Psamathe (moon)

From testwiki
Jump to navigation Jump to search

Template:Short description Template:Use dmy dates Template:Infobox planet

Psamathe (Template:IPAc-en), also known as Neptune X and previously as S/2003 N 1, is an irregular moon of Neptune. It was discovered by Scott Sheppard, David Jewitt, and Jan Kleyna at Mauna Kea Observatory on 29 August 2003. Named after one of the Nereids from Greek mythology, Psamathe follows a distant, highly eccentric, and highly inclined orbit with an average orbital period of about 25 Earth years. Like the majority of irregular moons, Psamathe's orbit is retrograde, meaning it revolves around Neptune in the opposite direction to the planet's orbit around the Sun.

Psamathe is estimated to have a diameter between Template:Cvt, though most of its physical properties are unknown. Psamathe shares similar orbital characteristics with Neptune's two outermost moons, Neso and S/2021 N 1, which suggests they originated from the collisional breakup of a once-larger moon of Neptune billions of years ago.

Discovery

Psamathe was discovered by astronomers Scott Sheppard, David Jewitt, and Jan Kleyna on 29 August 2003.[1][2] At the time, the team was searching for distant moons of Neptune, using the Template:Convert Subaru Telescope at Mauna Kea Observatory, Hawaii.[3] Their search strategy involved using the telescope's camera to photograph patches of the sky around Neptune at roughly 33-minute intervals, which revealed the planet's moons as faint, slowly-moving points of light.[3]Template:Rp The team detected Psamathe in images taken on 29 and 30 August 2003, and reported their discovery to the Minor Planet Center (MPC) on 1 September.[4]

Sometime later on 1 September 2003, Matthew Holman reported the identification of a candidate moon of Neptune in observations from 19 August 2003 and 11 August 2001.[4] These observations came from an earlier search for Neptunian moons, which was led by Holman at Cerro Tololo Inter-American Observatory, Chile.[5]Template:Rp Brian G. Marsden of the MPC recognized that Holman's moon candidate might turn out to be Psamathe, which became confirmed after Holman uncovered more observations from August 2002 and July 2003.[4] With over two years of recorded observations, the MPC announced the discovery of Psamathe on 3 September 2003.[6][4]

Name

When the discovery of Psamathe was announced, it was given the temporary provisional designation "S/2003 N 1" by the Minor Planet Center.[6] Sheppard's team named the moon "Psamathe" in a 2006 paper describing its discovery,[3] although the name did not receive official approval by the International Astronomical Union (IAU) until 3 February 2007.[7] The moon was named after Psamathe (Ψαμάθη), one of the fifty Nereids or daughters of Nereus and Doris from Greek mythology.[1][8] The moon was given a name ending with "e" to indicate its retrograde orbit, in a similar fashion to the naming convention for Jupiter's irregular moons.[9]Template:Rp When the name was approved, the IAU gave Psamathe its Roman numeral designation "Neptune X".[7]

Orbit

Psamathe is an irregular moon of Neptune, meaning it follows a distant, highly eccentric, and highly inclined orbit around the planet.[10]Template:Efn Like the majority of irregular moons, Psamathe's orbit is retrograde, meaning it revolves around Neptune in the opposite direction to the planet's orbit around the Sun.[11]Template:Rp Due to its great distance from Neptune, the moon is strongly affected by the Sun's gravity, which causes substantial long-term variations in its orbit.[10]Template:Rp For this reason, Psamathe's orbit is better described by proper orbital elements, which are calculated by averaging out its perturbed orbit over an extended period of time.[11]Template:Rp

Over a 10,000-year time span, Psamathe's semi-major axis from Neptune varies from Template:Convert, averaging about Template:Convert.Template:Efn In terms of average semi-major axis, Psamathe is the third-outermost known moon of Neptune, behind Neso and S/2021 N 1.[12] At its average distance, Psamathe occupies 41% of Neptune's Hill radius,Template:Efn placing it just over halfway to the outer limit at which retrograde moons can stably orbit the planet.Template:Efn

On average, Psamathe takes about Template:Convert to complete one orbit around Neptune, though perturbations by the Sun can vary the orbital period from Template:Convert.Template:Efn While Psamathe's orbit has an average eccentricity of 0.41 and an average inclination of 128° with respect to the ecliptic, both values vary substantially due to the Sun's perturbations.[11] The moon's eccentricity ranges from 0.07 to 0.88, while its inclination ranges from 117° to 148°.Template:Efn

Approximate dates and distances of
Psamathe's periapsis and apoapsis
Periapsis Apoapsis
DateTemplate:Efn
(UTC) 		Distance DateTemplate:Efn
(UTC) 		Distance
May 1988[13] Template:Convert Sep 1999[14] Template:Convert
Feb 2014[15] Template:Convert Jul 2026[16] Template:Convert
Nov 2039[17] Template:Convert Dec 2051[18] Template:Convert

Since Psamathe follows an eccentric orbit, its distance from Neptune varies by several tens of millions of km as it moves from periapsis to apoapsis in its orbit.[3] However, because of its variable semi-major axis and eccentricity, its periapsis and apoapsis distances can change.[19]Template:Efn For example, in May 1988, Psamathe passed periapsis at a distance of Template:Convert,[13] whereas in October 2014, Psamathe passed periapsis at a farther distance of Template:Convert.[15] Likewise, Psamathe passed apoapsis in September 1999 at a distance of Template:Convert,[14] whereas Psamathe passed apoapsis at a closer distance of Template:Convert.[16]

Psamathe is not in an orbital resonance, unlike its neighbors Neso and S/2021 N 1.[20]Template:Rp Over a period of 4.5 billion years, Psamathe has 1.3% chance of colliding with Nereid, one of Neptune's largest irregular moons.[5]Template:Rp Its orbit exhibits both apsidal and nodal precession with periods of 1,484 and 1,333 years, respectively.[12] Psamathe has a longer apsidal precession period than its nodal precession period, which causes its longitude of pericenter (ϖ) to precess in the opposite direction from its orbital motion.[10]Template:Rp This behavior makes Psamathe a "reverse circulator".[10]Template:Rp

A graphic showing the orbit of Psamathe (displayed as red) and other irregular moons of Neptune (displayed as gray) as seen from three different views
The orbit of Psamathe (red) and other irregular moons of Neptune (gray), as seen from three different views. These moons orbit far beyond Triton and Nereid, Neptune's largest moons (colored magenta). Psamathe's orbit does not form a closed ellipse because it is highly perturbed.

Group and origin

Psamathe shares similar orbital characteristics with two other Neptunian irregular moons, Neso and S/2021 N 1.[20] Together, they form the Neso group, a family of retrograde irregular moons of which Neso is the largest member.[20] Psamathe was first suspected to be related to Neso in 2004.[5]Template:Rp but it was not confirmed until the discovery of S/2021 N 1 as a third member in 2024.[20][21]Template:Efn The group is predicted to contain many more smaller members, though they are too faint to be detected with current technology.[21][20]Template:Rp

Because of their similar orbits, the moons of the Neso group have low mutual dispersion velocities of around Template:Val.[20]Template:Rp The dispersion velocity is the speed needed to eject a fragment from a parent body onto its current orbit.[20]Template:Rp For fragments produced in collisions, their dispersion velocities are typically below Template:Val, comparable to the parent body's escape velocity.[20]Template:Rp This suggests that the Neso group is a collisional family,[20]Template:Rp formed by the destruction of a once-larger parent body by a collision with an asteroid or comet billions of years ago.[21][1] The parent body was probably an irregular moon that was gravitationally captured by Neptune during the Solar System's early history, during or shortly after the formation of the planets.[20]Template:Rp

If the Neso group is a collisional family, then its members are expected to share similar surface characteristics, such as color. However, this remains yet to be verified, as Neso is the only member with a known surface color Template:Asof.[11]Template:Rp

  • Irregular moons of all four giant planets, plotted by average distance from their planet (semi-major axis in Hill radii) and orbital inclination (degrees with respect to ecliptic). The Neso group is the cluster of blue diamonds on the upper right, labeled in blue. Data is as of February 2024.
    Irregular moons of all four giant planets, plotted by average distance from their planet (semi-major axis in Hill radii) and orbital inclination (degrees with respect to ecliptic). The Neso group is the cluster of retrograde moons labeled in blue.
  • Evolution of Psamathe's orbital eccentricity (blue), inclination (orange), argument of pericenter (green), and periapsis distance from Neptune (red) from 1600 to 2400
    Evolution of Psamathe's orbital eccentricity (blue), inclination (orange), argument of pericenter (green), and periapsis distance from Neptune (red) from 1600 to 2400
  • Sped-up simulation of Psamathe's orbit around Neptune, from 1600 to 2400. Due to perturbations by the Sun, the orbit precesses and changes shape.
    Sped-up simulation of Psamathe's orbit around Neptune, from 1600 to 2400. Due to perturbations by the Sun, the orbit precesses and changes shape.

Physical characteristics

Little is known about Psamathe's physical characteristics.[1] In red light (R band), Psamathe has an apparent magnitude of about 25, making it extremely dim.[5][3] Because of this, Psamathe and most of Neptune's irregular moons can only be observed through long-exposure imaging with large optical telescopes.[11]Template:Rp

The diameter of Psamathe has not been directly measured, although it can be indirectly estimated from its brightness and an assumed geometric albedo.[3]Template:Rp Assuming a geometric albedo of 0.04, Psamathe's diameter would be about Template:Cvt.[3]Template:Rp For a higher albedo of 0.06, Psamathe would have a diameter of Template:Cvt.[5]Template:Rp The color of Psamathe is unknown.[11]Template:Rp If it shares a common origin with Neso, then both moons are expected to share similar colors.[11]Template:Rp

See also

Template:Portal Other Solar System moons discovered by Sheppard and Jewitt with the Subaru Telescope in 2003:

  • Narvi – moon of Saturn
  • Margaret – moon of Uranus (discovered on the same date as Psamathe)[2]

Notes

Template:Notelist

References

  1. ↑ Template:Cite web Cite error: <ref> tag with name "JPL-disc" defined in <references> is not used in prior text.
  2. ↑ Template:Cite web Cite error: <ref> tag with name "apsis-eq" defined in <references> is not used in prior text.
  3. ↑ Template:Cite web Cite error: <ref> tag with name "MPC-Explorer" defined in <references> is not used in prior text.
  4. ↑ Template:Cite web Check "Just the following Neptunian outer irregular satellites", then check "Neptune 10 (Psamathe)", then go to "Output Format(s) Required" and check "I require Orbital Elements", and then click the gray "Get Information" button. Cite error: <ref> tag with name "MPC-NatSats" defined in <references> is not used in prior text.
  5. ↑ Template:Cite web Cite error: <ref> tag with name "logeion" defined in <references> is not used in prior text.
  6. ↑ 1.0 1.1 1.2 1.3 Template:Cite web
  7. ↑ 2.0 2.1 Template:Cite web
  8. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Template:Cite journal
  9. ↑ 4.0 4.1 4.2 4.3 Template:Cite journal
  10. ↑ 5.0 5.1 5.2 5.3 5.4 Template:Cite journal
  11. ↑ 6.0 6.1 Template:Cite journal
  12. ↑ 7.0 7.1 Template:Cite journal
  13. ↑ Template:Cite book
  14. ↑ Template:Cite book
  15. ↑ 10.0 10.1 10.2 10.3 Template:Cite journal
  16. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 Template:Cite journal
  17. ↑ 12.0 12.1 Template:Cite web
  18. ↑ 13.0 13.1 Template:Cite web Periapsis occurs when Psamathe's radial velocity (deldot) changes from negative to positive (changes from moving toward to away from Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  19. ↑ 14.0 14.1 Template:Cite web Apoapsis occurs when Psamathe's radial velocity (deldot) changes from positive to negative (changes from moving away to moving toward Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  20. ↑ 15.0 15.1 Template:Cite web Periapsis occurs when Psamathe's radial velocity (deldot) changes from negative to positive (changes from moving toward to away from Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  21. ↑ 16.0 16.1 Template:Cite web Apoapsis occurs when Psamathe's radial velocity (deldot) changes from positive to negative (changes from moving away to moving toward Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  22. ↑ Template:Cite web Periapsis occurs when Psamathe's radial velocity (deldot) changes from negative to positive (changes from moving toward to away from Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  23. ↑ Template:Cite web Apoapsis occurs when Psamathe's radial velocity (deldot) changes from positive to negative (changes from moving away to moving toward Neptune). Psamathe's radial distance (delta) from Neptune is expressed in astronomical units (AU).
  24. ↑ Template:Cite web Ephemeris Type: Osculating Elements, Center: 500@8 (Neptune Barycenter), Timestep: 1 year, Units: km and days.
    Key: A = semi-major axis (km), PR = orbital period ("period of revolution"; days), EC = eccentricity, IN = inclination with respect to ecliptic (°), QR = periapsis distance (km), AD = apoapsis distance (km)
  25. ↑ 20.00 20.01 20.02 20.03 20.04 20.05 20.06 20.07 20.08 20.09 Template:Cite journal
  26. ↑ 21.0 21.1 21.2 Template:Cite web

Template:Commons category

Template:Moons of Neptune Template:Neptune Template:Portal bar

Retrieved from "https://en.wiki.beta.math.wmflabs.org/w/index.php?title=Psamathe_(moon)&oldid=7679"