# Other planetary systems

Are there any pictures of other planetary systems? Are there any close ones? I think I heard a while back of antoher system with planets..

## Answers and Replies

Staff Emeritus
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To the best of my knowledge there has been evidence of other planetary systems found. None are close enough to get actual images, generally the only evidence is irregularities in motion of a star which can only accounted for by orbiting bodies. None are very close.

Staff Emeritus
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This site is pretty comprehensive:

http://www.obspm.fr/encycl/encycl.html [Broken]

No images of exosolar planets yet, though a number of brown dwarfs have been seen (brown dwarfs are not much more massive than the heaviest planets found to date), and it seems only a matter of a few years before an isolated object (not in orbit around a star) with a mass approx the same as that of Jupiter is found.

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Theer are no images yet, but NASA has a project for a http://planetquest.jpl.nasa.gov/news/lbti_update.html [Broken] already in the works.

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Staff Emeritus
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I think we're upwards of 110 extrasolar planets discovered...all massive Saturn/Jupiter sized ones (due to limitations of the detection method). I'm looking forward to the program LURCH mentioned.

cooool. Thanks.

Staff Emeritus
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NASA TPF website

Terrestrial Planet Finder
http://planetquest.jpl.nasa.gov/TPF/tpf_index.html [Broken]

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Mentor

Originally posted by Nereid
Terrestrial Planet Finder
http://planetquest.jpl.nasa.gov/TPF/tpf_index.html [Broken]
Its not getting a whole lot of press (maybe when its about time to launch it) but it may be the most important project NASA has ever done.

edit: didn't realize how far away (2012-2015) the final phase is.

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Jeebus
Originally posted by Integral
To the best of my knowledge there has been evidence of other planetary systems found. None are close enough to get actual images, generally the only evidence is irregularities in motion of a star which can only accounted for by orbiting bodies. None are very close.

I have a question. What about Planet X that scientists bragged over a while ago -l- was that just a publicity stunt to get our attention?

Staff Emeritus
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Good question ... loooong answer

Originally posted by Jeebus
I have a question. What about Planet X that scientists bragged over a while ago -l- was that just a publicity stunt to get our attention?
This tale would take many an hour to tell ... just one person's very short summary:

- following the success in finding Neptune through obsersations of Uranus and much celestial mechanics (without computers! think log tables - anyone remember them?), the hunt was on for further planets

- Pluto was found later, not as big as expected, not really where it was expected, ... but then 'expected' depends on the input assumptions of your model

- some data (on long period comets, IIRC) suggested that there might be yet another planet, further out than Pluto, and possibly quite massive; got given the moniker "Planet X"

- not to be too cynical, given the public fascination with planets etc (waxed and waned over the years), sometimes an astronomer (more often a 'self-styled astronomer') got into the news with a story about Planet X; who's to say how often this was 'publicity-seeking push' vs 'thirst for news pull'?

Since the initial discoveries of Edgeworth-Kuiper Belt objects (Jewitt and Luu? 1992?), it's become increasingly clear that there isn't really a Planet X.

A good site (Jewitt's), if not as up to date as one would like:
http://www.ifa.hawaii.edu/faculty/jewitt/kb.html [Broken]

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Staff Emeritus
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Originally posted by Jeebus
I have a question. What about Planet X that scientists bragged over a while ago -l- was that just a publicity stunt to get our attention?

Aside from the old case Nereid mentioned, did you mean this?

Last I heard about the planet X thing they did find an object out there, but scientists said that it was too small for a planet, so they decided to call it an astroid. Pluto was also going to be considerded an astroid, but it had a moon so they kept it as a planet.

And about the first question, I don't know if scientists have found anything, but scientists say that mathimatically there has to be solar systems like ours.

Staff Emeritus
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EKB objects - some big

Originally posted by Eepl
Last I heard about the planet X thing they did find an object out there, but scientists said that it was too small for a planet, so they decided to call it an astroid. Pluto was also going to be considerded an astroid, but it had a moon so they kept it as a planet.

And about the first question, I don't know if scientists have found anything, but scientists say that mathimatically there has to be solar systems like ours.
Many hundred Edgeworth-Kuiper Belt objects have now been found, the largest of them is nearly the size of Pluto. It's clear that Pluto-Charon is just another EKB object, and the principal reason it's still called a planet is historical nostalgia. Several binary EKB objects have been found, so Pluto-Charon is not unique in this respect either.

Loren Booda
Have there yet been found (or even theorized) two or more mutually orbiting planetoids free of stellar gravitation?

Staff Emeritus
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Originally posted by Loren Booda
Have there yet been found (or even theorized) two or more mutually orbiting planetoids free of stellar gravitation?
Am not quite sure what you're asking here, so the following may miss the mark:

-> wandering planets certainly exist. These are objects which formed as part of a 'solar system' (not ours) and were subsequently liberated from their parent star. Several different liberation mechanisms are likely, including ejection in the early days of the system through close encounters with other planets, ejection after the system had a close encounter with another star, and liberation as a result of the parent star going supernova

-> isolated objects with at least Jovian+ planetary masses quite likely exist. When a gas cloud collapses and fragments, some of the fragments may be small enough to condense as objects with a mass as small as that of Jupiter (or smaller). The environment in which the gas cloud fragment finds itself is important; for example, too near an OB baby, and the fragment will likely be vapourised. The cloud's composition is also likely to be important; too primordial and the cloud won't cool enough to collapse.

-> binary objects may be possible under either formation scenario above, though they may comprise only a small fraction of the total number of objects.

-> more than two objects of approximately the same mass cannot exist in a stable orbital configuration. Of course, a massive parent with many low-mass satellites is a stable configuration. Could a low-mass gas cloud end up as a Jupiter-sized parent with a retinue of 'moons'? Good question.

-> there is at least one proposed observational program that might find some of these loose Jupiters - TAOS is its name (IIRC). It will also look for other sorts of objects.

-> the various gravitational lensing surveys - OGLE, MACHO, etc - would have found isolated Jupiters (and perhaps they did), including any binaries. At least they could give (did give?) a weak upper limit to the space density of such objects, in our part of the Milky Way (and towards the LMC too?)

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Loren Booda
Nereid,

Thanks for your thorough answer. It addressed my question well.

Jess
Originally posted by Integral
To the best of my knowledge there has been evidence of other planetary systems found. None are close enough to get actual images, generally the only evidence is irregularities in motion of a star which can only accounted for by orbiting bodies. None are very close.

No-one has successfully imaged an extrasolar planet yet, but we're getting closer!

http://www.roe.ac.uk/atc/news/pressrelease/20031201/index.html [Broken]

Jess

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Orion1

more than two objects of approximately the same mass cannot exist in a stable orbital configuration. Of course, a massive parent with many low-mass satellites is a stable configuration. - Nereid

Does anyone know what the exact equation is for determining the decay rate for an equal mass, binary system?

Loren Booda
(1/2S((GM/D2)-v2/D))-1/2=T

G=Newton's gravitational constant

M=masses of equivalent binaries

D=distance between centers of binaries

S=distance between surfaces of binaries

v=orbital velocities

T="decay rate"

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Orion1
Decay rate for an equal mass, binary system:

$$T_r = \sqrt{ 2S_d \left( g - a_r \right)^-1}$$

$$T_r = \sqrt{ 2S_d \left( \left( \frac{G M_1}{r_1^2} \right) - \frac{v^2}{r_1} \right)^-1}$$

$$T_r = \sqrt{ \frac{2S_d}{ \left( g - a_r \right)}}}$$

$$T_r = \sqrt{ \frac{2S_d}{ \left( \left( \frac{G M_1}{r_1^2} \right) - \frac{v^2}{r_1} \right)}}}$$

G=Newton's gravitational constant
M=masses of equivalent binaries
r=radius between centers of binaries
S=distance between surfaces of binaries
v=orbital velocities
g=gravitational acceleration
a=centripetal acceleration
T=decay rate

Loren, are these factors correct?

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