Earth-like Proxima Centauri Exoplanet Not So Earth-like

Like all other space nerds recently I’ve been excited by the discovery of an ‘earth-like’ planet around Proxima Centauri. It has been described as the most important exoplanet discovery there will ever be given that it is the nearest possible one; allowing for the exception of any rogue planets that might be out there. But how earth-like is it? And how certain are we that it is there? Do we need to be concerned that the news broke not through an announcement by the European Space Agency (ESA) or a peer reviewed article, but from a leak perpetrated by one of the team members?

Despite the, erm, proximity of Proxima Centauri (4.2 lightyears), it is not the brightest star in our sky as it is a red dwarf. It only gives out about 1000th of the light that our sun does and this has a profound impact on the nature of the newly discovered planet, known as Proxima B. We’ve all heard of the Goldilocks Zone, that area around a star that is just right for liquid water to exist on the surface. The Goldilocks Zone around such a measly star is very near to the star itself, in this case just 7.5 million km. For comparison, we are 149 million km from our star. A year, then, on Proxima B lasts only 11.2 of our days.

Personally, I think that saying Proxima B is in the Goldilocks Zone is pushing the limits of the definition to breaking point. The average surface temperature of the planet is estimated at -40 degrees Celsius, on earth the average is 15 degrees. Without an atmosphere there is unlikely to be the right conditions for liquid water on the surface without some kind of geothermal activity from within.

Proxima Centauri being a red dwarf doesn’t just mean that it is dim. During the first couple of billion years of the life of a red dwarf they can be quite erratic and unstable. The result is enormous solar flares that throw out very large amounts of radiation which, at just 7.5m km, could leave Proxima B a baron, sterile rock. It would need a very strong magnetic field and a dense atmosphere to be able to withstand that onslaught. This is sounding less and less earth-like by the minute.

One of the very few things we do know about the exoplanet so far is that it has to be at least 1.3 times the mass of the earth. There isn’t currently an upper mass limit and so whilst it could be a small rocky world like ours we don’t know for sure yet if it might be more of an ice giant like Neptune. A larger mass would give it more of a chance to standing up to the brutal flares it faces but if it were too massive then it could start to negatively impact the prospects for life.

Over the coming months and years there will certainly be a lot of attention turned on our new neighbour. If we’re lucky the planet will pass in front of the star giving us the opportunity of performing some spectrographic analyses which would reveal details of any atmosphere that may be present. It is estimated that there is only a 1.5% chance of a transit, however.

As for getting to the planet for more direct observations: unlikely. Even though this is the closest possible planet to us it would take our current fastest spacecraft more than 90000 years to get there. One suggestion has been to send a swarm of micro-satellites to the system. These would be very small and propelled by an extremely powerful 10 gigawatt laser shone from the earth. The satellites would have little sails that would be able to catch the momentum of the laser and, with time, it is thought they could get to 10-20% the speed of light permitting a travel time of just a couple of decades. But how they would slow down at the other end would be a non-trivial problem, as well as how to get the necessary communications equipment onto such small probes.

As I mentioned earlier the story broke because of a leak. It is known that someone in the team, part of the ESA, was the source of the leak but not precisely who. When contacted for comment the ESA didn’t deny the story, which they would if it were false, but they weren’t exactly pleased either. The finding has now been published properly in Nature.

I do not want to be relentlessly negative about this. When I heard about the discovery I was genuinely excited and watched an episode of Star Trek to celebrate (the one where La Forge falls in love with the hologram). It fires the imagination and sparks the eternal question of What If? As ever, I feel that the press has gotten a bit carried away with the reporting of the discovery, playing up the earthiness of the place instead of relaying the facts, which are awesome enough in their own right without having to sex them up. By the lay person’s definition I don’t think Proxima B is especially earth-like. It’s more likely to be an irradiated hell. We’ve all had neighbours like that at some point, though, and there’s not much you can do about it. Given we can’t move away I recommend getting to know them as well as we can and seeing if we can’t resolve our differences.

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The two bright stars are the neighbouring Alpha Centauri binary star system. Proxima Centauri is the tiny red dot inside the tiny red circle. Image courtesy of Skatebiker
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