View Full Version : Can we detect rogue planets?

Tom Mazanec
2012-Jan-12, 04:57 PM
Microlensing would be my proposal for doing this. Has anyone tried it? Has it worked?
And btw, what is a "steppenwolf"? A rogue planet that can support life? Is it a technical term?

2012-Jan-12, 06:00 PM
The OGLE and MACHO projects have looked for rogue planets among other things. MACHO against the backdrop of the LMC. They found stuff, but I don't have numbers at hand. ... I think Speppenwolf simply means escaped planet, and doesn't imply life capability.

2012-Jan-12, 09:00 PM
Microlensing would be my proposal for doing this. Has anyone tried it? Has it worked?
Yes, and yes. There are some technical limitations on this method. As I understand it, it is good for detecting roughly Jupiter mass gas giants, but not good for smaller planets.

And btw, what is a "steppenwolf"? A rogue planet that can support life? Is it a technical term?
Steppenwolf refers to a specific concept for a potentially habitable rogue planet: http://arxiv.org/abs/1102.1108

This concept posits a planet with a liquid ocean mantle, similar to Europa. This ocean is underneath layers of insulating water ice and frozen atmosphere, kept warm by geothermal heat. Depending on the composition of the planet, it may be ~3.5 Earth masses or as little as ~0.3 Earth masses.

As I understand the limitations of microlensing, 3.5 Earth masses is too low to be readily detectable.

The steppenwolf concept is different from the older rogue planet concept proposed by David J. Stevenson. Stevenson proposed the possibility of a rogue planet with a very thick hydrogen atmosphere to provide sufficient insulation for liquid water conditions on the surface of the planet. This would have been a very exotic planet, with extremely exotic (to us) high pressure surface conditions. In contrast, a steppenwolf could be a pretty normal planet, and the ocean's conditions familiar to us.

The strange Stevenson world would need to have a mass lower than ice giants, so it would be difficult to detect via microlensing (just like the steppenwolf).

2012-Jan-29, 04:37 PM
Am I thinking correctly? Planets formed at twice or more the goldilock distance, would be hot = plasma temperature both inside and cloud top for at least a million years. They could have a 20 bar hydrogen atmosphere, where the future surface would be, but it would fall to ten bar in about one million years, unless the surface gravity was higher than earth. If they were ejected in the first million years, hydrogen loss would be much less due only intersteller wind, so the hydrogen atmosphere could last 100 billion years, even if the cloud top gravity was only 1/6 g. With typical Earth convection and greenhouse gases, the heat loss would cause the surface temperature to drop to about 20 degrees c in a few million years, and keep cooling = not long enough for advanced species to evolve, but long enough for colonists, but colonists are very improbable even 1/10 th light year from a star, and even less probable while the surface was as hot as the photosphere of a cool M star = 2000 degrees k?
Neptune mass gas giants, would have 20 degree c cloud tops, perhaps a million years after they were ejected shortly after birth, but 10,000 kilometers from the center they would still be plasma temperature at age 5 billion years, so it might be 50 billion years before a solid surface formed about 10,000 kilometers from the center. Gravity would be about 10 g and increasing as the the solid surface cooled and contracted = not suitable for humans, and a long shot for radically different advanced life forms. Can someone suggest any scenario in which a rogue planet is likely to be inhabited by advance beings? Neil

2012-Jan-29, 05:47 PM
... Can someone suggest any scenario in which a rogue planet is likely to be inhabited by advance beings?
Is this for a story? Sure. A rogue planet with two large moons passes near our solar system in 3000 years, and we realize that it has warm nutrient rich oceans under an ice layer and is protected by a heavy atmosphere. At the bottom of the oceans are hot vents from geologic activity. Some of our people move there and build a colony using our advanced technology. ... 50,000 years later, the rogue passes through another planetary system, and intelligent life there is surprised to notice EMI coming out of the incoming rogue.

2012-Jan-31, 04:51 AM
Rogue planets (planemos?) are likly to be so common that they may represent the most common form of habitable environment. Even if abiogenesis can't happen on these worlds, they may be colonised by spacefaring civilisations, as Antoniseb has suggested.

Such a colony would be subject to severely constrained growth however; it would only have a very small energy flux to play with. They wouldn't have much energy to spare for communication, unless they started to use fission or fusion for extra power.

2012-Jan-31, 08:46 AM
Remember gentleman the OP.... ( your imaginings are fun no less...)

Rogue planets are going to be a challenge to find..

Will they be so obliging as to slip behind a nearby star giving up valuable information.. not likely.

Will they wander into direct auscultation.. just as unlikely. :) ..

At the present levels of equipment and resource..

I would not expect any rogue planet to be popping up in Wikipedia any day this century.. if ever..

and if it ain't in Wiki.. it just ain't... We do NOT have knowledge of a single one.. yet.

2012-Jan-31, 12:46 PM
Microlensing would be my proposal for doing this. Has anyone tried it? Has it worked?

Yes, and apparently, yes. See Sumi et al paper here:

Unbound or Distant Planetary Mass Population Detected by Gravitational Microlensing

Based on their data, there should be about 1.8 unbound planets of Jupiter mass and above per star. That leads to the conclusion that statistically there really ought to be one or more of these objects closer to us than the Alpha Centauri system. However I believe microlensing would not be the detection method of choice for these "nearby" objects (they're too close).

WISE is said to be able to detect a Jupiter out to one light year, and a Neptune to <insert very large number> AU.

Matese and Whitmore have done a bit of a search through the first release WISE data, however their search was designed to find a distant orbiting planet. This means it is limited to within 10 degrees either side of their theorised orbit of this planet. Also the WISE data is not yet complete, so their negative finding so far does not rule out unbound PMOs in the locality:

Searching the WISE preliminary catalog for massive planets in the Oort Cloud

2012-Feb-01, 06:53 PM
A bit of speculation here-
...microlensing will only uncover a fraction of such objects, and eventually telescopes will be sensitive enough to detect them directly. But these rogue planets would be so dim that they would be similar in brightness to the most distant galaxies. Maybe one day we'll map the whole sky, down to the limit of resolution, and any moving object could be detected by comparing it to the catalog of distant stars and galaxies; this would allow relatively small asteroids, oort cloud objects and even rogue planets to be detected, out to a certain distance anyway. An all-sky, deep field catalogue would be a vast database- but I'm sure it would be very useful.

How much of a fantasy is this? Well, I suppose that depends on the limit of resolution of future telescopes. But there are hundreds of billions of galaxies, and hundreds of billions of stars in our galaxy; in total that would represent a few trillion datapoints. Perhaps the information content of such a catalog would not be unfeasably large, and it would be very useful for discrimination between known objects and very small, very dim wanderers.

2012-Feb-01, 07:34 PM
Data banks filled with relevant information. Whole sky maps. Computer files of star charts..

Telescopes that 'can' actually see and record the positions and magnitudes.. NO ! but yes...

I do not have one in my little eclectic collection of telescopes.. BUT I do believe (know), such is already real.

Computer driven search and tracking devises that have massive catalogued reams of information.

connected to high speed tracking scopes.. Automated. We 'are' already at that point..

A multi national network of 'Fast' trackers. Is a reality now. ; and as a aside point,

'That this is a sensitive subject that is not generally in the public domain for the security of those involved.' Mark.

2012-Feb-01, 08:33 PM
True; but to detect rogue planets the catalogs would need to be much more comprehensive than they are today. Alternately these dim objects could be searched for by comparing images of the sky without cataloging every visible speck, by looking for differences between different images; but how easy that would be using electronic imaging I don't know.

2012-Feb-01, 09:31 PM
I thought all non repeated dimmings were treated as anomolies and discounted.

Wouldn't that automatically filter out rogues?

2012-Feb-01, 09:32 PM
I thought all non repeated dimmings were treated as anomolies and discounted.

Wouldn't that automatically filter out rogues?

No, because rogues use gravitational lensing to cause brightenings, not dimmings

2012-Feb-01, 09:49 PM
No, because rogues use gravitational lensing to cause brightenings, not dimmings

Wow, I didn't know that.

Well that changes everything. :)

2012-Feb-02, 10:59 PM
Closer than Proxima is about 100 cubic light years = 1.8 Jupiter dimentions/mass or more. Ejection of smaller objects is more likely, so ten per cubic light year Earth size or bigger is likely. Perhaps one passed though our inner solar system, 2 centuries ago; we could have missed it, or debunked it. Perhaps one is presently at about 10 AU heading straight for our Sun and an all sky survay will detect it, soon with confidence. That explains why it might be a security matter. Earth could get in it's path, but that is very low probability. Brown dwarfs are about Jupiter dimentions , but much more massive. Brown dwarfs would gravity lens more distant stars, but by enough to be noticed, one light year away? One earth gravity lensing would likely not be noticable 100 million kilometers away? Neil

2012-Feb-03, 09:03 AM
Microlensing can only detect planets which are very far away. The smaller the planet, the further away it would need to be because it bends light by a smaller amount. However, this also makes the microlensing event even harder to detect.

Microlensing can't be used to detect a nearby dark object.

A different method might be used instead--occultation. Due to the way diffraction works, the occultation event would appear as a symmetrical series of hills and valleys.