Whenever I think of a tidally locked planet, like say Mercury, the only image that comes to mind is one that is barren of all life. You see for tidally locked systems the face of the smaller body is always pointing towards the larger one, like our Moon is towards Earth. For planets and suns this means that the surface of the tidally locked planet would typically turn into an inferno with the other side becoming a frigid wasteland, both devoid of any kind of life. However new research shows that these planets might not be the lifeless rocks we once thought them to be and, in fact, they could be far more Earthlike than we previously thought.
Scientists have long theorized that planets of this nature could potentially harbour a habitable band around their terminator, a tenuous strip that exists between the freezing depths of the cold side and the furnace of the hot side. Such a planet wouldn’t have the day/night cycles that we’re accustomed to however and it would be likely that any life that evolved there would have adapted to the permanent daylight. There’d also be some pretty extreme winds to contend with as well due to the massive differences in temperature although how severe they were would be heavily dependent on the thickness of the atmosphere. Still it’s possible that that little band could harbor all sorts of life, despite the conditions that bookended its environment.
However there’s another theory that states that these kinds of planets might not be the one sided hotbeds that we initially thought them to be. Instead of being fully tidally locked with their parent star planets like this might actually still rotate thanks to the heavy winds that would whip across their surface. These winds would push against the planets surface, giving it enough rotation to overcome the tidal locking caused by the parent star’s gravity. There’s actually an example of this within our own solar system: Venus which by all rights should be tidally locked to our Sun. However it’s not although it’s extremely long days and retrograde rotation (it spins the opposite way to every other planet) hints at the fact that its rotation is caused by forces that a different to that from every other planet.
Counterintuitively it seems that Venus’ extremely thick atmosphere might be working against it in this regard as the modelling done shows that planets with thinner atmospheres would actually experience a higher rotational rate. This means that an Earthlike planet that should be tidally locked would likely not be and the resulting motion would be enough to make the majority of the planet habitable. In turn this would mean that many of the supposedly tidally locked planets we’ve discovered could actually turn out to be habitable candidates.
Whilst these are just beautiful models for now they can hopefully drive the requirements for future craft and observatories here on Earth that will be able to look for the signatures of these kinds of planets. Considering that our detection methods are currently skewed towards detecting planets that are close to their parent stars this will mean a much greater hit rate for habitable candidates, providing a wealth of data to validate against. Whether we’ll be able to get some direct observations of such planets within the next century or more is a question we won’t likely have an answer to soon, but hopefully one day we will.
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.