Alpha Centauri Has an Earth-Sized Planet

The Bad Astronomer writes "Astronomers have announced that the nearest star system in the sky — Alpha Centauri — has an Earth-sized planet orbiting one of its stars. Alpha Cen is technically a three-star system: a binary composed of two stars very much like the Sun, orbited by a third, a red dwarf, much farther out. Using the Doppler technique (looking for very small changes in the velocities of the stars) astronomers detected a planet orbiting the smaller of the two stars in the binary, Alpha Centauri B. The planet has a mass only 1.13 times that of the Earth, making it one of the smallest yet detected.However, it orbits the star only 6 million kilometers out, so it's far too hot to be habitable. The signal from the planet is extremely weak but solidly detected (PDF), giving astronomers even greater hope of being able to find an Earth-like planet orbiting a star in its habitable zone."

Comments

Dear /S/cientists

[DSS11Q13]

how do planets orbit binary star systems? I would think two stars would give the planets erratic orbits that would either send them into one of the suns or shoot them into space.

Re:Dear /S/cientists

[Anonymous Coward]

Any system of bodies is going to have a center of gravity. My guess (not having read TFA) is that this planet is many times further away from the binary stars than they are to each other.

From the PDF, it seems to be the opposite:

With a separation to its parent star of only 0.04 AU, the planet is orbiting very close to Alpha Centauri B compared to the location of the habitable zone.

Re:Dear /S/cientists

[harperska]

Having RTFA (I know), this planet is very close in to one of the stars, in this case Alpha Centauri B. There are two possibilities for planets in a binary system, either orbiting close in to one of the stars, or far away from both. I think I remember reading once that Alpha Centauri A and B are far enough apart from each other that there is a good chance that planets in either star's habitable zone would have stable orbits.

Re:Dear /S/cientists

[xigxag]

The planet is 6 million km from B, or roughly 10x closer than Mercury-sun.

A and B are roughly 3.5 billion km from each other, or roughly the Sun-Uranus distance.

So, no.

Re:Dear /S/cientists

[bjorniac]

It's rather the same way the moon orbits the earth. If you have a binary system, a planet can quite happily orbit very close to one of the two stars so long as the distance between the planet and the star it orbits is smaller than the distance between stars. The pair of stars will orbit their mutual center of mass, and the planet will orbit a single star.

Of course, the three body problem is an open question in physics, but if you make the assumption that one of the masses is much smaller than the other two it (which is the case for planets orbiting stars) it becomes quite solvable, especially if you're happy with numerical simulations of orbits.

A similar situation is possible if the planet is a long way from the pair of stars, and would then orbit their center of mass. That isn't the case here, but is certainly a feasible solution to the problem. You only really get orbits that are highly erratic when the planets orbital radius is over a quarter of the distance between the stars.

Throughout this I've assumed equal mass stars. Feel free to put a factor of M1/M2 in front of every distance I gave for non-equal mass stars.

Re:Dear /S/cientists

[Anonymous Coward]

The stars are actually very wide spaced compared to the planet-star system itself. As a result, the planet is well within the gravity well of B. At a minimum AB separation is 11AU - well over 200 times the B-planet separation.

Orbit centred on A: https://upload.wikimedia.org/wikipedia/commons/e/ee/Orbit_Alpha_Centauri_AB_arcsec.png

Simulation plus table of info: http://www.solstation.com/orbits/ac-absys.htm

Re:Dear /S/cientists

[wierd_w]

What are the prospects for a single orbiting planet (let's exclude other objects) orbiting both stars in a figure 8 configuration, crossing the barycenter of the star's combined rotations?

(Eg, both stars orbit clockwise as seen from plane of rotation north, and orbit each other in an elipse. A planet orbits first one star, then the other, crossing the barycenter at the period of maximal approach of the two stars, moving from one star to the other like a dance partner in a ballroom routine.)

Assuming that the objects are free from outside gravitational purturbations, are exactly the right distance apart, and that the periodicity of the planet's orbits between the stars is exactly synchronized, would such a system be stable?

Re:Dear /S/cientists

[MyLongNickName]

Not an erratic orbit at all. Picture Jupiter. If it suddenly increased its mass by a factor of 20, it might have enough mass to become a star, but would have virtually no impact on the orbit of Mercury, and very little on Earth or Venus. Just because a body becomes a star does not require planets to orbit both stars. In actuality, all planets orbit the center of mass of the solar system. In our solar system's case that resides inside the sphere of our sun.

Re:Dear /S/cientists

[Vekseid]

It'll get ejected - that configuration isn't stable.

For Alpha Centauri A and B, the 'stable zone' is out to roughly Jupiter's orbit from each star - plenty of room for both to have habitable worlds.

Re:Dear /S/cientists

[wierd_w]

Oh, I understand it would be absurdly touchy, pretty much garanteed to not exist, and almost certainly not stable long term.

We could juice it up a little, and say that there is a very massive object that orbits both stars at a very large radius out, around the combined center of rotation. Say, a class M star, or a brown dwarf. This object will perturb the orbit of the hypothetical figure-8 planet. (We will assume that the planet is very far frrom the parent stars, say jupiter orbit equiv, and that the companion stars are very far apart as well. (The distance between the locked stars at closest approach is slightly greater than the greatest distance of the planet's orbit.) The timing of the 3rd, distant star is such that it provides the nudge to push the planet out of orbit of the first star, and into the orbit of the second. (Let's view it this way: the planet is moving in toward the barycenter clockwise from the northwest quadrant. For visualization purposes, we are locking camera rotation so that both stars are fixed on the X axis and periodically approach and recede each other. The 3rd massive body orbits clockwise, and is say, 5 degrees off the X axis at the point of transit, in the north east quadrant. As the planet transits, it would gain a shitton of momentum, and woult tend to get thrown out like a stone from a sling. However, the location of the 3rd massive object curves the tradjectory, preventing ejection. The planet then orbits the second star eliptically, and rotates much faster on its own axis. As the system returns to the point of closest proximity again, the 3rd object has exchanged places such that it is at the complimentary angle, the planet passes the transit point, is again caught by the gravitational influence of the 3rd star, and forced into orbit with the original partner again. The change in orbital rotation (clockwise-anticlockwise) caused by the figure 8 orbit, causes the rotation of the planet to radically drop, possibly tide locking with the first star. The system then repeats. Orbital momentum of the 3rd star is conserved by the wobble of the system barycenter as the planet enters conjection with each star relative to its location.)

The 3rd star would shepherd the crazy figure8 planet, keeping it from being ejected.

I might pull an orbital simulator and see if this can actually work.

Re:Dear /S/cientists

[Vekseid]

And that's just it - all stars involved are shedding mass in different directions, at varying rates. You might have instances where a single figure-eight of sorts gets performed, but that means there's been a capture and likely a subsequent ejection. But unless you actually want to engineer this somehow, and have a means of keeping it stable (planetary thrusters go!) - it won't be seen. If we ever find something like that the first assumption is going to be aliens having fun, and that's what Occom's razor is going to boil down to.

Re:Dear /S/cientists

[MyLongNickName]

For those who care

Jupiter is about 0.0009 solar masses. Current models of nuclear fusion predict that if an object has mass of about 0.07 solar masses it will begin a fusion reaction. So Jupiter would need to swell to 80 times its current mass.

Re:Dear /S/cientists

[MyLongNickName]

More reading indicates that the center of mass of our solar system can be inside or outside of our solar system depending on the position of Jupiter relative to Saturn. I didn't know this before.... interesting stuff.

Re:Dear /S/cientists

[dotancohen]

What are the prospects for a single orbiting planet (let's exclude other objects) orbiting both stars in a figure 8 configuration, crossing the barycenter of the star's combined rotations?

I asked this very question not long ago:
http://physics.stackexchange.com/questions/31201/might-a-planet-perform-figure-8-orbits-around-two-stars

Re:Dear /S/cientists

[bjorniac]

A figure-8 is quite hard to find, since the symmetries involved would require almost perfectly equal masses between the stars and perfectly circular orbits of the stars. (This is from memory running simulations a long while back). However it is certainly possible to have a planet be orbiting one star for a few loops and then be captured by the other, orbit it a few times and keep getting passed back and forth.

The basic condition you need for this is for the planet to have enough energy to get over the maximum between the two gravity wells of the stars. If you think of kinetic and potential energy being like those of a ball rolling on a set of hills, you'd say that the ball is either trapped between two peaks or not. However with this case it would appear that the hills themselves are moving, so the "hump" between them will grow and shrink with time, sometimes letting the ball pass between valleys, sometimes trapping it in a single valley for a few cycles.

What's really remarkable is that this is all do-able without too much technical knowledge. You'd need:

About a second year undergrad level of physics - You could do it with Newtonian mechanics, but Lagrangians make it a LOT easier);

A bit of programming technique (two days or so with MATLAB and you'll get the basics of ODE solvers).

A LOT of patience :)

As an aside, you could just grab the game "Osmos" which has a lovely set of orbital levels that basically implement this :) I strongly suspect whoever was involved with it was well educated in physics, as finding the stable orbits they have requires an understanding of conservation laws and use of a symplectic integrator (eg Verlet's algorithm) to implement time updates, instead of just using Newton's method.

I'd leave well enough alone!

[p51d007]

If somehow we "made contact" with some "ET" type, and they had the means to get here "quickly", you think they would come in friendship? LOL, probably blow us up like the Klingons, Borg or some other crap. Just leave things alone will ya?

Re:I'd leave well enough alone!

[MyLongNickName]

Why is this modded down? Stephen Hawking would agree.

Re:I'd leave well enough alone!

[sakari]

If somehow we "made contact" with some "ET" type, and they had the means to get here "quickly", you think they would come
in friendship? LOL, probably blow us up like the Klingons, Borg or some other crap. Just leave things alone will ya?

That's what the television and movies tell you, don't they? Do you ever wonder why most of them tell that ETs are here to attack us ?
To keep us in Fear and to believe that if someone would come here, this would be automatically justify a reason for us to attack them.

Think about how the US & Hollywood portrays terrorists in movies, TV -series and mainstream news. Same thing with Extraterrestrial Life.

Oh, and btw. Imagine, that if there are civilizations out there who are _exponentially_ more evolved, have the capability to understand 100,000,000 times more of every aspect of technology and life, why would they travel here slowly ? They would have most probably already mastered Quantum Teleportation and other technologies we are still dabbling around with, and therefore would already know how to transfer themselves physically to our realms if needed.

And if a lifeform has gained such high insights into life itself, it would have already meant that they had gone through the phase of understanding that killing themselves and others is not the way. So why would such a race attack us ?

And now, if there is a race that wants us as their slaves, wouldn't they just infiltrate themselves into our society instead of attacking directly? What's the point of just killing everyone and taking the planet ? Any race that could come from such far distances would have to technologically and socially so much more advanced, they must have thought about more advanced tactics also.

  And maybe this has already happened, and we are living in such a society where we are slaves to some certain bloodlines who are in contact with these beings .. think about kings & queens, why are always the same f*ckers in control and most of the society feels like slaves to them ? Think about this possibility.

Oh yeah, and one more thing, we already are in contact with ETs and Aliens, and have been for so long time already. Our society has suppressed this information for so long to keep us blinded from the truth. The communication happens telepathically and during meditative states of mind, or during dreams. Research the subject, the information is out there.

Re:I'd leave well enough alone!

[mcgrew]

Our society has suppressed this information for so long to keep us blinded from the truth. The communication happens telepathically and during meditative states of mind, or during dreams.

WTF, slashdot? That's insightful??? Prove telepathy exists, prove that the "telepathic" subject actually had contact, prove it wasn't a stupid dream, do it with the scientific method and you could have a point. But you see, you can no more prove that than you can prove that sentience exists.

This was NOT the least bit insightful, rather Sakari has shown evidence of schitzophrenia in himself. Dude, see a mental health professional; I've known a few folks with your disease and the drugs do indeed work. Unfortunately, the symptoms of the disease keep the sufferer from taking his medication.

At least, lay off the coke and acid, dude, because you've gone off the deep end.

Re:That sounds really cool

[jamstar7]

Let's use that as a setting for a sci fi movie and waste it on contortionist zombies and scientists who act like complete douchebag morons. Awesome.

Seriously, dood, you gotta stop writing for SyFy Channel.

Re:That sounds really cool

[MachDelta]

Sounds good. Let's call it... Chiron. Or maybe Manifold 6?
Ooh, ooh, is it going to have telepathic worms?

Apparently there's a message there...

[Gort65]

...for us about some space bypass or something. Seems important for some reason.

Temperature = 1500K

[kf6auf]

That sounds really cool. Or hot since, unfortunately, the close proximity to its star means that it probably has a surface temperature of 1500 K.

I guess I'd be more interested in a different-sized planet a bit further away from its star.

Re:Temperature = 1500K

[harperska]

What makes this a big deal, is that prior to this it was an open question whether the Alpha Centauri system could support planets orbiting the individual stars or not. Now that it has been shown that planets can orbit the individual stars in this system, as opposed to orbiting outside both stars around the common center of gravity as is the case for most planets in binary systems, the probability of their being more planets including possible ones in the habitable zones of the stars just got a whole lot bigger.

Re:Temperature = 1500K

[v.dog]

Then they really are the real small furry creatures.

Re:That sounds really cool

[Anonymous Coward]

We should send seven leaders, who can't agree on anything, on a spaceship to go visit and check the place out.

Re:Heil Sid Meier

[cashman73]

We better get moving! It's already 2012 and the game ends in 2050!

Re:Unfortunately

[murdocj]

Not unfortunate, just a recognition of reality. At this moment in time, the science return for sending unmanned probes / orbiters / rovers vastly exceeds the return on sending humans. We'll continue to develop space capability and at some point it may make sense to send humans to Mars ... or maybe not.

And please do NOT invoke the whole "omg we have to get off this rock" argument. If an asteroid impact blew most of Earth's atmosphere and water into space and annihilated 99.999% of the species, Earth would STILL be easier to live on than Mars.

Re:Uh oh...

[Anonymous Coward]

lol, anonymous thinks the universe is twice as big as the solar system.

Man will never fly, and only a fool would think it possible to walk on the moon.

Re:That sounds really cool

[felixrising]

Let's use that as a setting for a sci fi movie and waste it on contortionist zombies and scientists who act like complete douchebag morons. Awesome.

Did you have a hand in Prometheus?!

Sure

[viperidaenz]

A very close and very fast orbit produces weak but detectable movements of its star. But what if the planet were moving much slower and was much further away? Would that not mean the star would move even less, and slower as well? How does this give more hope to detecting planets in the habitable zone? Its 25x closer to its star than Earth. It's also 13% heavier than Earth and Alpha Centauri B is 9% lighter than the Sun. If my napkin calculations are correct, this planet has ~700x more gravitational effect on its star than Earth has on ours.

Re:Uh oh...

[Anonymous Coward]

Man doesn't fly. We build machines that we sit inside of that can fly. Please describe the machinery required to traverse four light years of space, with absolutely no resources available from Earth once it's on its way, and is 100% fail safe and will get there either within a useful human lifespan, or describe a way to (on top of the machine from step 1) slow down life processes reversibly and safely.

That's the thing with all your "man will never fly" quotes. Someone BUILT a machine, using real materials, real energy sources and real engineering with a few YEARS.

Since the moon shots, the space loon brigade has had DECADES to show us something, ANYTHING, that manned space makes a shred of sense.

That's the thing. You think that because someone was wrong, you think anyone who predicts a negative outcome is wrong. But you skip the tiny little detail of you know, BUILDING what it is you claim is possible.

By your logic, any prediction that sounds wrong to you, for whatever reason, can be discarded.

Man will never extend his lifespan.

Understatement of the Year

[BlackGriffen]

"it's far too hot to be habitable."

That's an understatement. From the ArsTechnica article on the alpha Centauri planet:

"But don't start building the colony ship just yet. With a 3.3 day orbit, the planet is only 0.04 Astronomical Units (1 AU is the typical distance from the Earth to the Sun). That makes this planet blazingly hot, at about 1,500 Kelvin."

Re:That sounds really cool

[pellik]

Let's use that as a setting for a sci fi movie and waste it on contortionist zombies and scientists who act like complete douchebag morons. Awesome.

Seriously, dood, you gotta stop writing for SyFy Channel.

I don't get it. What does his comment have to do with wrestling?

And us space bloggers feel like chumps

[Nyrath the nearly wi]

Space bloggers (like me) who are signed up with the ESO news feed got word of this overnight. But the story was under embargo. You do not break the story until the embargo lifts or the ESO and Nature magazine gets very angry at you.

But some loud-mouth in Croatia violated the embargo. We were patiently waiting for the embargo to lift, biting our collective tongues, when mouthy jumped the gun.

We got an email from the ESO about an hour ago that said:

"I just spoke to the Head of Press at Nature, Ruth Francis, and we have agreed to LIFT THE EMBARGO on the Alpha Cen story IMMEDIATELY due to an unfortunate leak. You may run your stories."

Nature and ESO lift exoplanet embargo early following coverage by Croatian news outlet

Re:Obligatory:

[Geoffrey.landis]

This IS Beta Centauri Five!!! Beta Centauri Six exploded, six months after we were left here. The orbit of the planet shifted. ADMIRAL Kirk never came back to check on our progress...

Amusing, but, no, Alpha Centauri B is not Beta Centauri. Beta Centauri is a completely different star, about 300 light years away.

http://www.astro.wisc.edu/~dolan/constellations/hr/5267.html

Re:Heil Sid Meier

[cbhacking]

Err what? The game *starts* in 2100 (the Unity launches in 2060 and spends 40 years in transit). You may be thinking of one of the earlier Civ games. Alpha Centauri, depending on difficulty level, ends (you reach "mandatory retirement age") on 2300, 2400, or 2500. Each turn is one year, unlike typical Civ games.

There Could Be Habitable Planets Also

[crunchygranola]

It is entirely possible that there are undiscovered planets in the habitable zone. It is the planets closest to the star with the shortest orbital periods that are the easiest to discover, either because generate frequent perturbations that can be detected in the data set, or are the most likely to cross the stellar disk (when using the brightness fluctuation method).

Re:Uh oh...

[jamstar7]

Since the moon shots, the space loon brigade has had DECADES to show us something, ANYTHING, that manned space makes a shred of sense.

And every time we come up with something, the JOEs shoot it down by saying 'We can't do that now, therefore we'll never be able to do it so don't even bother getting out of bed'. And Congress seems to listen to the JOEs, especially when they can game the system to pump and dump 'development money' into their districts as purest pork without having to come up with anything tangible with the money, rinse and repeat.

Re:Unfortunately

[Hal_Porter]

He failed to predict the danger of Nazi WMD though, and allowed a "missile gap" to develop

http://en.wikipedia.org/wiki/Vannevar_Bush

The German V-1 flying bomb demonstrated a serious omission in OSRD's portfolio: guided missiles. While the OSRD had some success developing unguided rockets, it had nothing comparable to the V-1, the V-2 or the Henschel Hs 293 air-to-ship gliding guided bomb. Although the United States trailed the Germans and Japanese in several areas, this represented an entire field that had been left to the enemy. Bush did not seek the advice of Dr. Robert H. Goddard. Goddard would come to be regarded as America's pioneer of rocketry, but many contemporaries regarded him as a crank. Before the war, Bush had gone on the record as saying, "I don't understand how a serious scientist or engineer can play around with rockets", but in May 1944, he was forced to travel to London to warn General Dwight Eisenhower of the danger posed by the V-1 and V-2. Bush could only recommend that the launch sites be bombed, which was done.

Not a mistake his rather unjustly maligned namesake would have made.

Re:Uh oh...

[aaaaaaargh!]

Why? A generational ship is not a new concept.

It sucks, though, as it will invariably be overtaken by some dudes in a faster-than-light space yacht who make fun of the ancient crew. At least that's what my sci-fi reading experience tells me. :-)

What's the use

[Rexdude]

We're stuck here for good, destined to just keep looking at extra solar planets via telescope and speculating about whether they could support life as we know it. The nearest star, Proxima Centauri, is 4.3 light years away. The farthest man made object is just roughly 17 light hours from home after 35 years of travel; so forget about sending spaceships physically to the stars unless someone invents warp drive. It's laughable to talk of Alpha Centauri when no one in power is showing interest in returning to the moon, let alone Mars.
And leaving aside that, we're stuck with the reality of NASA facing budget cuts despite its overall budget being a drop in the ocean compared to what's been spent on war in the last 10 years.
Space exploration should've been incremental, start with a lunar refuelling base at the pole where there's water ice that can be broken down into hydrogen and oxygen for rocket fuel, and use that as a staging area for further exploration. Build a spacecraft for travelling to Mars in LEO stage by stage, and send a bunch of robots to assemble a modular base well before the first humans are sent (Kim Stanley Robinson's Mars series describes this approach).

While Curiosity, Opportunity & Spirit are testimony to NASA's engineering prowess, it still can't beat an actual geologist (areologist?) on Mars with a field laboratory who's able to directly analyse rocks and figure out what it was like in the past.

Want some perspective? Just the annual airconditioning budget for the US Army in Iraq/Afghanistan far exceeds that of NASA's.

Re:Unfortunately

[Tubal-Cain]

Unfortunately the United States can't even get off the planet anymore...

Sure we can.