APOD: Methone: Smooth Egg Moon of Saturn (2012 Nov 06)

[APOD Robot]

Methone: Smooth Egg Moon of Saturn

Explanation: Why is this moon shaped like a smooth egg? The robotic Cassini spacecraft completed the first flyby ever of Saturn's small moon Methone in May and discovered that the moon has no obvious craters. Craters, usually caused by impacts, have been seen on every moon, asteroid, and comet nucleus ever imaged in detail -- until now. Even the Earth and Titan have craters. The smoothness and egg-like shape of the 3-kilometer diameter moon might be caused by Methone's surface being able to shift -- something that might occur were the moon coated by a deep pile of sub-visual rubble. If so, the most similar objects in our Solar System would include Saturn's moons Telesto, Pandora, Calypso, as well as asteroid Itokawa, all of which show sections that are unusually smooth. Methone is not entirely featureless, though, as some surface sections appears darker than others. Although flybys of Methone are difficult, interest in the nature and history of this unusual moon is sure to continue.

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[/b]

[bystander]

http://asterisk.apod.com/viewtopic.php?t=29933

[Ann]

This is quite fascinating.

Ann

[Mistah T]

"SHAZBOT, Mork calling Orson, Mork calling Orson, come in Orson, The Earthlings Have discovered my landing craft. Please advise Sir Cumference. Over"

[BDanielMayfield]

I can think of two reasons why this moonlet is craterless.

(1) Methone is so small, it’s unlikely to be hit. There must be many areas of a like size on bodies around the solar system that, given the random nature of collisions, have escaped any impacts. That it hasn’t been hit by anything large is also self evident, because with its smallness and its position deep inside Saturn’s gravity well any large and/or heavy projectile hitting it at speed could have destroyed it completely. So it’s one lucky egg.

(2) We’re used to thinking in terms just of gravity when it comes to the shapes of these bodies, but in Methone’s case I suspect that the other long range attractive force, electromagnetism, might be at work here. Orbiting so close to a very active Saturn, couldn’t this moonlet be getting charged as it passes through Saturn’s magnetic field? If it was then it would be more attractive to particles from the E ring and to ice crystals from the cyrovolcanoes of Enceladus. So it’s like a frosted egg, collecting snowfall that over time has filled in all surface relief.

Well, those are my theories, I look forward to seeing how they might be dissected in today’s discussion.

Bruce

[500pesos]

Very interesting Bruce, especially your second hypothesis, i wouldn't have thought of that. Maybe one of the scientists can say if electromagnetism could be at play here?

My very first thought when I saw this perfect egg shape in the picture and read "3 km diameter" was 'snowball'; Methone is made out of soft ice. But I'll admit that your suggestion that Methone is one super lucky space-egg that has never been hit is way cooler

[emc]

Haumea... expanding this morning's egg menu...
http://apod.nasa.gov/apod/ap080923.html

[orin stepanek]

"SHAZBOT, Mork calling Orson, Mork calling Orson, come in Orson, The Earthlings Have discovered my landing craft. Please advise Sir Cumference. Over"

[neufer]

<<Cronus (Κρόνος Krónos) was the leader and the youngest of the first generation of Titans, divine descendants of Gaia, the earth, and Uranus, the sky. Cronus was also identified in classical antiquity with the Roman deity Saturn. He overthrew his father and ruled during the mythological Golden Age. Cronus was usually depicted with a sickle or scythe, which was also the instrument he used to castrate and depose Uranus, his father.

Cronus (i.e., Saturn) learned from Gaia and Uranus that he was destined to be overcome by his own sons, just as he had overthrown his father. As a result, although he sired the gods Demeter, Hestia, Hera, Hades and Poseidon by Rhea, he devoured them all as soon as they were born, to preempt the prophecy. When the sixth child, Zeus, was born Rhea sought Gaia to devise a plan to save them and to eventually get retribution on Cronus for his acts against his father and children. Another child Cronus is reputed to have fathered includes Chiron, by Philyra.

Rhea secretly gave birth to Zeus in Crete, and handed Cronus a stone wrapped in swaddling clothes, also known as the Omphalos Stone, which he promptly swallowed, thinking that it was his son.

Rhea kept Zeus hidden in a cave on Mount Ida, Crete. According to some versions of the story, he was then raised by a goat named Amalthea, while a company of Kouretes, armored male dancers, shouted and clapped their hands to make enough noise to mask the baby's cries from Cronus. Other versions of the myth have Zeus raised by the nymph Adamanthea, who hid Zeus by dangling him by a rope from a tree so that he was suspended between the earth, the sea, and the sky, all of which were ruled by his father, Cronus. Still other versions of the tale say that Zeus was raised by his grandmother, Gaia.

Once he had grown up, Zeus used an emetic given to him by Gaia to force Cronus to disgorge the contents of his stomach in reverse order: first the stone, which was set down at Pytho under the glens of Mount Parnassus to be a sign to mortal men, then the goat, and then his two brothers and three sisters. In other versions of the tale, Metis gave Cronus an emetic to force him to disgorge the children.>>

[BDanielMayfield]

Very interesting Bruce, especially your second hypothesis, i wouldn't have thought of that. Maybe one of the scientists can say if electromagnetism could be at play here?

My very first thought when I saw this perfect egg shape in the picture and read "3 km diameter" was 'snowball'; Methone is made out of soft ice. But I'll admit that your suggestion that Methone is one super lucky space-egg that has never been hit is way cooler

Thanks. I also think that your first impression, at least for the surface of Methone, was right on the dinero, 500pesos.

[neufer]

"SHAZBOT, Mork calling Orson, Mork calling Orson, come in Orson,
The Earthlings Have discovered my landing craft.

Please advise Sir Cumference. Over"

Click to play embedded YouTube video.

Click to play embedded YouTube video.

[The President] “sold Chrysler to the Orkians who are going to build Jeeps on Mimas.”

<<America's more ambitious manned space travel plans included the design of the Saturn series of heavy-lift launch vehicles by a team headed by Wernher von Braun. Chrysler's Huntsville operation, then designated the Space Division, became Marshall Space Flight Center’s prime contractor for the first stage of the Saturn I and Saturn IB versions. The design was based on a cluster of Redstone and Jupiter fuel tanks, and Chrysler built it for the Apollo program in the Michoud Assembly Facility in East New Orleans, one of the largest manufacturing plants in the world. Between October 1961 and July 1975, NASA used ten Saturn Is and nine Saturn IBs for suborbital and orbital flights, all of which were successful; Chrysler missiles and boosters never suffered a launch failure.>>

[Boomer12k]

This picture only shows an "egg" shape as it is not Full on to the Sun...we are seeing it in phase...

There are some features....4 o'clock, 5 o'clock, and 7 o'clock...that look darker, and are rounded, and could be craters, or at least indentations....this picture is not the most clear. Also the large darker area reminds me of Moon Maria. It also kind of looks like a "Valentines Heart". The bottom would be to our lower left. There are also some darker regions inside it...these could be frost covered, as has been suggested. I think a closer flyby is necessary...hopefully they can do one despite the difficulties.

Here is a CLEARER image, and you can see features better.

http://www.avaruus.fi/uutiset/aurinko-p ... uusta.html

:---[===] *

[Chris Peterson]

(1) Methone is so small, it’s unlikely to be hit. There must be many areas of a like size on bodies around the solar system that, given the random nature of collisions, have escaped any impacts.

Probably not. We've never seen any other body without evidence of collision, even small asteroids. Statistically, anything more than a few million years old is likely to be hit. So unless this body is unaccountably new, it should have been hit many times.

(2) We’re used to thinking in terms just of gravity when it comes to the shapes of these bodies, but in Methone’s case I suspect that the other long range attractive force, electromagnetism, might be at work here. Orbiting so close to a very active Saturn, couldn’t this moonlet be getting charged as it passes through Saturn’s magnetic field?

Bodies do not develop significant charges, but their surface dust/ice/regolith can become charged, which affects its behavior (this has been seen on the Moon, for instance).

[neufer]

---

<<Methone (Μεθώνη) is a very small natural satellite of Saturn lying between the orbits of Mimas and Enceladus. It was first seen by the Cassini Imaging Team and given the temporary designation S/2004 S 1. Methone [mi-THOH-nee] synchronous rotation: 1.009573975 d

Methone is visibly affected by a perturbing mean longitude resonance with the much larger Mimas. This causes its osculating orbital elements to vary with an amplitude of about 20 km in semi-major axis, and 5° in longitude on a timescale of about 450 days. Eccentricity also varies on different timescales between 0.0011 and 0.0037, and inclination between about 0.003° and 0.020°.

Methone was one of the Alkyonides,
the seven beautiful daughters of the Giant Alkyoneus.>>

[b][color=#0000FF]Arcs of material share an orbit with the tiny moons Anthe (top left) and Methone (bottom right). The arcs are confined by resonances with Mimas; the Methone arc only spans about 10 degrees of longitude.[/color][/b]

---

<<The E Ring is the outermost ring, and is extremely wide, beginning at the orbit of Mimas (72% of Enceladus) and ending somewhere around the orbit of Rhea. It is a diffuse disk consisting mostly of ice, with silicates, carbon dioxide and ammonia. Unlike the other rings, it is composed of microscopic rather than macroscopic particles. In 2005, the source of the E Ring's material was determined to be cryovolcanic plumes emanating from the "tiger stripes" of the south polar region of the moon Enceladus. The E ring is not made of ice chunks like the other rings. It is in fact see through and is rather like dust, gas and smoke.>>

The Methone Ring Arc, first detected in September 2006, covering a longitudinal extent of about 10 degrees is associated with the moon Methone. The material in the arc is believed to represent dust ejected from Methone by micrometeoroid impacts. The confinement of the dust within the arc is attributable to a 14:15 resonance with Mimas (similar to the mechanism of confinement of the arc within the G ring). Under the influence of the same resonance, Methone librates back and forth in its orbit with an amplitude of 5° of longitude.>>

---

<<Enceladus is the sixth-largest of the moons of Saturn. It was discovered in 1789 by William Herschel. Until the two Voyager spacecraft passed near it in the early 1980s very little was known about this small moon besides the identification of water ice on its surface. The Voyagers showed that the diameter of Enceladus is only 500 kilometers, about a tenth of that of Saturn's largest moon, Titan, and that it reflects almost all of the sunlight that strikes it. Voyager 1 found that Enceladus orbited in the densest part of Saturn's diffuse E ring, indicating a possible association between the two, while Voyager 2 revealed that despite the moon's small size, it had a wide range of terrains ranging from old, heavily cratered surfaces to young, tectonically deformed terrain, with some regions with surface ages as young as 100 million years old.>>

[ta152h0]

If I recall correctly, I remnember an astronaut aboard the ISS toying around with a droplet of water that did exhibit this egg shape, until the intrepid one suddenly gulped it up.

[neufer]

Click to play embedded YouTube video.

If I recall correctly, I remnember an astronaut aboard the ISS toying around with a droplet of water that did exhibit this egg shape, until the intrepid one suddenly gulped it up.

[saturno2]

2 days with images of Saturn, my favorite planet.
I think that Methone is a boulder, has been polished over time.
Meteorites not make a dent !!!

[jedireez]

maybe an dense atmosphere...

[BDanielMayfield]

(1) Methone is so small, it’s unlikely to be hit. There must be many areas of a like size on bodies around the solar system that, given the random nature of collisions, have escaped any impacts.

Probably not. We've never seen any other body without evidence of collision, even small asteroids. Statistically, anything more than a few million years old is likely to be hit. So unless this body is unaccountably new, it should have been hit many times.

(2) We’re used to thinking in terms just of gravity when it comes to the shapes of these bodies, but in Methone’s case I suspect that the other long range attractive force, electromagnetism, might be at work here. Orbiting so close to a very active Saturn, couldn’t this moonlet be getting charged as it passes through Saturn’s magnetic field?

Bodies do not develop significant charges, but their surface dust/ice/regolith can become charged, which affects its behavior (this has been seen on the Moon, for instance).

Ok, Chris. So you think I laid an egg or two with my Methone ideas. Well maybe so, but I still think that this moonlet is relatively fragile (egg-like in more than just shape). If it had ever been hit by anything with substantial momentum it could have easily been destroyed. (Think snowball versus bullet.) Since it hasn’t been destroyed yet maybe it isn’t that old (a freshly laid egg!) since as you point out anything old accumulates craters over time.

Another point, I think the thoughts about dust from this moonlet contributing to the E-ring largely have it backwards. If it is old, (likely, I agree) then it may indeed have craters, but these are being continually covered over by frost from the E-ring, whether it’s being attracted with an electromagnetic assist or not.

Bruce

[Chris Peterson]

Ok, Chris. So you think I laid an egg or two with my Methone ideas.

I wouldn't say that at all. The suggestions were reasonable... just wrong, I think.

Well maybe so, but I still think that this moonlet is relatively fragile (egg-like in more than just shape). If it had ever been hit by anything with substantial momentum it could have easily been destroyed. (Think snowball versus bullet.) Since it hasn’t been destroyed yet maybe it isn’t that old (a freshly laid egg!) since as you point out anything old accumulates craters over time.

It's hard to destroy something like this. The asteroids are proof of that. It's likely that this body, like many, is a fairly loose conglomeration of material. When hit, it can partly break up, but the pieces settle back together over time.

When I see smooth surfaces on bodies, I assume that some sort of resurfacing process is going on, not typically that it is a young object.

[ta152h0]

when I see smooth surfaces on a body, I am thinking Lagoinha beach in Sao Paulo state, Brazil. Oh wauit a minute, you are talking about Methjone. It has to be made of aerogel.