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32 votes
Accepted

If the Sun disappeared, could some planets form a new orbital system?

The issue here is whether pairs of planets can become gravitationally bound to each other. In the two-body problem the trajectories or orbits are ellipses (bound orbits), parabolas and hyperbolas (...
Anders Sandberg's user avatar
21 votes

Could rogue planets harbor life?

There's also the possibility that a rogue giant planet may have a moon with a subsurface ocean of liquid water due to tidal heating in an orbit close enough to its parent planet. E.g. if Jupiter was a ...
John's user avatar
  • 1,538
15 votes
Accepted

How much light would be received on a rogue planet close to the galactic center?

One can do a quick Fermi estimate: According to wiki, the densest parts in the centre and globular clusters have about 70 solar masses per cubic parsec. Let's assume it's all solar mass and thus solar ...
planetmaker's user avatar
  • 19.5k
14 votes
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Are there any probabilistic models for the likelihood of finding a rogue planet closer to us than Proxima Centauri?

I've found a paper(1) with estimates based on extrapolation of known data for stellar-mass objects toward smaller values, using a power law probability distribution: Sumi et al.[4] used microlensing ...
ksousa's user avatar
  • 1,161
13 votes

How well would the Moon protect the Earth from an Asteroid?

It would be much better for Earth if the impactor hit the moon... In this Worldbuilding answer, I used a paper on ejecta kinematics to do calculations for ejecta velocity upon impact. Without going ...
kingledion's user avatar
13 votes

Could rogue planets harbor life?

In short, if a rogue planet has enough internal heat and retains enough of that internal heat by a thick atmosphere or within a miles-deep ice crust, it could be warm enough for liquid water and thus ...
M. A. Golding's user avatar
11 votes
Accepted

Are Brown and Sub-Brown Dwarfs secretly more common than stars?

The answer to your first question is (now) fairly simple: No, brown dwarfs are not more common than red dwarfs. A crude approximation is that stars (which are indeed mostly red dwarfs) outnumber brown ...
Peter Erwin's user avatar
  • 17.1k
10 votes
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Are rogue planets ever born in isolation?

The minimum mass of a "planet" forming from a gas cloud (definitions of what a planet is are rather slippery, and some would say this is not a planet at all) is not determined by the time available. ...
ProfRob's user avatar
  • 153k
8 votes

What is the closest heavenly body to our solar system

The closest body we currently know to exist is Proxima Centauri which is part of the Alpha Centauri system at about 4.25 light years away. There may be rogue planets that are closer but we haven't ...
A. C. A. C.'s user avatar
8 votes
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How well would the Moon protect the Earth from an Asteroid?

The Moon orbits the Earth from $\approx$ 380000 km, but its radius is only $\approx$ 3500 km. The sky has 41253 sq degrees, and the Moon covers only $\approx$ 0.25 sq degree from it. Thus, the ...
peterh's user avatar
  • 3,161
8 votes

If the Sun disappeared, could some planets form a new orbital system?

No. The 8 planets would go into 8 different directions. It is because their relative velocity to each other is much higher than the escape velocity, even from their smallest distance. If it would not ...
peterh's user avatar
  • 3,161
7 votes

Motion of rogue planets

On the numbers Rogue planets are thought to be more abundant than stars in the milky-way and depending on where you make the cut-off, rogue dwarf-planets for example, are expected to enormously ...
userLTK's user avatar
  • 24.1k
7 votes
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Can two planets in an empty universe meet/be pulled together?

Yes, they would experience gravitational attraction. It would take a long time for them to collide... the formula (derived here and shown here) is: $$t = \frac{\pi}{2} \sqrt{\frac{d^3}{2G(m_1+m_2)}}$$...
James K's user avatar
  • 123k
7 votes

Is it possible that all dark matter is made of rogue planets (free-floating planet)?

The fact that there is not enough luminous matter to explain the gravitational properties of galaxies and clusters of galaxies does not inexorably lead to the conclusion of weird dark matter that does ...
ProfRob's user avatar
  • 153k
7 votes

Are rogue planets ever born in isolation?

Astronomers call the type of object you are describing-- one that condensed from an isolated nebula but was too small to undergo hydrogen fusion-- a sub-brown dwarf. They are quite difficult to ...
antlersoft's user avatar
  • 3,455
7 votes
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When was the concept of rogue planets first theorized?

I don't know the first use of the time rogue planet or the first use of such planets called something else. But if science fiction is anything to go by, rogue planets are as thick as fleas in ...
M. A. Golding's user avatar
7 votes

Are Brown and Sub-Brown Dwarfs secretly more common than stars?

This is an important question to ask about the initial mass function of objects in the Galaxy - and the final answer hasn't been cast as it is a matter of research. Yet, observational data (e.g. see ...
planetmaker's user avatar
  • 19.5k
6 votes

Is it likely that intergalactic stars would still retain their planets?

While near encounters with supermassive black holes are bad for the stability of solar systems [citation needed?], many intergalactic stars become intergalactic without a close encounter. They are ...
Anders Sandberg's user avatar
6 votes

Studies on planets without parent star

It would be more accurate to call them surveys than studies. A study looks at an object in detail. A survey counts and categorizes objects. Rogue planets are enormously difficult to see, and only ...
userLTK's user avatar
  • 24.1k
6 votes
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Is it possible that a star system ejects an object out of the galaxy?

Intergalactic planets have never been observed. They're too small and it's too great a distance, but intergalactic stars have, and if stars can be ejected from a galaxy, planets can to. The orbital ...
userLTK's user avatar
  • 24.1k
6 votes

If the Sun disappeared, could some planets form a new orbital system?

I gave a try at refining Anders Sandberg's answer with the equations for a two body system. Basically, a two body system is bound if the sum of the total kinetic energy and the (negative) ...
JanKanis's user avatar
  • 571
6 votes

Would a nearby "Orphan planet" be detectable?

The infrared satellite WISE did an all sky survey at near and mid-infrared wavelengths. A nearby "rogue planet" would likely be moving quickly on the sky and if the size of Jupiter would ...
ProfRob's user avatar
  • 153k
5 votes

How are rogue planets discovered?

Using microlensing the MOA (Microlensing Objects in Astrophysics), OGLE (Optical Gravitational Lensing Experiment) groups have found many free-floating planets. The stars, free floating planets etc ...
TazAstroSpacial's user avatar
5 votes

Astrophysics Ph.D. thesis on intergalactic rogue planets and their habitability; how active is this field of research?

This became too long for a comment, but shouldn't be considered a definite answer: Until recently, almost every rogue planet was found with microlensing, meaning that they're only observable for a ...
pela's user avatar
  • 38.5k
5 votes
Accepted

Would a nearby "Orphan planet" be detectable?

All sky surveys tend to be at optical or radio wavelengths and more rarely at infra-red or x-ray wavelengths using space-based telescopes. The exposure times are short, so the chances of finding a ...
Roger Wood's user avatar
  • 1,359
5 votes

How much light would be received on a rogue planet close to the galactic center?

Edit: there was a dumb mistake in my code (I had left out the square root in the distance calculation), which I noticed immediately after posting the answer. This changed the result downwards by ...
Dronir's user avatar
  • 151
4 votes
Accepted

How can we tell the age of a rogue planet?

At the moment there is basically only one way. That is to associate the planetary-sized object with a cluster of stars or moving group of stars of known age. That's basically it. If the planetary-...
ProfRob's user avatar
  • 153k
4 votes
Accepted

What would you find within a void?

The Wikipedia article on voids is pretty good (though IMO unusually awkwardly written.) The key thing is that voids are not empty, they are just large volumes which have a lower density (typically ...
Mark Olson's user avatar
  • 7,640
4 votes
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Is it possible that Venus was once a rogue planet?

This is considered very unlikely. It is actually very difficult for things to be captured into orbits. They pick up speed as they fall in towards the larger object, and that's automatically enough ...
Mark Foskey's user avatar
  • 3,916
4 votes

Could rogue planets harbor life?

The discussion will focus on the term rogue planet is an oxymoron, as it's missing the principle defining feature of a planet. a Jupiter-sized body without a sun will be warmer than you would have ...
JDługosz's user avatar
  • 1,000

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