Yesterday, in arguably what is the most important exoplanet discovery ever made, scientists from the Pale Red Dot project announced they had found a potentially Earth-like world on the closest star to our Sun, Proxima Centauri – a stone's throw away in astronomical terms.
The discovery of the planet, named Proxima b, has understandably sent the scientific world into raptures, with many commenting on how this world is close enough to study in detail, and perhaps even visit.
But what do we know about this world so far, could there be life there, and can we actually visit it? Let’s take a look at some of the biggest questions about Proxima b.
Does it definitely exist?
No, but it’s very likely. The planet was found by measuring wobbles in its parent star caused by the planet’s orbit, known as Doppler spectroscopy. While the scientists behind the discovery are almost certain the planet exists, there’s a small chance it doesn’t. Consider Alpha Centauri Bb, a proposed exoplanet around the nearby Alpha Centauri B star. This was later thought to be a mistaken discovery. However, this time around, the scientists say they have been more thorough. So, Proxima b probably exists.
Is it habitable?
We don’t know for sure yet. All we know about the planet so far is that it has at least 1.3 times the mass of Earth (and at most about 3 times), it is probably rocky, and it orbits its star at a distance 5 percent that of the Earth-Sun distance. Around a star like our own, such a world would be uninhabitable.
But Proxima b’s parent star is a much smaller star, a red dwarf, which means it emits less light than our Sun, so a habitable planet can exist closer in. Indeed, Proxima b is thought to be in the habitable zone of its star, where liquid water could exist. Such a star is prone to bursts of X-rays, though, which may complicate matters.
Could life exist on the planet?
Well, that depends on a number of things. First, we need to know what sort of atmosphere it has, if it has one all. The planet takes about 11.2 Earth days to orbit its star, and at that distance, it is almost certainly tidally locked. This means one of its sides always faces its star, and is in perpetual heat, while the other side points away with endless cold nights. A thick atmosphere, though, could transfer heat around the planet.
We also don’t know the planet’s size, which would be a factor in things. Red dwarfs also emit less light than our Sun, so there’s less energy available for life. The crux of it is that if life does exist there, it is likely to be microbial in nature, rather than anything bigger like on Earth.
How can we learn more about the planet?
We’re going to need bigger and better telescopes. Upcoming projects like the European Extremely Large Telescope (E-ELT) and the James Webb Space Telescope (JWST) will potentially give us a better glimpse at the world, and possibly even allow us to directly image it.
Studying the planet in greater detail, though, such as measuring its atmosphere, will heavily rely on whether the planet transits its star from our point of view or not. We don’t yet know if the planet’s orbit takes it in front of its star relative to us. If it does, we can measure the star’s light coming through the atmosphere to work out the planet’s atmospheric composition, and even see tell-tale signs of life on the surface. If it doesn’t transit, things will get a lot more difficult.
Can we ever go there?
At 4.2 light-years away, Proxima b is the closest exoplanet ever discovered. This distance, though, is still 40 trillion kilometers (25 trillion miles) away. Our furthest spacecraft from Earth, Voyager 1, has traveled a measly 20 billion kilometers (12 billion miles) in about 40 years. So, by conventional means, it would be tough, taking tens of thousands of years to get there.
But there is another way. Earlier this year, Russian billionaire Yuri Milner announced a project – in partnership with names such as Stephen Hawking – to send tiny spacecraft to the Alpha Centauri system, which contains Proxima Centauri. Called Breakthrough Starshot, the project would propel thousands of probes with large sails using lasers fired from Earth, reaching 20 percent the speed of light to make the journey in 20 years.
A recent study has suggested the probes might not survive the journey. But, if they could, it would give us a way to study Proxima b up close in decades, rather than many millennia.