APOD: Moons of Saturn (2019 Oct 17)

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APOD: Moons of Saturn (2019 Oct 17)

Post by APOD Robot » Thu Oct 17, 2019 4:07 am

Image Moons of Saturn

Explanation: On July 29, 2011 the Cassini spacecraft's narrow-angle camera took this snapshot and captured 5 of Saturn's moons, from just above the ringplane. Left to right are small moons Janus and Pandora respectively 179 and 81 kilometers across, shiny 504 kilometer diameter Enceladus, and Mimas, 396 kilometers across, seen just next to Rhea. Cut off by the right edge of the frame, Rhea is Saturn's second largest moon at 1,528 kilometers across. So how many moons does Saturn have? Twenty new found outer satellites bring its total to 82 known moons, and since Jupiter's moon total stands at 79, Saturn is the Solar System's new moon king. The newly announced Saturnian satellites are all very small, 5 kilometers or so in diameter, and most are in retrograde orbits inclined to Saturn's ringplane. You can help name Saturn's new moons, but you should understand the rules. Hint: A knowledge of Norse, Inuit, and Gallic mythology will help.

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Ann » Thu Oct 17, 2019 4:35 am

I'm often somewhat bored by pictures of the planets in the Solar system, but I must admire the composition of this APOD! :D

Little moon Pandora is sitting smack dab in what I assume is the F-ring of Saturn. Rhea is positioned so perfectly that it almost looks as if it had replaced Saturn in the center of the rings. Also I'm always happy to see smooth shiny Enceladus, and I like the heavily cratered surface of one of the Solar system's smallest spherical bodies, Mimas. And Janus at far left looks like a "little man" with a long nose and at least one eye, looking with some concern at the scene to the right of him.

This APOD is surely going to be one that generates enormous traffic, as people will no doubt be happy to suggest names for Saturn's new moons. So I'll suggest two names from the Norse mythology, Hel, goddess of the underworld, and Vale, avenger of the murder of Balder, who was everyone's favorite god in the Norse mythology. Or Vidar. I just like the name, and unlike the two others I suggested, it is a fairly popular name in Sweden.

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by sym666 » Thu Oct 17, 2019 6:02 am

Cassini, my love! I'm sure you can see us wherever you are! :cry:

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by gmPhil » Thu Oct 17, 2019 9:11 am

You can help name Saturn's new moons, but you should understand the rules.
So... no "Moony McMoonface then?

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Boomer12k » Thu Oct 17, 2019 10:21 am

Awesome image... great timing...

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by orin stepanek » Thu Oct 17, 2019 11:50 am

Saturn may have even more moons when you consider what makes up the rings! :mrgreen:
PIA12797-full.jpg
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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by orin stepanek » Thu Oct 17, 2019 11:52 am

Boomer12k wrote:
Thu Oct 17, 2019 10:21 am
Awesome image... great timing...

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+1 :wink:
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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by BDanielMayfield » Thu Oct 17, 2019 12:04 pm

orin stepanek wrote:
Thu Oct 17, 2019 11:50 am
Saturn may have even more moons when you consider what makes up the rings! :mrgreen: PIA12797-full.jpg
In the finding of new, even tinier moons there is no end. Oh no, I see the making of a new category, the “dwarf moon”. They’ll call any non round moon a dwarf.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Ann » Thu Oct 17, 2019 12:33 pm

BDanielMayfield wrote:
Thu Oct 17, 2019 12:04 pm
orin stepanek wrote:
Thu Oct 17, 2019 11:50 am
Saturn may have even more moons when you consider what makes up the rings! :mrgreen: PIA12797-full.jpg
In the finding of new, even tinier moons there is no end. Oh no, I see the making of a new category, the “dwarf moon”. They’ll call any non round moon a dwarf.
Than Janus may not be a moon! Janus does not look spherical to me.

Janus may be demoted and called a "dwarf moon" in the future! :shock:

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Chris Peterson » Thu Oct 17, 2019 12:39 pm

Ann wrote:
Thu Oct 17, 2019 12:33 pm
BDanielMayfield wrote:
Thu Oct 17, 2019 12:04 pm
orin stepanek wrote:
Thu Oct 17, 2019 11:50 am
Saturn may have even more moons when you consider what makes up the rings! :mrgreen: PIA12797-full.jpg
In the finding of new, even tinier moons there is no end. Oh no, I see the making of a new category, the “dwarf moon”. They’ll call any non round moon a dwarf.
Than Janus may not be a moon! Janus does not look spherical to me.

Janus may be demoted and called a "dwarf moon" in the future! :shock:
Well, a "dwarf moon" would still be a moon, right? (I don't imagine the category will be invented, however. "Moon" just means "natural satellite", and there's never been a concern about the shape or size or process by which it came into being. At times the Earth has had a second moon when asteroids were briefly captured in orbit.)
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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by sillyworm 2 » Thu Oct 17, 2019 1:21 pm

Jaw dropping image....beautiful.

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by bystander » Thu Oct 17, 2019 1:30 pm

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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“many moons ago”

Post by neufer » Thu Oct 17, 2019 1:35 pm

Art Neuendorffer

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Ann » Thu Oct 17, 2019 2:41 pm

Chris Peterson wrote:
Thu Oct 17, 2019 12:39 pm
Ann wrote:
Thu Oct 17, 2019 12:33 pm
BDanielMayfield wrote:
Thu Oct 17, 2019 12:04 pm


In the finding of new, even tinier moons there is no end. Oh no, I see the making of a new category, the “dwarf moon”. They’ll call any non round moon a dwarf.
Than Janus may not be a moon! Janus does not look spherical to me.

Janus may be demoted and called a "dwarf moon" in the future! :shock:
Well, a "dwarf moon" would still be a moon, right? (I don't imagine the category will be invented, however. "Moon" just means "natural satellite", and there's never been a concern about the shape or size or process by which it came into being. At times the Earth has had a second moon when asteroids were briefly captured in orbit.)
Moon Daphnis, non-moon ring particles.
Credit: NASA/JPL-Caltech/Space Science Institute.
Right, but there has to be a difference between a moon and a ring particle!

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by neufer » Thu Oct 17, 2019 3:43 pm

Click to play embedded YouTube video.
Ann wrote:
Thu Oct 17, 2019 2:41 pm
Chris Peterson wrote:
Thu Oct 17, 2019 12:39 pm
Ann wrote:
Thu Oct 17, 2019 12:33 pm
Than [sic] Janus may not be a moon! Janus does not look spherical to me. Janus may be demoted and called a "dwarf moon" in the future! :shock:
Well, a "dwarf moon" would still be a moon, right? (I don't imagine the category will be invented, however. "Moon" just means "natural satellite", and there's never been a concern about the shape or size or process by which it came into being. At times the Earth has had a second moon when asteroids were briefly captured in orbit.)
Right, but there has to be a difference between a moon and a ring particle!
Art Neuendorffer

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by khh » Thu Oct 17, 2019 9:51 pm

So just 2 planets have a total of 161 moons? This is lunacy!

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by MarkBour » Thu Oct 17, 2019 10:35 pm

This is one marvelous photo! I would really like to have a summer home on Pandora.

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.
Mark Goldfain

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by orin stepanek » Fri Oct 18, 2019 11:48 am

Ann wrote:
Thu Oct 17, 2019 12:33 pm
BDanielMayfield wrote:
Thu Oct 17, 2019 12:04 pm
orin stepanek wrote:
Thu Oct 17, 2019 11:50 am
Saturn may have even more moons when you consider what makes up the rings! :mrgreen: PIA12797-full.jpg
In the finding of new, even tinier moons there is no end. Oh no, I see the making of a new category, the “dwarf moon”. They’ll call any non round moon a dwarf.
Than Janus may not be a moon! Janus does not look spherical to me.

Janus may be demoted and called a "dwarf moon" in the future! :shock:

Ann
Maybe they'll be called moonatoids! :saturn:
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The horserace

Post by neufer » Sat Nov 16, 2019 2:27 pm


Art Neuendorffer

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Re: APOD: Moons of Saturn (2019 Oct 17)

Post by Fred the Cat » Sat Nov 16, 2019 11:45 pm

neufer wrote:
Thu Oct 17, 2019 3:43 pm
Click to play embedded YouTube video.
Ann wrote:
Thu Oct 17, 2019 2:41 pm
Chris Peterson wrote:
Thu Oct 17, 2019 12:39 pm

Well, a "dwarf moon" would still be a moon, right? (I don't imagine the category will be invented, however. "Moon" just means "natural satellite", and there's never been a concern about the shape or size or process by which it came into being. At times the Earth has had a second moon when asteroids were briefly captured in orbit.)
Right, but there has to be a difference between a moon and a ring particle!
Yes but would a moon by any other name smell as sweet? :wink:
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Moonlet

Post by neufer » Sun Nov 17, 2019 4:30 am

MarkBour wrote:
Thu Oct 17, 2019 10:35 pm

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.
https://en.wikipedia.org/wiki/Moonlet wrote:
<<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:
  • 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
https://en.wikipedia.org/wiki/87_Sylvia wrote:
Click to play embedded YouTube video.
<<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 Cybele group located beyond the core of the belt. Sylvia is the first asteroid known to possess more than one moon.

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).

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.>>
Art Neuendorffer