7 research outputs found
Towards an explanation of orbits in the extreme trans-Neptunian region: The effect of Milgromian dynamics
Milgromian dynamics (MD or MOND) uniquely predicts motion in a galaxy from
the distribution of its stars and gas in a remarkable agreement with
observations so far. In the solar system, MD predicts the existence of some
possibly non-negligible dynamical effects, which can be used to constrain the
freedom in MD theories. Known extreme trans-Neptunian objects (ETNOs) have
their argument of perihelion, longitude of ascending node, and inclination
distributed in highly non-uniform fashion; ETNOs are bodies with perihelion
distances greater than the orbit of Neptune and with semimajor axes greater
than 150 au and less than au. It is as if these bodies have been
systematically perturbed by some external force. We investigated a hypothesis
that the puzzling orbital characteristics of ETNOs are a consequence of MD. We
set up a dynamical model of the solar system incorporating the external field
effect (EFE), which is anticipated to be the dominant effect of MD in the ETNOs
region. We used constraints available on the strength of EFE coming from radio
tracking of the Cassini spacecraft. We performed several numerical experiments,
concentrating on the long-term orbital evolution of primordial (randomised)
ETNOs in MD. The EFE could produce distinct non-uniform distributions of the
orbital elements of ETNOs that are related to the orientation of an orbit in
space. If we demand that EFE is solely responsible for the detachment of Sedna
and 2012 VP, then these distributions are at odds with the currently
observed statistics on ETNOs unless the EFE quadrupole strength parameter
has values that are unlikely (with probability < 1) in light of the
Cassini data.Comment: 19 pages, 19 figures, 4 tables; accepted for publication in A&A; v2 -
language improve
Sedna and the cloud of comets surrounding the solar system in Milgromian dynamics
We reconsider the hypothesis of a vast cometary reservoir surrounding the solar system – the Oort cloud of comets – within the framework of Milgromian dynamics (MD or MOND). For this purpose we built a numerical model of the cloud, assuming the theory of modified gravity, QUMOND. In modified gravity versions of MD, the internal dynamics of a system is influenced by the external gravitational field in which the system is embedded, even when this external field is constant and uniform, a phenomenon dubbed the external field effect (EFE). Adopting the popular pair ν(x) = [1−exp(−x1 / 2)] -1 for the MD interpolating function and a0 = 1.2 × 10-10 m s-2 for the MD acceleration scale, we found that the observationally inferred Milgromian cloud of comets is much more radially compact than its Newtonian counterpart. The comets of the Milgromian cloud stay away from the zone where the Galactic tide can torque their orbits significantly. However, this does not need to be an obstacle for the injection of the comets into the inner solar system as the EFE can induce significant change in perihelion distance during one revolution of a comet around the Sun. Adopting constraints on different interpolating function families and a revised value of a0 (provided recently by the Cassini spacecraft), the aforementioned qualitative results no longer hold, and, in conclusion, the Milgromian cloud is very similar to the Newtonian in its overall size, binding energies of comets and hence the operation of the Jupiter-Saturn barrier. However, EFE torquing of perihelia still play a significant role in the inner parts of the cloud. Consequently Sedna-like orbits and orbits of large semi-major axis Centaurs are easily comprehensible in MD. In MD, they both belong to the same population, just in different modes of their evolution