[quote=MarkBour post_id=296262 time=1571351722 user_id=141361]
The Jupiter vs. Saturn moon race would seem to be a never-ending, ever-growing catalog. I suppose that just as we've done with planets, someone will propose a "cleared its orbital band" criterion for a moon as opposed to a moonlet or ring particle. Otherwise, we can already say with high confidence that Saturn has a trillion moons.[/quote][quote=https://en.wikipedia.org/wiki/Moonlet]
<<A moonlet, minor moon, minor natural satellite, or minor satellite is a particularly small natural satellite orbiting a planet, dwarf planet, or other minor planet. Up until 1995, moonlets were only hypothetical components of Saturn's F-ring structure, when the Earth passed through Saturn's ring plane. The Hubble Space Telescope and the European Southern Observatory both captured objects orbiting close or near the F-ring. In 2004, when Cassini caught an object 4-5km in diameter on the outer ring of the F-ring and then 5 hours later on the inner F-ring, showing that the object had orbited.
Three different types of small moons have been called moonlets:
[list] A belt of objects embedded in a planetary ring, especially around Saturn, such as those in the A Ring, S/2009 S 1 in the B Ring ("propeller" moonlets), and those in the F Ring
Occasionally asteroid moons, such as those of 87 Sylvia
Subsatellites[/list][/quote][quote=https://en.wikipedia.org/wiki/87_Sylvia]
[float=left][youtube]https://www.youtube.com/watch?v=o8vHk038_VY[/youtube][img3=Adaptive Optics observations of (87) Sylvia, showing its two satellites, Remus and Romulus.]https://upload.wikimedia.org/wikipedia/commons/5/52/CMSylvia.png[/img3][/float]
<<Sylvia (minor planet designation: 87 Sylvia) is the 8th-largest asteroid [(384 × 264 × 231) ±10 km] in the asteroid belt. It is the parent body of the Sylvia family and member of [url=https://en.wikipedia.org/wiki/Cybele_asteroid]Cybele group[/url] located beyond the core of the belt. [b][u][color=#0000FF]Sylvia is the first asteroid known to possess more than one moon.[/color][/u][/b]
[i][color=#0000FF]Sylvia was discovered by N. R. Pogson on May 16, 1866, from Madras (Chennai), India. A. Paluzie-Borrell, writing in Paul Herget's The Names of the Minor Planets (1955), mistakenly states that the name honours Sylvie Petiaux-Hugo Flammarion, the first wife of astronomer Camille Flammarion. In fact, in the article announcing the discovery of the asteroid, Pogson explained that he selected the name in reference to Rhea Silvia, mother of Romulus and Remus (MNRAS, 1866).[/color][/i]
Sylvia is very dark in color and probably has a very primitive composition. The discovery of its moons made possible an accurate measurement of the asteroid's mass and density. Its density was found to be very low (around 1.2 times the density of water), indicating that the asteroid is porous to very porous; from 25% to as much as 60% of it may be empty space, depending on the details of its composition. However, the mineralogy of the X-type asteroids is not known well enough to constrain this further. Either way, this suggests a loose rubble pile structure. Sylvia is also a fairly fast rotator, turning about its axis every 5.18 hours (giving an equatorial rotation velocity of about 230 km/h or 145 mph). The short axis is the rotation axis. Direct images indicate that Sylvia has an axial tilt of around 29.1°. Sylvia's shape is strongly elongated.
Sylvia has two orbiting satellites. They have been named (87) Sylvia I Romulus and (87) Sylvia II Remus, after Romulus and Remus, the children of the mythological Rhea Silvia.
Romulus, the first moon, was discovered on February 18, 2001, from the Keck II telescope by Michael E. Brown and Jean-Luc Margot. Remus, the second moon, was discovered over three years later on August 9, 2004, by Franck Marchis of UC Berkeley, and Pascal Descamps, Daniel Hestroffer, and Jérôme Berthier of the Observatoire de Paris, France. The orbital planes of both satellites and the equatorial plane of the primary asteroid are all well-aligned; all planes are aligned within about 1 degree of each other, suggestive of satellite formation in or near the equatorial plane of the primary.>>
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