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Alpha Centauri B may have "superhabitable" worlds

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January 27, 2014

The Alpha Centauri system and hypothetical planet (Image: European Southern Observatory)

The Alpha Centauri system and hypothetical planet (Image: European Southern Observatory)

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Since Earth is the only known inhabited planet and we happen to live here, it’s only natural to regard it as the ideal place for life to exist, and to assume that another life-bearing planet would be fairly similar. However, that is not the opinion of scientists René Heller and John Armstrong who contend that there might be a planet even more suitable for life than Earth 4.3 light years away orbiting the star Alpha Centauri B.

The nice thing about having a hypothetical “superhabitable” planet revolving around Alpha Centauri B, which is part of a triple star system, is that it makes it a lot easier to indulge in a bit of a thought experiment based on the arguments put forward by Heller, of the Department of Physics and Astronomy, McMaster University, Hamilton in Ontario, Canada, and Armstrong, of the Department of Physics, Weber State University in Ogden, Utah.

Imagine we’re in a spaceship approaching the planet in question. The first thing we’d notice is that its sun isn't a familiar yellow. Instead, it’s orange. That’s because where our Sun is a yellow G2 star, Alpha Centauri B is a K-type dwarf star, hence the orange tinge.

Comparison of star sizes in the Alpha Centauri system (Image: Courtesy of PHL @ UPR Arecib...

If you want a habitable planet, you need the right sun. The longer a sun lives and remains stable, the longer life has to emerge and evolve. If the sun in question is too large, then it will have a very short life. If it’s too small, it might last a long time, but the planet will have to be very close to stay warm and that can cause all sorts of problems, such as tidally locking the planet, so one side is always in daylight and the other in night, which isn't good. And then there’s the problem of suns that put out too much X-ray or ultraviolet radiation, or lack the elements needed to form planets that can support biochemistry.

Our Sun is a G2-type star. It’s fairly well behaved and has been so for 4.6 billion years. However, K-type dwarfs, which are smaller than the Sun, have lives longer than the age of the Universe. Heller and Armstrong argue that the longer a planet is inhabited, the more habitable it becomes due to a perpetual increase in biodiversity, so an older planet revolving around an older sun will be a better home for life. Alpha Centauri B is specifically a K1V-type star that fits the bill with an estimated age of between 4.85 and 8.9 billion years, and is already known to have an Earth-like planet called, disappointingly, Alpha Centauri B b.

As to the planet we’re looking for, if it exists, it will be located somewhere between 0.5 and 1.4 astronomical units (46 – 130 million mi, 75 – 209 million km) from Alpha Centauri B. Actually, we can be even more precise than that. All things being equal, it will be in a circular orbit 1. 85 AU (172 million mi, 276 million km) away. This would place it in the middle of the "stellar habitable zone," also known as the "Goldilocks zone" or the "Temperate Zone." This is the area surrounding Alpha Centauri B where it’s neither too hot for liquid water to exist, nor too cold for the planet to be anything but a giant snowball.

Different types of earth-like planets based on orbit and distance

Not surprisingly, the Earth sits in the Sun’s habitable zone, though Heller and Armstrong point out that it only just does, which means that our planet isn't exactly ideal because it could one day end up like Venus if things go pear shaped. Indeed, the researchers go so far as to say that Earth may not even be a typical inhabited planet.

Our superhabitable planet might not even be in the habitable zone. It could be a moon of some giant planet further away. Jupiter’s moon Io is a volcanic hellhole due to tidal heating. A larger moon that Heller and Armstrong call a "Super Europa" in the right orbit around a gas giant could heat enough to support life even if it’s technically outside the star’s habitable zone.

According to Heller and Armstrong, as we orbited above the planet, it would look very different from our own. It would be an older world, larger and more rugged, which would provide more places for life to exist. It would also be slightly more massive, which means more gravity.

The Alpha Centauri star system (Image: Courtesy of PHL @ UPR Arecibo)

That’s because for a planet to sustain life, it has to be geologically active. It has to have a rotating molten core to generate a magnetic field to ward off cosmic radiation and protect the atmosphere from being stripped away by solar winds. In addition, on Earth carbon dioxide is absorbed into silicates because of all the water present. Plate tectonics constantly draw these silicates into the molten interior, where they’re melted and the carbon dioxide returned to the atmosphere, which helps prevent the planet from overcooling and freezing. A slightly more massive planet with more gravity means more tectonic activity, so a better magnetic field and a more stable climate.

However, the most striking difference between the superhabitable world and Earth would be that the former would lack our continents and deep oceans. However much they may add to the aesthetic value of a planet and give it a nice baroque feel, large continents tend to have large deserts in their interiors and deep oceans are relatively lacking in life. Instead, Heller and Armstrong see a world with less water than ours, which would help to avoid both a runaway greenhouse effect and a snowball planet that an overabundance of water can trigger by either trapping heat or reflecting it away, depending on conditions.

Habitable zones of Alpha Centauri A and B (Image: Courtesy of PHL @ UPR Arecibo)

What water there is on our hypothetical planet would be evenly scattered across the surface in the form of lakes and small, shallow seas. This way, the shallow waters would hold much larger populations of more diverse life than is found on Earth, while the temperatures would be moderated. However, it would be a warmer world than Earth, which also makes for more diversity and potentially more oxygen, thanks to the higher gravity which helps retain any atmosphere.

One point that Heller and Armstrong make is that there may be more than one habitable planet in the Alpha Centauri B system. Cosmic bombardments early in the history of the Solar System is how the Earth got its water and minerals in the crust. If life had already emerged on one planet of Alpha Centauri B during its own early history, then the bombardment might have spread it to other worlds and back again as a sort of cross pollination, which would also make these worlds superhabitable.

Heller and Armstrong's paper is published in the January 16 issue of Astrobiology.

Source: Planetary Habitability Laboratory

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past.   All articles by David Szondy
22 Comments

More hypothetical planets to further waste dwindling resources, dreaming for 'a solution' (escape, from, for 'a few') to the effects of our earthly behaviour; we cannot even cope with terrestrial virus ...the first job on any new planet (hypothetically, but 1-1 odds) would be, we'd lumber about killing everything we could ..just in case it wanted to stop us paddling, or some such excuse ...it's us that needs changing, not the planet.

Jon Catling
28th January, 2014 @ 02:19 am PST

You want stability? You won't find any at Centauri. Any planet around either A or B is subject to wild perturbations of its orbit by the heavy presence of the other star. Orbits in such a system are so unstable as to be basically unpredictable. Heller and Armstrong are certain to know this; they're just having fun.

piperTom
28th January, 2014 @ 05:41 am PST

This is very exciting speculation. Exoplanets that are either 10s of light-years away or are barren aren't going to be important to us, but a potentially "super-habitable" planet next door is something we could potentially visit.

The previous commentator moaning about supposedly "dwindling resources" and the evil of mankind is a perfect illustration of how closely the Green position approaches mental illness. Reading such human-hating dysphoric drivel has only negative effects. His points are not just wrong, they're aimed at spreading his diseased worldview and making everyone as miserable as he is.

Ignore such anklebiters and marvel at the possibilities the universe has to offer. Life is not just Earth, our perspectives are going to widen unimaginably with the discoveries of the next few centuries.

EH
28th January, 2014 @ 06:08 am PST

Fascinating article David thank you! Just to let you know, moons have feelings too... I just checked in with Jupiter’s moon Io about your "volcanic Hell Hole" slight. Lo has been deeply hurt by this...

Paul Edwards
28th January, 2014 @ 08:29 am PST

At 4.22 light years away and 25.6 trillion miles we aren't going to be visiting anytime soon.

ezeflyer
28th January, 2014 @ 09:15 am PST

Interesting as such speculation always is, the article sounds more like a Terraforming wish-list than anything based in/on/around actuality.

Of course, without speculation, we might never have left the trees, and maybe someone will be inspired enough by this particular vision to invent/work on something that makes the detection of any such planets possible --- but this feels too nebulous to me at the moment.

leafygreen
28th January, 2014 @ 09:17 am PST

Well, perhaps that mathematician in Mexico back in the 90s might have figured a way to exceed the speed of light by riding one of the lesser neutrons or whatever it is called, if they have not already done that since. Our government isn't telling us anything these days.

dr. james willingham
28th January, 2014 @ 10:25 am PST

Where is your space ship that has odometer readings in "light years?" Where is your big lunch box that will last for that distance? Will you die of old age before you get there? Enjoy your trip. I have to get back to the real world.

donwine
28th January, 2014 @ 11:38 am PST

The imaginings of the "not real" world are what drive the workings of the "real" one. May we all soon remember.

EDDO
28th January, 2014 @ 03:44 pm PST

Life imitates art.

Coincidentally, I believe Alpha Centauri was the destination and planned new home of our space-faring nomads in the '60s TV series 'Lost in Space'.

Of course, that may be the only scientifically correct item from the show, what with the 'hot' comet that threw them off course in the first episode.

:-/

(Although, I always wanted that jet-pack!)

oldhacker
28th January, 2014 @ 04:02 pm PST

Who pays these guys? I hope it's not taxpayer money. Wayne and Garth had equally deep conversations on the hood of Garth's car.

RelayerM31
28th January, 2014 @ 04:11 pm PST

EH: Well said.

Earth is a death trap, species wise. We either find a way to exist in space or find another home. The womb is perfect to start life, but a death trap if you remain there. It's time for humanity to grow up and leave home.

Don Duncan
28th January, 2014 @ 06:32 pm PST

Man once stood on the shores of the great oceans and "wondered" at what might be on the other side, if anything at all (or a cliff with a dragon as some thought).

My point is, eventually, we created the "craft" required to "go find out" and we populated.

Space is our next great ocean to cross.

It looks as impossible now as crossing water did back then. And that's why I believe we'll do it. Because we've done it before. We've conquered the impossible.

Chris Winter
28th January, 2014 @ 07:20 pm PST

Yes, we did "go find out". And when we got there, it was already populated. No matter. 'THEY' aren't like 'US', so we pillage and slaughter.

I'm not so sure things would be all that different just because 'THERE' is another world.

Chris Hanagan
29th January, 2014 @ 04:23 am PST

I think our astronomer friends are simplifying things a little to much. Having a moon, deep oceans and tides are some of the major drivers for life on earth. Earth is a very special place for many, many reasons and the odds of finding something like it with intelligent life out in space are very, very small. Space is a far more hostile place and the challenges are far greater than most dreamers care to admit.

Bob
29th January, 2014 @ 07:10 am PST

Wow, what is wrong with all these cynical, defeatist, curmudgeons in the comments?

We're just going to slaughter any life we encounter? That's ludicrous. Even a cursory glance at the history of exploration will show that as tragic as it is when it does happen, systematically slaughtering the living inhabitants of new lands we discover is far from the norm. If it was, then all of South America would look European.

And even if we had, it's asinine to act like that kind of unthinking aggression is characteristic of civilized man. Read a newspaper, and then a history book and you'll see that we are, by far, as a whole, the most peaceful that we've ever been and only becoming more so.

4.26 light years is too far away so stop wasting time? You can't seriously think that if we discovered life on another planet, we'd have to be able to get there in an hour in order for it to be valuable information? 4.26 light years is well within communication range. Not to mention the many things we'd learn by the mere existence. Plus, Voyager 2 has traveled 15 billion miles in 30-something years... even without the many advances in space propulsion, we could theoretically land a probe on a planet 4.26 light years away in a little under 300 years. Take into account state-of-the-art propulsion and you can cut that my an order of magnitude. Not to even mention recent theoretical results that the speed of light may not be such a hard limit after all.

And lastly, half these commenters don't seem to have read the article. They act like the article said, "Aliens Found! Pack your bags, Earth 2, here we come!" The article doesn't say that anything except that Earth isn't a particular habitable planet and there are others, who fall more squarely into habitable zones, surprisingly close to us. Why that leads @bob to dismiss them as dreamers, or @leafygreen to call it a terraforming wishlist is beyond me. it's like they didn't read the same article.

I can say one thing: I'm kind of secretly glad that @donwine isn't interested in going. I can't imagine he'd be much fun in the confines of a generation ship. That is, if we could ever even get him to understand the concept of one.

M. Scott Veach
29th January, 2014 @ 08:49 am PST

Well, M. Scott Veach, you are right that the article didn't say "Aliens Found!..." But it does imply the fanciful idea that life could be far more plentiful and diverse there and had much longer to evolve than here on earth. If that were true, they likely would have discovered us long before we find them. If there isn't intelligent life, what would be the purpose of traveling many years to a slime planet with few natural resources and an unknown atmosphere? Dreamers fits perfectly. If there is intelligent life out there, they will be knocking on our door long before we can knock on theirs.

Bob
29th January, 2014 @ 02:53 pm PST

I do have to disagree on the “less water is better” concept.

Sounds a bit too much like Vulcan to me. ( 40 Eridani A )

We need an Ocean to support heat exchange between the equator and the northern regions, or you end up with the default; a blazingly hot equator, a pair of small semi-tropical bands, and giant icecaps.

I’m playing with the idea that the Genesis technology might work; what would my ideal planet look like?

The ideal planet would be one with dozens of small continents, none bigger than Australia.

The Gulf Stream equivalent winds between them on it’s way north, carrying heat away from the Equator.

The relatively small continents are warmed by this current, and there are few deserts.

William Carr
29th January, 2014 @ 03:34 pm PST

Frankly, if we can even achieve 10% the speed of light (which has been considered with conventional, available technology) would be 50 yrs to destination.

Nobody says a mission to Alpha has to be manned. Send a probe cluster, so at a certain point in the trip they break away from the craft body and as they pass Alpha they can each sent telemetry from different vantage points. It would be another five years before we get the data, but so what.

And who knows, 50 years from now we may even have FTL, but why wait for that to be available before attempting to get there conventionally.

As far as alien life, they would likely be older (wiser, civilized), and if gravity and oxygen is higher also physically stronger and bigger.

Our probe would be synonymous to a raccoon wondering from the Forrest into suburbia to look through garbage cans. ie - they will acknowledge our efforts in the log book and continue to silently monitor us as they have been since BC, or our first radio transmission in the early 1900s.

Their news headlines will read "Sol monkeys have achieved unmanned travel to Alpha". And I'm sure it will become a national holiday.

Nairda
29th January, 2014 @ 06:10 pm PST

Some really bizarre and tangential comments here.

M. Scott Veach is one of the few making sense.

How can anyone think that this article is about actually sending people to this or any other exoplanet, for colonising, terraforming, or generally hegemonising?

The spaceship reference is merely a thought experiment - "imagine you were there, hovering over the planet; what would you see"?

The point of the work by Heller and Armstrong isn't about "Where would we colonise next?". It's about deeper questions like "Is Earth itself unique? Is life on Earth unique? Do planets even need to be Earthlike to sustain life? Are we alone? ". Thanks to astronomical science, there is so much that we can, in time, answer about the prevalance of habitable planets and life-friendly environments, without ever hopping in a rocket...

Readout Noise
29th January, 2014 @ 07:38 pm PST

The grass always looks greener on someone else's planet!

donwine
29th January, 2014 @ 08:08 pm PST

You know, the point of the Astrobiology article was that K dwarf stars might have unusual habitable zones that might be more friendly to life than is Earth. Of course, this is based on no clear definition of life and a lot of vague handwaving. It happens that Alpha Centauri B is a K dwarf, but being in a triple star system is a bad thing for long-term stable conditions (although I am sure the authors would argue that instability gives more freedom for evolution). In addition, the fact that ACB has an Earth-sized planet with an orbital period of 3 days and a temperature likely in the thousands doesn't argue one way or the other to the presence of a "superhabitable" planet. I'm afraid this article belongs very close to the quack drawer.

Quansec
1st February, 2014 @ 12:08 am PST
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