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EyeOnTheCode
2007-Jul-11, 03:15 PM
Are there any gravitational evidence of dark matter at the solar system scale?

It had been mentioned that evidence of dark matter is seen in the rotation of galactic systems, but is there evidence of dark matter gravity at the solar system level? Do people who do calculations of planetary trajectory see evidence of dark matter gravity? Do they have to put “dark matter corrections” in their calculations?

American Scientific had an article a few years ago that mentioned that the trajectory of some of our own planets suggests the presence of invisible or undiscovered planets. Could that be caused by dark matter?

Peter Wilson
2007-Jul-11, 03:30 PM
There's the Pioneer spacecraft anomoly; I haven't followed it close enough to know if DM would explain it.

Ken G
2007-Jul-11, 03:32 PM
One hears of various "anomalies" in the solar system, but they are generally at the edge of detectability and could either be spurious or due to some other error in observational interpretation. Perhaps there are some real effects going on, but they are certainly quite small, so at present there is no compelling need to expect a significant dark matter contribution in the solar system. Dark matter is not expected to contract into solar systems the way hydrogen gas does, expressly because it does not radiate. Still, there's some of it around, and the Sun's gravity can focus it to some degree, so maybe it's potentially detectable on this scale. I think the main use of the solar system dark matter would come in the form of direct detection-- we have larger scales for getting the gravitational influences.

antoniseb
2007-Jul-11, 03:38 PM
If there is dark matter relatively uniformly distributed in our galaxy in the form of WIMPs, we would not detect it from the gravitational influence it had on the orbits of the planets in our solar system.

If there was some dark matter concentrated around our Sun, we might detect it by our probes leaving the solar system having a small excess gravity felt as they get further from the Sun... but this seems unlikely, and no one that I know of (including me) is claiming this as a cause for the Pioneer anomaly.

I don't know of any article suggesting that our planets trajectories indicate a dark planet is hidden out there somewhere. Can you give a more definite reference?

Peter Wilson
2007-Jul-12, 11:39 PM
Density of universe = 3E-27 kg/m^3. Most of this is thought to be DM. Assume density of DM in solar system is 1,000 times higher than universe overall, i.e. 3E-24 kg/m^3.

Approximate the size of the solar system @ 1 billion km across, or 1E12 m. Volume = approximately 10E36 m^3

Amount of DM would be: 3E-24 kg/m^3*(1E12 m)^3 = 3E12 kg.

The moon weighs 10E22 kg. In other words, all the DM in the solar system would amount to just 1/10,000,000,000th the mass of the moon!

Even if this estimate is low by half a dozen OOMs, there is no way such a small amount of matter evenly distributed--or even concentrated around sol, as antoniseb suggests--could be detected with present technology.

Of course, I said the same thing about SETI, and ain't stopped nobody from trying!

Cougar
2007-Jul-13, 12:41 AM
Do people who do calculations of planetary trajectory see evidence of dark matter gravity?
No. They see the lack of it. I was pretty astounded when I learned that "people who do calculations [and observations] of planetary trajectory" have known for hundreds of years that Mercury's orbit was precessing slightly more than newtonian dynamics would expect. This excess precession turns out to be something like 43 arc seconds per hundred years.

As Ken considered, there is probably dark matter throughout the region of our solar system - as there is throughout the galaxy - but its gravitational effect within a region as small as our solar system is apparently beyond the range that we can detect - next to nothing, you might say.


Density of universe = 3E-27 kg/m^3....

I appreciate the figures. But I think the mass and configuration of the dark matter just associated with our galaxy is pretty well known. Assuming the DM is fairly evenly spread, what's the size of the galaxy+halo vs. the size of our little system here?

RussT
2007-Jul-13, 01:47 AM
This has some pretty interesting things to say about this subject:)

Thanks Van Rijn:)

http://www.universetoday.com/2006/11/20/dark-matter-halo-around-the-milky-way/

I will be linking to and talking about this in other threads:)

Cougar
2007-Jul-13, 02:14 AM
This excess precession turns out to be something like 43 arc seconds per hundred years.
Oh, and I forgot to add, the "correction" to Mercury's orbit due to the difference between Newtonian and Einsteinian gravitation turns out to be something like 43 arc seconds per hundred years.

Doesn't leave much room for dark matter to slip in there and contribute to the gravitational effect within our solar system.

Nereid
2007-Jul-13, 04:26 PM
The amount of DM in the volume of space centred on the Sun and ~50 au in radius can be estimated from observations of the positions of solar system bodies ... or at least some constraints on that amount of DM can be made.

Estimates can also be made of the amount of DM one would expect to be in this solar system volume, at any one time, from models of the distribution of DM in the Milky Way, built to fit all relevant observations.

And so on.

AFAIK, there are quite a few papers on both these, and other, aspects of constraining DM - e.g. the mass of DM that has sunk to the core of the Earth or Sun.

The net: there is no observational evidence of DM in the solar system, nor would the tests we have done to find it, to date, be expected to detect it, if our understanding of the distribution of DM within the MW is within an OOM or 3 of being correct.

However, none of this is saying very much ... while DM is expected to be at least 3 OOM (and as much as 6, or 9?) times more dense, in this part of the MW than its universal average, it still amounts to very little mass - less than that of the Moon?

In a way, this exercise is a very nice illustration of just how BIG the distances between (local) stars are, let alone how BIG our home galaxy is ...

I'll dig up some references, if anyone's interested.

RussT
2007-Jul-13, 10:58 PM
And yet if DM is responsible for the curving of light paths in the lensing in galaxies and galaxy clusters, then it should follow that DM is responsible for the curving of the light paths around the Sun, Jupiter, etc:)

Nereid
2007-Jul-14, 12:48 AM
And yet if DM is responsible for the curving of light paths in the lensing in galaxies and galaxy clusters, then it should follow that DM is responsible for the curving of the light paths around the Sun, Jupiter, etc:)Mass is mass is mass ... whatever DM there is in the solar system will indeed deflect light.

However, if the total mass of such DM is less than the mass of the Moon, then the deflection will not be great - in fact, it will be far, far too small to be detected ...

RussT
2007-Jul-14, 01:10 AM
Mass is mass is mass ... whatever DM there is in the solar system will indeed deflect light.

However, if the total mass of such DM is less than the mass of the Moon, then the deflection will not be great - in fact, it will be far, far too small to be detected ...

Really, then mainstream's 'accounting'/'bookkeeping' has a problem:)

IF according to the L-CDM, the WIMP DM content in the solar system is about the mass of the moon, and according to the lensing of galaxies/clusters, WIMP DM is what is curving to cause the lens, THEN CDM WIMP models CANNOT account for the Shapiro Effect in the solar system for the DM curvature around the SUN, Jupiter, etc!!!

http://www.bautforum.com/showpost.php?p=894641&postcount=19

ASEI
2007-Jul-14, 02:16 AM
If we assumed dark matter was uniformly distributed across the solar system, would it create any sort of gravitational "drag" on planets as the planets interacted with it? Would this place any sort of useful upper bounds on it's density?

Nereid
2007-Jul-14, 02:27 AM
If we assumed dark matter was uniformly distributed across the solar system, would it create any sort of gravitational "drag" on planets as the planets interacted with it? Would this place any sort of useful upper bounds on it's density?Yes ... and something similar is indeed the approach taken in at least one paper which sets out to estimate an upper bound on the mass of DM in the solar system.

More specifically: the distribution of DM in the solar system may be estimated by starting with a 'spherical cow' model - the DM is distributed in such a way that it can be completely characterised by a density vs radius function*. The gravitational effects of such a DM distribution can be calculated, and the observational consequences estimated - e.g. minor deviations in the positions of planets and asteroids from the best ephemerides. The upper limits of such deviations then become bounds on the density, in the solar system, of DM.

*Note that a uniform density is merely a trivial subset of such.

Nereid
2007-Jul-14, 02:35 AM
Really, then mainstream's 'accounting'/'bookkeeping' has a problem:)

IF according to the L-CDM, the WIMP DM content in the solar system is about the mass of the moon, and according to the lensing of galaxies/clusters, WIMP DM is what is curving to cause the lens, THEN CDM WIMP models CANNOT account for the Shapiro Effect in the solar system for the DM curvature around the SUN, Jupiter, etc!!!

http://www.bautforum.com/showpost.php?p=894641&postcount=19RussT, I'm afraid I don't understand what this post of yours means ...

The deflection of EM/photons near the Sun/Jupiter/Earth, Shapiro effect, etc are - AFAIK - well accounted for by the estimated masses of the Sun, Jupiter, Earth, etc.

AFAIK, there are no inconsistencies in various estimates of the masses of the Sun, Jupiter, Earth, Moon, ... whichever method you choose to estimate these masses, you get the same result (within the error bars).

The link in your post is even more confusing to me ... all it says is that mass is mass is mass - as far as any experiment done to date is concerned, there is no way to distinguish between one form of (cold) mass and another, by purely gravitational means.

But perhaps I seriously misunderstand your post; would you be kind enough to clarify please?

Grashtel
2007-Jul-14, 03:07 AM
Really, then mainstream's 'accounting'/'bookkeeping' has a problem:)

IF according to the L-CDM, the WIMP DM content in the solar system is about the mass of the moon, and according to the lensing of galaxies/clusters, WIMP DM is what is curving to cause the lens, THEN CDM WIMP models CANNOT account for the Shapiro Effect in the solar system for the DM curvature around the SUN, Jupiter, etc!!!

http://www.bautforum.com/showpost.php?p=894641&postcount=19
Dark matter by definition doesn't interact with light, if it did we could see it direct and it wouldn't be dark. The lensing effects on light aren't a result of dark matter, they are caused by gravity and anything with mass can cause them be it dark matter, a planet, a star, or just about anything else.

neilzero
2007-Jul-17, 03:47 PM
Perhaps some kinds of dark matter does not interact with light. Are we no longer considering the asteroids and comets ejected from solar systems dark matter? Does the dark matter that cause uniform angular velosities of galaxies, need to be magical, or at least exotic or mysterious? Neil

Nereid
2007-Jul-18, 12:40 AM
Perhaps some kinds of dark matter does not interact with light. Are we no longer considering the asteroids and comets ejected from solar systems dark matter? Does the dark matter that cause uniform angular velosities of galaxies, need to be magical, or at least exotic or mysterious? Neil
There's a terminology confusion regarding 'dark matter' ...

I think the modern convention is that 'dark matter' ('DM') is, most often, a short-hand for 'non-baryonic dark matter'*, or 'cold, non-baryonic dark matter' (to exclude neutrinos).

DM in the solar system - DM of the cold, non-baryonic kind - is expected to be diffuse, like a collisionless gas. The 'baryonic' kind of DM will be in the form of gas (ionised or not), dust, pebbles, rocks, asteroids, dwarf planets, etc, and we have a very good handle on how much of this there is, at least out to ~50 au ... because we can observe it, one way or the other.

Anyway, I interpreted the OP to mean 'cold, non-baryonic DM', of the kind that comprises an estimated ~22% of the mass-energy of the universe (cf ~4% for baryonic matter).

*Which itself is a little confusing! This just means 'not composed of atoms, ions, electrons, etc' - forms of matter that do not 'feel' the electromagnetic force.

neilzero
2007-Jul-18, 09:09 PM
An other definition problem/ apparently there is little similarity between the voltage in an electrical circuit = EMF and the EMF = electromagnetic force in an atom and photons which are sometimes called electomagnetic waves and an electromagnet as opposed to a permant magnet. Four seperate concepts with the same or similar name? Neil