by neufer » Thu Sep 03, 2009 9:48 am
http://apod.nasa.gov/apod/ap090903.html
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http://en.wikipedia.org/wiki/Neptune wrote:
<<Neptune has 13 known moons. The largest by far, comprising more than 99.5 percent of the mass in orbit around Neptune and the only one massive enough to be spheroidal, is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, indicating that it was captured rather than forming in place; it probably was once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiraling inward because of tidal acceleration and eventually will be torn apart, in about 3.6 billion years, when it reaches the Roche limit. In 1989, Triton was the coldest object that had yet been measured in the solar system, with estimated temperatures of −235 °C (38 K).
Neptune's second known satellite (by order of discovery), the irregular moon Nereid, has one of the most eccentric orbits of any satellite in the solar system. The eccentricity of 0.7512 gives it an apoapsis that is seven times its periapsis distance from Neptune.
From July to September 1989, Voyager 2 discovered six new Neptunian moons. Of these, the irregularly shaped Proteus is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity. Although the second-most-massive Neptunian moon, it is only one-quarter of one percent the mass of Triton. Neptune's innermost four moons—Naiad, Thalassa, Despina and Galatea—orbit close enough to be within Neptune's rings. The next-farthest out, Larissa was originally discovered in 1981 when it had occulted a star. This occultation had been attributed to ring arcs, but when Voyager 2 observed Neptune in 1989, it was found to have been caused by the moon. Five new irregular moons discovered between 2002 and 2003 were announced in 2004. As Neptune was the Roman god of the sea, the planet's moons have been named after lesser sea gods.>>
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http://en.wikipedia.org/wiki/Naiad_(moon) wrote:
<<Naiad (pronounced /ˈneɪəd/ NAY-əd, /ˈnaɪəd/ NYE-əd, or as in Greek Ναϊάδ-ες), also known as Neptune III, is the innermost satellite of Neptune named after the Naiads of Greek legend.
Naiad was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated S/1989 N 6. Naiad is irregularly shaped and probably has not been modified by any internal geological processes after its formation. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Naiad orbits about 23,500 km above Neptune's cloud tops. Since this is below the synchronous orbit radius, its orbit is slowly decaying due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching. Naiad orbits Neptune well within its fluid Roche limit, and its density is expected to be low enough that it may be very close to its actual Roche limit already.
Since the Voyager 2 flyby, the Neptune system has been extensively studied from ground-based observatories and the Hubble Space Telescope as well. In 2002-03 Keck telescope observed the system using adaptive optics and detected easily the largest four inner satellites. Thalassa was found with some image processing, but Naiad was not located. Hubble has the ability to detect all the known satellites and possible new satellites even dimmer than Voyager 2. Still, Naiad has not been found. It is suspected that this is due to considerable errors in Naiad's ephemeris.
Orbital characteristics
Semi-major axis 48 227 ± 1 km
Eccentricity 0.0004 ± 0.0003
Orbital period 0.2943958 ± 0.0000002 d
Inclination 4.75 ± 0.03° (to Neptune equator)
Physical characteristics
Dimensions 96×60×52 km
Mean radius 33 ± 3 km
Mass ~1.9 × 10^17 kg
(based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.07
Surface temp. ~51 K mean (estimate)
Atmosphere none>>
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http://en.wikipedia.org/wiki/Thalassa_(moon) wrote:
<<Thalassa (pronounced /θəˈlæsə/ thə-LASS-ə, or as in Greek Θάλασσα), also known as Neptune IV, is the second innermost satellite of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea".
Thalassa was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. Thalassa is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit. Unusually for irregular bodies, it appears to be roughly disk-shaped.
Since the Thalassian orbit is below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching. Relatively soon after, the spreading debris may impinge upon Despina's orbit.
Orbital characteristics
Semi-major axis 50 075 ± 1 km
Eccentricity 0.0002 ± 0.0002
Orbital period 0.31148444 ± 0.00000006 d
Inclination 0.21 ± 0.02° (to Neptune equator)
Physical characteristics
Dimensions 108×100×52 km
Mean radius 41 ± 3 km
Mass ~3.5 × 10^17 kg
(based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.09
Surface temp. ~51 K mean (estimate)
Atmosphere none>>
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http://en.wikipedia.org/wiki/Despina_(moon) wrote:
<<Despina (pronounced /dɨˈspiːnə/ dis-PEE-nə, sometimes /dɨˈspaɪnə/ dis-PYE-nə, or as in Latin Despœna, Greek Δέσποινα), also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter.
Despina as seen by Voyager 2 (smeared horizontally)
Despina was discovered in late July, 1989 from the images taken by the Voyager 2 probe. It was given the temporary designation S/1989 N 3. Despina is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Despina's orbit lies close to but outside of the orbit of Thalassa and just inside the Le Verrier ring. As it is also below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
Orbital characteristics
Semi-major axis 52 526 ± 1 km
Eccentricity 0.0002 ± 0.0002
Orbital period 0.33465551 ± 0.00000001 d
Inclination 0.216 ± 0.014° (to Neptune equator)
Physical characteristics
Dimensions 180×148×128 km
Mean radius 75 ± 3 km
Mass ~2.1 × 10^18 kg (based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.09
Surface temp. ~51 K mean (estimate)
Atmosphere none>>
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http://en.wikipedia.org/wiki/Galatea_(moon) wrote:
Galatea (pronounced /ˈɡæləˈtiːə/ GAL-ə-TEE-ə, or as in Greek Γαλάτεια), also known as Neptune VI, is the fourth closest inner satellite of Neptune. It is named after Galatea, one of the Nereids of Greek legend.
Galatea was discovered in late July, 1989 from the images taken by the Voyager 2 probe. It is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Galatea's orbit lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
Galatea appears to be a shepherd moon for the Adams ring that is 1000 km outside its orbit. Resonances with Galatea in the ratio 42:43 are also considered the most likely mechanism for confining the unique ring arcs that exist in this ring. Galatea's mass has been estimated based on the radial perturbations it induces on the ring.
Orbital characteristics
Semi-major axis 61 953 ± 1 km
Eccentricity 0.00004 ± 0.00009
Orbital period 0.42874431 ± 0.00000001 d
Inclination 0.052 ± 0.011° (to Neptune equator)
Physical characteristics
Dimensions 204×184×144 km (±~10 km)
Mean radius 88 ± 4 km
Mass 2.12 ± 0.08 × 10^18 kg[6]
Mean density 0.75 ± 0.1 g/cm3
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.08
Surface temp. ~51 K mean (estimate)
Atmosphere none>>
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http://antwrp.gsfc.nasa.gov/apod/ap951104.html wrote:
Explanation: Proteus is the second largest moon of Neptune behind the mysterious Triton. Proteus was discovered only in 1982 by the Voyager 2 spacecraft. This is unusual since Neptune has a smaller moon - Nereid - which was discovered 33 years earlier from Earth. The reason Proteus was not discovered sooner is that its surface is very dark and it orbits much closer to Neptune. Proteus has an odd box-like shape and were it even slightly more massive, its own gravity would cause it to reform itself into a sphere.
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http://en.wikipedia.org/wiki/Proteus_(moon) wrote:
<<Proteus (pronounced /ˈproʊtiəs/, or as in Greek Πρωτεύς), also known as Neptune VIII, is the second largest Neptunian moon, and Neptune's largest inner satellite. It is the largest known non-spherical moon in the solar system. It is named after Proteus, the shape-changing sea god of Greek mythology.
Map of Proteus
Proteus was discovered from the images taken by Voyager 2 probe during the Neptune flyby in 1989. Proteus is more than 400 kilometres in diameter, larger than Nereid, another moon of Neptune. However, it was not discovered by Earth-based telescopes because it is so close to the planet that it is lost in the glare of reflected sunlight.
Proteus is very cratered, showing no sign of any geological modification. It is irregularly shaped; scientists believe Proteus is about as large as a body of its density can be without being pulled into a spherical shape by its own gravity.[8] Saturn's moon Mimas has a more spherical shape due to a lower density, despite being less massive than Proteus.
Orbital characteristics
Periapsis 117,584 ± 10 km
Apoapsis 117,709 ± 10 km
Semi-major axis 117,647 ± 1 km (0.00079 AU)
Eccentricity 0.00053 ± 0.00009
Orbital period 1.12231477 ± 0.00000002 d
Average orbital speed 7.623 km/s
Inclination 0.524° (to Neptune equator)
Physical characteristics
Dimensions 440×416×404 km (± ~15 km)
Mean radius 210 ± 7 km[4]
Volume 3.4 ± 0.4 × 107km³[5]
Mass ~5.0 × 10^19 kg (estimate)
Mean density ~1.3 g/cm³ (estimate)
Equatorial surface gravity ~0.06 m/s2 (0.006 g)
Escape velocity ~0.16 km/s
Rotation period synchronous
Axial tilt zero
Albedo 0.096
Temperature ~51 K mean (estimate)
Apparent magnitude 19.7>>
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[b] http://apod.nasa.gov/apod/ap090903.html[/b]
--------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Neptune"]
<<Neptune has 13 known moons. The largest by far, comprising more than 99.5 percent of the mass in orbit around Neptune and the only one massive enough to be spheroidal, is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, indicating that it was captured rather than forming in place; it probably was once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiraling inward because of tidal acceleration and eventually will be torn apart, in about 3.6 billion years, when it reaches the Roche limit. In 1989, Triton was the coldest object that had yet been measured in the solar system, with estimated temperatures of −235 °C (38 K).
Neptune's second known satellite (by order of discovery), the irregular moon Nereid, has one of the most eccentric orbits of any satellite in the solar system. The eccentricity of 0.7512 gives it an apoapsis that is seven times its periapsis distance from Neptune.
From July to September 1989, Voyager 2 discovered six new Neptunian moons. Of these, the irregularly shaped Proteus is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity. Although the second-most-massive Neptunian moon, it is only one-quarter of one percent the mass of Triton. Neptune's innermost four moons—Naiad, Thalassa, Despina and Galatea—orbit close enough to be within Neptune's rings. The next-farthest out, Larissa was originally discovered in 1981 when it had occulted a star. This occultation had been attributed to ring arcs, but when Voyager 2 observed Neptune in 1989, it was found to have been caused by the moon. Five new irregular moons discovered between 2002 and 2003 were announced in 2004. As Neptune was the Roman god of the sea, the planet's moons have been named after lesser sea gods.>>[/quote]--------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Naiad_(moon)"]
<<Naiad (pronounced /ˈneɪəd/ NAY-əd, /ˈnaɪəd/ NYE-əd, or as in Greek Ναϊάδ-ες), also known as Neptune III, is the innermost satellite of Neptune named after the Naiads of Greek legend.
Naiad was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated S/1989 N 6. Naiad is irregularly shaped and probably has not been modified by any internal geological processes after its formation. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Naiad orbits about 23,500 km above Neptune's cloud tops. Since this is below the synchronous orbit radius, its orbit is slowly decaying due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching. Naiad orbits Neptune well within its fluid Roche limit, and its density is expected to be low enough that it may be very close to its actual Roche limit already.
Since the Voyager 2 flyby, the Neptune system has been extensively studied from ground-based observatories and the Hubble Space Telescope as well. In 2002-03 Keck telescope observed the system using adaptive optics and detected easily the largest four inner satellites. Thalassa was found with some image processing, but Naiad was not located. Hubble has the ability to detect all the known satellites and possible new satellites even dimmer than Voyager 2. Still, Naiad has not been found. It is suspected that this is due to considerable errors in Naiad's ephemeris.
Orbital characteristics
Semi-major axis 48 227 ± 1 km
Eccentricity 0.0004 ± 0.0003
Orbital period 0.2943958 ± 0.0000002 d
Inclination 4.75 ± 0.03° (to Neptune equator)
Physical characteristics
Dimensions 96×60×52 km
Mean radius 33 ± 3 km
Mass ~1.9 × 10^17 kg
(based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.07
Surface temp. ~51 K mean (estimate)
Atmosphere none>>[/quote]-------------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Thalassa_(moon)"]
<<Thalassa (pronounced /θəˈlæsə/ thə-LASS-ə, or as in Greek Θάλασσα), also known as Neptune IV, is the second innermost satellite of Neptune. Thalassa was named after a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea".
Thalassa was discovered sometime before mid-September, 1989 from the images taken by the Voyager 2 probe. Thalassa is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit. Unusually for irregular bodies, it appears to be roughly disk-shaped.
Since the Thalassian orbit is below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching. Relatively soon after, the spreading debris may impinge upon Despina's orbit.
Orbital characteristics
Semi-major axis 50 075 ± 1 km
Eccentricity 0.0002 ± 0.0002
Orbital period 0.31148444 ± 0.00000006 d
Inclination 0.21 ± 0.02° (to Neptune equator)
Physical characteristics
Dimensions 108×100×52 km
Mean radius 41 ± 3 km
Mass ~3.5 × 10^17 kg
(based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.09
Surface temp. ~51 K mean (estimate)
Atmosphere none>>[/quote]-------------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Despina_(moon)"]
<<Despina (pronounced /dɨˈspiːnə/ dis-PEE-nə, sometimes /dɨˈspaɪnə/ dis-PYE-nə, or as in Latin Despœna, Greek Δέσποινα), also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter.
[size=150][b]Despina as seen by Voyager 2 (smeared horizontally)[/b][/size]
[img]http://upload.wikimedia.org/wikipedia/commons/5/5f/Despina.jpg[/img]
Despina was discovered in late July, 1989 from the images taken by the Voyager 2 probe. It was given the temporary designation S/1989 N 3. Despina is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Despina's orbit lies close to but outside of the orbit of Thalassa and just inside the Le Verrier ring. As it is also below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal decceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
Orbital characteristics
Semi-major axis 52 526 ± 1 km
Eccentricity 0.0002 ± 0.0002
Orbital period 0.33465551 ± 0.00000001 d
Inclination 0.216 ± 0.014° (to Neptune equator)
Physical characteristics
Dimensions 180×148×128 km
Mean radius 75 ± 3 km
Mass ~2.1 × 10^18 kg (based on assumed density)
Mean density ~1.2 g/cm3 (estimate)
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.09
Surface temp. ~51 K mean (estimate)
Atmosphere none>>[/quote]-----------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Galatea_(moon)"]
Galatea (pronounced /ˈɡæləˈtiːə/ GAL-ə-TEE-ə, or as in Greek Γαλάτεια), also known as Neptune VI, is the fourth closest inner satellite of Neptune. It is named after Galatea, one of the Nereids of Greek legend.
Galatea was discovered in late July, 1989 from the images taken by the Voyager 2 probe. It is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile re-accreted from fragments of Neptune's original satellites, which were smashed up by perturbations from Triton soon after that moon's capture into a very eccentric initial orbit.
Galatea's orbit lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration and may eventually impact Neptune's atmosphere, or break up into a planetary ring upon passing its Roche limit due to tidal stretching.
Galatea appears to be a shepherd moon for the Adams ring that is 1000 km outside its orbit. Resonances with Galatea in the ratio 42:43 are also considered the most likely mechanism for confining the unique ring arcs that exist in this ring. Galatea's mass has been estimated based on the radial perturbations it induces on the ring.
Orbital characteristics
Semi-major axis 61 953 ± 1 km
Eccentricity 0.00004 ± 0.00009
Orbital period 0.42874431 ± 0.00000001 d
Inclination 0.052 ± 0.011° (to Neptune equator)
Physical characteristics
Dimensions 204×184×144 km (±~10 km)
Mean radius 88 ± 4 km
Mass 2.12 ± 0.08 × 10^18 kg[6]
Mean density 0.75 ± 0.1 g/cm3
Rotation period assumed synchronous
Axial tilt ~zero presumably
Albedo (geometric) 0.08
Surface temp. ~51 K mean (estimate)
Atmosphere none>>[/quote]--------------------------------------------------------
[quote=" http://antwrp.gsfc.nasa.gov/apod/ap951104.html"]
Explanation: Proteus is the second largest moon of Neptune behind the mysterious Triton. Proteus was discovered only in 1982 by the Voyager 2 spacecraft. This is unusual since Neptune has a smaller moon - Nereid - which was discovered 33 years earlier from Earth. The reason Proteus was not discovered sooner is that its surface is very dark and it orbits much closer to Neptune. Proteus has an odd box-like shape and were it even slightly more massive, its own gravity would cause it to reform itself into a sphere. [/quote]--------------------------------------------------------
[quote=" http://en.wikipedia.org/wiki/Proteus_(moon)"]
<<Proteus (pronounced /ˈproʊtiəs/, or as in Greek Πρωτεύς), also known as Neptune VIII, is the second largest Neptunian moon, and Neptune's largest inner satellite. It is the largest known non-spherical moon in the solar system. It is named after Proteus, the shape-changing sea god of Greek mythology.
[size=150][b]Map of Proteus[/b][/size]
[img]http://upload.wikimedia.org/wikipedia/en/0/0a/Proteus_map_(Stooke).jpg[/img]
Proteus was discovered from the images taken by Voyager 2 probe during the Neptune flyby in 1989. Proteus is more than 400 kilometres in diameter, larger than Nereid, another moon of Neptune. However, it was not discovered by Earth-based telescopes because it is so close to the planet that it is lost in the glare of reflected sunlight.
Proteus is very cratered, showing no sign of any geological modification. It is irregularly shaped; scientists believe Proteus is about as large as a body of its density can be without being pulled into a spherical shape by its own gravity.[8] Saturn's moon Mimas has a more spherical shape due to a lower density, despite being less massive than Proteus.
Orbital characteristics
Periapsis 117,584 ± 10 km
Apoapsis 117,709 ± 10 km
Semi-major axis 117,647 ± 1 km (0.00079 AU)
Eccentricity 0.00053 ± 0.00009
Orbital period 1.12231477 ± 0.00000002 d
Average orbital speed 7.623 km/s
Inclination 0.524° (to Neptune equator)
Physical characteristics
Dimensions 440×416×404 km (± ~15 km)
Mean radius 210 ± 7 km[4]
Volume 3.4 ± 0.4 × 107km³[5]
Mass ~5.0 × 10^19 kg (estimate)
Mean density ~1.3 g/cm³ (estimate)
Equatorial surface gravity ~0.06 m/s2 (0.006 g)
Escape velocity ~0.16 km/s
Rotation period synchronous
Axial tilt zero
Albedo 0.096
Temperature ~51 K mean (estimate)
Apparent magnitude 19.7>>[/quote]---------------------------------------