Weird Worlds: Kepler 14b

This post follows the same theme as last week's: planets in binary star systems. Last week's planet, Kepler 16(AB)b, orbited two stars which closely spun around each other. This week's planet, Kepler 14b, orbits one star, which in turn orbits another star at a further distance. This paper, by Buchhave et al (2011), is the main source of my data on Kepler 14b.

Kepler 14b is unlikely to have any sort of solid surface.
However, the two stars could look something like this. Maybe.
Honestly, I think this might be a re-purposed Io illustration
but NASA did use it on a Kepler 14b page, so who am I to argue?
Image credit: Susan Stanley for NASA Kepler Mission Education
and Public Outreach.

It turns out that unlike originally thought from the Kepler satellite data, the star Kepler 14 is not a star, but is two stars. Buchhave et al (2011) discovered this when they went and looked at it with an Earth-based optical telescope. The two stars are so close together in the sky as seen from Earth that it took fancy adaptive optics to be able to resolve them. Resolving, by the way, means being able to distinguish that there are two separate sources of light, not a single blob. The stars were too close together to be able to separate out their spectra (because this uses a different instrument than the one that images them normally), so a few assumptions had to be made, but none that should strongly affect the planet.

Some facts

The two stars that make up Kepler 14 are designated A and B with A being the one the planet orbits, but the nomenclature is a little fuzzy because the binary nature of the system was discovered later. Going on the basis that the system is 980 parsecs away (3200 light years), then the two stars are separated by 280 AU (remember, 1 AU is the distance from Earth to sun and Pluto is about 40 AU from the sun). Both stars are bigger, hotter and brighter than the sun. The sun is a G type star and the Kepler 14 stars are F types, one spectroscopic class hotter/bluer. They are 1.51 and 1.39 times the mass of the sun and orbit each other once every 2800 years.

The planet, Kepler 14b -- I am tempted at this point to make up a name for it. I dub it Keforb -- is 8.4 times the mass of Jupiter. This makes it a fairly large gas giant and definitely not habitable by human standards. Could one of it's moons be habitable? Well, let's keep looking at the planetary parameters.

The orbital period, the length of one Keforbian year, is 6.79 Earth days. That's pretty quick. If you've been playing along at home, you might remember that planets orbit faster the closer in to their star they are. Keforb is only about 0.08 AU from it's primary sun. (Mercury is about 0.4 AU from the sun.) I don't need to do any calculations to know that this planet is going to be way too hot for life, even if it had a suitably-sized moon. It's the sort of planet that's known as a hot Jupiter.

I found this pretty awesome NASA page which shows everything you need to know about Keforb (except for my awesome name) including, if you click on the buttons down the bottom, where Kepler 14's habitable zone is and the orbits of solar system planets for comparison.

So the habitable zone for this system is out past Mars's orbit, in the range of 2.17–3.56 AU, roughly where the asteroid belt is in our solar system.

Similar configurations?

OK, so there's no hope for life on the one known planet in the Kepler 14 system, but what about other possible planetary systems of similar configuration. I mentioned Tatooine last week as being similar to the planet in the Kepler 16 system. The Kepler 14 system is different because the planet orbits only one star, not both of them.

A system of this sort that pops up in fiction every now and again is a planet orbiting a red dwarf star which is in turn orbiting a larger, brighter star. I'm pretty sure I've read about this sort of thing more than once but the series that springs to mind first is the Second Sons Trilogy by Jennifer Fallon. Partly this is because it's one of my favourite series, so I may be biased. In the first book, Lion of Senet, we are introduced to a world with two suns: a small red sun and a more distant yellow sun. The world orbits the red sun and the red sun orbits the second yellow sun. The residents experience two different types of sun sets and sun rises and their "nights" are when only the red sun are up in the sky. They also get to experience side-effects from the tidal forces of a) having two suns and b) being in a relatively close orbit with the red dwarf. This means lots of volcanoes and tidal waves (I think the first book even opens just after a volcano, but I may be wrong and I don't have it on hand to check).

It's billed as a fantasy series, and it's certainly written in a fantasy style with feudalism and political intrigue and war and things (the rest of Jennifer Fallon's books are indisputably fantasy). However, there isn't any more magic than in our world which makes me tempted to say that it's technically sort of science fiction. But without laser guns (or any sort of guns. There are swords, though). Maybe "sword and science" rather than "sword and sorcery".

Anyway, I highly recommend it, not just because of the interesting celestial mechanics, but also because it's a damn good read. The hero, Dirk, goes around applying his brain, not brawn. Also, if you go in solely for the celestial mechanics, you might be disappointed because, while good for the reasons I've mentioned above, it's not quite perfect, mostly for reasons of plot.

Sometimes, it's best not to let science stand in the way of a good story. (So long as you try and at least some of the science is sensible.)