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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.
“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.
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
I’m confused as well. How can the estimate be 100,000 rogues per star when our system managed only 8?
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.
Gotcha. Makes sense. Lots of stuff floating out there. Crazy really.
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. This suggests the planet Nibiru (sp) scenario is not that out of line, though there is no evidence for such a planet that will hit Earth this December. The other problem is 10^{15} rogue planets begins to change the distribution of atomic elements in the universe. It means nucleosynthesis of heavier elements has been at a much greater rate than thought.
The panspermia aspect to this is somewhat irrelevant. Panspermia is the most underwhelming proposal for the origin of life on Earth. Life still had to emerge by some process somewhere, so this does not remove the problem concerning the origin of self-replicating organic chemistry.
If I were told there were up to a trillion rogue planets in our galaxy I would not particularly raise eyebrows. However, a thousand times that number starts to raise questions.
LC
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.
“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?
“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?
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 birth cluster. I would surmise that most of them get captured in distant orbits around other stars in the cluster or get accelerated in close encounters right out of the galaxy, or at least to a different galactic orbit than more massive stars after they disperse from the inital cluster. I had posted a few years back how I thought it likely that the Oort cloud and smilar structures around other stars would likely contain such planets and that the number of them should be proportional to the mass of the star(s) in the system. This is based on how often we see a small dwarf star in a distant orbit around 2 larger stars. If this calculation is correct, then I believe it adds more weight to this earlier argument, as we aren’t seeing evidence of large numbers of nomads wandering about in interstellar space.
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 birth cluster. I would surmise that most of them get captured in distant orbits around other stars in the cluster or get accelerated in close encounters right out of the galaxy, or at least to a different galactic orbit than more massive stars after they disperse from the inital cluster. I had posted a few years back how I thought it likely that the Oort cloud and smilar structures around other stars would likely contain such planets and that the number of them should be proportional to the mass of the star(s) in the system. This is based on how often we see a small dwarf star in a distant orbit around 2 larger stars. If this calculation is correct, then I believe it adds more weight to this earlier argument, as we aren’t seeing evidence of large numbers of nomads wandering about in interstellar space.
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 minute that this is correct, it may so happen that they are either in transit or trapped in another galaxy / solar system. In which case, we stand a very good chance of finding a “rogue” planet from the time of formation of the very first stars and Galaxies. Planets older than their stars? Sounds interesting, right?
With all these numbers, it is REALLY hard to believe that we are struggling to find planets in the Universe. There are Oort Clods, Kuiper belts, Red Dwarfs and now rogue planets. Could these explain some % of missing matter in the Universe.
It may as well show that ‘dark’ matter is simply ‘normal’ matter that is numerous and too small to shine.
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.
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?
DIfferent paper. These researchers aren’t claiming any particular rate of visitation by rogue planets, but they aren’t refuting panspermia either.
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.
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.
“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.
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”.
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?
DIfferent paper. These researchers aren’t claiming any particular rate of visitation by rogue planets, but they aren’t refuting panspermia either.
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.
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.
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
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”.
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 the planet is warming up and we’re the cause of it”. Some people responded with “oh, but have you thought of changes in solar activity? Changes in volcanic activity? Changes in the earth’s albedo?” and they said “err, well, no…” and went back to study it some more. It turns out that all of those things are now taken into account, and the earth is *still* warming up in direct relation to the amount of CO2 in the atmosphere correlating with the amount of the gas that we dump into it.
See, in science, you get to poke holes in other people’s theories *all day long*. And the answer to that is to do more science. In the end, if the theory is wrong, then that, in and of itself, is an advancement of understanding.
Our understanding of the universe is fluid. And that makes it ambiguous. Which is a good thing, or we could just shut down all science tomorrow and declare our current understanding of the universe as perfect, and everything we know now as absolute truth.
It took us a thousand years to get out of *that* mindset the last time it happened.
Apologies if I’ve given the impression I’m attacking science – I’m not and that’s not my point either.
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. The observation stands regardless of context.
I would give references if I had time, but I suspect you would be less interested anyawy since you had your mind set before commenting.
– As for your “element of faith”, using predictions and tests is the precise and only means that eliminates assumptions and elevates them to observations or theory depending on your theory on theories.
– Labels are fuzzy and context dependent. String, or better M, theory is an apt name for the mathematical theory it is at the very least. Mind that mathematics use an entirely different concept of theory! It is more like “an area of work”.
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 inner mechanisms of gravity remain largely unexplained – despite us mastering the calculations by which objects move through gravitational fields. We understand the effect, but not the true mechanism(s) at work.
I am not hostile – honest!
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.
Too true. If we can imagine it, and it doesn’t violate the basic rules of physics, then someone somewhere someday will do it.
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.
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 be the heavy material (in small rocks or dust) out which the current planets exist) material disk, planets are formed by an until now unknown mechanism.
I would say let’s go to reality. We all know that stars are formed and born in large clouds in great numbers and in groups and clusters. We call them even star nurseries. As one of the examples we can take the orion nebulae.
Within such clouds stars are formed in clusters of 2, 4, 6 or more stars and within such a cluster there is initially a complicated interaction that holds those stars together. They all rotate round a virtual continuous moving centre.
As we don’t know the exact initial start position of the cluster where in our sun was born, we will present a docu-story how a star system is created and evolves. The initial number of stars neither as their respective large, neither as their initial distance between has any essential influence in the outcome.
We start with a star cluster of 5 stars that has been formed in a great dust cloud and we call 1S = one solar mass. So we have star: A = 30S, B = 15S, C = 5S, D = 1S and E = 0,5S. The stars in the cluster are interacting with each other, by which of course the main star “A” dominates the interaction. Due to their mass the star “A” burns extra rapid, “B” very rapid, “C” rapid, “D” normal (to our standards) and “E” slow (maybe it is in its ignition phase). The surrounding dust cloud where in they are born , has been blown away by star winds and star radiation. The eventual heavier material that would have remained is due to the interaction fluctuation: or thrown away, or has fallen towards the stars and is then absorbed.
After several 10s of millions of years, star “A” has reached his final phase and goes into supernova.
Characteristics of every explosion is that outer parts are blown away with the highest acceleration and that heavy material absorbing the same power will have a lower acceleration. In the case of star “A” the outer shells have the lightest material (hydrogen and helium), while the inner shells have the heavier material (going up to iron). During the supernova the explosive part of that star is like a witches cauldron where we can say all elements of the table of mendeljev are made in smaller and larger amounts. The outer shells are blown away at high speed , while the inner shells with the heavier material leaves the exploding star at lower speed. Some of the latter even falls backward into the black hole that is created.
At the same time the supernova creates a sudden and drastic disturbance in the unstable equilibrium of the interaction between the 5 stars of the cluster. The cluster falls apart. Some stars leave the cluster solo, others in pair. The light material of star “A” from the outer shells passes those stars at high speed. Some of the heavier material of the inner shells passes the stars at the right velocity, so it can be captured in the gravity field of those escaping stars. Heavy material like iron (f.i.) clumps easier together once temperature gets low enough so that it becomes liquid. Those liquid balls collect in a first stage the heavy more liquid material and once big enough they suck the more gassy material towards them. So within those systems the first proto-planets are formed. They are hot and liquid.
Back to our docu-story. The star “A” has exploded in a supernova. As consequence star “B” and “D” leave the cluster as a twin star. The distance between both stars becomes relatively large, but still star “D” orbits round star “B”. Star “C” and star “E” each leaves the cluster separately. All stars have known the passage of the material coming from the supernova. We now follow only the double star. They continue they way through the galaxy as a double system. Both are provided of hot proto-planets that are cooling down.
After maybe some 500 million years we have the following situation. The proto-planets orbiting star “D” and “B” have cooled down a lot. A crust has been formed. The heaviest materials has sunk to the middle. The crust isolates the proto-planets and makes that almost an equilibrium is obtained between the energy losses at the outside and the energy production at the inner-side. At the same time star “B” reaches his final stage and goes on his turn over in a supernova phase. Proto-planets and star material are blown away as well as the second star system together with its star “D”. Now Star “D” too goes his own way. The passages of the material coming from star “B” after its explosion, is smaller in amount ( as the star was smaller and the distance between both greater). However impacts leave their tracks on the existing proto-planets. If proto-planets or remains of them coming from star “B” cross the system of “D”, collisions may happen resulting in the worst case: in the destruction of already existing proto-planets, creating asteroids.
After time a new equilibrium is reached as well in the system as on the planets. Both, the system as well as the planets start their evolution. The evolution of the system is determined and commonly well known. The evolution of the planets not. This one is determined by the greatness and the composition of the planet.
I will not elaborate about this subject now as it would load the package. It is also new stuff and it explains a lot of current situations in our solar system.
Interesting, and no doubt one of many scenarios at work in our Galaxy.
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 good sign even before observations rejects it.
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.
this is not good news for star travel lol
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 to astrobiology, which main concern is characterising the pathways for biospheres. It is like discussing survivors of airplane crashes when elaborating on the transportation networks of a city.
Watch out for Trelaine. He’s a naughty boy….