Daphnis (moon)
Cassini Imaging Science Team
Daphnis ( Saturn XXXV) is the third and one of the smaller of the 62 known moons of the planet Saturn. He is the shepherd moon of the Keeler gap and the outer two moons within the A-ring of Saturn's rings.
- 3.1 size
- 3.2 Internal structure
- 3.3 Surface
Discovery and designation
Daphnis was discovered on 6 May 2005 on the images from Cassini Imaging Science Team on the Cassini mission. The recordings of the outer A- ring were formed on 1 May 2005 for 16 minutes in a time-lapse sequence with 0.18 seconds exposure time.
The existence of a moon within the Keeler gap was predicted before the recordings. Due to gravitational disturbances in the ring system generated wave pattern on the outer edge of the gap pointed to a possible moon and the position of Daphnis. The waves at the inner edge hurried ahead of the orbit of Daphnis, while lying on the outer edge behind him. The reason for this is the different relative velocities of the ring particles.
Later Daphnis was found on 32 images of the F- ring of 13 April 2005, which were made during 18 minutes. On two other high-resolution images (3.54 km / pixel) of 2 May 2005, the diameter of the moon was finally resolved in detail.
The discovery was given on 6 May 2005 by Carolyn C. Porco known, the director of the Imaging Science Team of the Cassini mission; the moon first received the provisional designation S/2005 S 1
On 17 July 2006 the moon was named after the shepherd Daphnis and poets from Greek mythology. Daphnis was the son of Hermes and a nymph and a descendant of the Titans, according to which the largest of Saturn 's moons are named. Daphnis went blind due to a betrayal by a nymph. He wanted to defeat Eros by would not give his awakened by Aphrodite love to Xenea. In addition, Pan fell in love with Daphnis and taught him how to play the panflute at. By his blindness he fell from a cliff and was turned down in the rock.
The name comes from the laurel grove where Daphnis was born and abandoned by his mother. Daphnis and Pan, the only other shepherd moon of Saturn's main rings within, were both named after mythological figures that are associated with shepherds.
The provisional designation S/2005 S 1 corresponds to the classification of the International Astronomical Union ( IAU).
Web properties
Orbit
Daphnis orbits Saturn on a prograde, nearly perfectly circular orbit at an average distance of approximately 136,505.5 kilometers (about 2.265 Saturn radii ) from its center, ie 73,237 km above the cloud tops. The orbital eccentricity of 0.0000331, the orbit is inclined 0.0036 ° relative to the equator of Saturn, that is almost exactly in the equatorial plane of the planet. Due to the small eccentricity varies the distance to Saturn were only about 10 km, due to the low inclination in height by only about 17 km.
The orbit of the next inner moon Pan is in the middle distance 2921 km of Daphnis ' orbit, the distance of the path of the next outer Moon Atlas is an average of 1165 km.
Daphnis orbits Saturn in 14 hours, 15 minutes and 28.5 seconds. This roughly corresponds to the orbital period of Uranus moon Cupid. Daphnis required for a round about 27 minutes longer than the neighboring inner pan.
The moon runs in the 42- km-wide named after James Edward Keeler Keeler Gap of the A ring, which is only about 270 km from the outer edge of the A ring, around the planet. It is effective as a shepherd moon and causes with his gravity that the Keeler gap remains largely free of ring particles. Scientists have observed no perturbations by further outward current moons.
The moon orbits Saturn within a critical distance, the so-called Roche limit, which would bring a larger moon in this field to shatter. Probably Daphnis is saved from this fate only because of its small size or a loose internal structure.
Rotation
The rotation period is equal to the orbital period and Daphnis has with how the Earth's moon, a synchronous rotation, which thus also takes place within 14 hours, 15 minutes and 28.5 seconds.
Physical Properties
Size
Daphnis has an average diameter of 7.8 km. Daphnis appears as an irregularly shaped elongated object with dimensions of 9 × 9 × 6 km, with the longitudinal axis is aligned with Saturn on the images of the Cassini-Huygens probe.
Internal construction
The mean density of Daphnis is 0.34 g / cm ³ by far lower than that of the earth and even much lower than the density of Saturn; she is so low that Daphnis would float on water. This indicates that the moon is composed mainly of water ice.
That Daphnis orbits Saturn within the Roche limit, indicates that he either has a very strong internal structure, or that he belongs to the so-called Rubble Piles, which, due to the relatively weak gravitational inside cavities. Due to the extremely low mean density, the latter hypothesis is more likely.
Surface
Daphnis has a high albedo of an estimated 0.5, which means that it has a bright surface, which reflects 50 % of the incident sunlight. The average surface temperature of Daphnis is estimated to be about -195 ° C ( 78 K).
Research
Due to the small size and the apparent magnitude of 24.0 m ( 1:2000000000 that of the central planet is ) as well as the close proximity to Saturn and the fact that he is outshone by this is, Daphnis with ground-based telescopes not identify.
Daphnis has so far been visited by three spacecraft, notably by the flyby probes Voyager 1 on 12 November 1980 and Voyager 2 on August 1981 and the Saturn orbiter Cassini, orbiting Saturn since July 2004 25. Daphnis was repeatedly taken by Cassini targeted so that its orbital parameters are now fairly well known. The next flyby of Cassini occurred on July 5, 2010, when the spacecraft Daphnis happened at a distance of 72,816 km.