Imagine yourself a young man--a helping hand on a farm--frustrated with the day-in, day-out work. Farm work is hard. You really don’t have the build for it--your friends always call you ‘skinny’. You do have a knack for fixing the farm machinery, though, and your step-parents, who own the farm, find that a very useful thing.

Your uncle, Owen, just purchased a couple new droids to help out on the farm, and tells you “Luke, take these two over to the garage, will you? I want you to have both of them cleaned up before dinner.” Even though you told him you were planning to go to Toshi Station to pick up some power converters, he said you could waste time with your friends later and that there was work to be done.

Later that evening, frustrated, you look up into the sky longing to escape this life as the two suns set--Alpha Centauri A and Alpha Centauri B.

Wait? What?!?

The Alpha Centauri System

Something along these lines could potentially be possible in the Alpha Centauri star system. The two main stars of the system are “main sequence” stars, Alpha Centauri A approximately 10% larger than our Sun (and very yellow), and Alpha Centauri B about 10% smaller than our Sun (and very orange).

These two stars orbit around each other every 80 years, at a distance that varies from about 11 AUs apart to 36 AUs apart (1 AU, or ‘astronomical unit’, is the distance between the Sun and the Earth, or about 93 million miles). This means, at their closest, they are about the distance between the Sun and Saturn apart; at the farthest, about the distance between the Sun and Pluto apart.

Even though it’s a binary star system, there is a chance that planets can still orbit these stars. Calculations show that planetary orbits within 3 AUs of each star would be stable, and not disrupted by the second star. Anyone standing on a planet within this range of either star would often have the rather unique sight of two suns being visible in the sky together. At other times, as the planet’s orbit around its main star progresses, you would have the pleasure of viewing that star set and the other star rise as “night” fell. Crazy possibilities!

There is also a third member of this star system--a red dwarf called Proxima Centauri, only about 15% the size of our Sun. Until recently, it was thought this might be a wayward dwarf star, not really a permanent part of the other two stars. But, just this year calculations confirmed Proxima is an actual permanent member, orbiting the two main stars every 550,000 years.

Original MetaPost program by David Benbennick* Program rendered as SVG by Qef, taken from Wikipedia under the Creative Commons 3 license.

Of course, this is the closest star system to us--Proxima Centauri at 4.24 light years away, and the two main stars at 4.37 light years distant. Using our hypothetical spacecraft traveling at 20% the speed of light, it could reach Proxima Centauri in just over 21 years, and the larger stars in the system in just under 22 years.

Photograph of the Alpha Centauri system, with Alpha Centauri A (left) and Alpha Centauri B (right). Proxima Centauri is the tiny red star in the center of the red circle. Courtesty of Skatebiker at English Wikipedia under the Creative Commons 3 license.

And guess what?!? The Alpha Centauri system has planets!!

Alpha Centauri System Planets

Because of how close they are to us, of course the Alpha Centauri stars have been the object of intense planet-hunting interest! So far, zero planets have been detected around Alpha Centauri A.

Alpha Centauri B is something of a different matter--although it is more of a huge question mark than anything. In 2012, European astronomers announced the discovery of an Earth-sized planet around this star. Named Alpha Centauri Bb, this planet was proposed to orbit very, very close to the star, so much so that it would have lakes of molten lava all over the world.

In 2015, scientists from the University of Oxford disproved the existence of Alpha Centauri Bb, finding that the results of the original observations (which spanned 4 years), were nothing but statistical noise. The original scientists agreed with the new analysis. So, Bb is almost certainly not real.

However, also in 2015, scientists from the United Kingdom using the Hubble Space Telescope discovered another potential Earth-sized planet around Alpha Centauri B, now commonly referred to as Alpha Centauri Bc. The orbit of this planet would be a little farther from the star than the disproven Bb planet, but still close enough to essentially be a “lava world.” Additional research needs to be done to confirm this planet, but if it exists, it is highly unlikely there is any life on it.

There could, of course, be other planets orbiting the main stars of Alpha Centauri, but as you can see, even at this close distance, planets as small as the Earth or smaller are exceedingly difficult to detect. So, the search continues. What has essentially been confirmed is that there are no gas giant planets around either of these stars.

I do propose, however, that if a planet is found in the habitable zone around either of these two stars, we name it Tatooine!

Proxima Centauri, however, is a different matter entirely.

Proxima Centauri b

In 2016, astronomers discovered a planet 1.3 times the size of the Earth orbiting Proxima Centauri. Proxima Centauri b has another novel feature--it orbits within the habitable zone of the star, meaning temperatures are such that liquid water can exist there!

Wow! That sounds awesome! It’s really near to us, temperatures are good, about the size of Earth. Right!?!

While very exciting, there are a few problems with Proxima Centauri b. First, it is probably ‘tidally locked’ to its star--meaning that the it orbits so close to the star that one side of the planet is always facing the star, and one side is always facing deep space. That’s not a sure thing, but it is likely. If true, this would mean the side facing the star would be very hot, and the side facing away from the star would be extremely cold, thus reducing the chance of liquid water existing anywhere on the planet.

Second, Proxima Centauri, like most red dwarf stars, is a “flare” star. Flare stars emit regular, very intense bursts of light and radio waves, but also X-rays that can be up to 10,000 times more intense than the X-rays our Sun gives off. On Proxima Centauri, these bursts can happen hourly. These bursts would be lethal to life as we know it, especially as the habitable zone around a red dwarf star is very close--Proxima Centauri b is about 4.6 million miles from its star (Mercury is about 28 million miles from the Sun for comparison).

Over millions of years, these flares would be likely to strip away the atmosphere of any planet nearby, unless the atmosphere of the planet was very thick, and unless the planet had a strong magnetic field to deflect these flares. Theoretically, a planet with these properties could happen, but it would be very unlikely to develop this way. Without the atmosphere and the magnetic field, there is almost no chance for life to exist.

Then, one final caveat--the red light emitted by red dwarf stars like Proxima Centauri is not conducive to photosynthesis as we know it. In other words, Earth plants could not function with light from the star alone.

Breakthrough Starshot Revisited

The Breakthrough Starshot project has selected Proxima Centauri b as its first flyby goal. If the planet is not tidally locked (possible), if it holds water (possible), and if it has a thick atmosphere and a strong magnetic field (somewhat possible), it does have an off chance of harboring some sort of life.

http://breakthroughinitiatives.org/Target/3

Even if so, this doesn’t solve the problem that Earth-style plants could not have developed there, but in honor of ghotiphaze’s comment from the earlier Kepler essay I wrote--it could be that a different type of life has evolved that utilizes red light in some way.

At any rate, the Alpha Centauri system is certainly a good first stop, and it likely will be!

And who knows . . . maybe there is a young Luke Skywalker there, looking up into the sky with two suns on a planet unknown to us--longing to give up farming and fly in spaceships.

Let’s next look at the other nearby stars and what they have to offer . . .

Sources:

http://solstation.com/stars/alp-cent3.htm

https://en.wikipedia.org/wiki/Alpha_Centauri

https://en.wikipedia.org/wiki/Alpha_Centauri_Bb

Previous (relevant) Space Escape essays:

https://caucus99percent.com/content/science-escape-3-kepler-mission

https://caucus99percent.com/content/science-escape-4-breakthrough-starshot