There’s lots of breathless speculation online today about what NASA is going to announce at their big news conference tomorrow. The usual suspect quacks and hacks are giddily predicting NASA is finally going to announce they’ve found alien life “out there”, but that’s not going to happen; when (and I do mean when; I am absolutely convinced it will happen one day, there’s no “if” about it) they do that the news will leak out on Twitter long before the press conference, because there’s no way such a huge thing will be kept secret by the people involved, or by the journalists given a sneak peek at the press release. Someone, somewhere, will blab, that’s just human nature. So, all you tin foil hat-wearing fruit loops jumping up and down in joyous anticipation of NASA finally “coming clean” tomorrow – calm down, and go back to your X Files dvds.
Tomorrow will be about science, not science fiction.
Back in reality, what do we know so far about tomorrow? Well, all we know is that it relates to something “beyond the solar system”, which on the face of it could mean anything, but come on you lazy lot, a quick look at the NASA press release itself tells us it’s exo-planet related (an exo-planet being a planet in orbit around another star).
So, logically, the announcement will relate to the discovery of a rocky planet, or more than one, in orbit around a nearby star. Which would be great news, but hardly worthy of a big NASA TV event. That means someone, somewhere, has found something along those lines which is a bit special, a bit unusual. So it looks like someone, somewhere, might have found one or more planets the same size as Earth orbiting another star..?
But as exciting as that would be part of me is already groaning at the prospect of hearing these new exo-planets being described as “Earth-like”.
You see, when astronomers and exo-planet hunters describe a planet as “Earth-like” they mean that it is Earth-sized, or roughly Earth-sized, made of rock, and that’s it’s in its star’s “Goldilocks Zone” – i.e. at a distance from the star which means it isn’t too hot and isn’t too cold but is just right – just right for liquid water to exist on its surface.. maybe.. possibly…perhaps.. – but few exo-planets are.
The problem is, when other people, like non-astronomers and the media, hear a world described as “Earth-like” they naturally assume it means the planet is, you know, actually “like Earth”, as in physically and visually like it – 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. After all, that’s what Earth is like, so when they hear another world described as “Earth-like” people think it’s Just Like Earth, in many ways, if not every way. They think it has its own seasons of sunshine and snow, rivers gurgling and tumbling down its 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 I know it winds others up too. I think the exo-planet community really, REALLY should stop referring to planets as being “Earth-like” when they’re really not, when they’re actually just “Earth-sized” or just potentially 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 hype. It gives people completely the wrong idea, raises false hopes and expectations, and generally causes avoidable confusion and misunderstanding. And god knows there’s enough of that in astronomy already. Water has been “discovered” on Mars so many times now people think it has swimming pools and bloody mermaids…
But more importantly I think the reckless use of the term “Earth-like” dilutes the impact of the forthcoming (when? No idea? But it will happen eventually) 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. THAT would be a truly Earth-like planet, and its discovery will be one of the greatest and most significant achievements in science. We’re a long, long way from making a discovery like that – but it will come, one day. And when it does, how many people will just raise an eyebrow and say “Really? I thought we’d found lots of planets like Earth?” because dozens of other planets have been described as “Earth-like” already?
So, as we await tomorrow’s news, please, everyone, familiarise yourselves with what the scientists will mean when they talk about “Earth-like planets”. They don’t mean “other Earths”, other lush, blue and green worlds dripping with water and covered with life. They mean rocky worlds, roughly the same size as Earth, which may or may not be in an orbit around their star which makes them suitable for water to exist on their surface, which might, in turn, make them possible habitats for life. Finding worlds like that will give us great candidates for follow-up science, with instruments that can look for certain gases in their atmospheres or the signature of water, but it won’t mean we’ve found Earth #2, or #3, or #4 (or #7… 😉 ) out there, and that we could just hop over to it in a super space ship and live there, ok?