The galaxy may swarm with billions of wandering planets

**Descensus** · 05-18-2011 06:29 PM

The galaxy may swarm with billions of wandering planets | Bad Astronomy | Discover Magazine

A new result from astronomers who have spent years peering toward the center of the Milky Way has led to a startling conclusion: there may be billions of Jupiter-sized planets wandering the space between the stars, unbound by the gravity of a parent sun. In fact, there may be nearly twice as many of these free floating planets as there are stars themselves in our galaxy, and they may even outnumber planets orbiting stars!

The study, published in Nature, is the result of the Microlensing Observations in Astrophysics (MOA) project. Instead of looking for tell-tale blips of light near stars, or the effect of planets on their parent stars, microlensing looks for the effect of the planet on background stars that are far more distant than the planet itself.

Warped view
It’s a little weird, and is due to gravity warping space. Imagine me sitting on a flat floor, rolling marbles away from me in all directions. If you’re sitting a few meters away, you can only catch the marbles that are aimed at you. But if there’s a dip in the floor between us, some of the marbles I roll that might have otherwise passed you will get their path diverted toward you as they curve around the dip. You get more marbles!

The same thing with light and gravity. A star emits light in all directions, but we only see the small amount of light headed our way. If a massive object like a planet gets between us and the star, the gravity of that planet can warp space, causing light we otherwise wouldn’t see to bend toward us. We see more light: the star gets brighter! This is called a gravitational lens. If that massive object is a planet moving in space, then we the starlight get brighter as the planet moves between us and the star, and then fainter as the planet moves on. The way the light changes is predicted by Einstein’s equations of relativity, and can be used to find the mass of the planet doing the warping.

OGLEing a MOA
So the astronomers with MOA sat down and stared at a patch of sky near the center of the Milky Way. In fact, they looked at an astonishing 50 million stars near the galactic bulge — stars are densely packed there, maximizing the chance of seeing a rare event. The lensing of starlight by a passing planet only lasts for a couple of days, so they took images every 10 – 50 minutes to make sure they caught as many as possible. The amount of data they amassed is fiercesome.

And even with all that, in a year of observations (from 2006 – 2007) they only caught about a thousand events. At first that sounded like a lot to me, but it’s only one lensing event per 50,000 stars! Yikes. Anyway, of those 1000, a bit less than half were solid enough observations to use in the study. And of these, only 10 — ten — had that magic characteristic time of about 2 days, indicating the lens was a planet with about the mass of Jupiter. Stars are more massive, and the lensing effect can take weeks from start to finish; only a planet can make such a short event.
Being careful, the astronomers took those 10 events and asked the folks using a different survey (OGLE, for Optical Gravitational Lensing Experiment; acronyms using "GL" tend to be somewhat droll) to see if they saw them as well. OGLE caught 7 of the 10 seen by MOA, confirming their results.

So what makes the astronomers think these are free-floating planets, and not ones orbiting stars like Earth does? Well, the lensing events themselves show only a single rise and fall of the background starlight. If the planets were orbiting stars, those stars would also act like lenses, and their effect would be seen. They weren’t. Now, it’s possible that if a planet were on really wide orbit, the parent star would be too far away to have a significant lensing effect. However astronomers can determine statistically how often that should happen, and the likelihood is only about 25%, meaning a significant number of the events must have been caused by planets without stars.

Goose! Eject! Eject!
Amazing! But where did these planets come from?

Since they’re floating free in space, they either formed like stars, directly from the collapse of interstellar gas clouds, or they formed in solar systems like our own and somehow got tossed out.
The first case — that these objects form like stars — makes a definite prediction on the distribution of masses of the objects (in other words, how many will have a mass 0.1 times Jupiter, how many 0.5 times, and so on). The mass distribution seen doesn’t fit the predictions at all, making that unlikely.

So that leaves them forming in solar systems like our planets did. But how does a planet get ejected from a star? Actually, this comes about naturally, and in fact may be common.
I’ve long suspected this was the case; it makes sense. We see lots of massive planets huddling close in to their parent stars, far closer than any reasonable model can predict. Most likely, these planets form farther out in their native solar system and then migrate inwards toward the star as they plow through the material left over from their formation. Any planet between them and their star will be affected; some will shift orbit, dropping toward the star themselves, others will get flung into wide orbits, and others still will be tossed out of the system entirely.

It’s those last that are so interesting. If the inward-moving planet is, say, five times the mass of Jupiter, it can gravitationally eject a smaller planet, even one as massive as Jupiter. And we do see lots of very massive planets orbiting close in to their stars. This strongly implies that for every "hot super-Jupiter" we see, there is one or more planet that got kicked out of the system, sent out into the galaxy at large á la Space: 1999.

Living la vida interstellar
The MOA results seem to confirm this idea: the statistics imply that there may be twice as many Jupiter-mass free-floating planets in the galaxy as there are stars! Just to let you know, there are hundreds of billions of stars in the galaxy, so there must be many, many billions of planets floating in the vast, empty regions between stars.

Billions. Wow. In fact, these free-floaters may outnumber "regular" planets by a factor of 1.5 or so. There are more of them than there are of us!

Mind you, the MOA survey is sensitive to planets with masses about that of Jupiter. They can’t see smaller planets, which should in fact be more common.

These planets, surprisingly, may not be frozen solid as you might expect. Jupiter and Saturn, for example, give off more energy than they receive from the Sun. The centers of both planets are still warm from a number of heat sources, including radioactive decay as well as having trapped a considerable amount of the tremendous heat generated when they formed 4.6 billion years ago. Any free-floating planet in the galaxy may be presumed to contain as much heat, keeping them gaseous despite the intense cold of interstellar space.

You may be wondering about any potential habitability of these nomads. The planets found are gas giants, not Earth-like at all. But they might have moons orbiting them that could be heated by tides the same way Jupiter’s Io and Saturn’s Enceladus are. It seems unlikely that any moon could stay orbiting a planet ejected from a solar system — I would think they’d get stripped from their parent planet in the process — but nature has surprised us before. Like, say, it’s doing now with this whole "wandering planet" thing. I’d love to see some studies of that.

Also, while there may be an even greater number of smaller planets out there, these likely would be frozen through and through. Too bad. The view would be cool.

So to speak.

Conclusion
The MOA study in question is pretty interesting to me scientifically. The results look pretty good, and come from only a year’s worth of data; as the astronomers look at more data they’re bound to find more of these suckers. I expect to see their statistics get better with time. They seem to have done their work carefully and skeptically; it’s a fascinating result and I’m glad they sought out OGLE observations to back them up.

Personally, too, this is exciting. Imagine, a galaxy full of roaming planets! It’s not like they present a navigational hazard were we to fly starships through space; the galaxy is vast indeed and even a hundred billion planets would be spread pretty thinly. But it sparks my imagination to think of these planets — dark, cold, lonely — plying their way through the blackness of interstellar space. If we ever could voyage to one, what would we find?

It’s thoughts that like which make me glad to be an astronomer, especially one living now. Just when you think the Universe is running low on surprises, it reminds us it’s a lot more clever than we are.

**Xei** · 05-18-2011 07:16 PM

Wow, awesome. I find it hard to believe that the reason they've found gas giants is because they are more numerous though; seems far more likely that this is just the inherent bias in the planets being very large and easier to detect. A wandering Earth-like planet could still harbour life, but it'd probably be the primitive kind of thing we find around hydrothermal vents.

**Seroquel** · 05-18-2011 08:17 PM

Excellent thread.

Space is oh so mysterious.. It's too bad everything is on such a mind numbingly grand scale that we only get to see the black and white speculations from scientists and artists interpretations.

**sloth** · 05-18-2011 09:07 PM

We need to find out who is responsible for this, and put a stop to it.

**ninja9578** · 05-18-2011 10:59 PM

Originally Posted by Xei

Wow, awesome. I find it hard to believe that the reason they've found gas giants is because they are more numerous though; seems far more likely that this is just the inherent bias in the planets being very large and easier to detect. A wandering Earth-like planet could still harbour life, but it'd probably be the primitive kind of thing we find around hydrothermal vents.

Unlikely, in deep freeze it is likely that even planets the size of earth would freeze solid quickly without orbiting something. Our elliptical orbit and our moon is what helps keep our core hot. It is more likely that there is life on wandering gas giants' moons. Even in deep space, the gravitational tidal forces could keep a core hot.

It's not a new thought that wandering planets might be a dime a dozen. There are so many scenarios in which it could happen. Stars expel plants, stars start to form but run out of material before fusion starts...

**DrunkenArse** · 05-18-2011 11:06 PM

It's quite possibly nuclear fission in the core which keeps the earth hot. If such was the case for a wondering planet then it could quite possibly have areas that were hot enough for life to develop. It would be similar to our hydrothermal vents. So we would expect that the life might be similar to the primitive kind of thing we find around hydrothermal vents...

**Xei** · 05-18-2011 11:07 PM

Originally Posted by ninja9578

Unlikely, in deep freeze it is likely that even planets the size of earth would freeze solid quickly without orbiting something. Our elliptical orbit and our moon is what helps keep our core hot. It is more likely that there is life on wandering gas giants' moons. Even in deep space, the gravitational tidal forces could keep a core hot.

It's not a new thought that wandering planets might be a dime a dozen. There are so many scenarios in which it could happen. Stars expel plants, stars start to form but run out of material before fusion starts...

Hmmm. From what I've heard, a planet's internal heat is largely due to residual heat from formation, and/or nuclear decay. I don't think tidal forces play much of a part, because people were so surprised that Io is active; also, I know that people think Mars has no atmosphere because it has no magnetosphere to protect it from solar winds, which is in turn because it has no molten core, which is in turn because it is smaller than Earth and so lost its initial heat faster.

**ninja9578** · 05-19-2011 02:45 AM

Originally Posted by PhilosopherStoned

It's quite possibly nuclear fission in the core which keeps the earth hot..

Where did you get that info? One, it takes several million degrees to produce fusion, the earth core is estimated to be about 10000. (I assume you meant fusion, as I couldn't even contemplate how you think fission works.) But, the larger the atom, the more power it takes to create fusion, our core is nickle and iron, only a star could produce the pressure and heat required to start fussion.

Originally Posted by Xei

Hmmm. From what I've heard, a planet's internal heat is largely due to residual heat from formation, and/or nuclear decay. I don't think tidal forces play much of a part, because people were so surprised that Io is active; also, I know that people think Mars has no atmosphere because it has no magnetosphere to protect it from solar winds, which is in turn because it has no molten core, which is in turn because it is smaller than Earth and so lost its initial heat faster.

Not true, and you mentioned Io, which is warm specifically due to tidal heating (granted it's much smaller, and Jupiter is much larger.) It's the tidal fluxes that produce the heat to KEEP the planets warm, yes, the original heat from formation is still there, but the tidal flux from our moon and the sun are what keep it molten. Venus is the same size as Earth much closer to the Sun, has 10 times the atmosphere, a surface temperature hot enough to melt lead, but it's core is significantly cooler than ours. Most likely because it has no Moon to pull on its core as the earth rotates. We have the largest moon in the solar system by a huge margin in terms of percentages in size to its host planet, and the earth spins fairly fast. Now radioactive decay does help, but very little. There is also tons and tons of friction from currents rubbing against each other and the crust.

**khh** · 05-19-2011 02:50 AM

Originally Posted by ninja9578

Where did you get that info? One, it takes several million degrees to produce fusion, the earth core is estimated to be about 10000. (I assume you meant fusion, as I couldn't even contemplate how you think fission works.) But, the larger the atom, the more power it takes to create fusion, our core is nickle and iron, only a star could produce the pressure and heat required to start fussion.

No, he ment fission. A google search spits out amongst others this article (The interesting bit is the last paragraph), so if it's not right it's probably a common misconception.

**ninja9578** · 05-20-2011 03:26 AM

Uhm.... no. There is no evidence of fission at the earth's core, or even in the giant planets. That is complete crap, no legitimate scientist would even consider that as a possibility, have you any idea the amount of power it takes to produce fission? Significantly more than even Jupiter can produce, less than fusion, but more than the earth can produce. Nuclear fission - Wikipedia, the free encyclopedia Learn more about nuclear physics. Nuclear decay != nuclear fission, not even close. Do I need to explain the huge difference or is it common knowledge? Yes, fission happens naturally, but it's rare, and doesn't produce nearly as much energy as required to heat the earth. It's not as powerful as you might think, bombs are CHAIN FISSION reactions, which are very different than natural ones.

**Xei** · 05-20-2011 04:41 AM

Originally Posted by ninja9578

Not true, and you mentioned Io, which is warm specifically due to tidal heating (granted it's much smaller, and Jupiter is much larger.)

You didn't read my point: why did Io surprise people?

It's the tidal fluxes that produce the heat to KEEP the planets warm, yes, the original heat from formation is still there, but the tidal flux from our moon and the sun are what keep it molten. Venus is the same size as Earth much closer to the Sun, has 10 times the atmosphere, a surface temperature hot enough to melt lead, but it's core is significantly cooler than ours.

The Wiki tells me that Venus is thought to have cooled at the same rate as Earth due to its similar size.

**ninja9578** · 05-20-2011 05:02 AM

Originally Posted by Xei

You didn't read my point: why did Io surprise people?

I did, Io made scientist rethink what they know about how planet's core stay molten. The scientific method at it's finest, they found a counter example to the current theories, and they revised it. True science at work

The Wiki tells me that Venus is thought to have cooled at the same rate as Earth due to its similar size.

Then why does it have no tectonic plates? If Venus has intense core activity like Earth, it should have tectonic plates. Everything I've read states that Venus' core is significantly cooler than Earth's despite being the same size.

**DrunkenArse** · 05-20-2011 08:43 PM

Originally Posted by ninja9578

Uhm.... no. There is no evidence of fission at the earth's core, or even in the giant planets. That is complete crap, no legitimate scientist would even consider that as a possibility, have you any idea the amount of power it takes to produce fission?

Absolutely none. Uranium is unstable. When it gets hit by a neutron, its nucleus breaks down. It emits more neutrons which may hit other uranium nuclei. The process continues as a function of the density of the uranium nuclei. It takes a moderate amount of energy to comress the uranium enough for a chain reaction to occur. Something on the order of magnitude of a thousand kilos of plastic explosives (rough estimate. the upper bound is the lighest nuclear bomb) should do the trick nicely if they're well placed and their detonation are well timed. Sometimes it takes no energy at all: Natural nuclear fission reactor - Wikipedia, the free encyclopedia.

To say that no legitimate scientist would consider it as a possibility is complete crap.

Significantly more than even Jupiter can produce, less than fusion, but more than the earth can produce.

So you're claiming that the entire pressure of Jupiter is less then that of spherically placed plastic explosives? Get real dude.

Learn more about nuclear physics.

Quote for truth.

Nuclear decay != nuclear fission, not even close.

Nuclear fission is one form of nuclear decay: Spontaneous fission - Wikipedia, the free encyclopedia.

Yes, fission happens naturally, but it's rare, and doesn't produce nearly as much energy as required to heat the earth. It's not as powerful as you might think, bombs are CHAIN FISSION reactions, which are very different than natural ones.

See my first link for an example of a natural CHAIN FISSION reaction. Given that uranium is fairly common (a few parts per million) in the earth, and that it's one of the heaviest elements and hence likely to be concentrated towards the center (and hence under tremendous pressure), it's quite a real possibility that there is a low-level, sustained chain reaction going on.

**ninja9578** · 05-21-2011 05:10 AM

Originally Posted by PhilosopherStoned

Absolutely none. Uranium is unstable.

No, it's not. Look up the different between U235 and U238. U235 is unstable... and man made. It's for the bomb. U238 is the natural uranium, it's not fissionable. Fast fission is possible, but not true fission, there is a subtle, but VERY big difference. True fission can only happen in a star (or a man made plasma) The centre of the earth is liquid, neutrons don't travel fast enough to generate real fission. Stars are plasma, there is a lot more space between subatomic parts and more energy, and subatomic particles can move MUCH faster, only high speed neutrons can produce real fission.

So you're claiming that the entire pressure of Jupiter is less then that of spherically placed plastic explosives? Get real dude.

No, that's not what I'm saying. Jupiter's core produced thousands of time the pressure of atomic bombs. By the way, plastic explosives, don't produce the energy required to make a bomb, there are special explosives that produce X to Gamma ray radiation to create the reaction. The difference is that when a bomb goes off, the pressure of the regular blast creates the fission, but it immediately goes to zero once the explosive is burned off, letting it expand. In Jupiter, that pressure is constant, so no explosion happens, so no expansion, no thermal release. It's comparable to the fact that in the ocean water at thermal vents can reach 800 degrees, even though it boils at 212 and flash-vaporizes at 375. Different medium, same analogy.

See my first link for an example of a natural CHAIN FISSION reaction. Given that uranium is fairly common (a few parts per million) in the earth, and that it's one of the heaviest elements and hence likely to be concentrated towards the center (and hence under tremendous pressure), it's quite a real possibility that there is a low-level, sustained chain reaction going on.

Fission != fusion. Fission takes significantly more energy, and occurs much much faster. If fission ever happened at our core, it well past over. The sun is sustainable because of fusion, which is slow burning and release HUGE amounts of energy. Fission happens fast and doesn't produce very much energy n comparison to fusion. In Fusion H + H = He, which is still fusible, with very little energy (compared to fission.) In fission, uranium splits close to in half, which are two very stable and rare element. If fission was happening, we would have more heavy metals in our core instead of iron and nickel.

You may think I'm a dumbass hippie, but I actually understand nuclear physics. I took several years of it.

**cmind** · 05-26-2011 04:09 AM

Originally Posted by ninja9578

Not true, and you mentioned Io, which is warm specifically due to tidal heating (granted it's much smaller, and Jupiter is much larger.) It's the tidal fluxes that produce the heat to KEEP the planets warm, yes, the original heat from formation is still there, but the tidal flux from our moon and the sun are what keep it molten. Venus is the same size as Earth much closer to the Sun, has 10 times the atmosphere, a surface temperature hot enough to melt lead, but it's core is significantly cooler than ours. Most likely because it has no Moon to pull on its core as the earth rotates. We have the largest moon in the solar system by a huge margin in terms of percentages in size to its host planet, and the earth spins fairly fast. Now radioactive decay does help, but very little. There is also tons and tons of friction from currents rubbing against each other and the crust.

Umm...no. The moon doesn't have much of an effect. The main source of heat is the heat of formation, combined with radioactive decay. The reason it's not cooling very quickly is because the geometry of Earth (volume to surface area ratio) is such that it would take a long time to dissipate the heat. In fact, it just so happens that it would take more time to cool than the lifetime of the sun. You can read about all of this here:

Earth - Wikipedia, the free encyclopedia

**Dthoughts** · 05-27-2011 08:23 AM

This is cool news ! very interesting. I know i'm speculative and full of fantasy but anyone ever thought that advanced species might have transformed their home planets into a sort of space ship and travel the universe without ever leaving their homeplanet? You see maybe these planets are wandering because they are going somewhere.

Surely the planet must have started near a star once maybe when intelligence evolves they get to a point where they have absolute controll over the planet. I wonder if astrologists ever saw planets pass a star but never seen them again, this i would see as evidence that they might actually do this in outer space. Damn i wish i had a telescope.

**ludr** · 05-27-2011 03:34 PM

Those aliens on the wandering planet would probably freeze to death.

**Dthoughts** · 05-27-2011 06:41 PM

That is to say if there is no inner core to warm ur bones with. Or to say that aliens haven't invented the technology to keep them warm.

**ludr** · 05-28-2011 12:55 AM

What? The inner core will cool down! And it does not warm the planet, sorry. If Earth went wandering around, we will probably freeze to death. If the aliens have spacecraft technology, why don't they return to their home system?

**Dthoughts** · 05-28-2011 12:21 PM

Originally Posted by ludr

What? The inner core will cool down! And it does not warm the planet, sorry. If Earth went wandering around, we will probably freeze to death. If the aliens have spacecraft technology, why don't they return to their home system?

U talk as if u have been to outer space and seen one of those planets up close. You can't imagine what technology we have in 30 years from now. Forget about a real civilization thousands of years ahead of us.
Why? well.. It's not like i can ask E.T. Maybe their star is about to explode and since they don't want to fly to another planet and mess with other races they decided to take their own planet so they don't have to steal a planet from another race. Also since a planet is just about big enough to carry their entire race. It seems like a waste to make spaceships to carry the people trough space while the planet is already perfect.

Thread: The galaxy may swarm with billions of wandering planets

LinkBack

Thread Tools

Display

The galaxy may swarm with billions of wandering planets

Similar Threads

A swarm of insects at the foot of my bed upon waking up

Alien Swarm (Free Steam Game)

galaxy

Bookmarks

Bookmarks

Posting Permissions