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Blobrana


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RE: Uranian satellites
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Uranus might have two dark moons we've never seen before

Uranus may have two small moons that no one has ever seen, orbiting closer to the planet than any of its other satellites and making wavy patterns in the planet's rings.
The ice giant has 27 known moons, far fewer than the 67 and 62 of its neighbours Jupiter and Saturn, respectively. Uranus is a smaller planet, which may explain the difference.
But it might just be that we haven't previously had a chance to look for more moons. Unlike its larger brethren, Uranus has entertained only one passing spacecraft - Voyager 2, which tripled the number of known Uranian moons in its 1986 flyby. Uranus is also yet to receive an orbiting spacecraft like Jupiter's Galileo and Juno, or Saturn's Cassini.
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Blobrana


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Uranus satellites
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Title: Astrometry of the main satellites of Uranus: 18 years of observations
Author: J.I.B. Camargo, F.P. Magalhăes, R. Vieira-Martins, M. Assafin, F. Braga-Ribas, A. Dias-Oliveira, G. Benedetti-Rossi, A.R. Gomes-Júnior, A.H. Andrei, D.N. da Silva Neto

We determine accurate positions of the main satellites of Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those of these satellites, are also determined. The observational period spans from 1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil.
We used the software called Platform for Reduction of Astronomical Images Automatically (PRAIA) to minimise (digital coronography) the influence of the scattered light of Uranus on the astrometric measurements and to determine accurate positions of the main satellites. The positions of Uranus were then indirectly determined by computing the mean differences between the observed and ephemeris positions of these satellites. A series of numerical filters was applied to filter out spurious data. These filters are mostly based on the comparison between the positions of Oberon with those of the other satellites and on the offsets as given by the differences between the observed and ephemeris positions of all satellites.
We have, for the overall offsets of the five satellites, -29 (±63) mas in right ascension and -27 (±46) mas in declination. For the overall difference between the offsets of Oberon and those of the other satellites, we have +3 (±30) mas in right ascension and -2 (±28) mas in declination. Ephemeris positions for the satellites were determined from DE432+ura111. Comparisons using other modern ephemerides for the solar system -INPOP13c- and for the motion of the satellites -NOE-7-2013- were also made. They confirm that the largest contribution to the offsets we find comes from the motion of the barycenter of the Uranus system around the barycenter of the solar system, as given by the planetary ephemerides. Catalogues with the observed positions are provided.

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Blobrana


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The Uranian moons, Cupid and Mab, were discovered by Mark R. Showalter and Jack J. Lissauer using the Hubble Space Telescope on the 25th August, 2003.



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Blobrana


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Title: NOTE: Explaining why the Uranian satellites have equatorial prograde orbits despite the large planetary obliquity
Authors: Alessandro Morbidelli, Kleomenis Tsiganis, Konstantin Batygin, Aurelien Crida, Rodney Gomes

We show that the existence of prograde equatorial satellites is consistent with a collisional tilting scenario for Uranus. In fact, if the planet was surrounded by a proto-satellite disk at the time of the tilting and a massive ring of material was temporarily placed inside the Roche radius of the planet by the collision, the proto-satellite disk would have started to precess incoherently around the equator of the planet, up to a distance greater than that of Oberon. Collisional damping would then have collapsed it into a thin equatorial disk, from which the satellites eventually formed. The fact that the orbits of the satellites are prograde requires Uranus to have had a non-negligible initial obliquity (comparable to that of Neptune) before it was finally tilted to 98 degrees.

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