cooler than what we're used to, making its habitable zone much closer in.
There are significant hurdles to the prospect of life on Proxima b, like the fact that it is likely tidally locked to its star, meaning one side is always facing its sun, while the other is forever cold and dark. And then there are the flares.
"The biggest downside of Proxima Centauri for alien hunters is that it's a flare star, dramatically and unpredictably varying in brightness over the course of a few minutes due to its magnetic activity," Doug Vakoch of METI (Messaging Extraterrestrial Intelligence) International told me.
"On Earth, X-rays can lead to genetic mutations that serve as a driving force for evolution. But in too high a dose, harsh radiation could threaten nascent life in the Proxima Centauri system," he said.
It's possible that Proxima b has a thick enough atmosphere, a strong enough magnetic field, or radiation-resistant-enough life forms to negate the affects of the flares. But for now we have no way to know if any one of those elements is there. Not yet, at least.
Even if there is no life on Proxima b now, there could still be plenty of time for that to change. Perhaps the planet could even become a nearby life raft of sorts, centuries or millennia down the road.
"Proxima Centauri will exist for several hundreds or thousands of times longer than the sun," Artie Hatzes concludes in an accompanying Nature News & Views article. "Any life on the planet could still be evolving long after our sun has died."
It can be tough to put a discovery like this into perspective. Although it's the closest exoplanet we've ever seen, it would still take a human thousands of years to get there with current technology.
"It's only human to wonder about traveling there someday, but for our generation the opportunity is to study this planet telescopically," Harvard astronomy professor David Charbonneau told me. "Our telescopes are our spaceships, allowing us to know the conditions on distant worlds without the benefit of a direct visit."
It could be possible to get a closer look at Proxima b within our lifetimes, however. Not in the flesh, but in the form of a tiny nanocraft. The Breakthrough Starshot initiative, announced earlier this year with the support of luminaries including Stephen Hawking and Mark Zuckerberg, plans to send a tiny nanocraft toward the Centauri system at one-fifth the speed of light, taking 20 years to arrive.
One astronomer told me discussions are already happening with the Breakthrough Starshot leaders to make sure the nanocraft swings by Proxima b.
I reached out to Breakthrough Starshot for confirmation and advisory committee chair Abraham Loeb told me the discovery "is strategically important for motivating the Breakthrough Starshot initiative, since it provides an obvious target for a flyby mission."
For more on Breakthrough Starshot's emerging plans for Proxima b, check out my detailed post here.
So what happens now? The answer is simple for Anglada-Escudé. "The search for life on Proxima b comes next," he said.
Just how likely is it that Anglada-Escudé will succeed in that search as well? More on that here.