Researchers say galaxy may swarm with 'nomad planets'

Feb 23, 2012 BY ANDY FREEBERG
This image is an artistic rendition of a nomad object wandering the interstellar medium. The object is intentionally blurry to represent uncertainty about whether it has an atmosphere. A nomadic object may be an icy body akin to an object found in the outer solar system, a more rocky material akin to asteroid or even a gas giant similar in composition to the most massive solar system planets and exoplanets. Image: Greg Stewart / SLAC National Accelerator Laboratory

(PhysOrg.com) -- Our galaxy may be awash in homeless planets, wandering through space instead of orbiting a star.

In fact, there may be 100,000 times more "nomad planets" in the Milky Way than stars, according to a new study by researchers at the Kavli Institute for and Cosmology (KIPAC), a joint institute of Stanford University and the SLAC National Accelerator Laboratory.

If observations confirm the estimate, this new class of will affect current theories of and could change our understanding of the origin and abundance of life.

"If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist," said Louis Strigari, leader of the team that reported the result in a paper submitted to the . Although nomad planets don't bask in the warmth of a star, they may generate heat through internal and tectonic activity.

Searches over the past two decades have identified more than 500 , almost all of which orbit stars. Last year, researchers detected about a dozen nomad planets, using a technique called , which looks for stars whose light is momentarily refocused by the gravity of passing planets.

The research produced evidence that roughly two nomads exist for every typical, so-called main-sequence star in our galaxy. The new study estimates that nomads may be up to 50,000 times more common than that.

To arrive at what Strigari himself called "an astronomical number," the KIPAC team took into account the known gravitational pull of the , the amount of matter available to make such objects and how that matter might divvy itself up into objects ranging from the size of Pluto to larger than Jupiter. Not an easy task, considering no one is quite sure how these bodies form. According to Strigari, some were probably ejected from solar systems, but research indicates that not all of them could have formed in that fashion.

"To paraphrase Dorothy from The Wizard of Oz, if correct, this extrapolation implies that we are not in Kansas anymore, and in fact we never were in Kansas," said Alan Boss of the Carnegie Institution for Science, author of The Crowded Universe: The Search for Living Planets, who was not involved in the research. "The universe is riddled with unseen planetary-mass objects that we are just now able to detect."

A good count, especially of the smaller objects, will have to wait for the next generation of big survey telescopes, especially the space-based Wide-Field Infrared Survey Telescope and the ground-based Large Synoptic Survey Telescope, both set to begin operation in the early 2020s.

A confirmation of the estimate could lend credence to another possibility mentioned in the paper – that as nomad planets roam their starry pastures, collisions could scatter their microbial flocks to seed life elsewhere.

"Few areas of science have excited as much popular and professional interest in recent times as the prevalence of life in the universe," said co-author and KIPAC Director Roger Blandford. "What is wonderful is that we can now start to address this question quantitatively by seeking more of these erstwhile planets and asteroids wandering through interstellar space, and then speculate about hitchhiking bugs."

Additional authors included KIPAC member Matteo Barnabè and affiliate KIPAC member Philip Marshall of Oxford University. The research was supported by NASA, the National Science Foundation and the Royal Astronomical Society.

Explore further: Millisecond pulsars clearly demonstrate that pulsars are neutron stars

Related Stories

Is The Solar System Unique in The Universe?

Aug 03, 2004

On the evidence to date, our solar system could be fundamentally different from the majority of planetary systems around stars because it formed in a different way. If that is the case, Earth-like planets will be very rar ...

When stars play planetary pinball

Feb 08, 2012

Many of us remember playing pinball at the local arcade while growing up; it turns out that some stars like it as well. Binary stars can play tug-of-war with an unfortunate planet, flinging it into a wide ...

Planets smashed into dust near supermassive black holes

Oct 28, 2011

(PhysOrg.com) -- Fat doughnut-shaped dust shrouds that obscure about half of supermassive black holes could be the result of high speed crashes between planets and asteroids, according to a new theory from ...

Recommended for you

Image: The Pillars of Creation

10 minutes ago

The Pillars of Creation (seen above) is an image of a portion of the Eagle nebula (M16) taken by Hubble Space Telescope in 1995. It soon became one of the most iconic space images of all time. The Eagle nebula ...

How small can galaxies be?

Sep 29, 2014

Yesterday I talked about just how small a star can be, so today let's explore just how small a galaxy can be. Our Milky Way galaxy is about 100,000 light years across, and contains about 200 billion stars. Th ...

The coolest stars

Sep 29, 2014

One way that stars are categorized is by temperature. Since the temperature of a star can determine its visual color, this category scheme is known as spectral type. The main categories of spectral type are ...

User comments : 31

Adjust slider to filter visible comments by rank

Display comments: newest first

Oscar_D
4.7 / 5 (13) Feb 23, 2012
Weird and really cool. When I grew up some 30 years ago the universe was a cold static void. This is better.

The woo woos will take this and run with it, though.
Watch out for Planet X, fellas!!!
Lurker2358
2.2 / 5 (6) Feb 23, 2012
If the planets average Earth mass, then that comes to something like 15% of the ordinary matter of the Galaxy as rogue planets.

Most planets we've discovered so far are above Earth mass.

I think James Webb should be able to spot lots of rogue planets in the nearby stellar neighborhood, if this is the case.

It comes to around 700 per cubic light year, which is a large volume of space, but then again planets are big. Any rogue Jupiter size objects or even super-earths should have some infrared signature.
Judgeking
2.8 / 5 (9) Feb 23, 2012
If there were enough rogue planets, I wonder if they could account for some of the expected 'dark matter'?
Demitroy
2.6 / 5 (7) Feb 23, 2012
I was wondering the same thing Judgeking. If it's confirmed it's going to change a lot of previous assumptions used to determine the mass of the galaxy.
Anda
2.4 / 5 (7) Feb 23, 2012
Really a weird extrapolation this one... Not much based on facts
Graeme
3.4 / 5 (5) Feb 23, 2012
If microlensing supports the idea of 2 planets per star, would there not be 50000 times as much microlensing going on with 100,000 planets per star? Also we should be getting random ecclipses of remote stellar disks that should show up in Kepler images. We could use two widely separated Keplar telescopes (perhaps in solar orbit 6 months apart) that could determine differences in the start or end time of ecclipses to tell that a planet was very far from the star, rather than in a nearby orbit.
Lurker2358
2.9 / 5 (8) Feb 23, 2012
Graeme:

You might think so, but at around 700 to maybe 1500 per cubic light year, the rogue planets will almost never pass in front of a star, seeing as how most stars are 3 or 4 light years from their nearest companion, except in the case of binaries.

63239 linear astronomical units in a light year.

That means there's only one Rogue planet per 360 billion cubic astronomical units.

Counting Pluto as a planet, and using round numbers, our own solar system has about 1 planet per 30,000 cubic astronomical units out to Pluto's distance.

So planets in the solar system are about 12 million times more common than rogue planets would be.

Outer planets in our solar system were discovered by observing gravitational perturbation on each previous planet, and then calculating a possible location and watching it for a long time.

With rogue planets, you don't have that luxury. The telescope needs to be looking EXACTLY at it ahead of time, without a prior prediction to say when that should be..
Deesky
3.9 / 5 (13) Feb 23, 2012
If the planets average Earth mass, then that comes to something like 15% of the ordinary matter of the Galaxy as rogue planets.

Really? How did you come to that conclusion?

Most planets we've discovered so far are above Earth mass.

Because that's all we can discover with current tech.
Deesky
4 / 5 (13) Feb 23, 2012
If there were enough rogue planets, I wonder if they could account for some of the expected 'dark matter'?

No, not even close. Ordinary low luminosity matter has been ruled out as a possible candidate for DM a long time ago. Give it a Google.
Deesky
3.6 / 5 (14) Feb 23, 2012
You might think so, but at around 700 to maybe 1500 per cubic light year, the rogue planets will almost never pass in front of a star, seeing as how most stars are 3 or 4 light years from their nearest companion, except in the case of binaries.

63239 linear astronomical units in a light year.

That means there's only one Rogue planet per 360 billion cubic astronomical units.

Counting Pluto as a planet, and using round numbers, our own solar system has about 1 planet per 30,000 cubic astronomical units out to Pluto's distance.

And...he's off! Batten down the hatches mateys. :)
Lurker2358
2.3 / 5 (9) Feb 23, 2012
Really? How did you come to that conclusion?


Using official NASA and other astronomical data from the number of stars in the galaxy and the galactic mass, etc.

It's called "math". You should try it.
Deesky
3.5 / 5 (10) Feb 23, 2012
Really? How did you come to that conclusion?


Using official NASA and other astronomical data from the number of stars in the galaxy and the galactic mass, etc.

It's called "math". You should try it.

And you should show how you arrived at that particular figure instead of handwaving it away.
Lurker2358
2.6 / 5 (7) Feb 23, 2012
Really? How did you come to that conclusion?


Using official NASA and other astronomical data from the number of stars in the galaxy and the galactic mass, etc.

It's called "math". You should try it.

And you should show how you arrived at that particular figure instead of handwaving it away.


I used 600 billion stars, the upper limit, though most sources say less than that.

I used an estimate of 50,000ly for radius and 10,000 for thickness*(see below,) since the official numbers vary on the width and thickness of the Galaxy.

I used 10,000ly for thickness, in spite of the usual cited thickness of 1,000ly. I justify this because when you LOOK at a star map, the hub of the galaxy is easily at least 10% as thick as it is wide in diameter, if not a bit more than that.

Now I could do a volume for tapered spiral arms, but that's a bit more complicated and I wasn't concerned with that.

10,000* pi* 50,000^2 = 7.854 E13.

continued.
Lurker2358
2.6 / 5 (7) Feb 23, 2012
divide 7.845E13 ly^3 by the number of stars.

gives 130.9 cubic ly per star.

divide 100,000 rogue planets per star by 130.9 ly^3 per star gives.

764 planets per cubic light year.

Now, this is a very rough estimate of planetary density, and under estimate as I implied, since the entire galaxy is not as thick as the obviously 1 to 10 ratio thickness of the hub.

A better estimate of the volume would be to treat the arms as triangular (in cross section, i.e. a stacked, tapered saucer shape,) and rotate that in 3d, which gives a volume of slightly more than 1/2 the origindal calculation, but the same number of stars, therefore a planetary density of 1500 planets per cubic light year.

http://en.wikiped...pan1.jpg

that is nowhere near a 1 to 100 ratio of thickness vs width. It is much closer to 1 to 10...giving 10,000ly thickness.
Deesky
3.6 / 5 (11) Feb 23, 2012
QC, all you have done is constructed a house of cards based on one dubious assumption after another.
dusanmal
3.4 / 5 (5) Feb 24, 2012
Oddly enough nobody attempts to remember what is our current definition of a planet... Made with clear purpose to minimize number of planets per star and minimize distance at which a planet can be found from the star.
So, none of these objects are planets. Though, same as researchers who wrote above - we intuitively know that they should be classified as such.
Lurker2358
1.6 / 5 (9) Feb 24, 2012
QC, all you have done is constructed a house of cards based on one dubious assumption after another.


This entire article is a dubious assumption, or hadn't anyone noticed?

So what?
scidog
4 / 5 (1) Feb 24, 2012
if we wrote this sort of research off as a house of cards we would not be any farther along than the Dick and Jane books i was looking at 60 years ago "oh Jane look at the stars" end of story.
why does Heartland Institute come to mind?
antialias_physorg
4.6 / 5 (5) Feb 24, 2012
Most planets we've discovered so far are above Earth mass.

Only because they are much easier to detect - not because they are necessarily more abundant.

Rob_Cypher
1.7 / 5 (3) Feb 24, 2012
I doubt that any of these "rogue" planets would be able to maintain a stable environment long enough to evolve any sort of life past the bacterial stage. I bet the percentage of rogue planets that are Earth-like is much smaller than the percentage of all the star-orbiting planets that could be considered Earth-like.
antialias_physorg
4.6 / 5 (5) Feb 24, 2012
I doubt that any of these "rogue" planets would be able to maintain a stable environment long enough to evolve any sort of life past the bacterial stage.

If anything the environment on these nomad planets should be more stable than that of planets which orbit around suns. If the energy is simply gained from radioactive decay you have
- no seasons
- no possibility for tidally locked planets with extreme temeprature differentials (i.e. less turbulent atmospheres)
- no chance of sterilizing or atmosphere destroying solar flare events
- no effects from solar variability of any kind (sudden ice ages, draught periods)
- fewer impacts from other bodies (the sun is the major attractor for stuff from outlying reagions in our solar system),
- ...
Birger
5 / 5 (3) Feb 24, 2012
Sticking to objects flung out of planetary systems, the number depends on how you define "planet".
As the giant planets migrated radially in the solar system, a zillion grillion tiny icetorids (and many small stony asteroids) were flung outwards at near or beyond escape velocity.

A small fragment of those remain bounded and eventually formed the Oort cloud (those flung out by Neptune and Uranus had less energy and now form the "scattered" component of the Kuiper belt).
It is very likely that at least one bona fide planet (terrestrial or ice giant) was flung out as well, leaving the remaining planets in nice, stable and well separated orbits.

So, yes interstellar space is full of junk, but most of it is tiny, and spread across distances so enormous that you need a poetic talent like the late Douglas Adams to bring home just how vast space is.
The few dark objects we may spot in the near future are brown dwarf stars in the solar neighbourhood that emit enough IR to be seen.
antialias_physorg
3.7 / 5 (3) Feb 24, 2012
and spread across distances so enormous that you need a poetic talent like the late Douglas Adams to bring home just how vast space is.

It's further down than to the chemist's?
Jeddy_Mctedder
1.6 / 5 (5) Feb 24, 2012
consider that WISE discovered A NEW CLASS of super cold brown dwarf stars (Y dwarfs) in 2011 and found one that is under 10 light years---one of the closest star to our sun.

It was discovered ONLY with hyper advanced telescope technology. it is SUPER close and maybe the 2nd or 3rd closest start to planet earth---its surface is about the temperature of boiling water 100c.

its almost certain that more advanced telescopes will find non fusion dwarf 'stars'--gas bodies, even closer to earth.
adwarakanath
2 / 5 (1) Feb 24, 2012
If there were enough rogue planets, I wonder if they could account for some of the expected 'dark matter'?


Nope, dark matter is stuff that doesn't shine. At all. It is around you, it is flowing through you. It is not matter as we know it.
SleepTech
4 / 5 (1) Feb 25, 2012
Also we should be getting random ecclipses of remote stellar disks that should show up in Kepler images.


The way the Kepler team discovers planets, as explained every time an article is published, is by looking for an eclipse to occur three times in front of the same star. That is how they can determine the object is in orbit around it's sun. A free-floating planet would not cross in front of the same star twice from our perspective. That makes gravitational lensing useless for what you're hoping to accomplish.
determinist
not rated yet Feb 26, 2012
On the Dark Matter issue...Perhaps 'SPACE' is more than just a volume that objects populate. Is matter the froth of space? Do sub-atomic particles not pop from the nothingness? Lets get outside the box!
Hal_McCombs
not rated yet Feb 26, 2012
If there were enough rogue planets, I wonder if they could account for some of the expected 'dark matter'?


Nope, dark matter is stuff that doesn't shine. At all. It is around you, it is flowing through you. It is not matter as we know it.


Angels and demons apparently have mass.
engineer JP
not rated yet Feb 26, 2012
What is more interesting in my opinion is that this discovery maight give more data on planetary formation. There seems to be a whole bunch of weak astro physics theories out there. The Dark Matter/Energy is one - as far as I can discern those items are just established as theoretical constants because we have no means of validation at this time. To validate theories of planetary formation we need more than one solar system. If we have Jupiter s floating around out there is there reason to believe there is a continuum between planets and stars (below brown dwarves?). Is the nebular theory just a reasonable theory that has no basis in evidence? What would the role or Dark matter be in planetary (or solar system) information? I think the Webb telescope will crack some of that open, or at least confirm 100 years of speculation. The bottom up stuff (CERN) cant tell us everything.
Graeme
not rated yet Feb 27, 2012
SleepTech - I am not suggesting that Kepler team would announce discovery of a planet, but the technology would see light dips in stars, that were not repeated. Already there would be plenty of measurements of this occurrence and it could help place a upper limit on how many rougue planets are floating around.

Also these rogue planets should encounter the Solar System at times.
SleepTech
not rated yet Mar 03, 2012
Graeme, I believe Kepler team finds anomalous one-time eclipses on a regular basis. Kepler has to confirm every planet they find, and sometimes a potential planet is dropped from the list. They say things like sunspots could cause false-readings. I was incorrect to say a Kepler probe/sat would be "useless", if a rouge-planet passed in front of a star it could see it. With a secondary probe to confirm a sighting, I guess it's possible I don't know. However, wouldn't a rouge-planet's eclipse look entirely different from an interplanetary eclipse? I would imagine Kelper seeing stars not just "wobble" but disappear for a brief period completely as rogue-planets much closer to us blot it from view. Personally I'm betting their estimate is way off. Maybe I have too-high expectations here but if there were as many rogue-planets as estimated I think we would have seen something by now. That being said, I think it would be a good thing to research this further, as you suggest.