Artist's concept of a free-floating Jupiter-like planet. (NASA / JPL-Caltech)

Worlds Without Suns: Nomad Planets Could Number In The Quadrillions

30 May , 2012 by

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The concept of nomad planets has been featured before here on Universe Today, and for good reason. Not only is the idea of mysterious lone planets drifting sunless through interstellar space an intriguing one, but also the sheer potential quantity of such worlds is simply staggering. If some very well-respected scientists’ calculations are correct there are more nomad planets in our Milky Way galaxy than there are stars — a lot more. With estimates up to 100,000 nomad planets for every star in the galaxy, there could be literally quadrillions of wandering worlds out there, ranging in size from Pluto-sized to even larger than Jupiter.

That’s a lot of nomads. But where did they all come from?

Recently, The Kavli Foundation had a discussion with several scientists involved in nomad planet research. Roger D. Blandford, Director of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University, Dimitar D. Sasselov, Professor of Astronomy at Harvard University and Louis E. Strigari, Research Associate at KIPAC and the SLAC National Accelerator Laboratory talked about their findings and what sort of worlds these nomad planets might be, as well as how they may have formed.

One potential source for nomad planets is forceful ejection from solar systems.

“Most stars form in clusters, and around many stars there are protoplanetary disks of gas and dust in which planets form and then potentially get ejected in various ways,” said Strigari. “If these early-forming solar systems have a large number of planets down to the mass of Pluto, you can imagine that exchanges could be frequent.”

And the possibility of planetary formation outside of stellar disks is not entirely ruled out by the researchers — although they do impose a lower limit to the size of such worlds.

“Theoretical calculations say that probably the lowest-mass nomad planet that can form by that process is something around the mass of Jupiter,” said Strigari. “So we don’t expect that planets smaller than that are going to form independent of a developing solar system.”

“This is the big mystery that surrounds this new paper. How do these smaller nomad planets form?” Sasselov added.

Of course, without a sun of their own to supply heat and energy one might assume such worlds would be cold and inhospitable to life. But, as the researchers point out, that may not always be the case. A nomad planet’s internal heat could supply the necessary energy to fuel the emergence of life… or at least keep it going.

“If you imagine the Earth as it is today becoming a nomad planet… life on Earth is not going to cease,” said Sasselov. “That we know. It’s not even speculation at this point. …scientists already have identified a large number of microbes and even two types of nematodes that survive entirely on the heat that comes from inside the Earth.”

Researcher Roger Blandford also suggested that “small nomad planets could retain very dense, high-pressure ‘blankets’ around them. These could conceivably include molecular hydrogen atmospheres or possibly surface ice that would trap a lot of heat. They might be able to keep water liquid, which would be conducive to creating or sustaining life.”

And so with all these potentially life-sustaining planets knocking about the galaxy,  is it possible that they could have helped transport organisms from one solar system to another? It’s a concept called panspermia, and it’s been around since at least the 5th century BCE when the Greek philosopher Anaxagoras first wrote about it. (We’ve written about it too, as recently as three weeks ago, and it’s still a much-debated topic.)

“In the 20th century, many eminent scientists have entertained the speculation that life propagated either in a directed, random or malicious way throughout the galaxy,” said Blandford. “One thing that I think modern astronomy might add to that is clear evidence that many galaxies collide and spray material out into intergalactic space. So life can propagate between galaxies too, in principle.

There could be quadrillions of nomad planets in our galaxy alone -- and they could even be ejected into intergalactic space. (Image: ESO/S.Brunier)

“And so it’s a very old speculation, but it’s a perfectly reasonable idea and one that is becoming more accessible to scientific investigation.”

Nomad planets may not even be limited to the confines of the Milky Way. Given enough of a push, they could be sent out of the galaxy entirely.

“Just a stellar or black hole encounter within the galaxy can, in principle, give a planet the escape velocity it needs to be ejected from the galaxy. If you look at galaxies at large, collisions between them leads a lot of material being cast out into intergalactic space,” Blandford said.

The discussion is a fascinating one and can be found in its entirety on The Kavli Foundation’s site here, and watch a recorded interview between Louis Strigari and journalist Bruce Lieberman here.

The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

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Lawrence B. Crowell
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Lawrence B. Crowell
May 31, 2012 12:56 AM

With this number of rogue planets in our galaxy it is not hard to estimate that each cubic light year of volume could hold around 30 of them. It starts to become difficult to imagine how any solar system can exist for billions of years without some major catastrophic gravitational encounter or outright collision between planets. These numbers seem inflated.

LC

bugzzz
Member
bugzzz
May 31, 2012 3:08 AM

I’m confused as well. How can the estimate be 100,000 rogues per star when our system managed only 8?

Greg
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Greg
May 31, 2012 3:34 AM

Many large stars have come and gone, but their ejected planets have not. This system very likely had 9 planets and a Neptune size planet was ejected. Any number of others may have been ejected, especially the KBOs scattered by Neptune and other planetismals that were trying to form a planet where the asteroid belt is now were likely ejected by Jupiter as it migrated in. The article also describes how Jupiter sized planets may form independent of a star by the same mechanism that creates stars,a gravitational collapse of a smaller-sized molecular cloud in a nascent star forming region.

bugzzz
Member
bugzzz
May 31, 2012 12:31 PM

Gotcha. Makes sense. Lots of stuff floating out there. Crazy really.

Lawrence B. Crowell
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Lawrence B. Crowell
May 31, 2012 1:39 PM
As Gregthethird indicates orbital instabilities of planetary systems should result in ejections of planets. Our own solar system may well have ejected a Neptune mass planet early in its evolution. Maybe some gas giant planets form outside of solar systems. It is then not surprising to me that these should exist, and some have been found by microlensing. The problem I have with a number like a quadrillion or 10^{15} is this starts to press on a number of things. As I indicated this would populate the galaxy to the point that every cubic light years would contain dozens of these. Over the lifetime of a solar system this means encounters with rogue planets would be fairly common.… Read more »
Ernie Dunbar
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June 1, 2012 7:40 AM

If we’re talking pluto-sized planets (and I would expect that the bulk of these rogue planets would be about that size), then it’s entirely possible that our solar systems managed *far* more than 8. We could have 20 more planets this size orbiting the sun right now in the kuiper belt or the oort cloud, and it would be exceedingly difficult or impossible to find them. They could whiz by our solar system on a daily basis and we’d never be the wiser, either.

Tim McDaniel
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Tim McDaniel
May 31, 2012 1:47 AM

“With estimates up to 100,000 nomad planets for every star in the galaxy …” I had understood that finding to mean that scientists had concluded that, if there were more, they would have been observed already. That is, it was merely an upper bound, but the total number could be just the two (I think it is) that we already know about. Did I misunderstand? If not, isn’t it really premature to talk about how so many could have been formed?

Tim McDaniel
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Tim McDaniel
May 31, 2012 1:47 AM

“With estimates up to 100,000 nomad planets for every star in the galaxy …” I had understood that finding to mean that scientists had concluded that, if there were more, they would have been observed already. That is, it was merely an upper bound, but the total number could be just the two (I think it is) that we already know about. Did I misunderstand? If not, isn’t it really premature to talk about how so many could have been formed?

Greg
Member
Greg
May 31, 2012 2:03 AM
With Gliese 710 coming in for a close shave in just 1.5 million years, you have to wonder how accurate this estimate is. Over a much longer period of time and with them being so numerous, they should have wreaked havoc upon the solar system by now. Perhaps it is a matter of distribution and the orbit of the sun is relatively safe with regards to where most of these nomads are located. Most stars form in fairly large and dense clusters and most of the planetary ejections would occur early in a star’s development, so these nomads should have clustered together in close proximity to other stars with potentially much more opportunity for interactions in the nascent… Read more »
Greg
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Greg
May 31, 2012 2:03 AM
With Gliese 710 coming in for a close shave in just 1.5 million years, you have to wonder how accurate this estimate is. Over a much longer period of time and with them being so numerous, they should have wreaked havoc upon the solar system by now. Perhaps it is a matter of distribution and the orbit of the sun is relatively safe with regards to where most of these nomads are located. Most stars form in fairly large and dense clusters and most of the planetary ejections would occur early in a star’s development, so these nomads should have clustered together in close proximity to other stars with potentially much more opportunity for interactions in the nascent… Read more »
Ravi Shankar S P
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May 31, 2012 4:25 AM
Though, on one hand, this sounds like information based on facts, there are some curious results as well. When stars “die” it is reasonable to assume that some of the planets get consumed and some are left to drift. For any “live” star, the total number of planets is a sum of rogue planets & normal ones. 1,00,000 “rogue” planets means that there is an additional population of normal planets. Does this mean that we are going to be able to find about 1,00,000 planets, one fine day (we have hardly reached 1000)? Some of these could be the “dwarf planets” like Pluto or even major satellites like Ganymede. But this is an interesting fact! Assuming for a… Read more »
M Peter Selman
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May 31, 2012 6:19 AM

It may as well show that ‘dark’ matter is simply ‘normal’ matter that is numerous and too small to shine.

magnus.nyborg
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magnus.nyborg
May 31, 2012 7:14 AM

Only a small fraction of the ‘Missing mass’ can be in the form of planets/dwarf planets. I do suspect there are plenty of these rogue planets, but their contribution to mass will still be far less than the contribution made by stars and gasclouds.

Ray Fowler
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Ray Fowler
May 31, 2012 12:30 AM

Didn’t they try to peddle this panspermia garbage a few weeks ago with the absurd claim that there are so many rogue planets that one visits our solar system every 25 million years?

Can we please keep the pseudo-science out of UT?

Jason Major
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May 31, 2012 1:55 AM

DIfferent paper. These researchers aren’t claiming any particular rate of visitation by rogue planets, but they aren’t refuting panspermia either.

Ray Fowler
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Ray Fowler
May 31, 2012 2:45 AM

You don’t think it’s a leap to latch onto an “upper boundary” of rogue planets that would perhaps double the mass of the entire galaxy while citing a 5th-century philosopher to argue for panspermia?

Also, suggesting that since galaxies can spew matter out of them that intergalactic panspermia is now possible?

This is all fanciful speculation with barely a shred of observational data to support it.

Eppur_si_muove
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Eppur_si_muove
May 31, 2012 4:40 AM

“double the mass of the entire galaxy”?? and you claim that they’re the ones making a leap. 400 Billions stars, plus their planets alone have a larger mass than 40 Quadrillion Nomad planets, (assuming their upper limit). We are far from doubling the mass of the Milky Way.

Ray Fowler
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Ray Fowler
June 1, 2012 6:56 PM

What are you talking about? The sun is 300,000 times the mass of the Earth. Considering that the average star is much less massive than the Sun and the average planet is much less massive than Earth, then 100,000 additional planets per star is certainly within an order of magnitude being comparable masses.

It was not a leap, but a rough mental estimate, which is why I qualified it with “perhaps”.

Jason Major
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May 31, 2012 2:17 PM

While Anaxagoras may have coined the term, his concept of panspermia was a bit different than what’s referred to now. Still, the name has stuck, and the modern usage has some potential to actually exist in some form in the history of the galaxy. Is it so impossible that worlds carrying life — or at least its key ingredients — could be scattered between solar systems via ejections?

Ray Fowler
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Ray Fowler
May 31, 2012 2:45 AM

You don’t think it’s a leap to latch onto an “upper boundary” of rogue planets that would perhaps double the mass of the entire galaxy while citing a 5th-century philosopher to argue for panspermia?

Also, suggesting that since galaxies can spew matter out of them that intergalactic panspermia is now possible?

This is all fanciful speculation with barely a shred of observational data to support it.

Jason Major
Guest
May 31, 2012 1:55 AM

DIfferent paper. These researchers aren’t claiming any particular rate of visitation by rogue planets, but they aren’t refuting panspermia either.

M. Malenfant
Member
M. Malenfant
May 31, 2012 11:14 AM

If I remember correctly the high number 100 000 resulted from an extrapolation to relatively small planets assuming a distribution of planet sizes. Thus in case such a high number applies, the vast majority would consist of relatively small objects. This would also limit the gravitational impact on planetary systems – and of course the mass they contribute.
It might be interesting to estimate how many objects fitting the definition of a planet (>= 1000 km?) have been ejected from the solar system during it’s lifetime for a comparison.

Jon Souter
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Jon Souter
May 31, 2012 11:24 AM

Modern cosmology seems to require almost as much faith these days as any form of religion!

Dark Matter / Dark Energy / Nomadic Planets

Seems in some corners of science, you don’t need good data if the mathematical models are beautiful enough!

For the record, I’m not an advocate of alternative EU / Plasma theories – I just get annoyed across the board when someone states as fact something that is *at best* a theory and at worst a mere opinion.

Lawrence B. Crowell
Member
Lawrence B. Crowell
May 31, 2012 1:20 PM

You appear to not understand what a theory is. A hypothesis is a proposed model for the world, or some aspect of it, that is not yet tested. A theory is a model that has its predictions tested successfully by observations and measurements. When ever I hear somebody say “it’s just a theory,” I know instantly such a person has a poor idea of how science works.

LC

Jon Souter
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Jon Souter
June 1, 2012 1:44 AM

I’d really have thought that an hypothesis could model the environment *beyond* the world… but hey, I clearly have a poor idea of how science works.

/s

Despite your comments – modern science really is full of ambiguity and does require an element of faith, which may be ill-placed in certain instances.

Interesting though that a branch of hypothetical particle physics is known as “String Theory” and not “String Hypothesis”.

Ernie Dunbar
Guest
June 1, 2012 7:29 AM
Really? So your argument is that science is too ambiguous? I prefer ambiguity. It sure beats immutable “facts” that no matter the evidence against them, are always true. *That’s* the realm of religion and faith. Where the people in charge have *all* the answers, and anyone who questions them are damned. In science, you’re allowed to say “Oh, that sounds like a load of malarky” so long as you can come up with reasoned arguments against a theory. Heck, even if you can’t come up with good arguments and just ask “well, did you think of this, this, and this?” My favourite example of that is climate science. Climate scientists came out and said “Hey, it looks like… Read more »
Jon Souter
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Jon Souter
June 1, 2012 1:05 PM

Apologies if I’ve given the impression I’m attacking science – I’m not and that’s not my point either.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 1, 2012 11:46 AM
Funny how all three of your examples are firm observations. – Nomads have been observed by gravitational microlensing. This is where the lower limit of at least one sizeable nomad for each star comes from. – Dark matter has been unabigiously observed by gravitational lensing in galaxy cluster collisions. The evidence for DM is better than the evidence for atoms at the time they were accepted, atoms that just recently were more or less ‘directly’ observed by various means. – Dark energy is just a label on an observation in a standard cosmology context. It translates to an increased rate of expansion in the mature universe, and in terms of standard cosmology it shows up as an energy.… Read more »
Jon Souter
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Jon Souter
June 1, 2012 4:47 PM
Again apologies if I appeared to attack science – this is not the case. Tone of voice is not something that can be conveyed in a textual comment. It is my understanding that only the effects of Dark Matter / Energy have been observed – not the Dark Matter/Energy itself. Maybe it’s my own limitations that have me fail to recognise evidence that dark matter has to be non-baryonic in nature? I fully accept Dark Energy as a place-holder for the unexplained expansion effect that has been observed but not yet unaccounted for. But again, I was trying to highlight that this is a force we don’t understand and have not managed to observe it’s cause. Even the… Read more »
Walter Palmer
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May 31, 2012 12:18 PM

This is wild speculation on my part:

Advanced species have figured out how to heat the planet – Dyson Sphere – and take the planet for an interstellar trip. That could be why there are so many.

Remember, anybody traveling over 30 miles per hour will die of a nosebleed – they had number to back it up too. Somethings are impossible, but I am sure that there is a difference between what is impossible and what we have not figured out how to do.

skipdallas
Member
skipdallas
May 31, 2012 6:07 PM

Too true. If we can imagine it, and it doesn’t violate the basic rules of physics, then someone somewhere someday will do it.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 1, 2012 11:48 AM

Ironically IIRC they have found that Dyson spheres are impossible, too much stresses in actual gravity fields.

Dyson clouds would be a good substitute though. They would have some leakage besides IR, natch.

GoGo Mix
Guest
May 31, 2012 12:35 PM

this is not good news for star travel lol

the_only_fan
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the_only_fan
May 31, 2012 2:25 PM
Are planets formed out of the residual clouds surrounding a star or can it happen in another way. Here a hypothetical story of how it could happen otherwise. The genesis of a solar (star) system as it is presented nowadays is according me wrong. There are a lot of arguments against it that I could give you the one after the other, but I prefer to present you the substitute for it. The basic mistake is that there is started from a dust cloud where in our sun (star) formed itself by sucking up most of the material. Out of the remaining (after blowing away by that star of the hydrogen and helium), (the remaining is supposed to… Read more »
skipdallas
Member
skipdallas
May 31, 2012 6:04 PM

Interesting, and no doubt one of many scenarios at work in our Galaxy.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 1, 2012 11:55 AM
The area of planetary system formation is no doubt dynamic at the time, with the accelerating stream of observations. However, you do not present any problems for the current major theory. Proposing a contender theory is a good idea, the trick is that to prove other theories wrong it will have to explain observations at least as much. It is correct that our planetary system was born in a molecular cloud seeded by a supernova, isotope ratios test this hypotheses nicely. However many systems have been observed, and this is a minor pathways. Many young systems are born nowhere near a supernova. Besides that I think your model is as non-parsimonious as a theory can be. Not a… Read more »
Raimo Kangasniemi
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May 31, 2012 3:57 PM

I have one big problem when it comes to these calculations about the number of rogue planets in the galaxy: The MACHO projects searching for normal matter explanation for dark matter – mainly in the 1990s, before WIMPs won the day – should have, I think, seen far more occultations of stars if they would be as numerous as they are now claimed to be.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
June 1, 2012 11:30 AM
Already transpermia, life migrating between planets, is an underwhelming idea and the nomad planets adds to the problem. If life arises so easily as it seems to have done here, there will be very few planets that will establish a biosphere by transpermia. It will take an extraordinary set of circumstances to set up such an establishment. Now add nomads which shows how robust and common established bisopheres are. The upper quick and dirty estimate of nomads stress observations and will probably have to be adjusted down considerably as the area solidifies. Mind that Sasselov is prone to extravagant media excursions, his TED talk got a lot of internal criticism goes the rumor. This idea adds very little… Read more »
ITSRUF
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ITSRUF
June 4, 2012 7:17 PM

Watch out for Trelaine. He’s a naughty boy….

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