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NOT “Earth 2” – But Fascinating…

Today could be a rather exciting and important day for astronomers, professional and amateur alike, and anyone “into” space. Later today there will be a press conference by astronomers from the European Southern Observatory which will, if the rumours are true, be used to announce the discovery of a planet orbiting the star Proxima Centauri.

Why would that be a big deal? Because Proxima is the closest star to the Sun, “just” 4.3 light years away, so any planets found orbiting it will become the targets of research projects and intense study for years to come – and, without doubt, the target destinations for the first interstellar probes we make and despatch, sometime in the more distant future. And yes, looking even further ahead than that, it might seem like science fiction to even think about it, but any planet found whirling around Proxima Centauri will probably be the world the first human beings to journey to another star see through a spacecraft window – and then land on and walk on, if it has the right conditions to allow them to do that. It really could be that important.

If you’re into this kind of thing you’ll know that there is already a lot of excitement – and, it has to be said, hype – about this announcement and discovery. Again, yet again, an extra-solar planet is being labelled “Earth-like” (even before its discovery is officially announced!) just because (if the rumours, whispers and gossip prove accurate) of its size and where it is in that star’s solar system. That’s what astronomers looking for exo-planets mean by “Earth-like” when they describe a planet like that. The problem is, other people, like non-astronomers and the media, think “Earth-like” means actually “like Earth”, as in physically and visually – a world the same size as our own, a beautiful blue and white planet with surging oceans kissing warm sandy beaches, billowing clouds blown by soft summer winds, and life, life everywhere – in the sky, under the water, and in the fields. A truly Earth-like world would have seasons of sunshine and snow, rivers gurgling and tumbling down mountains, and kittens sleeping by crackling fires. That’s what people – and I know this for a fact, because I meet and talk to a lot of them in the course of my Outreach work – think a planet is like when they hear it described as “Earth-like”; not just a rocky-ish planet orbiting a star at roughly the Earth-equivalent distance from it.


Personally, this really winds me up, and others too, I know. I think the exo-planet community has to stop referring to planets as “Earth-like” when they’re really not, when they’re actually just “Earth-sized” or just in a star’s habitable zone. Why? two reasons. Firstly, I think at best it’s lazy science communication, and at worst misleading, even deceptive. But more importantly it will dilute the impact of the CONFIRMED discovery – and even imaging – of the first truly “Earth-like” planet: a world that is the same size as Earth (or a bit bigger or smaller), at the right distance from its star for terrestrial conditions to exist on its surface, and with the tell-tale chemical signatures of life detected on its surface or in its atmosphere. We’re a long, long way from making a discovery like that – but it will come, one day. But when it does, many people will just raise an eyebrow and say “Really? I thought we’d found lots of planets like Earth already?”

Already there has been a lot of speculation about the nature of the planet found orbiting Proxima, but we won’t know anything for certain until the big announcement later today. So what do we know?

Well, Proxima Centauri is a star in the southern celestial hemisphere, and is so far south that it is never visible from the UK. If you want to know where it is, here’s a finder chart – basically, on the next clear night, look for Mars and Saturn, shining low in the south west, then drop your gaze so you’re looking into the ground beneath them – that’s where Proxima is in the sky…


Proxima is a red dwarf star, much smaller than our Sun (only 1/7 its diameter in fact) and is too faint to be seen with the naked eye. It’s also a “flare star”, meaning it undergoes repeated violent burst of activity, which has led to many exo-planet hunters suggesting that would result in an unsuitable environment to support life on any planet orbiting it. Basically, Proxima itself is nothing like our own Sun, so calling any planet orbiting it “Earth-like” is a bit of a stretch from the very start, I think.

Having said that…

If a planet has been detected around it, it’s possible it MIGHT be a vaguely Earth-like planet, in the sense that it is the same size as our own, or roughly the same size, and is in Proxima’s habitable zone, meaning it’s not too hot or too cold for liquid water to exist on its surface. If that’s the news then I’ll personally shout out (in my head, not literally!) YESS!!! and celebrate, because it will be exciting and have real consequences for both the future of astronomy and the future of space exploration, because we’ll finally, finally have a potential destination for future un-crewed probes and, eventually, crewed expeditions. Yes, that will definitely be a big deal.

And if that is the discovery then we need to get serious about this planet. We need to give it a name, and a good name, quickly, because that will allow us in the astronomy community, especially those of us involved in outreach and education, to start thinking of it as a real place, a real destination “out there”, and to tell people about it and make it real for them, too.

There are already lots of exo-planets with names, thanks to the much- (and, it has to be said, sometimes fairly- ) maligned IAU. You can read about them here. But very few people outside of the astronomical community know any of them – in fact, I wonder how many people IN the astronomical community know them? Some are brilliant and sound suitably planetary and epic (“Arkas”, “Musica”) while others somehow don’t seem right at all (“Lich”, “Poltergeist”) but that’s just my opinion, others may love them. All have their own stories, so I’m sure each one has its own fans.

But I really think there’s a case for giving this planet orbiting Proxima a suitably historic and inspiring name, just because it will play an important part in our future. If it’s real, it will be studied by telescopes and astronomical instruments more than any other exoplanet. If it’s real, it is so tantalisingly close – in astronomical terms – that it has to be the destination for our first interstellar probes, even though a journey there would take a horrendously long time? If it’s real surely, surely it will be the destination for the first crewed starship to leave Earth, whenever that is built and launched, in some faraway science fiction future?

If/when people do eventually travel to Proxima Centauri, if it has any planets or not, they will see a starry sky remarkably similar to Earth’s. Using the Sky Safari app on my phone I was able to fly to Proxima and found that it is so close to the Sun that the relative positions of the more distant stars won’t appear to shift very much, so most of the constellations we see from here on Earth will look pretty much the same from Proxima. Of course, there are a couple of noteworthy exceptions. If you were to look at Orion, either from orbit around Proxima itself or from the surface of any planets it has, you’d see the famous Hunter’s familiar hourglass shape, with the belt tight across his waist, but you’d notice a bright blue-white star very close to Betelgeuse that definitely isn’t there from Earth: Sirius…


And if you looked towards Cassiopeia you’d see an unfamiliar golden star close to it… Our own Sun, over 4 light years away…


Anyway, let’s see what the announcement (or a leak of its contents sometime during the day, which is very possible) brings, shall we? I’m sure the science will be fascinating, whatever it is – but I’m also sure that if they use the term “Earth-like” too much during their press conference, without a very detailed clarification of what they actually mean when they use it, while astro-aware reporters will (hopefully!) cover the story accurately, the scientifically inaccurate mainstream media will go into feeding frenzy, as journalists latch on to the term “Earth-like” and think that means the new world is actually “like Earth”, writing about it in their subsequent papers and on their websites as if it is a shining blue-and-green world, complete with blue skies, fluffy white clouds, and unicorns drinking cool water from crystal ponds, in faerie glens deep in enchanted forests.

And aliens, maybe. Don’t forget the aliens. They’ll HAVE to speculate that the new planet has aliens on it: It’s the Law. -)



One Response

  1. Thanks for this informative write-up.

    I have a question on the violence of the activity reported on Proxima Centauri. Would these flare ups present significant risk to any travelling probe (or even people) when the eventual visit happens?

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