The idea of planets orbiting other stars doesn’t seem like a particularly novel idea today but it’s only recently that we’ve been able to definitively prove that there are planets outside our own solar system. Whilst there was the beginnings of evidence surfacing back in 1988 the first, definitive proof we had of an extrasolar planet came in 1992, a mere 2 decades ago. As our technology has increased in capability the number of planets we discover year by year has increased dramatically and, even cooler still, the different types of planets we’re discovering is also increasing. Heck we’ve even found planets that don’t have a parent star, something which was almost a fantasy as they were thought to be nearly impossible to detect.
What the last decade has revealed is that planets are not only a common occurrence in the universe but systems like are own, ones with multiple planets in them, are also commonplace. Initially most of the exoplanet discoveries were limited to certain types of planets, namely large gas giants with short orbital periods, but as our technology has improved we’ve been able to discover smaller bodies that orbit further out. Depending on the size of the star and the planet they could end up in what we refer to as the habitable (or Goldilocks) zone, the area where liquid water could exist on the surface. Finding one of these is cause for celebration as that closely matches our own solar system so you can imagine the excitement when we found 3 potentials orbiting Gliese 667C.
Gliese 667C is actually part of a ternary star system which means that each of these planets technically has 3 suns, although the other 2 appear to more like bright stars that have the same illumination capacity as the full moon does here on earth. The diagram above makes it look like there’s potentially 5 planets in the habitable zone (just barely for H and D) but those ones are far more likely to be closer to Venus and Mars respectively. C, F, and E on the other hand are what we call super earths, rocky planets that have a mass around 2 to 10 times that of earth. Typically they’re also quite a bit larger than earth as well which means that the gravity on these kinds of planets is actually quite comparable. Out of all of them Gliese667Cf is the best candidate for habitability and thus extraterrestrial life.
What’s particularly exciting for me is this provides more evidence for the idea that other stars are typically swamped in planets, making the configuration of our solar system quite common. This adds fuel to the already intense discussion that surrounds the Drake Equation which I’d argue has now been tipped towards increasing the left hand side dramatically. Of course you can’t consider that equation without also considering the Fermi Paradox since, as far as we can tell, we’re still all alone out here. The only solution is for us to visit these planets and to see if there is anything there although doing so in an acceptable time frame is still beyond the current limits of our technical ability (but not our theoretical capacity, however).
It’s really quite amusing to see the stuff of science fiction rapidly turn into science fact. As time goes on it seems that the wildest things we could dream of, like planets with multiple suns, are not only real but may not be that unusual either. Hell it’s almost an inevitability that we’ll one day go to places like this just because it’s there. It might not be this century or heck even this millenium but we’ve shown in the past that we’re a stubborn race when it comes to things like this and we’ll be damned if anything will stop us from achieving it. I can only hope medical science advances enough for me to be able to see that and, hopefully, experience such planets for myself.
Are they able to (relatively) reliably gauge the gravity of these planets? I know gravity and planet size isn’t a linear relationship, but are they confident that the gravity of these rocky planets isn’t double (or more) that of earth’s?
These planets were discovered via the Radial Velocity method which only gives us a minimum mass and orbit of the exoplanet in question. So for these particular ones we can’t reliably calculate their gravity at this point in time. If these planets happen to transit their host star relative to us we can then figure out their radius and thus surface gravity but these are unfortunately rare, so usually all we have to go on is mass.
So yes it’s quite possible these have double or possibly even more gravity than that of earth. We can probably make some statistical judgements based around other planet systems we’ve seen in order to have a guess at it but apart from that you’re spot on.