zbvhs wrote:Note the large crater at the top of the side facing us: Material seems to be "falling down" and collecting on the "bottom" wall of the crater. Why do you suppose that is? Gravity gradient?
The lighter albedo seems to be solid rock while the darker albedo seems to be dust or loose material that has found it's way somehow to the lower spots on Epimetheus.
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A good rule of thumb is that both gravity & escape velocity
generally scale directly with the satellite diameter:
Earth's moon diameter = 3500 km
moon gravity = 1/6 (earth's)
moon escape velocity = 2400 m/sec
Epimetheus diameter = 115 km __________ [ = 3500/30 km ]
Epimetheus gravity = 1/180 (earth's)___ [ = (1/6)/30]
Epimetheus escape velocity = 80 m/sec ______ [ = 2400/30 m/sec]
A major league pitcher would weigh 1 pound
and be able to throw a baseball into Saturn orbit
[; albeit that the ball would eventually land
back on Epimetheus (or it's brother Janus)
due to intersecting orbits].
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http://en.wikipedia.org/wiki/Epimetheus_%28mythology%29
<<In Greek mythology, Epimetheus (Greek: Ἐπιμηθεύς) ("hindsight", literally "hind-thought") was the brother of Prometheus ("foresight", literally "fore-thought"), a pair of Titans who "acted as representatives of mankind" . They were the inseparable sons of Iapetus, who in other contexts was the father of Atlas. While Prometheus is characterized as ingenious and clever, Epimetheus is depicted as foolish.
According to Plato's use of the old myth in his Protagoras, where he puts it in the mouth of the old philosopher, the twin Titans were entrusted with distributing the traits among the newly-created animals; Epimetheus was responsible for giving a positive trait to every animal, but when it was time to give man a positive trait, lacking foresight he found that there was nothing left. His brother Prometheus then stole fire from Zeus and gave it to man, and was punished for his impiety by being strapped to a mountain top and visited by an eagle who ate his liver every day. Since Prometheus was a Titan and therefore practically immortal, his liver grew back every day, so the eagle had to come back, keeping Prometheus in constant pain. As further punishment, Zeus created Pandora, the first woman, for Epimetheus, knowing that he would fall in love with her despite the warnings of his brother, the embodiment of foresight, who told him never to accept a gift from the Olympian gods, with whom the primordial Titans, sprung from Mother Earth, were ever at odds.
According to Hesiod Epimetheus and Pandora were married. Pandora had been given a covered pithos, or storage jar, by Hermes and was instructed never to open it. However, Hermes also gave her curiosity, so she opened it anyway, releasing all the misfortunes of mankind. She shut it in time to keep one thing in reserve: hope. Thus mankind always has hope in times of evil. The daughter of Epimetheus and Pandora was Pyrrha, who married Deucalion and was one of the two who survived the deluge.>>
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[quote="zbvhs"]Note the large crater at the top of the side facing us: Material seems to be "falling down" and collecting on the "bottom" wall of the crater. Why do you suppose that is? Gravity gradient?[/quote]
The lighter albedo seems to be solid rock while the darker albedo seems to be dust or loose material that has found it's way somehow to the lower spots on Epimetheus.
-----------------------------------------------
A good rule of thumb is that both gravity & escape velocity
generally scale directly with the satellite diameter:
Earth's moon diameter = 3500 km
moon gravity = 1/6 (earth's)
moon escape velocity = 2400 m/sec
Epimetheus diameter = 115 km __________ [ = 3500/30 km ]
Epimetheus gravity = 1/180 (earth's)___ [ = (1/6)/30]
Epimetheus escape velocity = 80 m/sec ______ [ = 2400/30 m/sec]
A major league pitcher would weigh 1 pound
and be able to throw a baseball into Saturn orbit
[; albeit that the ball would eventually land
back on Epimetheus (or it's brother Janus)
due to intersecting orbits].
-----------------------------------------------
http://en.wikipedia.org/wiki/Epimetheus_%28mythology%29
<<In Greek mythology, Epimetheus (Greek: Ἐπιμηθεύς) ("hindsight", literally "hind-thought") was the brother of Prometheus ("foresight", literally "fore-thought"), a pair of Titans who "acted as representatives of mankind" . They were the inseparable sons of Iapetus, who in other contexts was the father of Atlas. While Prometheus is characterized as ingenious and clever, Epimetheus is depicted as foolish.
According to Plato's use of the old myth in his Protagoras, where he puts it in the mouth of the old philosopher, the twin Titans were entrusted with distributing the traits among the newly-created animals; Epimetheus was responsible for giving a positive trait to every animal, but when it was time to give man a positive trait, lacking foresight he found that there was nothing left. His brother Prometheus then stole fire from Zeus and gave it to man, and was punished for his impiety by being strapped to a mountain top and visited by an eagle who ate his liver every day. Since Prometheus was a Titan and therefore practically immortal, his liver grew back every day, so the eagle had to come back, keeping Prometheus in constant pain. As further punishment, Zeus created Pandora, the first woman, for Epimetheus, knowing that he would fall in love with her despite the warnings of his brother, the embodiment of foresight, who told him never to accept a gift from the Olympian gods, with whom the primordial Titans, sprung from Mother Earth, were ever at odds.
According to Hesiod Epimetheus and Pandora were married. Pandora had been given a covered pithos, or storage jar, by Hermes and was instructed never to open it. However, Hermes also gave her curiosity, so she opened it anyway, releasing all the misfortunes of mankind. She shut it in time to keep one thing in reserve: hope. Thus mankind always has hope in times of evil. The daughter of Epimetheus and Pandora was Pyrrha, who married Deucalion and was one of the two who survived the deluge.>>
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