Atlas (Moon)

Atlas
	Color photo taken by Cassini on 12 April 2017
Discovery
Discovered by	Terrile, Voyager 1
Discovery date	October, 1980
Designations
Designation	Saturn XV
Pronunciation	/ˈætləs/
Named after	Ἄτλας Ātlās
Alternative names	S/1980 S 28
Adjectives	Atlantean /ætlænˈtiːən/
Orbital characteristics
	Epoch December 31, 2003 (JD 2453005.5)
Mean orbit radius	137670±10 km
Eccentricity	0.0012
Orbital period	0.6016947883 d
Inclination	0.003°±0.004°
Satellite of	Saturn
Group	Outer shepherd moon of the A Ring
Physical characteristics
Dimensions	40.8 × 35.4 × 18.6 km; (± 0.2 × 0.4 × 0.6 km)
Mean diameter	29.8±0.4 km
Volume	13950±50 km3
Mass	(5.490±0.042)×1015 kg
Mean density	0.3935±0.0033 g/cm3
surface gravity	0.0001–0.0017 m/s2
escape velocity	0.006 km/s at longest axis; to 0.009 km/s at poles
Rotation period	synchronous
Axial tilt	zero
Albedo	0.4
Physics	≈ 81 K

Short description: Moon of Saturn

Atlas is an inner satellite of Saturn which was discovered by Richard Terrile in 1980 from Voyager photos and was designated S/1980 S 28.^[5] In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth.^[6] It is also designated Saturn XV.

Atlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a shepherd satellite for this ring. However, now it is known that the outer edge of the ring is instead maintained by a 7:6 orbital resonance with the larger but more distant moons Janus and Epimetheus.^[7] In 2004 a faint, thin ring, temporarily designated R/2004 S 1, was discovered in the Atlantean orbit.^[8]

High-resolution images taken in June 2005 by Cassini revealed Atlas to have a roughly spherical centre surrounded by a large, smooth equatorial ridge. The most likely explanation for this unusual and prominent structure is that ring material swept up by the moon accumulates on the moon, with a strong preference for the equator due to the ring's thinness. The size of the equatorial ridge is comparable with the expected Roche lobe of the moon, which means that for any additional particles impacting the equator, the centrifugal force will nearly overcome Atlas's tiny gravity, and they will probably be lost.^[7]

Atlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, leading to excursions in longitude of up to 600 km (~0.25°) away from the precessing Keplerian orbit with a rough period of about 3 years. Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.^[2]

Gallery

Atlas from above its south pole (June 12, 2007)
Atlas - Cassini
(June 8, 2005).
Atlas - A and F rings
(June 30, 2006).
Atlas near the A ring
(December 6, 2015).
Atlas near the F ring
(May 9, 2005).

Notes

↑ Calculated from the standard gravitational parameter GM = (3.664±0.028)×10⁻⁴ km³·s^–2 given by Lainey et al. (2023), divided by the gravitational constant G = 6.6743×10⁻² km³·kg^–1·s^–2.^[4]

References

Citations

↑ Atlantean (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=Atlantean (Subscription or UK public library membership required.)
↑ ^2.0 ^2.1 Spitale Jacobson et al. 2006.
↑ ^3.0 ^3.1 ^3.2 Thomas & Helfenstein 2020.
↑ ^4.0 ^4.1 ^4.2 Lainey et al. 2023.
↑ IAUC 3539.
↑ IAUC 3872.
↑ ^7.0 ^7.1 Lakdawalla 2007.
↑ IAUC 8401.

Sources

Green, Daniel W. E. (September 9, 2004). "S/2004 S 3, S/2004 S 4, and R/2004 S 1". IAU Circular 8401: 1. Bibcode: 2004IAUC.8401....1P. http://www.cbat.eps.harvard.edu/iauc/08400/08401.html. Retrieved 2011-12-30.
Lakdawalla, Emily (June 13, 2007). "Funny little Atlas". The Planetary Society weblog. http://www.planetary.org/blog/article/00001003/.
Marsden, Brian G. (November 13, 1980). "1980 S 28" (discovery). IAU Circular 3539: 2. Bibcode: 1980IAUC.3539....2M. http://www.cbat.eps.harvard.edu/iauc/03500/03539.html. Retrieved 2011-12-30.
Marsden, Brian G. (September 30, 1983). "Satellites of Jupiter and Saturn" (naming the moon). IAU Circular 3872. http://www.cbat.eps.harvard.edu/iauc/03800/03872.html. Retrieved 2011-12-30.
Spitale, J. N.; Jacobson, R. A.; Porco, C. C.; Owen, W. M. Jr. (2006). "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". The Astronomical Journal 132 (2): 692–710. doi:10.1086/505206. Bibcode: 2006AJ....132..692S.
Thomas, P. C. (July 2010). "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission". Icarus 208 (1): 395–401. doi:10.1016/j.icarus.2010.01.025. Bibcode: 2010Icar..208..395T. http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf. Retrieved 2015-09-04.
Thomas, P. C.; Helfenstein, P. (July 2020). "The small inner satellites of Saturn: Shapes, structures and some implications". Icarus 344: 20. doi:10.1016/j.icarus.2019.06.016. 113355. Bibcode: 2020Icar..34413355T.
Lainey, V.; Rambaux, N.; Cooper, N.; Dahoumane, R.; Zhang, Q. (February 2023). "Characterising the interior of five inner Saturnian moons using Cassini ISS data". Astronomy & Astrophysics 670: 6. doi:10.1051/0004-6361/202244757. L25. Bibcode: 2023A&A...670L..25L.

External links

Atlas Profile by NASA's Solar System Exploration
The Planetary Society: Atlas
NASA factsheet

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[5] Calculated from the standard gravitational parameter GM = (3.664±0.028)×10⁻⁴ km³·s^–2 given by Lainey et al. (2023), divided by the gravitational constant G = 6.6743×10⁻² km³·kg^–1·s^–2.^[4]

[1] Atlantean (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=Atlantean (Subscription or UK public library membership required.)

[FOOTNOTESpitale_Jacobson_et_al.2006-2] 2.0 ^2.1 Spitale Jacobson et al. 2006.

[FOOTNOTEThomas_&_Helfenstein2020-3] 3.0 ^3.1 ^3.2 Thomas & Helfenstein 2020.

[FOOTNOTELainey_et_al.2023-4] 4.0 ^4.1 ^4.2 Lainey et al. 2023.

[FOOTNOTEIAUC_3539-6] IAUC 3539.

[FOOTNOTEIAUC_3872-7] IAUC 3872.

[FOOTNOTELakdawalla2007-8] 7.0 ^7.1 Lakdawalla 2007.

[FOOTNOTEIAUC_8401-9] IAUC 8401.

v t e Moons of Saturn
Listed in approximately increasing distance from Saturn.
Ring shepherds	S/2009 S 1 Ring moonlets Pan Daphnis Atlas Prometheus Pandora
Co-orbitals	Epimetheus Janus
G Ring	Aegaeon
Alkyonides	Methone Anthe Pallene
Inner large (with trojans)	Mimas Enceladus Tethys Telesto Calypso Dione Helene Polydeuces
Outer large	Rhea Titan Hyperion Iapetus
Inuit group	Kiviuq Ijiraq Paaliaq S/2004 S 29 S/2004 S 31 Siarnaq Tarqeq
Norse group	Phoebe Skathi S/2004 S 37 S/2007 S 2 Skoll S/2004 S 13(?) Greip Hyrrokkin Jarnsaxa Mundilfari S/2006 S 1 S/2004 S 17(?) Bergelmir Narvi S/2004 S 20 Suttungr Hati S/2004 S 12(?) S/2004 S 27 Farbauti Thrymr S/2004 S 30 Aegir S/2007 S 3(?) Bestla S/2004 S 7(?) S/2004 S 22(?) S/2004 S 23(?) S/2004 S 25(?) S/2004 S 32(?) S/2006 S 3 S/2004 S 38(?) Fenrir S/2004 S 28(?) Surtur Kari S/2004 S 35(?) Ymir S/2004 S 21(?) Loge S/2004 S 36(?) S/2004 S 39(?) S/2004 S 33(?) S/2004 S 34(?) Fornjot S/2004 S 26(?)
Gallic group	Albiorix Bebhionn Erriapus Tarvos
Prograde outer satellites	S/2004 S 24
Rings of Saturn Cassini–Huygens Themis Chiron S/2004 S 6 S/2004 S 4 S/2004 S 3 In fiction

v t e Saturn
Outline of Saturn
Geography	Dragon Storm Great White Spot Hexagon Magnetosphere Rings
Moons	S/2009 S 1 Ring moonlets Pan Daphnis Atlas Prometheus S/2004 S 6 S/2004 S 4 S/2004 S 3 Pandora Epimetheus Janus Aegaeon Mimas Methone Anthe Pallene Enceladus Tethys Telesto Calypso Dione Helene Polydeuces Rhea Titan Hyperion Iapetus Kiviuq Ijiraq Phoebe Paaliaq Skathi S/2004 S 37 Albiorix S/2007 S 2 S/2004 S 29 Bebhionn Erriapus Skoll S/2004 S 31 Siarnaq Tarqeq S/2004 S 13 Greip Hyrrokkin Jarnsaxa Tarvos Mundilfari S/2006 S 1 S/2004 S 17 Bergelmir Narvi S/2004 S 20 Suttungr Hati S/2004 S 12 S/2004 S 27 Farbauti Thrymr S/2004 S 30 Aegir S/2007 S 3 Bestla S/2004 S 7 S/2004 S 22 S/2004 S 23 S/2004 S 25 S/2004 S 32 S/2006 S 3 S/2004 S 38 Fenrir S/2004 S 28 Surtur Kari S/2004 S 35 Ymir S/2004 S 21 S/2004 S 24 Loge S/2004 S 36 S/2004 S 39 S/2004 S 33 S/2004 S 34 Fornjot S/2004 S 26
Astronomy	Delta Octantis Saturn-crossing minor planets
Exploration	Cassini–Huygens (Huygens) timeline retirement Pioneer 11 Voyager program Voyager 1 Voyager 2
Related	Fiction Moons The Day the Earth Smiled In Saturn's Rings (2018 documentary)

Discovery
Color photo taken by Cassini on 12 April 2017
Discovered by	Terrile, Voyager 1
Discovery date	October, 1980
Designations
Designation	Saturn XV
Pronunciation	/ˈætləs/
Named after	Ἄτλας Ātlās
Alternative names	S/1980 S 28
Adjectives	Atlantean /ætlænˈtiːən/^[1]
Orbital characteristics ^[2]
Epoch December 31, 2003 (JD 2453005.5)
Mean orbit radius	137670±10 km
Eccentricity	0.0012
Orbital period	0.6016947883 d
Inclination	0.003°±0.004°
Satellite of	Saturn
Group	Outer shepherd moon of the A Ring
Physical characteristics
Dimensions	40.8 × 35.4 × 18.6 km (± 0.2 × 0.4 × 0.6 km)^[3]^(p2)
Mean diameter	29.8±0.4 km^[3]^(p2)
Volume	13950±50 km³^[4]^(p4)
Mass	(5.490±0.042)×10¹⁵ kg^{[lower-alpha 1]}
Mean density	0.3935±0.0033 g/cm³^[4]^(p4)
surface gravity	0.0001–0.0017 m/s²^[3]^(p3)
escape velocity	0.006 km/s at longest axis to 0.009 km/s at poles
Rotation period	synchronous
Axial tilt	zero
Albedo	0.4
Physics	≈ 81 K