Then Endless Universe

[AstroTiger]

I am currently reading this book, which goes into depth on dark matter etc.

This seems to be an intruiging concept. Matter we cannot "see" but it must be there, like black holes.

It does not contain any conventional matter from the periodic table as we know it.

Does not contain protons, neutrons, or electons.

Yet is believed to be the main thing holding galaxies together.

Has anyone else read anymore into this?

Apparently the earth passes through a lot of it, so how comes we have never discovered any on earth?

Also if dark matter exists in the solar system, could it be this that for example hold saturns rings together?

I look forward your responses

[George Jones]

Apparently the earth passes through a lot of it, so how comes we have never discovered any on earth?

A related question: why don't the vast numbers of neutrinos (produced in the Sun's nuclear reactions) that pass through our bodies every second produce noticeable effects?

Roughly, there are four forces in nature: gravity, the weak nuclear force, electromagnetism, and the strong nuclear force. Any noticeable effect is produced ultimately by these forces.

Neutrinos interact with matter only via gravity and the weak nuclear force. Since neutrinos have small mass/energy, there are not enough neutrinos to produce noticeable local gravitational effects. Thus, neutrinos interact noticeably only via the weak nuclear force, which is very weak. According to quantum theory, this means the probability that a neutrino interacts with normal matter is very small. In fact, a neutrino would have to pass through several light-years of lead for its probability of interaction to be 50%.

Similarly, dark matter particles are thought to interact only via gravity and the weak nuclear force. in spite of their elusiveness, neutrinos have been observed, and dark matter particles will eventually be observed directly, possibly in the Large Hadron Collider.

Also if dark matter exists in the solar system, could it be this that for example hold saturns rings together?

The particles in Saturn's rings are held in orbit by the normal gravity of Saturn

[AstroTiger]

I think there is more to it that just gravity for holding saturns rings together.

The ripple effects caused by satalites orbiting the rings gives the rings an almost fluid property.

[George Jones]

Also if dark matter exists in the solar system, could it be this that for example hold saturns rings together?

The particles in Saturn's rings are held in orbit by the normal gravity of Saturn

I think there is more to it that just gravity for holding saturns rings together.

The ripple effects caused by satalites orbiting the rings gives the rings an almost fluid property.

Yes, I used the politician's ploy of answering a question different from the one asked. Heading to my shelf to pull down my lone (if cosmology doesn't count as astrophysics) quantitative astrophysics book.

The dynamics of ring system are complex, and not all features are completely understood. Stuff like, for example, collisions, diffusion, Shepherd moons, orbital resonances, etc., play roles.

I am fairly certain, though, that dark matter doesn't play a role in maintaining the structure of Saturn's rings.

[AstroTiger]

No, indeed George, the saturns moons seems to be the generally accepted explaination as to what holds the rings together.

With my limited knowledge though, i do not see how their effect alone is strong enough.

Still being a chemist by training and an IT Trainer by trade i guess its a little crass for me to challenge those with Phd's :-) I am sure i am probably wrong

[Jim M]

No, indeed George, the saturns moons seems to be the generally accepted explaination as to what holds the rings together.

With my limited knowledge though, i do not see how their effect alone is strong enough.

Still being a chemist by training and an IT Trainer by trade i guess its a little crass for me to challenge those with Phd's :-) I am sure i am probably wrong

I thought that the generally accepted idea was that Saturn's rings are relatively young (of the order of millions of years) and that is why they are still there.

[AstroTiger]

I thought that the generally accepted idea was that Saturn's rings are relatively young (of the order of millions of years) and that is why they are still there.

First time i heard that one.

Does this mean they are degrading in some way as we speak?

Certainly the overall structure appears to remain constant.

I read somewhere though that they will get fainter as time goes by. Shame if that happens, i regard saturn as one of the finest sights in the night sky

[Jim M]

First time i heard that one.

Well yeah, I think it was thought the rings were as old as the planet but I was reading recently on the web about some new idea - that they are recently formed when a moon/object reached the Roche limit and was broken up and formed the rings. Apparently the rings have an atmosphere of oxygen!

Structure and evolution of Saturn's rings

ESA - Cassini-Huygens - Saturn?s rings have own atmosphere

Does this mean they are degrading in some way as we speak?

Certainly the overall structure appears to remain constant.

I read somewhere though that they will get fainter as time goes by. Shame if that happens, i regard saturn as one of the finest sights in the night sky

Perhaps it takes longer than a couple of hundred years for any observable degradation.

[AstroTiger]

If the rings have an atmosphere that would perhaps explain why they are more prominent than say jupiters rings :-)

[astropete]

just jumping the gun a bit, could dark matter in our solar system be a contributing factor of the planet uranus orbital fluctuations, that lead to the discovery of the planet neptune?

[Jim M]

just jumping the gun a bit, could dark matter in our solar system be a contributing factor of the planet uranus orbital fluctuations, that lead to the discovery of the planet neptune?

Stephen Adler discusses the possible effect of DM on the Jovian planets here:

[0903.4879] Solar System Dark Matter

No mention of what you are asking about though the rest is interesting.

Worth a read if you haven't come across it already.