Fenrir (moon)

{{Short description|Moon of Saturn}}

{{Infobox planet

| name = Fenrir

| discovery_ref = {{cite web

|date=2005-05-04

|title=IAUC 8523: NEW Sats OF SATURN

|publisher=International Astronomical Union

|author=Daniel W. E. Green

|url=http://www.cbat.eps.harvard.edu/iauc/08500/08523.html}}

| discovery_site = Subaru, Gemini
Jan T. Kleyna
Brian G. Marsden

| alt_names = S/2004 S 16{{cite web

|date=2007-04-05

|title=IAUC 8826: Sats OF JUPITER, SATURN

|publisher=International Astronomical Union

|author=Daniel W. E. Green

|url=http://www.cbat.eps.harvard.edu/iauc/08800/08826.html}}

| mpc_name = Saturn XLI

| pronounced = {{IPAc-en|ˈ|f|ɛ|n|r|ɪər}}{{dict.com|Fenrir}} or {{IPAc-en|ˈ|f|ɛ|n|r|ər}}Merriam-Webster's Encyclopedia of Literature (1995)

| adjective = Fenrian {{IPAc-en|ˈ|f|ɛ|n|r|i|ə|n}}{{efn|The oblique stem of the name is Fenri, as in Fenrisulfr. The -r is the nominative case ending.}}

| named_after = Fenris Wolf

| orbit_ref = {{cite web

|date=2009-04-03

|title=Planetary Satellite Mean Orbital Parameters

|publisher=JPL/NASA

|author=Jacobson, R.A. (2007) SAT270, SAT271

|url=http://ssd.jpl.nasa.gov/?sat_elem#saturn

|access-date=2009-07-30}}

| semimajor = 22 454 000 km

| eccentricity = 0.1363

| period = 1260.35 d (3.45 yr)

| inclination = 164.955°

| mean_anomaly = 146.614°

| arg_peri = 120.264°

| asc_node = 330.95°

| satellite_of = Saturn

| group = Norse group

| physical_ref = {{cite book |last1=Denk |first1=Tilmann |url= |title=Enceladus and the Icy Moons of Saturn |last2=Mottola |first2=Stefano |last3=Tosi |first3=Frederico |last4=Bottke |first4=William F. |last5=Hamilton |first5=Douglas P. |publisher=The University of Arizona Press |year=2018 |isbn=9780816537075 |editor1=Schenk, P.M. |series=Space Science Series |volume=322 |location=Tucson, AZ |pages=409–434 |chapter=The Irregular Satellites of Saturn |bibcode=2018eims.book..409D |doi=10.2458/azu_uapress_9780816537075-ch020 |editor2=Clark, R.N. |editor3=Howett, C.J.A. |editor4=Verbiscer, A.J. |editor5=Waite, J.H. |chapter-url=https://tilmanndenk.de/wp-content/uploads/DenkEtAl2018_IrregularMoons.pdf}}

| mean_diameter = 4 km

| albedo = 0.06 (assumed)

| magnitude = 25.0

| abs_magnitude = 15.9

}}

Fenrir {{IPAc-en|ˈ|f|ɛ|n|r|ɪər}}, or Saturn XLI (provisional designation S/2004 S 16), is a natural satellite of Saturn. Its discovery was announced by Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden on May 4, 2005, from observations taken between December 13, 2004, and March 5, 2005. Fenrir has an apparent magnitude of 25,{{cite web

|title=Saturn's Known Satellites

|publisher=Carnegie Institution (Department of Terrestrial Magnetism)

|author=Scott S. Sheppard

|author-link=Scott S. Sheppard

|url=http://www.dtm.ciw.edu/users/sheppard/satellites/satsatdata.html

|access-date=2009-07-30}} making it one of the faintest known moons in the Solar System, and was discovered using some of the largest telescopes in the world. It is even too dark to have been observed by the Cassini spacecraft when it was in orbit around Saturn, for which it never got brighter than approximately 17th apparent magnitude.{{Cite web |title=Fenrir (S/2004 S 16) – Tilmann Denk |url=https://tilmanndenk.de/outersaturnianmoons/fenrir/ |access-date=2024-02-10 |language=en-US}} Fenrir was named after Fenrisulfr, a giant wolf from Norse mythology, father of Hati and Skoll, son of Loki, destined to break its bonds for Ragnarök.

Fenrir is about 4 kilometres in diameter, and orbits Saturn at an average distance of 22,454 Mm in 1260 days, at an inclination of 163° to the ecliptic (143° to Saturn's equator) with an eccentricity of 0.136. The Fenrian orbit is retrograde: it orbits Saturn in a direction opposite to the planet's spin, suggesting that this irregular moon was captured by Saturn.{{cite web |title=Twelve New Moons for Saturn - 2005 May 03 |publisher=University of Hawaii (Institute for Astronomy) |author=David C. Jewitt |author-link=David C. Jewitt |url=http://www.ifa.hawaii.edu/~jewitt/saturn2005.html |access-date=2009-07-30 |url-status=dead |archive-url=https://web.archive.org/web/20090918101304/http://www.ifa.hawaii.edu/~jewitt/saturn2005.html |archive-date=September 18, 2009 }}