It’s now confirmed: Proxima Centauri has a planet

Proxima Centauri has a planet.

The “Pale Red Dot” project, designed specifically to study Proxima Centauri (the closest known star to our own Sun, at a mere 4.2 light years) in search of planets, has paid off.  Using the European Southern Observatory in Chile’s high Atacama Desert, astronomers discovered the planet, designated Proxima b, and determined that it has a mass of at least 1.3 Earths, which means it is almost certainly a rocky planet, a “super-Earth”.

Proxima Centauri is a red dwarf, a small, dim, cool, but very long-lived and common type of star. Since it’s so cool, the “goldilocks zone”, where a planet could theoretically host liquid surface water, is very close in.  Happily, Proxima b is within that zone — but since this is a red dwarf we’re talking about, that means it’s just seven million kilometers from its primary, with an orbital period of just 11.8 days.  (So it’s year is less than a fortnight!)  This close in, there’s a pretty good chance it’s tidally locked, forever turning the same face towards its sun, which would be bad news for habitability, except possibly in a thin zone around its day/night terminator, where libration would cause at least something approximating a day/night cycle.  (Libration is the apparent wobble of a tidally locked body in the sky of its primary.  Our own Moon does it, due to its orbit being elliptical — given enough time, you can actually get to see slightly more than half of the Moon thanks to libration.)  Or it could be in another resonance; the planet Mercury is in a 3:2 resonance, where it completes three rotations for each two orbits, and that would also be a long-term stable solution — but potentially almost as bad for life as the tide-locking.  Of course, even worse news is the fact that, like many other red dwarfs, Proxima Centauri is famous for its gigantic solar flares.  When Proxima flares up, its total x-ray output can equal that of our own Sun.  Which is fine at Earth’s distance, but would be lethal at a scant 7 million km.  Plus, it’s likely the solar wind picks up dramatically during these events, which could strip a close satellite of any atmosphere.  That said, if Proxima b has an ocean, or perhaps subterranean life, it could potentially survive and even be adapted to this hostile environment.

But the coolest part of all is that Proxima Centauri, unlike almost every other star mankind has studied besides our own Sun, is actually close enough to make a probe feasible with current technology.  It would still take decades, but within the span of a human lifetime.  Sure, the Voyagers would take over 60,000 years at their current speed, but we have the ability to make things go much faster, if we’re willing to seriously invest in this.  If the Voyagers could last 40 years, if the B-52s could be expected to each last for a century of service, if our ancestors could build cathedrals that took three generations of architects to complete, then surely we can build something that can do this — if we but have the will.

So how about it?  Wanna go to Proxima b?  😉

Of course, there’s still plenty to be learned about the Proxima system even without leaving Earth. Proxima b was discovered by the radial velocity shift method, where they look at Doppler shifts in a star’s radial velocity, which can tell them if it’s being tugged around by an unseen companion.  Equipment is now sensitive enough even to measure the tug of planets.  But there are unexplained deviations in the signal from Proxima Centauri; these are probably the weaker signatures of other planets, but it will time and a lot of careful computation to tease that out of the data.  And then there’s the fact that Proxima Centauri is very close compared to other stars.  There is a better chance of direct imaging of this planet than any other exoplanet yet discovered, purely because of its proximity.  So you can bet that astronomers worldwide are now clamoring for instrument time on the biggest and most sensitive telescopes, hoping to catch a glimpse of this strange new world.

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