Phoebe (moon)#Named features

File:William Henry Pickering.jpg

Phoebe was discovered by William Henry Pickering on 18 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart.{{cite journal |author=Pickering EC |title=A New Satellite of Saturn |url=http://adsabs.harvard.edu//full/seri/BHarO/0049//0000001.000.html |journal=Harvard College Observatory Bulletin |date=1899-03-17 |volume=9 |issue=221 |page=456 |doi=10.1126/science.9.221.456 |pmid=17844472 |s2cid=30496398 |access-date=2004-07-14 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303194618/http://adsabs.harvard.edu//full/seri/BHarO/0049//0000001.000.html |url-status=live }}{{cite journal |last1=Pickering |first1=E. C. |title=A New Satellite of Saturn |journal=Science |date=24 March 1899 |volume=9 |issue=221 |pages=456 |doi=10.1126/science.9.221.456|pmid=17844472 |s2cid=30496398 }}{{cite journal |author=Pickering EC |url=http://adsabs.harvard.edu//full/seri/AJ.../0020//0000013.000.html |title=A New Satellite of Saturn |journal=Astronomical Journal |volume=20 |issue=458 |date=1899-03-23 |page=13 |bibcode=1899AJ.....20...13P |doi=10.1086/103076 |access-date=2004-07-14 |archive-date=2013-11-12 |archive-url=https://web.archive.org/web/20131112100406/http://adsabs.harvard.edu//full/seri/AJ.../0020//0000013.000.html |url-status=live }}{{cite journal |author=Pickering EC |url=http://adsabs.harvard.edu//full/seri/ApJ../0009//0000274.000.html |title=A New Satellite of Saturn |journal=Astrophysical Journal |volume=9 |date=1899-04-10 |pages=274–276 |issue=4 |bibcode=1899ApJ.....9..274P |doi=10.1086/140590 |pmid=17844472 |doi-access=free |access-date=2004-07-14 |archive-date=2016-04-11 |archive-url=https://web.archive.org/web/20160411003004/http://adsabs.harvard.edu//full/seri/ApJ../0009//0000274.000.html |url-status=live }}{{cite journal |doi=10.1002/asna.18991491003 |author=Pickering EC |url=http://adsabs.harvard.edu//full/seri/AN.../0149//0000100.000.html |title=A New Satellite of Saturn |journal=Astronomische Nachrichten |volume=149 |date=1899-04-29 |pages=189–192 |issue=10 |bibcode=1899AN....149..189P |access-date=2004-07-14 |archive-date=2013-11-12 |archive-url=https://web.archive.org/web/20131112100429/http://adsabs.harvard.edu//full/seri/AN.../0149//0000100.000.html |url-status=live }} (same as above){{cite journal |url=http://adsabs.harvard.edu//full/seri/Obs../0022//0000158.000.html |title=A Ninth Satellite to Saturn |journal=The Observatory |volume=22 |date=April 1899 |pages=158–159 |issue=278 |bibcode=1899Obs....22..158. |access-date=2004-07-14 |archive-date=2013-11-12 |archive-url=https://web.archive.org/web/20131112100403/http://adsabs.harvard.edu//full/seri/Obs../0022//0000158.000.html |url-status=live }} It was the first satellite to be discovered photographically.

Phoebe is named after Phoebe, a Titaness in Greek mythology associated with the Moon, who was the sister of Cronus (the Greek equivalent of the Roman god Saturn). It is also designated Saturn IX in some scientific literature. The IAU nomenclature standards have stated that features on Phoebe are to be named after characters in the Greek myth of Jason and the Argonauts. In 2005, the IAU officially named 24 craters (see Named features).[http://www.spaceflightnow.com/cassini/050224phoebecraters.html Features on Saturn's moon Phoebe given names] {{Webarchive|url=https://web.archive.org/web/20160110070432/http://www.spaceflightnow.com/cassini/050224phoebecraters.html |date=2016-01-10 }}, Spaceflight Now, February 24, 2005

Toby Owen of the University of Hawaiʻi at Mānoa, chairman of the International Astronomical Union Outer Solar System Task Group said:

{{Quote|We picked the legend of the Argonauts for Phoebe as it has some resonance with the exploration of the Saturn system by Cassini–Huygens. We can't say that our participating scientists include heroes like Hercules and Atalanta, but they do represent a wide, international spectrum of outstanding people who were willing to take the risk of joining this voyage to a distant realm in hopes of bringing back a grand prize.}}

File:Animation of Phoebe orbit around Saturn.gif

Phoebe's orbit is retrograde; that is, it orbits Saturn opposite to Saturn's rotation. For more than 100 years, Phoebe was Saturn's outermost known moon, until the discovery of several smaller moons in 2000. Phoebe is almost 4 times more distant from Saturn than its nearest major neighbor (Iapetus), and is substantially larger than any of the other moons orbiting planets at comparable distances. All of Saturn's regular moons except Iapetus orbit very nearly in the plane of Saturn's equator. The outer irregular satellites, including Phoebe, follow orbits that can be moderately to highly eccentric, and none are expected to rotate synchronously as all the inner moons of Saturn (except for Hyperion) do. Phoebe orbits within a group of irregular satellites called the Norse group.

There are a number of satellites with similar orbits that are speculated to be fragments from collision events Phoebe has experienced in the past, such as S/2006 S 20, S/2006 S 9, S/2019 S 2, and S/2007 S 2.{{cite arXiv |last1=Ashton |first1=Edward |last2=Gladman |first2=Brett |last3=Alexandersen |first3=Mike |last4=Petit |first4=Jean-Marc |date=10 March 2025 |title=Retrograde predominance of small saturnian moons reiterates a recent retrograde collisional disruption |class=astro-ph.EP |eprint=2503.07081}}

Image:Saturn largest ring Spitzer telescope 20091006.jpg, which dwarfs the main rings]]

{{Main|Rings of Saturn#Phoebe ring}}

The Phoebe ring is one of the rings of Saturn. This ring is tilted 27 degrees from Saturn's equatorial plane (and the other rings). It extends from at least 128 to 207{{cite journal |last=Verbiscer| first=Anne |author2=Skrutskie, Michael |author3=Hamilton, Douglas |title=Saturn's largest ring |journal=Nature |date=2009-10-07 |doi=10.1038/nature08515 |bibcode = 2009Natur.461.1098V|pmid=19812546 |volume=461|issue=7267 |pages=1098–100| s2cid=4349726 }} times the radius of Saturn; Phoebe orbits the planet at an average distance of 215 Saturn radii. The ring is about 40 times as thick as the diameter of the planet.{{cite web|url=http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007b.html|title=The King of Rings|publisher=NASA, Spitzer Space Telescope center|date=2009-10-07|access-date=October 7, 2009|archive-date=2009-10-10|archive-url=https://web.archive.org/web/20091010072014/http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007b.html|url-status=dead}} Because the ring's particles are presumed to have originated from micrometeoroid impacts on Phoebe, they should share its retrograde orbit,{{cite journal|last=Cowen|first=Rob|url=http://www.sciencenews.org/view/generic/id/48097/title/Largest_known_planetary_ring_discovered|title=Largest known planetary ring discovered|journal=Science News|date=October 6, 2009|access-date=October 6, 2009|archive-date=August 22, 2011|archive-url=https://web.archive.org/web/20110822023022/http://www.sciencenews.org/view/generic/id/48097/title/Largest_known_planetary_ring_discovered|url-status=dead}} which is opposite to the orbital motion of the next major moon inward, Iapetus. Inwardly migrating ring material would thus strike Iapetus's leading hemisphere, contributing to its two-tone coloration.[https://www.newscientist.com/article/dn17928-largest-ring-in-solar-system-found-around-saturn.html Largest ring in solar system found around Saturn] {{Webarchive|url=https://web.archive.org/web/20150518234316/http://www.newscientist.com/article/dn17928-largest-ring-in-solar-system-found-around-saturn.html |date=2015-05-18 }}, New Scientist{{Cite web

| last = Mason

| first = J.

| author2 = Martinez, M.

| author3 = Balthasar, H.

| title = Cassini Closes In On The Centuries-old Mystery Of Saturn's Moon Iapetus

| work = CICLOPS website newsroom

| publisher = Space Science Institute

| date = 2009-12-10

| url = http://ciclops.org/view.php?id=6033

| access-date = 2009-12-22

| archive-date = 2012-02-03

| archive-url = https://web.archive.org/web/20120203132024/http://ciclops.org/view.php?id=6033

| url-status = dead

}}{{Cite journal

| last = Denk | first = T. |display-authors=etal

| title = Iapetus: Unique Surface Properties and a Global Color Dichotomy from Cassini Imaging

| journal = Science | volume = 327| issue = 5964 | pages = 435–439

| date = 2009-12-10

| doi = 10.1126/science.1177088

| pmid = 20007863|bibcode = 2010Sci...327..435D | s2cid = 165865 }}{{Cite journal

| last = Spencer | first = J. R. |author2=Denk, T.

| title = Formation of Iapetus' Extreme Albedo Dichotomy by Exogenically Triggered Thermal Ice Migration

| journal = Science | volume = 327| issue =5964 | pages =432–435

| date = 2009-12-10 | doi = 10.1126/science.1177132 | pmid = 20007862|bibcode = 2010Sci...327..432S | citeseerx = 10.1.1.651.4218 | s2cid = 20663944 }} Although very large, the ring is virtually invisible—it was discovered using NASA's infrared Spitzer Space Telescope.

Material displaced from Phoebe's surface by microscopic meteor impacts may be responsible for the dark areas on the surface of Hyperion.{{efn|The composition implied by spectra does not seem to support the earlier suggestion that Phoebe could be the source of the dark material deposited on Iapetus.}} Debris from the biggest impacts may be the origin of some of the other moons of the Norse group—almost all of which are less than 10 km in radius.

File:PocketSizedPhoebe.jpg and the Moon{{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 = 2011-09-27| archive-url = https://web.archive.org/web/20110927185355/http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf| url-status = dead}}]]

File:Cratersofphoebe.jpg]]

Phoebe is roughly spherical and has a diameter of {{val|213|1.4|u=km}} ({{convert|213|km|mi|disp=out}}), approximately one-sixteenth that of the Moon. It is Saturn's ninth-largest moon, but it is the eighth-most massive. Hyperion, another one of Saturn's moons, has a larger radius, but is less massive than Phoebe. Phoebe rotates every nine hours and 16 minutes, and completes a full orbit around Saturn in about 18 months. Its surface temperature is on average {{convert|75|K|°C|abbr=on}}.

File:Phoebe 13-06-2004.jpg{{'s}} closeup of Phoebe from 13 June 2004; the crater Euphemus is at top center]]

Most of Saturn's inner moons have very bright surfaces, but Phoebe's albedo is much lower in comparison ({{Value|0.100|0.005}}), though relatively bright compared to other irregular moons with measured albedos.{{Cite journal |last1=Grav |first1=T. |last2=Bauer |first2=J. M. |last3=Mainzer |first3=A. K. |last4=Masiero |first4=J. R. |last5=Nugent |first5=C. R. |last6=Cutri |first6=R. M. |last7=Sonnett |first7=S. |last8=Kramer |first8=E. |date=2015-08-01 |title=NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn |url=https://ui.adsabs.harvard.edu/abs/2015ApJ...809....3G |journal=The Astrophysical Journal |volume=809 |issue=1 |pages=3 |doi=10.1088/0004-637X/809/1/3 |issn=0004-637X|arxiv=1505.07820 |bibcode=2015ApJ...809....3G }} The Phoebean surface is heavily scarred. The largest crater, Jason, is roughly 100 km in diameter.

Phoebe's dark coloring initially led to scientists surmising that it was a captured asteroid, as it resembled the common class of dark carbonaceous asteroids. These are chemically very primitive and are thought to be composed of original solids that condensed out of the solar nebula with little modification since then.

However, images from Cassini indicate that Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some {{convert|300|to|500|m|ft}} thick. In addition, quantities of carbon dioxide have been detected on the surface, a finding that has never been replicated for an asteroid. It is estimated that Phoebe is about 50% rock, as opposed to the 35% or so that typifies Saturn's inner moons. For these reasons, scientists are coming to think that Phoebe is in fact a captured centaur, one of a number of icy planetoids from the Kuiper belt that orbit the Sun between Jupiter and Neptune.{{cite journal |last1=Johnson |first1=Torrence V. |last2=Lunine |first2=Jonathan I. |title=Saturn's moon Phoebe as a captured body from the outer Solar System |journal=Nature |volume=435 |issue=7038 |pages=69–71 |doi=10.1038/nature03384 |date=2005 |bibcode=2005Natur.435...69J |pmid=15875015 |s2cid=4390697 }}{{cite web|last=Martinez |first=C. |url=http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=568 |title=Scientists Discover Pluto Kin Is a Member of Saturn Family |work=Cassini–Huygens News Releases |date=May 6, 2005 |url-status=dead |archive-url=https://web.archive.org/web/20080501033138/http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=568 |archive-date=May 1, 2008 }} Phoebe is the first such object to be imaged as anything other than a dot.

Spectroscopic observations of Phoebe by the James Webb Space Telescope and the VIMS instrument on Cassini have confirmed the presence of water ice and carbon dioxide on its surface, with ambiguous evidence for organic compounds. The overall shape of the spectrum resembles that of Kuiper belt objects, providing a compositional confirmation that Phoebe is a captured body. Phoebe also appears to have distinctly more water ice than other similarly observed Saturnian irregular satellites, such as Siarnaq and Albiorix.{{Cite journal |last1=Clark |first1=Roger N. |last2=Brown |first2=Robert H. |last3=Jaumann |first3=Ralf |last4=Cruikshank |first4=Dale P. |last5=Nelson |first5=Robert M. |last6=Buratti |first6=Bonnie J. |last7=McCord |first7=Thomas B. |last8=Lunine |first8=J. |last9=Baines |first9=K. H. |last10=Bellucci |first10=G. |last11=Bibring |first11=J.-P. |last12=Capaccioni |first12=F. |last13=Cerroni |first13=P. |last14=Coradini |first14=A. |last15=Formisano |first15=V. |date=May 2005 |title=Compositional maps of Saturn's moon Phoebe from imaging spectroscopy |url=https://www.nature.com/articles/nature03558 |journal=Nature |language=en |volume=435 |issue=7038 |pages=66–69 |doi=10.1038/nature03558 |pmid=15875014 |bibcode=2005Natur.435...66C |issn=1476-4687|url-access=subscription }}{{Cite journal |last1=Belyakov |first1=Matthew |last2=Brown |first2=Michael E. |date=2025-04-01 |title=Saturnian Irregular Satellites as a Probe of Kuiper Belt Surface Evolution |journal=The Planetary Science Journal |volume=6 |issue=4 |pages=97 |doi=10.3847/PSJ/adc55d |doi-access=free |arxiv=2503.20046 |bibcode=2025PSJ.....6...97B |issn=2632-3338}}

Despite its small size, Phoebe is thought to have been a spherical body early in its history, with a differentiated interior, before solidifying and being battered into its current, slightly non-equilibrium shape.{{cite web |date=2012-04-26 |author=Jia-Rui C. Cook and Dwayne Brown |title=Cassini Finds Saturn Moon Has Planet-Like Qualities |url=http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20120426/ |publisher=JPL/NASA |archive-url=https://web.archive.org/web/20120427192715/http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20120426/ | archive-date=2012-04-27 |url-status=dead}}

Apart from one regio named after Phoebe's daughter, Leto, all named features are craters named after characters from the Greek legend of Jason and the Argonauts.[https://planetarynames.wr.usgs.gov/SearchResults?target=PHOEBE&featureType=Crater,%20craters Phoebean craters] {{Webarchive|url=https://web.archive.org/web/20200925072351/https://planetarynames.wr.usgs.gov/SearchResults?target=PHOEBE&featureType=Crater,%20craters |date=2020-09-25 }}, USGS

Phoebe 2005 Mercator PIA07795.jpg|Map of Phoebe's middle latitudes. The higher latitudes have been clipped from the main map, but can be seen in the polar projections.

Phoebe 2005 south polar projection PIA07797.jpg|Map of Phoebe's south polar region

Phoebe north polar region PIA 07796.png|Map of Phoebe's north polar region

Phoebe contour map PIA15507.jpg|3D map showing Phoebe's once spherical shape

Phoebe formed in the Kuiper belt within three million years after the origin of the Solar System. This was early enough that sufficient radioactive material was available to melt it into a sphere and stay warm enough to have liquid water for tens of millions of years.

File:Phoebe-2010Mar09.jpg in the lower right corner) as imaged with a 24" telescope]]

File:Saturn's outer satellite - Phoebe PIA02229.jpg

Unlike Saturn's other moons, Phoebe was not favorably placed for the Voyager probes. Voyager 2 observed Phoebe for a few hours in September 1981. In the images, taken from a distance of 2.2 million kilometres at low phase angle, the size of Phoebe was approximately 11 pixels and showed bright spots on the otherwise dark surface.{{Cite journal |last1=Thomas |first1=P. |last2=Veverka |first2=J. |last3=Morrison |first3=D. |last4=Davies |first4=M. |last5=Johnson |first5=T. V. |date=1 November 1983 |title=Phoebe: Voyager 2 observations |url= |journal=Journal of Geophysical Research: Space Physics |volume=88 |issue=A11 |pages=8736–8742 |bibcode=1983JGR....88.8736T |doi=10.1029/JA088iA11p08736 |issn=0148-0227}}

Cassini passed {{convert|2068|km|mi}} from Phoebe on 11 June 2004,{{Cite web |title=Encounter with Phoebe |url=https://www.esa.int/Science_Exploration/Space_Science/Cassini-Huygens/Encounter_with_Phoebe |access-date=2024-03-09 |website=www.esa.int |language=en}} returning many high-resolution images, which revealed a scarred surface. Because Voyager 2 had not been able to produce any high-quality images of Phoebe, obtaining them was a priority for the Cassini mission and its flight path was deliberately designed to take it close by; otherwise, Cassini would likely not have returned images much better than Voyager's. Because of Phoebe's short rotation period of approximately 9 hours, 17 minutes, Cassini was able to map virtually the entire surface of Phoebe. The close fly-by enabled the mass of Phoebe to be determined with an uncertainty of only 1 in 500.Roth et al., AAS Paper 05-311

{{Commons category|Phoebe}}

• Moons of Saturn

{{Reflist|group=lower-alpha}}

{{Reflist

|refs=

{{cite journal |last1=Castillo-Rogez |first1=Julie |last2=Vernazza |first2=Pierre |last3=Walsh |first3=Kevin |title=Geophysical evidence that Saturn's Moon Phoebe originated from a C-type asteroid reservoir |date = June 2019 |journal=Monthly Notices of the Royal Astronomical Society |volume=486 |issue=1 |pages=538–543 |doi=10.1093/mnras/stz786 |doi-access=free |bibcode=2019MNRAS.486..538C }}

{{cite journal |last1=Rambaux |first1=N. |last2=Castillo-Rogez |first2=J. C. |title=Phoebe's differentiated interior from refined shape analysis |date=19 September 2020 |journal=Astronomy & Astrophysics |volume=643 |pages=L10 |doi=10.1051/0004-6361/202039189 |bibcode=2020A&A...643L..10R }}

}}

{{Spoken Wikipedia|Phoebe_(moon).ogg|date=2010-01-10}}

• [https://web.archive.org/web/20070609074747/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Phoebe Phoebe Profile] at [http://solarsystem.nasa.gov NASA's Solar System Exploration site]
• [https://web.archive.org/web/20060915055252/http://saturn.jpl.nasa.gov/multimedia/images/images.cfm?subCategoryID=8 Cassini–Huygens Multimedia: Images: Moons: Small Moons]
• [http://news.bbc.co.uk/2/hi/science/nature/3798485.stm Cassini Pass Reveals Moon Secrets], BBC News, June 14, 2004
• [https://web.archive.org/web/20060901051557/http://www.planetary.org/explore/topics/saturn/phoebe.html The Planetary Society: Phoebe]
• Asaravala, A.; [https://www.wired.com/news/space/0,2697,67419,00.html?tw=wn_story_related Saturn's Odd Moon Out], Wired, (May 4, 2005)
• [http://ssd.jpl.nasa.gov/?sat_phys_par NASA: Natural Satellite Physical Parameters]
• [http://ciclops.org/search.php?x=20&y=7&search=Phoebe Cassini images of Phoebe]
• [http://photojournal.jpl.nasa.gov/target/Phoebe Images of Phoebe at JPL's Planetary Photojournal]
• Movie of [https://web.archive.org/web/20100601171554/http://sos.noaa.gov/videos/Phoebe.mov Phoebe's rotation] from the National Oceanic and Atmospheric Administration
• [http://ciclops.org/view.php?id=1743 Phoebe basemap] (December 2005) from Cassini images
• [http://ciclops.org/view.php?id=1843 Phoebe atlas (March 2006) from Cassini images]
• [http://planetarynames.wr.usgs.gov/Page/PHOEBE/target Phoebe nomenclature] from the [http://planetarynames.wr.usgs.gov USGS planetary nomenclature page]
• [https://tilmanndenk.de/outersaturnianmoons/phoebe/ Phoebe on T. Denk's Outer Saturnian moons websites]

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