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An interesting question, in which the brightest discoveries of the 20th century in Astrophysics (dark matter, dark energy) are connected with the ingenious model of the movement of the planets of the solar system, proposed by Ptolemy about 2000 years ago. Ptolemy's model, describing the motions of the planets known at that time, unfortunately had nothing to do with reality, and therefore we will leave the ancient mechanic with his epicycles alone and move from history to astrophysics.
Dark matter in our galaxy has a local density of ~ 0.2 GeV / cm3 or ~3 × 10-2⁵ g / cm3 or ~0.005 Solar masses per cubic parsec. There are ideas that dark matter can accumulate in the Sun, affecting the energy balance of the inner and outer layers. Dark matter provides the existence of such structures in the universe as observable galaxies, galactic clusters, and superclusters. Dark matter distributions in galactic clusters have been measured from gravitational lensing, and more recently, from rogue stars ejected from galaxies by the pull of dark matter.
Dark energy is distributed more evenly across the universe. The dark energy density is estimated as the vacuum density and, from the observed accelerated expansion of the universe, is estimated as ~10-3⁰ g / cm3.
Apparently, not everyone understood the meaning of Artyom's question.
Artyom wanted to ask if it might turn out that dark matter, like epicycles, will only turn out to be a convenient mathematical model that does not correspond to reality and will be replaced by another model that is simpler or explains more than the previous one.
Yes, this is possible and it is a normal course of science. In this sense, classical mechanics is also an epicycle of its time, later absorbed by another model.
But here we must also understand that the epicycle was not a fiction that had nothing to do with reality. Relative to the Earth, the planets really describe very difficult trajectories, which are described quite well by epicycles, in particular, the fact that at some point the planets move in the opposite direction.
I don't know if it was intentional or not, but it's a pretty neat rhyme. Finally, only Kepler was able to get rid of epicycles by proposing his three laws (Copernicus ' planets moved in circles and evenly, according to Aristotle, so we had to use epicycles). And the concept of dark matter was introduced, among other things, in order to comply with Kepler's laws, as applied to the movement of stars in galaxies.
As for the rest, I completely agree with Nikita.