Astronomers have found a new 7 km diameters moon of Uranus and new 14 km and 23 km moons around Neptune, which also shed light on the respective planet-moon-dust formation around these two planets. They believe that they have now detected all moons up to 8 km diameter around Uranus and up to 14 km around Neptune. But there are likely to be many undetected moons of up to 5 km diameter.
We have conducted extremely ultra-deep pencil beam observations for new satellites around both Uranus and Neptune. Tens of images on several different nights in 2021, 2022 and 2023 were obtained and shifted and added together to reach as faint as 26.9 and 27.2 magnitudes in the r-band around Uranus and Neptune, respectively. One new moon of Uranus, S/2023 U1, and two new moons of Neptune, S/2021 N1 and S/2002 N5, were found.
S/2023 U1 was 26.6 mags, is about 7 km in diameter and has a distant, eccentric and inclined retrograde orbit similar to Caliban and Stephano, implying these satellites are fragments from a once larger parent satellite. S/2023 U1 almost completely overlaps Stephano in orbital phase space.
S/2021 N1 was 26.9 mags, about 14 km in size and has a retrograde orbit similar to Neso and Psamathe, indicating they are a dynamical family. We find S/2021 N1 is in a Kozai-Lidov orbital resonance.
S/2002 N5 was 25.9 mags, is about 23 km in size and it makes a family of distant prograde satellites with Sao and Laomedeia.
All three new moons show for the first time dynamical groups of moons exist around both Uranus and Neptune. The creation of these groups likely produced dust that could be the source of red material seen on the leading hemispheres of some larger inner satellites like Titania, Oberon and Umbriel.
We also detected all known outer moons of Uranus and Neptune on multiple nights. This survey mostly completes the outer satellites of Uranus to about 8 km and Neptune to about 14 km in diameter.
The size distributions of satellite dynamical families around the giant planets shows a strong steepening in the power law size distribution smaller than 5 km in diameter. The satellites of a family become much more common smaller than 5 km and their size distribution is consistent with a collisional break-up of a once larger parent satellite.
Scott Sheppard, "New Moons of Uranus and Neptune from Ultra-Deep Pencil Beam Surveys" arXiv:2410.00108 (September 30, 2024) (Accepted Astronomical Journal).
arXiv:2410.02612 (astro-ph)
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On the nature of the missing mass of galaxy clusters in MOND: the view from gravitational lensing
Benoit Famaey, Lorenzo Pizzuti, Ippocratis D. Saltas
Modified Newtonian Dynamics (MOND) has long been known to fail in galaxy clusters, implying a residual missing mass problem for clusters in this context. Here, using mass profiles derived from strong- and weak-lensing shear, as well as magnification data, for a sample of clusters from the CLASH survey, we characterize the density profile of this residual MOND missing mass in the central Mpc of galaxy clusters. In line with results obtained in the literature from the hydrostatic equilibrium of hot gas, we find that an inner constant density core and an outer power-law slope between −4 and −6 provides a good description within ∼1 Mpc. We also show that the data in the central parts of clusters can be even better represented by a `dark mass-follows-gas' profile with an exponential cut-off. Clusters with X-ray emitting gas masses Mgas≥1014M⊙ display a remarkable uniformity for the missing-to-hot-gas density ratio in the inner parts, of order ∼10, and for the exponential cut-off radius, of order ∼450 kpc. Clusters with lower observed gas mass display larger and more scattered values for both the density ratio and cut-off radius. These lensing results can in principle serve as a crucible for relativistic theories of MOND in galaxy clusters, or for any other tentative hypothesis regarding the nature of the clusters residual missing mass in the MOND context.
Comments: 12 pages, 4 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:2410.02612 [astro-ph.CO]
(or arXiv:2410.02612v1 [astro-ph.CO] for this version)
https://doi.org/10.48550/arXiv.2410.02612
Saw it. Digesting the results.
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