Atlas (moon)
{{Short description|Moon of Saturn}}
{{Infobox planet
| name = Atlas
| mpc_name = Saturn XV
| alt_names = S/1980 S 28
| adjectives = Atlantean {{IPAc-en|æ|t|l|æ|n|ˈ|t|iː|ə|n}}{{OED|Atlantean}}
| pronounced = {{IPAc-en|ˈ|æ|t|l|ə|s}}
| named_after = Ἄτλας Ātlās
| image = Atlas color PIA21449.png
| image_scale =
| caption = Color photo taken by Cassini on 12 April 2017
| discoverer = Terrile, Voyager 1
| discovered = October, 1980
| orbit_ref = {{sfn|Spitale Jacobson et al.|2006}}
| epoch = December 31, 2003 (JD {{val|2453005.5}})
| mean_orbit_radius = {{val|137670|10|u=km}}
| eccentricity = {{val|0.0012}}
| period = {{val|0.6016947883|u=d}}
| inclination = {{val|0.003|0.004|u=°}}
| satellite_of = Saturn
| group = Outer shepherd moon of the A Ring
| dimensions = {{val|40.8|x|35.4|x|18.6}} km
(± {{val|0.2|x|0.4|x|0.6}} km){{sfn|Thomas & Helfenstein|2020}}{{rp|page=2}}
| mean_diameter = {{val|29.8|0.4|u=km}}{{sfn|Thomas & Helfenstein|2020}}{{rp|page=2}}
| volume = {{val|13950|50|u=km3}}{{sfn|Lainey et al.|2023}}{{rp|page=4}}
| mass = {{val|5.490|0.042|e=15|u=kg}}{{efn|Calculated from the standard gravitational parameter GM {{=}} {{val|3.664|0.028|e=-4|u=km3·s–2}} given by Lainey et al. (2023), divided by the gravitational constant G {{=}} {{val|6.6743|e=-2|u=km3·kg–1·s–2}}.{{sfn|Lainey et al.|2023}}}}
| density = {{val|0.3935|0.0033|u=g/cm3}}{{sfn|Lainey et al.|2023}}{{rp|page=4}}
| surface_grav = {{val|0.0001|-|0.0017|u=m/s2}}{{sfn|Thomas & Helfenstein|2020}}{{rp|page=3}}
| escape_velocity = {{V2|5.490e-6|20.4|3}} km/s at longest axis
to {{V2|5.490e-6|9.3|3}} km/s at poles
| rotation = synchronous
| axial_tilt = zero
| albedo = 0.4
| single_temperature = ≈ 81 K
}}
Atlas is an inner satellite of Saturn which was discovered by Richard Terrile in 1980 from Voyager photos and was designated {{nowrap|S/1980 S 28}}.{{sfn|IAUC 3539}} 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.{{sfn|IAUC 3872}} It is also designated {{nowrap|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.{{sfn|Lakdawalla|2007}} In 2004 a faint, thin ring, temporarily designated {{nowrap|R/2004 S 1}}, was discovered in the Atlantean orbit.{{sfn|IAUC 8401}}
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.{{sfn|Lakdawalla|2007}}
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.{{sfn|Spitale Jacobson et al.|2006}}
Gallery
File:Cassini Atlas N00084634 CL.png|Atlas from above its south pole (June 12, 2007)
File:Atlas Rev09.2x.jpg|Atlas - Cassini
(June 8, 2005).
File:Atlas with rings.jpg|Atlas - A and F rings
(June 30, 2006).
File:PIA17206-SaturnMoon-Atlas-Flyby-20151206.jpg|Atlas near the A ring
(December 6, 2015).
File:F Ring and Atlas PIA10448.jpg|Atlas near the F ring
(May 9, 2005).
Notes
{{notelist}}
References
= Citations =
{{reflist}}
= Sources =
- {{cite journal
| last = Green
| first = Daniel W. E.
| title = S/2004 S 3, S/2004 S 4, and R/2004 S 1
| date = September 9, 2004
| journal = IAU Circular
| volume = 8401
| page = 1
| url = http://www.cbat.eps.harvard.edu/iauc/08400/08401.html
| access-date = 2011-12-30
| ref = {{sfnRef|IAUC 8401}}
| bibcode = 2004IAUC.8401....1P
}}
- {{cite web
| last = Lakdawalla
| first = Emily
| date = June 13, 2007
| title = Funny little Atlas
| work = The Planetary Society weblog
| url = http://www.planetary.org/blog/article/00001003/
| access-date = 2011-12-30
}}
- {{cite journal
|last=Marsden
|first=Brian G.
|title=1980 S 28
|date=November 13, 1980
|format=discovery
|journal=IAU Circular
|volume=3539
|page=2
|url=http://www.cbat.eps.harvard.edu/iauc/03500/03539.html
|access-date=2011-12-30
|ref={{sfnRef|IAUC 3539}}
|archive-url=https://web.archive.org/web/20111213152218/http://www.cbat.eps.harvard.edu/iauc/03500/03539.html
|archive-date=2011-12-13
|bibcode=1980IAUC.3539....2M
}}
- {{cite journal
| last = Marsden
| first = Brian G.
| title = Satellites of Jupiter and Saturn
| date = September 30, 1983
| format = naming the moon
| journal = IAU Circular
| volume = 3872
| url = http://www.cbat.eps.harvard.edu/iauc/03800/03872.html
| access-date = 2011-12-30
| ref = {{sfnRef|IAUC 3872}}
}}
- {{cite journal| doi = 10.1086/505206| last1 = Spitale| first1 = J. N.| last2 = Jacobson| first2 = R. A.| last3 = Porco| first3 = C. C.| last4 = Owen| first4 = W. M. Jr.| year = 2006| title = The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations| journal = The Astronomical Journal| volume = 132| issue = 2| pages = 692–710| bibcode = 2006AJ....132..692S| ref = {{sfnRef|Spitale Jacobson et al.|2006}}| doi-access = free}}
- {{cite journal| doi = 10.1016/j.icarus.2010.01.025| last1 = Thomas| first1 = P. C.| date = July 2010| title = Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission| journal = Icarus| volume = 208| issue = 1| pages = 395–401| url = http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf| bibcode = 2010Icar..208..395T| access-date = 2015-09-04| archive-date = 2018-12-23| archive-url = https://web.archive.org/web/20181223003125/http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf}}
- {{cite journal
|ref = {{sfnRef|Thomas & Helfenstein|2020}}
|first1 = P. C. |last1 = Thomas
|first2 = P. |last2 = Helfenstein
|title = The small inner satellites of Saturn: Shapes, structures and some implications
|journal = Icarus
|date = July 2020
|volume = 344
|id = 113355
|page = 20
|doi = 10.1016/j.icarus.2019.06.016
|bibcode = 2020Icar..34413355T|s2cid = 197474587 }}
- {{cite journal
|ref = {{sfnRef|Lainey et al.|2023}}
|first1 = V. |last1 = Lainey
|first2 = N. |last2 = Rambaux
|first3 = N. |last3 = Cooper
|first4 = R. |last4 = Dahoumane
|first5 = Q. |last5 = Zhang
|title = Characterising the interior of five inner Saturnian moons using Cassini ISS data
|journal = Astronomy & Astrophysics
|date = February 2023
|volume = 670
|id = L25
|page = 6
|doi-access = free
|doi = 10.1051/0004-6361/202244757
|bibcode = 2023A&A...670L..25L}}
External links
{{Commons category|Atlas (moon)}}
{{Spoken Wikipedia|Atlas (moon).ogg|date=2010-01-13}}
- [https://web.archive.org/web/20070609074757/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Atlas Atlas Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
- [https://web.archive.org/web/20060830142335/http://www.planetary.org/explore/topics/saturn/atlas.html The Planetary Society: Atlas]
- [https://web.archive.org/web/20041031221550/http://sse.jpl.nasa.gov/planets/profile.cfm?Object=Sat_Atlas&Display=Facts NASA factsheet]
{{Moons of Saturn}}
{{Saturn}}
{{DEFAULTSORT:Atlas (Moon)}}