In article ,
Nicolaas Vroom writes:

The main problem around dark matter related to galaxies is in the name,
which is is confusing.
In simple language there are three types of matter: visible baryonic
invisible baryonic and non-baryonic.

In the case of the solar system it consists of two:
visible baryonic: the Sun. Invisible: the planets and the kuiper belt.
You can consider the Oort Cloud as the Halo of the solar system
There is (almost) no non-baryonic matter.

[[Mod. note -- In the context of dark matter, "visible" means
"interacts with electromagnetic radiation (which includes light,
radio, X-rays, etc)". So anything baryonic (including stars,
planets, the Kuiper belt, neutron stars, interstellar dust, and
the interstellar and intergalactic (gaseous) mediums) are all
"visible". Electrons and positrons are also "visible".

I think the OP was referring to "missing baryons" or "dark baryons". If
we believe the BBN values for baryons, then not all are accounted for.
They COULD be visible but they are not detectable by us now.

If we assume that all the stars in the disc of our Galaxy are equal
than it means that there is no non-baryonic directly outside each
star. i.e. all non-baryonic can only be in interstellar space (or
in halo)

The reason why there is no non-baryonic matter in the solar system
is because all the planets (the movements) are accordingly (almost)
to Newton's law.

Depending on what the dark matter is and how it is distributed, there
could be dark matter in the solar system. Its density wouldn't be high
enough to affect the dynamics. Some people think that dark matter might
actually accumulate inside stars.

In the paragraph:
https://en.wikipedia.org/wiki/Dark_m...otation_curves
Keppler's law is mentioned. IMO in relation to galaxy rotation
curves Keppler's law should not be mentioned. Even if you want to
study the movement of the planets you should use Newton's law. If
curve B is what is observed than the true size of the galaxy is
much larger than what is shown. It is easy possible that the full
curve also starts to level off. (MOND does not support such an
behaviour. It will always be flat)

[[Mod. note -- Kepler's law (strictly speaking, Kepler's 3rd law)
is a mathematical consequence of Newton's law (strictly speaking,
Newton's 2nd law & his law of universal gravitation), and vice versa,
so "using Newton's law" is the same thing as using Kepler's law.
-- jt]]

By the time the flat-rotation-curve region is reached, there is so
little baryonic matter that one can assume that all such matter is
interior to the orbit. Assuming it is spherically distributed, the
effect is the same as that of a point mass at the centre.