Dark Matter is Denser in the Solar System

Dark Matter is a ubiquitous and mysterious type of matter that comprises about 23% of the energy density of the universe, much more than the 4% accounted for by the visible and more familiar matter known as baryonic matter. The Milky Way, like all other known galaxies, is nestled in a dark matter halo that extends over a much larger distance than the visible galaxy radius. A recent study by researchers at the University of Arizona shows that the dark matter density in the solar system is enhanced by three to five orders of magnitude compared to the galactic halo dark matter density.




 What is visible in the above image, first and foremost, are many spectacular galaxies that are part of CL0024+17 itself, typically appearing tan in color. Next, a close inspection of the cluster center shows several unusual and repeated galaxy shapes, typically more blue. These are multiple images of a few distant galaxies, showing that the cluster is a strong gravitational lens. The relatively weak distortions of the many distant faint blue galaxies all over the image, however, indicates the existence of the dark matter ring. The computationally modeled dark matter ring spans about five million light years and has been digitally superimposed to the image in diffuse blue. (credit: NASA, ESA, M. J. Jee and H. Ford et al. (Johns Hopkins University)
What is visible in the above image  are many
spectaculargalaxies that are part of CL0024+17.
Next, a close inspection of the cluster center
shows several unusual and repeated galaxy
shapes, typically more blue. These
are multiple images of a few distant
galaxies, showing that the cluster is
a strong gravitational lens. The relatively weak
distortions of the many distant faint blue
galaxies all over the image, however, indicates
the existence of the dark matter ring.
The computationally modeled dark matter ring
spans about five million light years and has
been digitally superimposed to the image in
diffuse blue (Credit: NASA, ESA, M. J. Jee and
H. Ford et al. Johns Hopkins University).

As the solar system moves through the galaxy, it interacts gravitationally with dark matter particles. Researchers Xiaoying Xu and Ethan R. Siegel from the Steward Observatory at the University of Arizona developed an analytic method to determine when such an interaction is strong enough to result in a particle’s capture by a planet in the solar system. They were then able to compute the amount of dark matter accumulated in the solar system during its 4.5 billion years due to these interactions, and to compare it to the amount of dark matter present in the solar system as part of the galactic halo. 

The findings show that the amount of dark matter captured by a planet in the solar system depends on the mass of the planet and its distance from the sun. The more massive a planet is and the farther it is from the sun, the more matter it will accrete. For example, the dark matter mass captured by Neptune, the third most massive planet and the farthest from the sun, is 300 times greater than galactic halo dark matter mass surrounding the planet.

The results of this research make it evident that the dark matter distribution in the solar system does not conform to the galactic halo distribution. This can lead to a reevaluation of the significance of the dark matter in our solar system and its possible influence on objects and processes within the solar system. The density figures obtained in this research have already ruled out the option of dark matter causing the Pioneer anomaly (sudden changes in the velocities of spacecrafts).

Understanding the properties of dark matter and its behavior is currently one of the most studied problems in contemporary astrophysics. This research is one of the first to consider the dark matter within our solar system. It paves the way for further work, for example the study of back-reaction effects, which can cause captured dark matter particles to be ejected, thus reducing the amount of dark matter in the solar system. In addition, the results obtained in this research can be used to better execute dark matter direct detection searches. 

TFOT recently covered the launch of GLAST, a new space observatory NASA hopes will improve our understanding of the Milky Way galaxy, the solar system, dark matter, and other topics. TFOT also covered the construction of a large camera intended to detect dark energy, another mysterious substance estimated to comprise a whopping 75% of the universe.

Further information on the recent research on dark matter in our solar system can be obtained at the arXiv website.