I’ve been talking a lot lately on this channel about certain types of star systems, such
as M-type red dwarves, dropping in probability of hosting earth-like planets and the type
of life that might arise on them.
But take heart, there is another type of star system that for a long time was seen as likely
to be hostile to planet formation but now that seems to be the exact opposite.
These are the double star systems.
While it’s not well established just what percentage of star systems in the milky way
contain one or more companion stars, it’s a lot.
But as our knowledge of the orbital dynamics of these systems has increased, so have the
chances of planets forming around them, indeed we’ve found several examples already.
But in one hypothetical situation, having double suns in just the right orbital positions
would favor life where it would not normally be favored.
Let’s look at a few cases of planets in these kinds of systems.
The first is the nearest star system to our own, Alpha Centauri.
This system is made up of a trio of stars, Alpha centauri A, Alpha Centauri B and Proxima
Centauri.
Alpha Centauri A is sun-like in some regards, it too is a G type star, though a bit larger
than the sun.
Alpha Centauri B on the other hand is a K type orange star, just a bit smaller than
the sun, though these types of stars are currently favored as among the best for life and earthlike
worlds to develop around.
And then there is Proxima Centauri.
This little red dwarf orbits the other two, though just barely, since it’s very distant.
But that distance allows it to have a planet, the closest known exoplanet to Earth in fact
and is so close that we can imagine colonizing it some day even at sublight speeds.
It’s shaping up to not be a great planet though, and it’s potential suitability to
host life has taken serious hits since the announcement of its discovery.
But what it does show is one instance where a stable planet can exist in a triple star
system.
There has also been periodic talk of other planets orbiting the two principal stars in
the system, though nothing is definitive yet.
One possibility is a planet orbiting close to Alpha Centauri B, but it would be hopelessly
baked and not suitable for life.
And there has been talk of other potential planets, but they would be small and hard
to detect.
What doesn’t seem to be present are any obvious gas giants, which are thought to be
needed to clear systems of debris that pose a threat to life, at least complex life like
dinosaurs.
Subsequently, through the Kepler spacecraft, gas giants were found orbiting double stars,
so the possibilities have really opened up for multiple star systems to host rocky worlds
orbiting around them that might not be subject to constant bombardment.
But how stable can planetary orbits be in these kinds of systems?
Another example is gamma cephei, where you have another orange type K star orbited by
a red dwarf with a confirmed planet.
This is a compact system, and it’s unclear how stable the planet’s orbit is, but there
are models that show that it could be in a completely stable orbit within the system.
In 2013 and 2014 papers by Paul Mason and colleagues, links in the description below,
advance that binary star systems, at least certain ones, may work to create better habitable
zones than single stars might produce, most notably the sun.
The idea is that the interactions of the two stars can serve to cancel out, at least somewhat,
some of the detrimental effects that stars can have on their planets, such as high stellar
wind.
A pair of lower mass stars are thought to be the best possibility here, since the combined
energy of the stars would push the habitability zone of the system further out.
This solves some of the issues regarding smaller stars, especially those surrounding M type
dwarf stars.
They seem ideal and are very long-lived, trouble is if you have a single one you need to be
so close to it that it bathes your planet in radiation.
If you have two, that may change the equation.
But, the double stars that might be most suitable to life, such as orange dwarfs, would probably
need to orbit pretty closely or else you get into chaotic orbital conditions.
But if the two were close enough and the planets were out in the extended habitable zone, it
would be more like a solar system orbiting a single star.
The interesting thing here is that the odds of finding more pairs of stars suitable for
earth-like life is pretty good, low mass stars are the most common kind in the galaxy and
there are no shortage of them in binary arrangements.
And if you had just the right combination, it could yield a habitable earth-like planet
that would survive many billions of years longer than earth will orbiting around our
own sun.
That leaves lots of time for life and intelligence to arise.
Wouldn’t it be poetic if binary stars that were once thought unsuitable for life may
turn out to be the most suited for it.
Perhaps once we head out into the universe and make contact with other civilizations
they will marvel at how we managed to evolve around a cranky, rather violent G type star
and have no idea what it’s like to grow up with two suns in the sky.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently worried what the
aliens will think because we only have one star, I can already hear them whispering jokes
now and be sure to check out my books at your favorite online book retailer and subscribe
to my channel for regular, in-depth explorations into the interesting, weird and unknown aspects
of this amazing universe in which we live.