Binary Planets Possible if they are Earth Sized

This makes great space art:




But how possible is this outcome in reality?

According to new research modelling planetary systems it now seems as though it is indeed possible for binary or "double planets" to form which would consist of two planets orbiting a common center of gravity as they orbit their star:



From this Space.com article:

Two Earth-size planets that orbit each other might exist around distant stars, researchers say.

The solar system has many examples of moons orbiting planets; Jupiter and Saturn both possess more than 60 satellites. However, these moons are usually much smaller than their planets — Earth is nearly four times wider than its moon and more than 80 times its mass.

Still, some moons are as large as planets. For instance, Ganymede, Jupiter's largest moon, is larger than Mercury, and three-quarters the diameter of Mars. Also, moons at times are nearly as large as their worlds; Pluto's largest moon, Charon, is about half the diameter of the dwarf planet itself. This raises the intriguing possibility that planets of equal size could orbit each other.

The Pluto/Charon system which NASA's New Horizons probe (the fastest spacecraft we've ever built btw) will arrive at this coming spring could be viewed almost as binary dwarf planet system. We also have long known of binary asteroids in our solar system but it was a question of whether larger, planet sized bodies could be in binary configurations. Until now...

The scientists ran about two dozen simulations. However, these simulations often resulted in the planets colliding, typically merging or accreting together into a larger planet and sometimes leaving behind a disk of debris from which a moon could form. Also, in some simulations, the planets collided in a grazing manner at high speeds, resulting in "hit and run" interactions in which the worlds escaped from one another.

Still, about one-third of the simulations resulted in binary planets forming. These involved relatively slow, grazing collisions.

"Previously, the only expected outcomes of large-body impacts of this sort were escape or accretion — that is, either the two bodies do not stay together or they merge into one, occasionally with a disk of debris," study co-author Keegan Ryan, an undergraduate student at the California Institute of Technology in Pasadena, told Space.com. "Our findings suggest the possibility of another outcome — binary planets. The bodies stay mostly intact, but end in a bound orbit with one another."

So now that they have modelled this if they are as persistent as their model suggests, it is only a matter of time before the first one is found in collected data. It is even possible one or two exist in Kepler data where I can tell you there are some weird light curves of candidate planets which -might- indicate binary planet candidates or terrestrial or superearth sized planets with large ring systems like Saturn.

Back to the article....

These binary planets would loom extraordinarily close to one another, separated by a distance of about half the diameter of each of the worlds. Over time, the rate at which both planets spin would fall into lockstep, with each world only turning one face toward its partner.

Such binaries can persist for billions of years, researchers say, provided they form at least half an astronomical unit or more away from their parent stars — far enough away for the star's gravitational pull to not disrupt the binary planet system. (One astronomical unit, or AU, is the average distance between the sun and Earth, about 93 million miles, or 150 million kilometers.)

This leads to the intriguing possibility of what is pictured above. A terrestrial binary planet system with life around a Sunlike star. The stuff of sci-fi may very well in some not-so-rare instances be the stuff of sci-fact! The conditions on such planets might be very different from the Earth (I can only imagine the tidal effect on their oceans for example) but they might not rule out life developing.

Imagine for a moment, if we lived on such a world.

Much of our myths, religions and stories and eventually science would involve that other world whose oceans and continents and perhaps forests and city lights which we could see with our naked eyes on the night sky.

Such a world could fill a good part of the sky similar to this space art below, but without the ring system and moons obviously:



For such a civilization on such a world technological development leading to space travel would not be side issue but would probably become imperative if their species was as curious as us.

Perhaps they would develop space travel much earlier in their history than we did in ours as the nearest habitable planet would not be many light years away but right next door like our Moon beckoning them throughout the ages.

Back to the science...

The abstract from their presentation is within this link (see 201.02 - Binary Planets)


If we were to find such a double planet system in the habitable zone of a Sunlike star it would represent an extremely fascinating "two for one".

This makes me want to go digging through the Kepler data archives on MAST at STSci

a reply to: JadeStar

Regarding the possibility of life there, I am more concerned about the gravitational pull on one planet over the other and how this could affect the shape of the planets, if not their water distribution or period of rotation.

Extraordinary find nevertheless, a definitive S&F from me!

a reply to: JadeStar

Wonderful thread, and wow. The tides on a planet with a binary planet companion. Surfs up! lol I wonder what kind of civilizations would develop? I agree the inhabitants learn flight early to get to the other planet. Could two separate life forms develop? I hope the resources on each planet are equal. For some reason I keep thinking of that Star Trek episode with the two races of half black and half white people, just on opposite sides and how they hated each other. Hopefully it would all be nice and peaceful.

originally posted by: swanne
a reply to: JadeStar

Regarding the possibility of life there, I am more concerned about the gravitational pull on one planet over the other and how this could affect the shape of the planets, if not their water distribution or period of rotation.

From my very rough back of hand calculations this would depend on their distance from each other but more importantly the size ratio.

If it is two equally sized worlds (say with ~5-10% +/- of each other) or a 1:1 ratio at the distance they postulate (1/2 diameter) then the gravitational pull would be equally transferred into angular momentum. Both planets would balance each other out and that instead might have an influence on their revolution about each other, their axial tilt over time or precession, as well as perhaps the wiggle of the two planets orbital path around the star.

They would however like our moon, be tidally locked with one side facing each other at all times.

Our moon stabilizes our planet's spin around its orbital access. Two relatively equally sized planets would do the same for each other.

Where it gets fun/bizarre is if one world were to be significantly larger than the other. In such cases the larger world would make the smaller one less round and more elliptical.

It would also pull on its oceans and crust leading to perhaps a very turbulent world of massive waves, volcanos and quakes.

Think of a more warm version of Jupiter's moon IO.

This might happen if the worlds were closer than the 1/2 diameter they mentioned and in a ratio of < 2:1 ratio.

But at that point you're really just talking about a planet with a close, large moon.

PS: If i got the math a little wrong, remember I am just an undergrad with a lot still to learn and prone to making some major errors sometimes

Extraordinary find nevertheless, a definitive S&F from me!

Thanks

BTW: It appears the modelling they did was to see how common a large moon like ours would be and how itcould form. It's thought our moon formed as a result of a collision between the Earth and another planet early in our solar system's history. This is a fine example of where when science looks for one thing it often can find something quite different in the process.

originally posted by: Iamschist
a reply to: JadeStar

Wonderful thread, and wow. The tides on a planet with a binary planet companion. Surfs up! lol I wonder what kind of civilizations would develop? I agree the inhabitants learn flight early to get to the other planet. Could two separate life forms develop? I hope the resources on each planet are equal.

All excellent plot lines for a great sci-fi movie which would examine our use of resources, our drive to explore, our reactions to those who are different from us etc but in the context of two civilizations separated by a space smaller than the diameter of each other's planet.

One could easily imagine one civilization being in the Stone Age while the other one is space travelling because there is no reason why they would arise at the same time or develop at the same rate. In fact it would seem more likely one would be first to flight than both getting there at roughly the same time.

Or perhaps one would develop technology while the other was more introspective or contemplative/artistic.

Maybe one was individualistic like us and the other a hive mind like an ant hill or The Borg?

So many possibilities for a great story/movie.

For some reason I keep thinking of that Star Trek episode with the two races of half black and half white people, just on opposite sides and how they hated each other. Hopefully it would all be nice and peaceful.

One of my favorite old Star Trek episodes. One of the nice things about sci-fi is that it can often help us see our earthly problems/issues in a different light and by doing so help us to begin to resolve them.

And then build a bridge to that big thing in the sky! Now!

Sorry, engineer here..

a reply to: JadeStar

Our moon stabilizes our planet's spin around its orbital access. Two relatively equally sized planets would do the same for each other.

I thought hey would pull into each other, slowly closing the distance and then joining in a cataclysm? Isn't that why all "moons' are smaller than their "planets"?

If unequal in mass the pull of gravity finds a Lagrange point to settle into. If equal in mass they both pull each other together?

I don't really know what I'm talking about, just not seeing any body in our solar system with an equal "partner".

originally posted by: intrptr
a reply to: JadeStar

Our moon stabilizes our planet's spin around its orbital access. Two relatively equally sized planets would do the same for each other.

I thought hey would pull into each other, slowly closing the distance and then joining in a cataclysm?

In most cases yes, or they have a near miss which flings them apart from each other into separate orbits or out of the system entirely.

That is why this research is surprising. In 1/3rd of the computer models they end up with a binary planet. That's far higher than conventional wisdom would suggest. It's also higher than what we have observational evidence for so far but like i said, there are some odd lightcurves in the Kepler data which could possibly indicate a binary planet system.

Isn't that why all "moons' are smaller than their "planets"?

Most of the time but not necessarily always. I asked this question once in high school physics class and my teacher told me in no uncertain terms that a double planet system would be nearly impossible because of that.

However we're always learning more about the universe and in some cases what we may have thought impossible might just be rare or simply unlikely. It is usually through the use of a new instrument, tool, computer model or mission that examines a question in greater detail that this occurs.

I am skeptical that such systems will be as common as what they modelled. It seems like out of the 4178 Kepler planet candidates there would be a clear binary planet system in there. And if there was you can bet it would have been announced by now.

If unequal in mass the pull of gravity finds a Lagrange point to settle into. If equal in mass they both pull each other together?

Not if they are in that "sweet spot" of 1/2 the diameter which these researchers seem to have modelled.

I don't really know what I'm talking about, just not seeing any body in our solar system with an equal "partner".

Well there are two which come close. The Earth and Moon and Pluto and Charon. While one is still smaller than the other they are often thought of as examples of a "double planet" system because the ratio of big to small is not as high as other planet/moon combinations in our solar system though neither is really a binary planet.

There are several searches for exomoons which hopefully will yield some other examples but it is slow going, tedious, "bleeding edge" work so it may be some years before we have an exomoon "periodic table" or gallery to compare to the moons in our solar system.

Exciting times lay ahead though and I expect we'll continue to be surprised by mother nature.

a reply to: JadeStar

Thanks for that reply and the information.

I asked this question once in high school physics class and my teacher told me in no uncertain terms that a double planet system would be nearly impossible because of that.

I understand that many star systems are binary, it would follow that 'as macro, so micro' might apply. Our solar system model is but one drop in a big bucket.

related topic: Did you read the article about scientists have figured out a way to characterize the magnetic fields of exo-planets. this is important in determining if a exo-earth is protected from stellar and cosmic rays like earth is. it is one more thing that would be used to determine potential probe targets, additional scope time, and even colonization targets.

www.sciencedaily.com...

originally posted by: intrptr
a reply to: JadeStar

Our moon stabilizes our planet's spin around its orbital access. Two relatively equally sized planets would do the same for each other.

I thought hey would pull into each other, slowly closing the distance and then joining in a cataclysm? Isn't that why all "moons' are smaller than their "planets"?

If unequal in mass the pull of gravity finds a Lagrange point to settle into. If equal in mass they both pull each other together?

I don't really know what I'm talking about, just not seeing any body in our solar system with an equal "partner".

in our moons case it's the tidal forces and "sloshing" that are actually pushing the moon away. when it first formed it would have filled a huge portion of the sky. trying to remember the figure... i wanna say it moves away about an inch a year?

a reply to: stormbringer1701

Yes
Is the moon moving away from Earth?

Yes, it is! But it is moving only about an inch farther away each year.
solarsystem.nasa.gov...

a reply to: stormbringer1701

in our moons case it's the tidal forces and "sloshing" that are actually pushing the moon away. when it first formed it would have filled a huge portion of the sky. trying to remember the figure… i wanna say it moves away about an inch a year?

Thanks. I was speculating about equal sized planets in orbit about each other, though. Pretty big size diff with the moon…

Image

originally posted by: stormbringer1701
related topic: Did you read the article about scientists have figured out a way to characterize the magnetic fields of exo-planets. this is important in determining if a exo-earth is protected from stellar and cosmic rays like earth is. it is one more thing that would be used to determine potential probe targets, additional scope time, and even colonization targets.

www.sciencedaily.com...

Yes! I was just about to post something about this but please go ahead and post it up and talk about it cause i'm kinda snowed under with work.

originally posted by: JadeStar

originally posted by: stormbringer1701
related topic: Did you read the article about scientists have figured out a way to characterize the magnetic fields of exo-planets. this is important in determining if a exo-earth is protected from stellar and cosmic rays like earth is. it is one more thing that would be used to determine potential probe targets, additional scope time, and even colonization targets.

www.sciencedaily.com...

Yes! I was just about to post something about this but please go ahead and post it up and talk about it cause i'm kinda snowed under with work.

im way to multi-tasked to do it now. we'll see who gets to it. i only have a little to say about it beyond the article, anyway.

a reply to: JadeStar

That would be amazing and awesome to see. You could just think about what that other life would look like. How similar and how different it is to each other? Do we have similar lifestyles or are they more advanced then each other?

It just causes so many questions and really cool ideas to make stories/theories upon.

I would just worry about the gravity pulling the two planets closer and the tides like others said. Those would be my only worries.


Beautiful find!

moar Stuff!

phys.org...

a reply to: JadeStar

There is a sci-fi novel from the 1980s calledFlight of the Dragonfly, where a mission to Barnard's Star is undertaken. They arrive and discover a binary planetary system. The original version of tbe book was interesting. The author later updated the book, added some sex scenes that was written by his wife. Still, it was/is an interesting premise. It would actually make a good movie.

originally posted by: PrinceRupertsDog
a reply to: JadeStar

There is a sci-fi novel from the 1980s calledFlight of the Dragonfly, where a mission to Barnard's Star is undertaken. They arrive and discover a binary planetary system. The original version of tbe book was interesting. The author later updated the book, added some sex scenes that was written by his wife. Still, it was/is an interesting premise. It would actually make a good movie.

in the past an astronomer thought he detected a gas giant at barnards star. (the same thing happened with proxima as well) so for a while everyone thought banard's star was the place to go. unfortunately subsequent searchers ruled out anything larger than neptune i believe and no wobble or transit was observed above statistical noise level. still that does not mean barnard's star does not have smaller planets. it will be interesting in the next decade to see which of the abundant dwarf stars in our neigborhood turn out to have planets. i mean there are a lot of them.

EDIT: did some checking on the mass allowable by the limits of our detection capability for barnards star. from the wiki:

M dwarfs such as Barnard's Star are more easily studied than larger stars in this regard because their lower masses render perturbations more obvious.[42] Gatewood was thus able to show in 1995 that planets with 10 times the mass of Jupiter (the lower limit for brown dwarfs) were impossible around Barnard's Star,[38] in a paper which helped refine the negative certainty regarding planetary objects in general.[43] In 1999, work with the Hubble Space Telescope further excluded planetary companions of 0.8 times the mass of Jupiter with an orbital period of less than 1,000 days (Jupiter's orbital period is 4,332 days),[4] while Kuerster determined in 2003 that within the habitable zone around Barnard's Star, planets are not possible with an "M sin i" value[44] greater than 7.5 times the mass of the Earth, or with a mass greater than 3.1 times the mass of Neptune (much lower than van de Kamp's smallest suggested value).[18]

Even though this research has greatly restricted the possible properties of planets around Barnard's Star, it has not ruled them out completely; terrestrial planets would be difficult to detect. NASA's Space Interferometry Mission, which was to begin searching for extrasolar Earth-like planets, was reported to have chosen Barnard's Star as an early search target.[23] However, this mission was shut down in 2010.[45] ESA's similar Darwin interferometry mission had the same goal, but was stripped of funding in 2007.[46]

so for now we can rule out anything bigger than 7 earth masses.

but the reason project Daedalus chose barnard's star as a probe destination rather than alpha proxima despite the extra 20 something years of flight time at ten percent c was that everyone thought it had planets at the time.

There have been two instances of observations or data indicating companions planets or brown dwarfs for Proxima:

Proxima Centauri b?

Using data collected up to early 1994, astronomers using the Hubble Space Telescope discerned a 77-day variation in the proper motion of Proxima (Benedict et al, 1994). The astrometric perturbations found could be due to the gravitational pull of a large planet with about 80 percent of Jupiter's mass at a 1994 separation from Proxima of about 0.17 AUs -- 17 percent of Earth's orbital distance in the Solar System from the distance, or less than half Mercury's orbital distance. The Hubble astrometry team calculated that the chance of a false positive reading from their data -- same perturbations without a planet -- to be around 25 percent.


© Estate of John Whatmough -- larger image
(Artwork from Extrasolar Visions, used with permission from Whatmough)
Glowing red through gravitational contraction, the candidate brown dwarf companion
to Proxima Centauri is depicted with two moons (one eclipsing the flare star) with
distant Alpha Centauri A and B at upper right, as imagined by Whatmough.


In 1996, another group of astronomers using the Hubble Space Telescope discovered that they might have directly observed a companion to Proxima with the implied brightness of a brown dwarf and an apparent visual separation of only about half the Earth-Sun distance -- 0.5 AU (Schultz et al, 1998). A substellar companion at that distance would imply an orbital period of around a year, or it could be in a highly eccentric orbit with a much greater average distance from Proxima. However, later observations by other astronomers using interferometric astrometry and recent radial velocity data found no evidence to support the existence of a companion greater than 0.8 Jupiter mass with an orbital period around Proxima Centauri of between one and about 2.7 years (Benedict et al, 1999). Proxima has been selected to be one of the Tier 1 target stars for NASA's Space Interferometry Mission (SIM) -- which is planned for launch as early as 2011 -- to detect a planet as small as three Earth-masses within two AUs of its host star.

from: www.solstation.com...



alpha proxima, Proxima, or alpha centauri C is .2 light years closer to earth than alpha centauri A. let's go. 42.6 years at ten percent C. let's go! or at least send a probe. voyager has been travelling for 36+ years. proving our craft can last that long and our human attention span funding and manning of monitors can last that long. let's go!

a reply to: JadeStar

Very interesting

One of my first thoughts too, was of the mythology, stories, cosmology and so forth that would be developed on such worlds.

I imagine that some of them would also be wonderfully apocalyptic! I can almost see an alien Vercingetorix (of the cartoon variety) being carried around on his shield shouting about the sky falling in on his head tomorrow.