# Are we in danger from a rogue planet?

By Phil Plait | May 19, 2011 10:44 am

Yesterday, I wrote about a new study that indicates that free-floating planets in the Milky Way may outnumber planets orbiting stars, and even be more numerous than stars themselves. It’s an amazing result! The most likely scenario is that these planets formed in solar systems similar to ours, but got ejected due to gravitational interactions with other planets in the system. These planets get literally tossed out into space, wandering the galaxy forever*.

This made me wonder: if these numbers are correct, how likely is it that such a rogue planet might actually be close by on a cosmic scale? And given the kind of topic I like to write about, are we in any danger from a close encounter with one of these galactic nomads?

These wandering planets are so dark and distant they are currently essentially impossible to detect using regular techniques, so we don’t know if any are in our galactic neighborhood or not. The only way to get a grip on how close one might be is to look at it in a statistical sense: on average in the galaxy, how many of these planets are there per cubic light year of space? Then we can fiddle with the number a bit to see how far away one of these planets could be.

Let me be clear up front about something. No doubt there will be people who may want to claim these rogue planets might explain Nibiru or Planet X or the Mayan apocalypse. These people are wrong (again, and as usual). As you’ll see, the math absolutely does not support such a claim at all. So if you hear someone talking doomsday, send ‘em here.

And I might as well address the TL;DR crowd: the conclusions I draw here are that a) on average, a rogue planet may be closer than I would’ve initially guessed, but 2) not nearly close enough to be a concern in any way.

OK then, got it? Onward to the math!

Crank up the volume

Basically, all we need to do is take the number of rogue planets in the galaxy and divide it by the volume of the galaxy, and that gives us the density of these planets in space: how many there are in a cube a light year on a side. If the answer is, say, 1 then we expect to have one rogue planet inside a one-light-year-wide cube centered on the Sun. So let’s see what the math tells us.

First, there are a lot of rogue planets. In the study, they say there are very roughly as many of them as there are stars in the Milky Way. Let’s call it 200 billion.

Second, the volume of the galaxy isn’t hard to estimate. I’ve done it before, and the details are there if you want them. Let me cut to the chase: the Milky Way has a volume of roughly 2 x 1013 cubic light years: that’s 20 trillion cubic light years!

That’s a lot, too. Dividing them to find the density, we get:

2 x 1011 planets / 2 x 1013 cubic light years = 0.01 planets per cubic light year

In other words, We’d expect to find one of these wandering planets in a volume of space encompassing 100 cubic light years. That’s a cube about 4.6 light years on a side (or, if you prefer, a sphere about 3 light years in radius).

Hey, wow, wait a second: The nearest star, the Alpha Centauri triple star, is about 4.3 light years away. That means there’s a pretty good chance that, statistically speaking, there may be one of these rogue planets closer to us than the nearest star!

That’s actually quite shocking to me. Seriously: wow. I’ve often wondered if we’d ever find a brown dwarf — a faint, "failed" star — closer than Alpha Cen, but it never occurred to me there might be a planet closer by! That’s pretty cool.

Stranger planet danger

OK then. Are we in any danger from these puppies? Could one pass close enough to us to cause earthquakes, say?

No! And I mean categorically, no. 100 cubic light years is a vast, mind-numbing volume of space: about 1041 cubic kilometers! That’s a huge amount of real estate to tool around in. Even if a planet got as close as a light year away — ten trillion kilometers, or 6 trillion miles — the effect on us would be essentially nothing.

Remember, we’re talking about planets with about the same mass as Jupiter. Our Jupiter gets as close as about 600 million kilometers from Earth. The Moon itself has no substantial effect on earthquakes, and at most Jupiter’s effect is a tiny fraction of that. A planet ten thousand times farther away than Jupiter may as well not exist as far as gravitational effects are concerned.

Oh comets, where Oort thou?

So we’re safe from direct problems. What about indirect ones?

Out way past Neptune is a population of icy bodies that, when they fall toward the Sun, turn into comets. There may be a trillion of these guys within a light year or so from the Sun, in a region called the Oort cloud. Could a rogue planet dislodge a bunch of these and drop them toward us, triggering impacts and a mass extinction?

In a word, no. Again, the volume of space we’re talking about here is staggering. Even a trillion comets spread out over that amount of space makes things pretty thin out there; on average those objects are a billion kilometers apart. The odds of a planet getting close enough to dislodge even a single Oort cloud object is pretty small. And even if it did, it’s only one comet! The odds of it hitting the Earth are even teenier. We’re a pretty small target in a whole lot of solar system.

And let’s have a sanity check: if this were a real danger, we’d see evidence of it in the fossil record. A planet-wide bombardment of giant comets — even from a single big comet — in recent geological history would be hard to miss. We don’t see it, therefore this isn’t a danger.

I’m not saying asteroid and/or comet impacts aren’t a danger at all, just that ones triggered by a rogue planet whizzing past us is incredibly small. We need to take impacts seriously in general, no matter what the cause. But in this case, interstellar planets doing the deed specifically aren’t a worry.

You can breathe easy

These results both surprise and don’t surprise me. I’m very much surprised that one of these interstellar nomads could be closer than even the nearest star; that’s amazing. But I’m not surprised they pose no real danger. The solar system and the Earth are terribly old, and there’s been lots of time for disasters to occur. If these planets were a real and immediate threat it seems clear we’d have known about it long before now (as we know about, say, asteroid impacts). The very fact that life has been around for billions of years, and complex life for hundreds of millions, means rogue planets don’t create cosmic calamities often enough to be a worry.

In a nutshell: I’m not concerned about it.

That is, in an "Oh my FSM we’re all gonna die!" kind of concern. As a scientist, I find these objects totally fascinating. If there is one within a couple of light years, and it’s still retained enough heat from its formation to glow in the infrared (as I discussed in the post yesterday), it may be possible to detect one directly in the next few years. It would be too far away to send a space probe (let alone visit), but with sensitive telescopes it’s not crazy to think we might actually be able to actually see one.

And that would be truly cool.

* For those prone to worry, this is not going to happen here in our solar system. The planets ejected likely suffered their indignity when their systems were very young, and super-Jupiter-sized planets still migrated in toward their parent star. Our solar system should be pretty stable over the next few billion years.

Related posts:

- The galaxy may swarm with billions of wandering planets
- How many habitable planets are there in the galaxy?
- Is there another planet in the solar system?
- No, there’s no proof of a giant planet in the outer solar system (this may seem to contradict the link above, but it’s a different topic!)

1. This assumes a constant density of wandering planets throughout the galaxy. I’d expect a higher density close to star forming regions as there wouldn’t be enough time for the wandering planets to have gone very far. Of course, the distance depends on how fast these things are moving but it must be on the order of the velocity they were originally orbiting their parent star so fairly slow in cosmic terms.

2. Chris

The question I’d like to raise is:

IF, I repeat IF, there was 1 of those heading directly our way (I’d ask the same of asteroids), how far in advance would we be able to detect its presence?

3. jules

It does offer all kinds of new potential for plot stories in sci-fi. Think deep-space refueling stations between stars to top up the hydrogen or other necessities. Hidden rebel bases away from tell-tale stars. Others may think of other scenarios.

4. Michael

Planet density should also vary with distance from the center of the galaxy. The center is far more dense than the outer sections. Judging roughly from the Milky Way diagram above we’re about half way between the center and the rim. We’re in an arm so that ups our local density a bit perhaps. Could we make a better estimate of the closeness of a rogue planet knowing all this? Anyone know an equation to estimate density of stars in our galaxy relative to radius from center?

Why do you need to know the volume of the galaxy? Isn’t more reasonable to assume that the local density of stars in the galaxy is roughly equal to the local density of rogue planets? If you know that, and assume there are as many rogue planets as stars, it follows that they must be roughly as close to us as stars are. This result can hardly be called “shocking”.

6. Maybe the JWST will be sensitive enough to pick up one of these. I imagine if there is one within four light years – that would be the one we’d see. Granted it would still be a rare thing just to be lucky enough to spot it.

I wonder what sort of velocities we’re looking at here? I guess it would be determined by how they were ejected… When I first commented on this yesterday, I speculated that the interaction between stars could eject planets from their orbit. Anyone think that’s possible? I figure a star formed in a binary pair wouldn’t really get a lot of planet building, but if a star moved closer it could be a pretty wild slingshot…

7. Rick

Re Dominic’s point above about the possibility of a non-constant density, in the last couple of paragraphs of the NY Times story on this Alan Boss suggests that it is more likely that these “rogues” are for the most part very distant but still gravitationally bound to the parent stars. That might make it more likely that one or more of these is in our neighborhood.

8. Marc

Rogue planets are something I’ve figured was very likely out there in interstellar space. Those and the dead stars and solar systems that that we just can’t see. The amount of nearly invisible stuff that’s likely out there makes me wonder if that’s part of why we haven’t encountered ET. It’s just too hard to actually travel any long distance. Just what would it be like to run into a rock at 30% light speed, much less encounter a whole planet? At such speeds would it even be possible to see and avoid these things. I hope we just don’t know the solutions yet.

9. noname

Chris;

As far away as we can see/sense other objects.

10. Sam H

I second Chris (#2)’s comment: Even though a rouge planet doesn’t have enough gravity to dislodge Oort Cloud objects (a passing red dwarf might, and I remember reading that one of the Gliese stars is on it’s way for a 1.3 ly close pass in a few million years), If one of them were headed our way how early would we know about it, and what would happen to it (would it be captured? Would it screw up planetary orbits? Might it eject a whole lot of asteroids and possibly a planet?) I imagine a scenario similar to Phil’s black hole intrusion from Death from the Skies, but on a much smaller scale.

11. Kevin

Does this discovery in any way effect the understanding of dark matter, dark energy, etc? I apologize if it this is a dumb question, but what I’m getting at is the discovery of rogue planets enough to add the necessary mass to galaxies to explain how gravity keeps them together, without the use of dark matter.

12. Um…Phil, I think your calculation leaves out something important…

What we should be thinking about is the flux of rogue planets, not the density. If the average velocity of the rogue planets is high relative to our solar system, then even if their density is low, we should encounter them fairly frequently.

13. Bob_In_Wales

Why do I find myself thinking of Nancy?

14. Roger

Could planets be ejected from a system when a Red Giant dies and forms a planetary nebula?

15. Mike

Sam @10: Mars is the rouge planet, n’ est pas? Not to be confused with rouge dwarfs.

16. chris j.

wasn’t the predicted count something like twice the number of stars, not the same? that reduces the volume of space predicted to contain at least one sunless planet. and if the calculations show such planets close to the 1 ly limit of the oort cloud, then these objects should, over the 4.6 billion year life of the solar system, interact with the cloud all the time. it probably happened a lot more often when the solar system formed, when its “sister” stars and “cousin” rogue planets were in closer proximity.

not only do i think encounters with rogue planets are more likely in close proximity to star-forming regions, there is even the remote possibility that the late heavy bombardment could have been induced by such an event. the sun was certainly much closer to where it formed back then.

i also think that models that predict rogue planet counts by either ejection or independent cloud collapse will undercount rogue planets. nothing precludes dust grain accretion into ceres-earth size objects, particularly in gas clouds that remain relatively unperturbed over long periods. and what happens to the planets of stars that go supernova (beyond what a certain t.v. show demonstrated with explosives and paper mache models)?

17. Any of these planets running for governor of Alaska?

18. Chris

@ Kevin 11
Jupiter is about 0.001 times the mass of the sun. So even if they were all jupiters, that would add 0.1% to the mass of the galaxy (overly simplifying here since not all stars weight the same as the sun and most are small red dwarfs). But since most of the planets would be much much smaller (mass of Earth is 3 millionths of the sun), the effect would be much less. So Yes it would add some of the dark matter, but not an appreciable amount.

19. Brian

Think of all the names that the first rogue planet found in our vicinity could be called: Mondas, Meta, Ultra, Gothos….

20. AJKamper

Okay, I think I have to make fun of Phil here. The first article says that there may be twice as many rogue planets as stars in the Milky Way. The second article registers shock that such planets might be closer than stars.

Doesn’t that mean, as long as the density of stars in our region of the Milky Way is “average” or less than average, that the second necessarily follows from the first? It shouldn’t be a surprise at all.

Results estimating the number of these things are VERY preliminary. I’ve often wondered if rouge planets, small ort-cloud-type rocks, and small black-holes might be numerous enough to account for dark matter. Is that possible, Phil, or would the number required result in an obvious and constant flickering of star brightness, or even a dimming of the whole sky?

Also, can anybody estimate how close a Jupiter or maybe Mars-side planet would have to get to us before somebody would notice it?

It also makes me wonder if maybe these super-jupiters wandering through space, picking up mass, if they ever wander through a nebula might form the nucleus of new stars.

22. Mark

Might a past encounter with a rogue planet be responsible for the aberrant axial tilt of Uranus?

23. Dragonchild

I really don’t know why the math had to go through so many steps. Here’s a more simple logical path: If rogue planets number double the stars in the galaxy, then it’s not a bad bet that the number of rogue planets in the neighborhood is twice the number of stars in the local neighborhood. So if there are x stars within 50 ly of Earth, there are 2x rogue planets. And a rogue planet would be only twice as likely to get “close” to Earth as a star would. . . with a whole hell of a lot less gravitydeath than a star. Thanks to that good ol’ inverse square law, there could be TEN times as many (which isn’t unreasonable at this preliminary stage, as rocky planets are bound to be horribly undercounted) and their impact on the solar system would be a big fat nil.

There are a ton of questions I’d like to ask these planets, though. How fast do you go? How are you dispersed? What are you made of?

I’d imagine their makeup would be comparable to that of our outer planets, such as Jupiter, Neptune, Pluto and Titan. Frozen rocks, ultra-cold gas giants and lonely supra-Jupiters up to small brown dwarfs. But that failure of the imagination doesn’t do them justice. Every assumption we’ve made about planets being boring turned out to be flat wrong.

24. Since you already assume the number of rogue planets equal to the number of stars in our galaxy, wouldn’t the distributions be the same too?

Especially since these rogue planets have to come from one of those star systems, I would think these planet would be distributed denser towards the center of the galaxy and sparser towards where we are.

25. Jon

Phil,

Since this is extremely relevant, I wondered if you could comment on the absurdity of the Smallville series finale.

In it, Darkseid’s rogue planet, Apokolips, wanders into our solar system. It shows the rogue planet passing by Saturn — it was roughly the same size or larger. It’d certainly be way more massive…. Apokolips appears to be solid and rocky, in addition it’s an ecumenopolis. So Problem #1: It actually appears to swipe Saturn, taking out much of its rings, and who knows how many satellites. Wouldn’t such a brush likely send Saturn out of the system, or worse, pull it toward the inner part of the solar system? Could we survive without Saturn (e.g. does it provide balance/stability)?

Later on, Apokolips is close enough to Earth to take up a good part of the sky. Problem #2: Somehow it has magically shrunken, though. If a Saturn sized planet were closer than our Moon, wouldn’t it take up nearly all of our sky? Problem #3: Could Earth even withstand a Saturn-sized, rocky planet looming so closely? When would earthquakes start, and the crust breaking off?

Later on, you can tell definitively that they’ve magically shrunken the planet. Because it… enters our atmosphere. Our lower, lower, lower atmosphere. In some shots, the curvature of Apokolips makes it apparently much smaller than Earth. In other shots, from space, when it’s nearly colliding with Earth, it appears to have grown again… appearing to be equal or slightly larger than Earth based on curvature. Problem #3: Wouldn’t even a Mars-sized planet entering our atmosphere likely end all life even without even colliding? Wouldn’t it at least start ripping the crust off the side of Earth that it’s facing?

Problem #4: Where was the Moon during all of this? I’m surprised to learn that even if Apokolips were still Saturn-sized it would fit between us and the Moon (but everyone has distorted views of the actual Earth-Moon distance), but even if the Moon were on the opposite side of Earth, assuming a gaseous mass of 95 Earths, or worse, a rocky mass of 750-800 Earths (as Apokolips first appeared to be), wouldn’t the Moon get pulled much closer to Earth? Apokolips lingered for several hours… I assume even if it was merely Earth-sized it would pull the Moon ever so slightly closer, maybe even undoing some of the Moon’s orbital retreat?

Lastly (and hilariously), Clark manages to push Apokolips away, but doesn’t bother to check its trajectory. He could be sending it right for Mars, Jupiter, or whatever is left of Saturn.

Here you can see how its size differs in every shot: http://smallville.wikia.com/wiki/Apokolips

26. GrogInOhio

Question… doesn’t at least one theory of the evolution of our solar system predict at least some ejected planets? Wouldn’t they hover closer than a rogue from any ejected from other star systems?

27. Dragonchild

Re: the use of a rogue planet as a plot point, I’d prefer to avoid thinking of one as a threat. Come to think of it, I realize that Star Trek is in bad need of another reboot or spin-off. Not the unfortunate reboots of late attempting to make it more accessible to the lowest common denominator (that’s another rant), but one that revisits the spirit of the original with our improved understanding of the universe. I doubt a rogue planet would be interesting enough to sustain an ongoing story, but it sure would rock to see an away team explore one! And at least in the foreseeable future, the only way we’re going to walk on the surface of a sunless world is in our imagination.

Firoz – I think we can forgive BA for making an excited, back-of-a-napkin calculation. Besides, local density and average density are two very different things. The planetary population can be expected to be similar to that of stars, but also clumped much like the stars are. Not only that, they’re constantly in motion, bunching and un-bunching and only very rarely colliding. The dynamics of the galaxy’s population can be roughly thought of as a bunch of chocolate chips in a swirling cake batter. There’s no way to tell at this point if the local distribution of rogue planets is higher or lower than average.

28. Oli

A while ago, I read an article (can’t remember where) claiming that Sedna might be an ex rogue planet. That would explain its weird orbit…

29. TechBear

I’m curious: why the assumption that a “rougue” planet must have formed around a star? Couldn’t the same processes that gave rise to stars — a compression of cosmic gas sufficient to allow gravity to take over — also give rise to Jupiter like planets? Red dwarves are the most common visible star in the galaxy, and I recall a hypothesis that brown dwarves should be just as common. Why not “black dwarves”?

30. Larry

One way of looking at the density is to derive a timescale of collision. Somewhat arbitrarily, I picked as the time scale the period it would take a rouge planet (the kind the Princess Leia would like) to traverse half of its characteristic volume of 100 cubic light years. Then, t=50 ly^3/(pi*(2r)^2*Vesc), where r is some interaction distance (larger than the radii of planets due to gravity) and Vesc is the typical escape velocity of a star’s gravitational well.

So, doing a little simplifying and not worrying too much about factors of 2, you get:

t (years) = 1e41/(r^2*Vesc). Plop in some anthropically biased values (r = earth’s radius, Vesc=50 km/s for the sun, roughly) and you get something on the order of 1e22 years, or roughly a billion times the age of the Universe. Sleep soundly tonight, y’all.

31. reidh

you mean that all those “kooks” that have been warning about planet X etc, have a valid point, of any percentage? After telling us all along that they were full of crop? Now why should I listen to you anymore?

32. Floyd

Just a thought about big meteorites and craters I know about, Superman not needed for these:

On the North American side of things, there’s Meteor Crater in Arizona (fairly small), the Manicouagan crater in Quebec (bigger), and Chixhulub Crater (sp?) in the Gulf of Mexico.

There’s also the small Kentland anomaly in northwestern Indiana. Not too many large meteorites, but they exist.

You can discuss the Sudbury District (big chunk of metal, being mined to this day) in Ontario, if you want.

33. Since you already assume the number of rogue planets equal to the number of stars in our galaxy, wouldn’t the distributions be the same too?

And since the nearest star is 93,000,000 miles away I would expect the nearest rogue planet to be a similar distance. So maybe the rouge planet is the rogue planet after all!

Just kidding.

34. Sam

Hi Phil: I was wondering, is this to say the Nemesis theory has been disproven? Or is it just not properly proven because Dr Muller never found his companion star? Does this change that?

I just finished reading his book and I wondered why I’d never heard of the theory of periodic extinctions before

35. Ken

It’s been 4.5 billion years, give or take, without the Earth being wiped out or ejected by one of these things. It’s incredibly implausible – or phenomenally bad luck – that one would happen to show up within a few decades of the time we realize they exist, or for that matter any time during humanity’s tenure.

36. Carbone

@ Chris (#2)

Depends what you mean by “directly our way”. Coliding with Earth? Entering Solar system? Also depends how fast it’d travel. But I think if there was such an object that could disrupt our lives in the coming decades we’d already know about it.

@ Phil
“That means there’s a pretty good chance that, statistically speaking, there may be one of these rogue planets closer to us than the nearest star!”

Not really that surprising even without any math. Since they say there may be as many of these planets as there are stars it’s logical to say that there are as many stars per cubic light year as there are free-floating planets. Add the fact that majority of stars are binary (or more) you have to come to the conclusion that one of these planets is probably closer to us than the nearest star.

37. Now why should I listen to you anymore?

Well, for starters, then you might be able to ask a question that is based on something Phil actually said.

38. Wolfram

It’s too sad we aren’t able to detect these guys better. I would believe they might be tremendously useful for a slingshot into interstellar space if the velocities between them and our solar system differ enough, right?

39. Stuart

Surely we need a new name for these things, they can’t be planets, they aren’t even in orbit around something. http://en.wikipedia.org/wiki/Definition_of_planet

40. Idris Idmonster

Of course this was already done. The original novel of “when worlds collide” featured a gas giant with a terrestrial planet sized moon enter the solarsytem. (The film had a star and planet). Impressive as the novel was written in 1933 and worth a read if you can find a copy. The science in the novel is better than the film though with some quiant notions about atomic power.

For more details see http://en.wikipedia.org/wiki/When_Worlds_Collide

41. Darrell

Given that there is a possibility of numbers of orphan planets being more abundant than stars…could these rogue worlds be playing a role as dark matter?

42. Charlie

Phil!,

Perhaps the NYTs is misrepresenting the science (I haven’t read the actual article), but their report leaves me with an interpretation quite different than yours. (At least when I read the report and not just the headline.)

1. Planets may be “going their own lonely way” OR “at least 10 times as far away as the Sun is from the Earth.” So I did my own deep research (consulting the Wiki) and found that the latter interpretation basically fits 3 of our own 4 gas giants. (OK, Saturn is 9 AU at perihelion but close enough.)

2. At the end of the NYT report, a putative authority (a “Dr. Boss”; I’m a biologist so I don’t know who the authorities are here) said that the latter is much more likely than the former. (I.e., the report ends by providing evidence exactly contradicting the headline, as so many NYT reports do.)

Everyone likes a rogue (or rouge as the case may be) but it seems like there is a much more parsimonious interpretation. I.e., most solar systems are like ours.

43. Anders

Well, this calculation is aimed at jupiter size (and pephaps +size) planets, there is no reason (that I can think of) why smaller planets shouldn’t be lodged into “freeroaming state”, is there? so there could be 3 or 4 or 5 times the number of freeroaming planets out there, right? I’m no expert here , but it seems to me it would be rather obvious that there may be hundreds of small planets for every very big planet.. why not? Of course, you cant say this with any scientific basis, but I think its a reasonable assumption, based on the fact that we (until the mid 90′s) knew of thousands of smaller objects than the 9/8 planets themselves..

44. DigitalAxis

@30 reidh:

I’m thinking POE?

“a valid point, of any percentage?”

Ok, if we’re going to admit ANY theories that have ANY statistical chance of being true, then everything everyone has ever said has been wrong.

Seriously, the idea of Nemesis or rogue planets is not new at all, and Phil has addressed the point before. Seriously, take a look at this one: If there’s one planet per 100 cubic light years, that’s 1 planet per every 2.5×10^16 AU^3. Jupiter does not affect us all that much, and it’s between 4.2 and 6.2 AU away. Let’s be generous and take a radius of 6.2 AU; that’s 1 Jupiter within a volume 1000 AU^3 = 1×10^3 AU^3. That means the chance of finding a randomly positioned Jupiter that could affect us as much or more than Jupiter is 1:2.5×10^13. That’s 1 in 25 trillion, not accounting for gravitational deflection toward stars. And we would *definitely* be able to see it if it were within that distance (we can see Neptune, after all) and definitely spot the gravitational effects on the planets of the Solar System, so… no, it’s not there.

Never mind that most things I’ve seen about Nibiru are impossible for other reasons (we can’t see it and it’s due to enter the inner solar system in just over a YEAR? Right. It’s going really fast AND it’s invisible, so it must not have any heat AT ALL, because we’d see the giant cloud of obscuring dust emitting thermal infrared with telescopes like WISE, and occulting stars with any other telescope)

Then there’s Nemesis. Mathese and Whitmire have a testable hypothesis about where and how a brown dwarf could be hiding, but the parameters he set are for an object that couldn’t affect us either like Planet X doomsday folks suggest, even if their test with WISE data does find a very close brown dwarf.

45. Oli

By the way, what about rogue dwarf planets and asteroids? Seems to me like a lot of those would also be ejected…

46. Sean H.

Could this have already happened? Could a rogue planet have hit Earth rather than a Theia in an L5 Sun/Earth orbit destabilized? And if Theia hadn’t hit Earth would its trajectory have ejected it from the Solar system? Interesting things to think about. And how would a rogue planet be affected by passing the heliopause? Depending on entry point and trajectory through the Solar system, what perturbations would a rogue planet cause (I will whole-heartedly admit that it would be extremely interesting to see a small planet or dwarf planet hit Jupiter). Would a small planet or a large planet be more likely to be ejected from its parent star? Very, very interesting things to think about, thank you, Phil.

47. DigitalAxis

@42 Charlie:

Dr. Alan Boss is legit. I don’t have a link to the NYT article, but the obvious point to make is that these planets were considered rogue planets because there was only one small microlensing event. That does not necessarily mean there IS no star involved, just that it was too far away in angular separation to contribute to the lens.

The biggest problem with current planetary statistics is that radial velocity searches capable of finding planets (eg, California) have only been going since 1987. That’s 24 years, ie still less than the orbital period of Saturn, and the reflex motion of the Sun due to Saturn is pretty tiny compared to those earliest planets. So, we don’t know how unlikely very distant (100 AU) planets actually are. There are some known planets with orbital periods longer than Saturn, but they would have to be calculated from incomplete datasets, or they were visually discovered, like Fomalhaut B or HR8799′s planets.

I’ve seen plots that suggest that the distribution of orbital elements of planetary orbits (inclinations, semimajor axes, eccentricities) are no different from stars minus the observational bias toward shorter periods, so it might not be unreasonable to assume planets can be distributed as far from their stars as binary star components can be. Then you easily get thousands of AU…. although the formation mechanisms for planets probably require enough material and enough density to form themselves.

48. IVAN3MAN_AT_LARGE

Oli:

A while ago, I read an article (can’t remember where) claiming that Sedna might be an ex rogue planet.

Did you mean this one?

49. Matt B.

Name suggestion: orphan world (avoiding the term “planet”)

If an orphan world got ejected with a velocity of 1/10000 c, (same as Earth’s orbital v) it could have gone 2000 light-years in the last 2 billion years. You may have to increase the effective volume of the galaxy, Phil.

50. It strikes me that if one of these wanderers came near us we would know about it decades in advance just from its effect on the orbits of the outer planets. I’m sure we would have a pretty good position for it long before it was directly detectable.

51. Messier Tidy Upper

Great article and fascinatiing conclusions – thanks BA.

I don’t think we have tooo much to fear from rogue planets – unless they’re like Mongo :

and have some hostile inhabitants!

(Mongo btw. was described in that serioes as both a “comet” and a “rogue wandering planet!”)

They may present some interesting opportunies for us though – if we can find and ideally encounter them in any detail.

Perhaps they could be stepping stones to the stars and benefit our eventual hopeful interstellar voyages?

52. Messier Tidy Upper

@49. Matt B. : Name suggestion: orphan world (avoiding the term “planet”)

I for one prefer “rogue planet” and a broader re-definition of that term to include such objects – and the ice dwarfs like Pluto, Eris and Sedna as well.

Personally, my preferred definition would be :

1) Is it round because of its own gravity? If too small then its a comet /asteroid /planetoid.

2) Is it – or has it ever been – self-luminous via its own core nuclear fusion of some variety?
If so then its a brown dwarf or star incl. black holes, neutron stars, white dwarfs etc ..

&

3) Is it orbiting another planet directly instead of orbiting a primary sun or brown dwarf? If so then its a moon.

If not (& it meets criteria 1 & 2 too) then its a planet.

That seems like a sensible and reasonable if broad definition to me and one that allows us to determine a world’s status fairly easily – and one that includes rogue planets. Don’t get me started on the idiocy of the IAU’s anti-Pluto definition!

I’ll just add that I have also seen the alternatives ‘planemo’ for ‘planetary mass object’ and ‘sub-stellar object’ occassionally used for such rogue planets as well. Orphan world is better than those at least methinks!

53. gopher65

Dragonchild #27:

Enterprise already did that. The episode was kinda “meh” (although in retrospect it *might* have been intended to be deeper than it came off at first glance, but it’s hard to tell with writers like that). The rogue planet, however, was cool, except for the plants, which were entirely the wrong colour (I’m guessing that they weren’t suppose to be photosynthetic either, but the props department failed miserably on that front).

54. chris j.

Sean H. @46:

the strongest argument against theia being extrasolar is that the moon’s orbit is in the same plane as all of the planets. the odds of something that with something that didn’t form from the sun’s accretion disk are really, really, really low.

55. Messier Tidy Upper

BA, what are the odds of a star capturing a rogue planet into orbit – wouldn’t the gravity wells of stars esp. high mass one’s enable this to happen at least on some rare occassions?

Any chance you or somebody else kind and skilled enough to do so could calculate that?
(My own mathematical ability is, alas, woeful. )

The odds of a planet getting close enough to dislodge even a single Oort cloud object is pretty small.

What about a close pass by a star such as the encounter we’re predicted to have with orange dwarf star Gliese 710 in about 1.4 million years. Is the extra stellar mass (& its extra radiation pressures) likely to make a big difference and make it a real threat in terms of ejecting vast numbers of comets our way or not? Have you written about that before? If so, I haven’t seen it.

56. Messier Tidy Upper

Link for the Gliese 710 encounter in the distant future :

http://en.wikipedia.org/wiki/Gliese_710

***

is currently about 63.0 light years from Earth, but its proper motion, distance, and radial velocity[5] indicate that it will approach within a very small distance—perhaps under one light year—from the Sun within 1.4 million years, based on past and current Hipparcos data.[2] At closest approach it will be a first-magnitude star about as bright as Antares. The proper motion of Gliese 710 is very small for its distance, meaning it is traveling nearly directly in our line of sight … recent calculations by Bobylev in 2010 suggest Gliese 710 has an 86 percent chance of passing through the Oort cloud, considering the Oort cloud to be a spheroid around the Sun with semiminor and semimajor axes of 80,000 and 100,000 astronomical units. The distance of closest approach of Gliese 710 is difficult to compute precisely as it depends sensitively on its current position and velocity; Bobylev estimates that it will pass within 0.311 ± 0.167 pc (1.01 ± 0.54 light years) of the Sun.

***

Wonder how many close stellar encounters we’ve had over thelifespan of teghsolar system so far – and whether their planets if they have any could have added totheeffect or been ejceted or captured in the process!

57. Brian Too

@8. Marc,

There was a proposal, very conceptual you understand, several years back. The author wanted to construct interstellar spacecraft that were flat and travelled flat side forward. The whole idea was that it was a huge ship constructed in hexagonal sections and meant to have a travel time of decades to centuries.

In order to protect against collisions it was to use powerful forward looking radar. The ship’s radar system would look for impending debris collisions (this only works for comparatively small objects, nothing so big as a Jupiter class planet I’d guess). Then calculating what segment of the ship the collision would hit, they’d move that segment and nothing else out of the way! In other words the ship does not have to alter it’s course. The ship can alter it’s large scale configuration instead.

There are lots of caveats I’m sure. It doesn’t work with objects that are large relative to the ship. It doesn’t work with clouds/debris fields. The segments need to have modular interconnects and be relatively easy to move. The ship modules need to be large enough to make such a reconfiguration worthwhile from a collison avoidance perspective. You are also placing a lot of faith in the accuracy of your collision detection system!

Finally, when you start to achieve a significant fraction of c velocity, I’m unclear as to how much lead time you can expect as a collision warning. 30% of c is awfully fast!

58. Hey, wasn’t Proxima Centauri the nearest star?

59. amphiox

Of course, the distance depends on how fast these things are moving but it must be on the order of the velocity they were originally orbiting their parent star so fairly slow in cosmic terms.

I would hazard the guess that these rogue planets should be moving at velocities faster than the escape velocities of their parent stars. Should be a bit faster than regular orbital velocities, and could be all the way up to the velocities of hypervelocity stars (perhaps?). Still pretty slow on the grand scheme, of course.

60. Great, now I’m gonna go to sleep worrying about Bronson Alpha and Bronson Beta.

61. Michael Simmons

@Messier Tidy Upper
By the way the References section of wikipedia article contains links to articles that consider the number and probability aspects of stars passing close to our solar system

“We find that the rate of close approaches by star systems (single or multiple stars) within a distance D (in parsecs) from the Sun is given by N= 3.5D^2.12 Myr^-1, less than the number predicted by a simple stellar dynamics model. However, this value is clearly a lower limit because of observational incompleteness in the Hipparcos data set.”

My understanding is that Hipparcos data set targeted stars above a certain brightness and with a large proper motion. It would be missing a lot of brown dwarfs and darker objects and of course any estimate from rogue planets.

@Phil
“A planet-wide bombardment of giant comets — even from a single big comet — in recent geological history would be hard to miss. We don’t see it, therefore this isn’t a danger.”

Not on human time scales.

35 million years ago this

From http://sciencewise.anu.edu.au/articles/big%20impact
“Around the same time as the Mount Ashmore impact, a 100 kilometer wide asteroid impact structure formed in Siberia, and another measuring 85 km in diameter in Chesapeake Bay, off Virginia, in the United States. Likewise a large field of tektites – molten rock fragments splashed by impact – fell over northeast America. This defined a major impact cluster across the planet,” Dr Glikson says.

Perhaps this was a passing star or rouge gas giant.
These impacts might have occur over few million years as the disturbed objects happened to hit the earth.

Someone needs to run some simulations and publish a paper on this.
Perhaps an initial assessment of the effect on the planets using Swarm-NG.
Followed by a all known solar objects simulation of a large number of different masses, velocities and approach vectors.

62. Timothy from Boulder

I recently did an analytical study on this very topic — “Effects of a Large Perturbing Body on the Stability of the Solar System” (Phil, I can provide a copy for you if you’re interested.) The surprising result is that it takes a body *much* larger or *much* closer than you think to have any effect on the Earth. Here are the introduction and conclusion:

“1. Introduction The question of the long-term dynamical stability of the Solar System has been of continuing interest to astronomers since the 17th century. While the paths of the heavenly bodies were once thought to be unchangeable and perpetual, Newton’s development of the Law of Universal Gravitation quickly pointed to fluctuations in the motions of the planets. While curiosity about the eventual fate of the Solar System on the time scale of the Sun’s lifetime motivates the investigation of long-term stability among the existing planets, short-term stability is only a concern if the Solar System is perturbed by an outside force. A frequent trope of classic science fiction literature is the “rogue planet” whose passing through the Solar System wreaks havoc on Earth and humanity, as in the archetypal 1933 novel “When Worlds Collide.” Although the situation is of negligible practical importance, as an intellectual exercise in planetary stability we investigate the implications of a large perturbing body passing through the inner Solar System.”

and

“6. Summary and conclusions A perturbing body passing through the Solar System requires 10–100 Earth masses to have anything other than a trivial effect. Even at a huge mass of 10 Jupiters a trajectory with a closest approach of ~1 AU to one of the outer planets is required to produce a perturbation that initiates an interaction between the planets that results in a catastrophic instability. In the cases examined in this study, even a catastrophic instability that ejects Saturn and Uranus from the Solar system did not adversely affect the inner planets.
The passage of a 10 Jupiter mass through the inner solar system causes immediate change to the orbits of the terrestrial planets, but even at closest approaches of 0.35 AU, the changes are moderate and do not create the high eccentricities required to cause interactions between planets. It is likely that the reason for the difference between the effects on the inner and outer planets is the time spent in the vicinity of the perturbing body. The velocity of the perturbing body on a parabolic trajectory is much higher in the inner Solar System than near Saturn; the amount of time it spends exerting a perturbing force is therefore much smaller.
As far as the fictional motivation for this investigation, the random passage of a mass of 1–3 Jupiters on a parabolic trajectory within 0.5 AU of the Sun may change the temperature of Earth by a few tenths of a percent to a percent but is unlikely to have a major effect on the habitability of Earth.”

63. Messier Tidy Upper

@58. Daniel Drehmer : “Hey, wasn’t Proxima Centauri the nearest star?”

It is – *if* it is NOT bound to the other two stars of Alpha Centauri.

If it *is* orbiting them then on average it will be located at the same distance of the Alpha Cen pair.

Proxima Centauri (or Alpha Centauri C) does happen to be positioned a bit closer than Alpha Centauri A & B at the present moment – 4.2 versus 4.3 light years away. Proxima takes 1 million years or more to orbit the Alpha Centauri duo (if it indeed does so) and is separated from the main binary by 13,000 AU ie. 1thirteen thousand times the Earth-Sun distance. (Sources : Kaler, 2002 & Croswell, April,1991.)

There were suggestions the WISE space observatory might detect a brown dwarf if there was one closer than Proxima Centauri currently is – but I haven’t heard of any news to suggest they have yet. A couple of astronomers have also suggested that WISE data hints at the existence of “Tyche” a tenth planet orbiting beyond Pluto – but, again, no further developments have occurred in that regard that I’m aware of.

64. Brie987

Its about time the Anunnaki came back for a visit and see how we are doing.

65. IanS

@26
yes they would be closer than Phil’s back of a napkin average but…. they would by definition be moving away from the solar system and therefore pose no threat.

66. Brian

When this story first came out two days ago I did some quick maths based on the figures supplied and came to the conclusion that the closest rogue planet was probably at least two lightyears away. The figures you give indicate about three lightyears so the answer you said was surprising (that there may be a rogue planet closer to us than the nearest star) really isn’t that surprising. Although this is an interesting story it doesn’t worry me at all.

67. Bill3

It’s been posted several times, but I’m surprised at you too Phil. If estimates place rogue planet counts in the neighborhood of the number of stars in the galaxy, the instant estimate should come to mind that they’re about as close as neighboring stars too.

And if the stars aren’t barreling towards us, I feel pretty safe that rogue planets aren’t either.

68. OmegaBaby

Yea…this sounds a lot like taking a number, then multiplying it by 1 million, then dividing it by a million, and then being AMAZED at the coincidence that you ended up with the number you started off with

Anyway…if you look at what is known about stars in general, there’s a clear pattern that the number of objects is inversely correlated with the mass of the object…
# black holes < # massive stars < # medium (yell0w) stars < # red dwarfs

Why would we not expect that pattern to hold?…
# black holes < # massive stars < # medium (yell0w) stars < # red dwarfs < # brown dwarfs < # gas giants < # rocky planets < # comets/asteroids

And if so, it seems like rouge planets would vastly outnumber visible stars, perhaps by a factor of 100x or more.

69. Assuming an even distribution brings a lot of simplicity to the mathematical table, but it seems like you need a probability density function here? Of course, *that* math would make the article inaccessible to a lot of potential readers … keep up the great work, the world needs more scientists with the time and patience to explain things and carry on the battle against superstition and ignorance. PS Stop by for a beer if you’re ever in Nashville (www.fleetstreetpub.com).

70. Michel

The next thing they´ll find is Lawless Planets.

71. Austin

72. Mike

@71: lawless planets are often followed by vigilante planets and a posse of deputised comets

73. Aleina

The New York Times on March 15th 2009 brought out another sensation. The noted Chinese official, Mao Kan mentioned that he has obtained more than 1000 secret photographs which reveal not only human footprints but a human dead body on the surface of the moon. It was also stated by the said official that some bones from that dead body was missing. It is believed that the human dead body have been dropped on the moon from alien spaceship and extraterrestrials kept few tissues for research.
http://funnyandspicy.com/three-extraterrestrial-spaceships-will-attack-earth-in-2012

74. Ryan

There is an upcoming big budget movie about this very topic. It’s called “Melancholia” http://en.wikipedia.org/wiki/Melancholia_(2011_film) About a rogue planet heading for Earth and ending Earth’s existence. I CAN’T wait to watch it!!!

75. Nefarious Wheel

Of course, random distribution means it’s just as likely there’s one in our armpit* as one we’ll never discover.

*Bet-al-Geus, “The Armpit” — Look up at Orion sometime, find where the big red one is…

76. Wzrd1

Phil, Phil, Phil. How many times must you be reminded that there is NO such thing as NO in probability equations?
The probability spread for an Earth effecting rogue planet is 3. Slim, fat and none.
As none is NOT valid in statistics, the chances of effect are slim and fat.
As in a slim chance of even NOTICING the thing.
As in a FAT chance of even directly observing the thing.
Because, as you’ve said, space is really, really, really, really, REALLY big and we’re miniscule.
Still, it’d be uber cool if we DID bump into one passing by within a few lightyears, it might JUST be able to be observed in the next few generations of space telescopes.
Assuming the tea party LETS us “waste” money on REAL science…

77. Michael Simmons

@Wzrd1
http://www.phrenopolis.com/perspective/solarsystem/
as far as hitting or coming close to a planet.

Gravitationally to have any effect the object as to be around for a long time.
Any coming though is going to fly in and out before it affects any of the planets.

However…. anything flying though this
http://www.minorplanetcenter.net/iau/Animations/Outer_2011.gif

or worst this
http://www.minorplanetcenter.net/iau/Animations/Middle_2011.gif
is probably going to throw something out of wack.

(gif animations are from http://www.minorplanetcenter.net/iau/Animations/Animations.html)

78. Peter Ravn Rasmussen

“1041 cubic kilometers”? Really?

79. Although it seems there is much speculation concerning “seven confirmed sitings” and a conclusion that there may be 100′s of billions of rogue planets in the galaxy, if such a conclusion is valid then I think there would be a greater worry concerning the interaction of such planets with the sun and other planets than with our planet.

The idea is that the sun would gravitationally attract such planets passing through our solar system and some could collide or raise havoc with the sun on close approach, or be captured by the sun, any of which could cause great disturbances to the Earth and solar system.

Also I’m thinking there probably are many rogue stars out there that move counter to the normal motions of the Milky Way that also could cause similar problems. Additionally the Nemesis hypothesis that could be a very small distant companion star to our sun (a red dwarf), a brown dwarf, a very large planet of some kind, all of the above being food for though for some final edition of Phil’s book, “Death from the Skys, part 86.”

80. Michael Simmons

@ forrest noble

sigh is nobody actually reading other peoples posts.
read what “Timothy from Boulder” said

If you want the software used in a a lot of scientic papers for nbody simulations get
John Chambers Mercury program from here http://www.arm.ac.uk/~jec/
It is text based and in fortran.

81. Geo

Someone already pointed out the potential for cool sci-fi stories around rogue planets, but your math also points out a flaw in science fiction that I’ve always found rather annoying.

In sci-fi, it is always ridiculously easy to FIND THINGS. In Star Trek, the Enterprise can scan planets and isolate the life signs of individual people. They can also detect space ships from light years away. In Star Wars, the Empire can find a rebel base with relative ease, just by sending out a few probe droids to random planets.

And the list goes on and on. I realize that this is in part a plot-moving device. Just as in crime stories, the pursuing killer and the fleeing victim always manage to bump into each other at a random gas station (even though the odds of that are astronomical), it’s necessary for protagonists and antagonists to find each other if they story is going to move forward at all. After all, it would be a pretty boring story if it read like this: “And so our hero fled the evil Zorgons and they never found him. The End.”

However, I also think it has something to do with the human mind’s inability to think about large numbers. If you wanted to get lost in this galaxy, NOBODY is going to find you, EVER. Period. I do not care how advanced their technology is, it WILL NOT happen. Space is just too damn big. I don’t care how sensitive the sensors are, they are NOT going to find some tiny little spaceship parked on a random ice moon between two stars. First off, it would take thousands of years to search a volume that large, and that’s only if you consider local space. If you start talking about the volume of a galaxy (like the Empire’s search for the rebels), you’d need the lifetime of the universe (and then some) to find something as small as a ship or a base. And quite frankly, if your stealth technology cannot mask you in a volume that large, then it is seriously CRAP technology.

So that’s something that I wish sci-fi would start addressing in a more “realistic” fashion. I realize that might seem like a silly request of a genre that regularly defeats Einstein by merely flicking the “hyperdrive” switch, but this is different. This isn’t a simple matter of finding a fictional shortcut around the universe’s speed limit. Doing a “sensor sweep” of a SECTOR of the galaxy and finding the ship you’re looking for borders on “magical”. It would be the difference between asking us to buy into Harry Potter having a magic wand that helps him cast spells or asking us to buy into Harry Potter putting on a magic ring and saying, “I wish Voldemort was dead, and that everyone he ever killed was alive again. Ta Da!”

The former is “believable” bit of fiction, but the latter is just a God-like deus ex machina. A ship drive that can generate a wormhole or drop the ship into a “hyper dimension” that speeds travel between two points? OK, sure, I’ll buy that “impossibility” for the sake of the story. But a magical, God-like “sensor array” that can find anyone, anywhere IN SPACE? Come on!! If the Romulans wanted to park an armada within 100 AU of Earth, NOBODY would ever find it, even without cloaking technology. It’s not like seaching for a needle in a haystack. It’s like searching for a needle in ALL the wheat fields on the planet!!

Rant over

82. jess tauber

The Queen’s visit to Ireland this past week proves that there is at least one BROGUE planet in the Milky Way, and it is ours….

83. Timothy from Boulder

@ Michael Simmons

Chambers’ MERCURY symplectic integrator was used for my analysis, which ran the model for 500,000 years.

Another point people are missing is the time involved. Even in the one extraordinary case in the model where a 10-Jupiter mass passes closely by Saturn and sets up a catastrophic orbital instability (Jupiter and Saturn trade places 5 times; Saturn and Uranus are eventually ejected from the Solar System) the process takes over 100,000 years to occur.

84. Michael Simmons

@Timothy from Boulder
I’d be interested in the number of scenarios you tried.
I’d imaging a super computer would be needed to run a large number of scenarios for extended times.

For those that might not have access to a super computer to study this , there are two GPU base n body simulators.
http://astro.pas.rochester.edu/~aquillen/qymsym/
“QYMSYM: GPU accelerated 2nd order hybrid symplectic integrator that permits close encounters. This is a parallel code running with CUDA on a video card that puts the many processors on board to work while taking advantage of fast shared memory. It is meant to do the same thing as John Chambers’ code mercury6 but in parallel on the GPU. ”
paper http://arxiv.org/abs/1007.3458

The second is Swarm-NG
“Swarm-NG will focus on the integration of an ensemble of N-body systems evolving under Newtonian gravity. Swarm-NG does not replicate existing libraries that calculate forces for large-N systems on GPUs, but rather focuses on integrating an ensemble of many systems where N is small. This is of particular interest for astronomers who study the chaotic evolution of planetary systems. In the long term, we hope Swarm-NG will allow for the efficient parallel integration of user-defined systems of ordinary differential equations.”

Given the result that gas giant size planets and larger can fly though with little effect on the planets, the first thing that I think of is how common could this be occurring and what is the effect on the huge number of small objects in the solar system.

85. Messier Tidy Upper

There’s a New Scientist issue of relevant interest here – this is the 24th November 2001 issue if folks can find a copy somewhere – that has “Dark Worlds : The strange Planets that Roam Deep Space” as its cover story complete with a good piece of space art depicting such a world. This is also titled (inside the mag.) “Lost Worlds and was written by Marcus Chown featuring these free-floating planets.

Also in the NewScientist issue 23rd July 2005 and again a cover story no less was an article titled “How many Planets in the solar System?” with the artwork having crossed out ’9′ and written ’23′ in red over it. This article dealt with the “oligarchic theory” of the formation of our solar system and suggested – based on claims by Eugene Chiang of the University of California and on Scott Kenyon’s computer models and theorising – that there may have been about 60 Mars sized bodies formed early in our solar system’s history and many of them were ejected out to now orbit around 1,000 to 10,000 AU with others being entirely ejected from our solar system.

What a co-incidence it might be if we could find one of those lost “sibling” worlds some day!

@84. Geo : I think the Enterprisecomes complete with astronomical charts and information provided already by the previous reserach of Humans and Vulcans and other Federation groups. I also do recall the ship(s) spending time on charting and stellar and planetary surveying missions,FWIW.

86. Messier Tidy Upper

@83. Michael Simmons asked : “sigh is nobody actually reading other peoples posts?”

Well *I* am!

@75. Ryan : “There is an upcoming big budget movie about this very topic. It’s called “Melancholia” [Snip] about a rogue planet heading for Earth and ending Earth’s existence. I CAN’T wait to watch it!!!

I can. I’ll wait till its out on DVD or broadcast on the box.

@62. Michael Simmons : Thanks.

87. mike burkhart

Thanks Phil this takes a lot off of my mind. I’m sorry for bringing it up but when I read the other post, the novels When Worlds Collide and After Worlds Collide (and movie) poped into my head.

88. I seem to remember that Space:1999 was all about people trapped on the moon when it was hurled out of the Solar System and catapulted to wander through space…
…not so far-fetched after all!!

89. @michael Simmons,

” … is nobody actually reading other peoples posts.
read what “Timothy from Boulder” said.”

I agree that Timothy’s posting is a very informative and that you are correct, I did not read his posting before posting my own. I did discuss both rogue stars and rogue planets up to 75 Jupiter masses (smallest possible stars) in my posting however. My statements did not say how big or how close these object would need to be to raise havoc with our sun. On close approach generally meaning the inner solar system including an impact with the sun, I think there is no doubt in the case of impact with the sun of a body of 75 times the mass of Jupiter, that serious repercussions would result concerning the Earth. On closest approach within .1 angstrom units from the sun, the repercussions concerning the Earth would be open for conjecture.

90. Ron

Ok. so you are quick to minimize the risk because the mass expanse of space and the mathematical probabilities, huh? Ok. So please explain why we can have near run in’s and even collisions with objects like the one in syberia or the much larger one that killed off the dinosaurs, many instantly? Do not speak in absolutes in science my friend, you will be proved wrong almost every time! ANYTHING, well almost, is possible if not probable over a 13 billion year period.

91. Ben

Given your assumptions, it should not be surprising that you have calculated that a rogue planet could be found closer than the nearest star. First, you assumed a similar number of planets to stars; second, you assumed they were equally distributed in the volume. If these were true then you would expect the nearest rogue planet to be the same distance as the nearest star. However, that is not the case. The galaxy is more dense toward the middle and less dense (fewer stars/volume) out where where we are. So if you calculated equal distribution for planets and compared it with the actual distances where we were, it would be almost a certainty that the calculated nearest planet would be closer than the real nearest star. In reality, you would expect fewer rogue planets per volume the further out you would go in the galaxy, just like stars.

92. dave lee

lovely explanation but thats like saying only one car a year passes through a remote area of Arizona so you will never be in danger of collision with it, statistically this is correct, unless you happen to cross that one cars path at the wrong time………

93. LogicalSkeptic

Why does it surprise you that using your formula you get a planet closer to us than the nearest star? I think that would have been simply logical. You took the number of stars, the volume of the galaxy, and calculated the perfectly even distribution to figure out the avg case… Many stars are mixed up with other stars close by, so on avg they are not ideally evenly spread throughought the galaxy. But using your math you basically calculated how close a star would be if they were, and got one pretty close to the same distance to us as the closest star (slightly closer makes sense then)

edit: I kept saying stars since you were using the number of stars as the basis for the number of rogue planets. I could have inserted rogue planets in at many places instead, hope I didnt confuse the comment

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