But that phrase ‘Earth-like’ can be a bit misleading: What, at this point, do we actually know?
Let’s start with the star: Proxima Centauri is a red dwarf, just 4 light years from Earth. The existence of a planet orbiting it has been suspected for a long time, but because red dwarfs are badly behaved stars it has taken until now for the international Pale Red Dot team of astronomers to confirm its existence using the European Southern Observatory's instruments.
Pale Red Dot haven’t actually clapped telescopes on the planet – they’ve detected it from the way it makes the Proxima star itself wobble as it orbits. That’s a standard way of detecting a dim exoplanet, and the size and length of the wobble gives us some information:
- The planet is at least 1.3 Earth masses.
- It orbits close to Proxima, and has an 11 (Earth) day long year.
- Because Proxima is a small dim star, that puts the planet in the right distance range for liquid water on its surface.
|I'll stop abusing this meme after today, I promise. It's just... look at his hair!
What we don’t know is almost everything else – a Venus-like hell world, or an Io type volcanic planet, would look exactly the same to this detection method. 'At the right distance for water' isn't the same as 'has liquid water'. To add some more uncertainty, red dwarf stars are grumpy little buggers: They’re prone to massive flares, and Proxima b will be getting an unhealthy X-ray dose about 250 times bigger than Earth.
So we need to find out more. How?
|Above: The process of a stellar transit. When the planet is in front of the star the star's light shining through the atmosphere can be used to determine the atmosphere's composition.
This method needs a huge dollop of luck but, if it works, could start gathering data on Proxima b this year. The idea is this: If, as seen from Earth, the planet’s orbit takes it across the disc of Proxima itself, the starlight will shine right through its atmosphere (more detail here). That would let us look for changes in the starlight that indicate what he atmosphere is made of. But if nature doesn’t co-operate we’ve still got some good options…
Use the JWST and E-ELT:
|Above: The anatomy of the James Webb Space telescope, courtesy of NASA.
Send a probe:
|Above: An artists impression of the 4 meter wide StarShot miniprobe design. Courtesy of the Breakthrough Foundation.
Now… this one will won’t happen for a bunch of years. But… maybe fewer than we think: Earlier this year I was writing about a project called ‘Breakthrough Starshot’ – a $100,000,000 effort to start developing the technologies needed to send a (very) small spacecraft to another solar system.
Despite what has been said about it, the project is not trying to actually launch a probe: The basic physics of their laser driven design is sound, but the engineering is rather more unknown. Starshot’s current incarnation is just meant to prove some of the concepts behind it…. and the discovery of possible target like Proxima b, within the range of a Starshot type probe, is a huge boost for the project.
Even if its air isn’t too thick (like Venus) or too thin (like Mars) and there’s liquid water on the surface, Proxima b would be a strange world to human eyes: Proxima would be a dull orange orb three times larger than our Sun from Earth, but dimmer and cooler, delivering about two thirds as much heat to the surface as our Sun does to Earth.
|Above: An artist's impression of Proxima rising over Proxima b. Courtesy of Pale Red Dot.
Maybe this is a habitable planet close enough to one day be within humankind's reach...