Siarnaq

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Siarnaq, also designated Saturn XXIX, is the second-largest irregular moon of Saturn. It was discovered on 23 September 2000 by a team of astronomers led by Brett J. Gladman. It was named after the Inuit goddess of the sea, Siarnaq, who is more commonly known as Sedna. Siarnaq is the largest member of Saturn's Inuit group of prograde irregular moons, which orbit far from Saturn in the same direction as the planet's rotation. The moons of the Inuit group are believed to have originated as fragments from the collisional breakup of a larger progenitor moon after it was gravitationally captured into orbit around Saturn several billion years ago.<ref name="Sheppard2023"/><ref name="Bottke2010"/> Several other small Inuit group moons share similar orbits to Siarnaq, indicating that the moon had experienced another collision after forming from its progenitor.<ref name="Sheppard2023"/>

DiscoveryEdit

File:Siarnaq-discovery-CFHT.gif

Discovery images of Siarnaq taken by the CFHT in September 2000

Siarnaq was discovered on 23 September 2000, by an international team of astronomers consisting of Brett J. Gladman, John J. Kavelaars, Jean-Marc Petit, Hans Scholl, Matthew Holman, Brian G. Marsden, Phil Nicholson and Joseph A. Burns.<ref name="Gazetteer"/> The discovery of Siarnaq formed part of an observational campaign to search for distant irregular satellites around Saturn. The campaign was coordinated by Gladman in late 2000 using various ground-based telescopes equipped with sensitive CCD cameras to survey Saturn's Hill sphere, the region within which satellites can have stable orbits around the planet.<ref name="satpress2001"/><ref name="Brand2000"/>

In September 2000, Gladman and collaborators conducted a wide-area survey around Saturn down to a R-band limiting magnitude of 24.5 with the 3.6-meter Canada-France-Hawaii Telescope (CFHT) at the Mauna Kea Observatory in Hawaii.<ref name="Gladman2001"/> They reobserved their previous irregular satellite discoveries from August 2000 (Ymir and Paaliaq) and identified two new irregular satellite candidates: Siarnaq and Tarvos.<ref name="satpresse1"/> Siarnaq, the brighter of the two, was detected at an apparent magnitude of 20.<ref name="IAUC7513"/>

Follow-up and confirmationEdit

File:Saturn-irregulars-offset-31jan01.jpg

Offset plot showing the positions and ephemerides of 13 irregular satellites relative to Saturn in 2001. Siarnaq Template:Nowrap is located at the upper left from the center.

Between 25–29 September 2000, follow-up observations of Siarnaq and other newly-discovered Saturnian irregular satellites were made at various observatories.<ref name="siarnaq-astrometry"/> Preliminary orbit calculations ruled out the possibility that the satellites could be foreground asteroids and confirmed they were indeed orbiting Saturn.<ref name="satpresse1"/> The discovery of Ymir, Paaliaq, Siarnaq, and Tarvos were formally reported by the International Astronomical Union on 25 October 2000<ref name="IAUC7513"/><ref name="IAUC7512"/> and announced by Gladman's team a day later at a meeting hosted by the American Astronomical Society's Division for Planetary Sciences.<ref name="Brand2000"/> The discovery of the four satellites raised Saturn's known moons to 22, surpassing Uranus's moon count of 21 at the time.<ref name="satpresse1"/>

Although Siarnaq was confirmed as a satellite, the orbit was poorly known due to an insufficient number of observations.<ref name="IAUC7521"/> The moon was reobserved by the Kitt Peak National Observatory in December 2000,<ref name="MPEC-2000-Y14"/> and later by the Palomar and La Palma observatories in early 2001.<ref name="siarnaq-astrometry"/> In the interim, Gladman's team had discovered eight more irregular satellites of Saturn, raising the planet's number of known moons to 30 and resultingly overtaking Jupiter as the planet with the most known moons until 2003.<ref name="satpress2001"/><ref name="Hamilton2001"/>

NameEdit

The moon is named after Siarnaq, the Inuit sea giantess or goddess and ruler of the Inuit underworld Adlivun.<ref name="NASA"/> In other variants of Inuit legend, she is also known by other names such as Nuliajuk and Sedna. Siarnaq is said to reside at the bottom of the ocean and to have conceived all sea life, which she will withhold from Inuit hunters when angered. In some versions of Inuit legend, Siarnaq was once a beautiful maiden who was tricked into marrying a bird-man and then was rescued by her father. They came under attack by a storm, which provoked the desperate father to sacrifice her to the sea in order to save himself.<ref name="Petten2003"/><ref name="Blunck2010"/>

The moon received its name in a formal notice published by the IAU on 8 August 2003, one month after its approval by the IAU's Working Group for Planetary System Nomenclature in a general assembly held in July 2003.<ref name="Petten2003"/> Siarnaq was also assigned the Roman numeral designation Saturn XXIX, the 29th moon of Saturn.<ref name="IAUC8177"/>

BackgroundEdit

Before Siarnaq was given its name, it was formerly known by the provisional designation S/2000 S 3 assigned by the IAU in the discovery announcement.Template:Efn The provisional designation indicates that it was the third Saturnian satellite identified in images taken in 2000.<ref name="IAUC7513"/> Siarnaq is among the first Saturnian irregular satellites discovered since Phoebe in 1898; the discovery of new satellite groups of Saturn provided the opportunity for their discoverers to establish new naming conventions for each of them.<ref name="satpress2001"/><ref name="Petten2003"/>

Kavelaars was advised by his colleagues to deviate from the traditional Greco-Roman mythology theme for Saturnian moons and instead propose names from different cultures. Throughout late 2000, Kavelaars spent several months consulting Amerindian scholars for appropriate name suggestions that were both multicultural and Canadian in origin. In March 2001, he was reading the Inuit tale Hide and Sneak to his children and had a revelation. He contacted the author of the tale, Michael Kusugak, to get his assent, and the latter suggested the names Kiviuq and Sedna.<ref name="Spitzer2001"/><ref name="Blunck2010"/> Kavelaars then decided that the selected Inuit names should end in the letter q to distinguish the group—hence the name Sedna was changed to Siarnaq.<ref name="Petten2003"/> The former name was later used for 90377 Sedna, a distant trans-Neptunian object discovered in 2003.<ref name="NASA"/>

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Physical characteristicsEdit

File:Siarnaq Cassini.gif

Cassini images of Siarnaq moving among background stars on 30 December 2013. The moon was observed Template:Convert away from the spacecraft.

File:Siarnaq lightcurve shape model.png

3D model created based on lightcurve data

Diameter and albedoEdit

From infrared observations by the Wide-field Infrared Survey Explorer (WISE) spacecraft, Siarnaq is estimated to be Template:Cvt in diameter.<ref name="Grav2015"/>

Surface and compositionEdit

Siarnaq is light red in color, and the Siarnaupian (Siarnaqan)Template:Efn spectrum in the infrared is very similar to the Inuit-group satellites Paaliaq and Kiviuq, supporting the thesis of a possible common origin in the break-up of a larger body.<ref name="Grav2007"/><ref name="Grav2004"/><ref name="Grav2003"/>

The James Webb Space Telescope obtained the spectrum of Siarnaq over the 0.7-5.3 micron region with NIRSpec, finding a 3.0 micron absorption feature associated with hydrated minerals. Water ice was not found to be present in substantial quantities on Siarnaq, in contrast to Phoebe, the largest Saturnian irregular satellite. Additionally, carbon dioxide formed by irradiation of organic compounds was detected on Siarnaq's surface. Siarnaq appears nearly identical in its composition to Albiorix, another Saturnian irregular satellite observed by James Webb Space Telescope.<ref>Template:Cite journal</ref>

Observations of Siarnaq at different phase angles show that its brightness stays relatively constant at high phase angles, where it produces a shallow phase curve, but exhibits a strong opposition surge, where it sharply brightens by 0.2 magnitudes at opposition (zero phase).<ref name="Bauer2006"/>Template:Rp This phase curve behavior of Siarnaq suggests it has a highly porous surface likely covered with substantial regolith.<ref name="Bauer2006"/>Template:Rp

Shape and rotationEdit

The rotation period of Siarnaq was measured by the Cassini spacecraft to be 10.19 hours; this is the shortest rotation period of all prograde irregular moons of Saturn.<ref name="Denk2019"/> Siarnaq displays a light curve with three maxima and minima over a full rotation, implying a roughly triangular shape similar to that of Ymir.<ref name="Denk2018"/> From Cassini observations of Siarnaq at different phase angles, the orientation of its north rotational pole has been determined to be pointing toward 98° ecliptic latitude and −23° ecliptic longitude.Template:Efn This corresponds to a sideways axial tilt, indicating that Siarnaq experiences long, extreme seasons similar to the planet Uranus.<ref name="Denk2018"/>

Orbit and groupEdit

Template:Irregular satellite

File:Saturn irregular moon orbits a vs. i.png

Diagram illustrating the orbits of the irregular satellites of Saturn. The inclination and semi-major axis are represented on the Y and X-axis, respectively. The satellites with inclinations below 90° are prograde, those above 90° are retrograde. The X-axis is labeled in terms of Saturn's Hill radius. The prograde Inuit and Gallic groups and the retrograde Norse group are identified.

File:Animation of Saturn's Inuit group of satellites.gif

Animation of Saturn's Inuit group of satellites from 2018–2027
Template:Legend2 Template:·Template:Legend2 Template:·Template:Legend2 Template:·Template:Legend2 Template:·Template:Legend2

Siarnaq orbits Saturn at an average distance of Template:Convert in 896 days (2.45 years).<ref name="MPC127090"/> Due to gravitational perturbations the Sun and other planets, the orbit of Siarnaq varies of time. Over a 200-year period, Siarnaq's semi-major axis fluctuates between Template:Convert, eccentricity between 0.089–0.554, and inclination between 41.4°–54.3° with respect to the ecliptic.<ref name="Jacobson2022"/>Template:Rp The moon is in a temporary secular resonance with Saturn, in which Siarnaq and Saturn have matching apsidal precession periods.<ref name="Nesvorny2003"/><ref name="Cuk2004"/>Template:Efn Siarnaq's high orbital eccentricity and inclination places it close to the threshold for Lidov–Kozai resonance.<ref name="Beauge2007"/>

Siarnaq belongs to Saturn's Inuit group of prograde irregular moons, which have average semi-major axes between Template:Convert and high average inclinations between 45°–50°. The Inuit group is further split into three distinct subgroups at different semi-major axes: the Kiviuq group, the Paaliaq group, and the Siarnaq group.<ref name="Sheppard2023"/> The Siarnaq group is the outermost Inuit subgroup and includes seven known members: Siarnaq, Tarqeq, S/2004 S 31, S/2019 S 14, S/2020 S 3, S/2019 S 6, and S/2020 S 5.<ref name="jpl-satelem"/> Moons in the Inuit group appear to be less abundant at smaller sizes, which implies that the Inuit group has existed long enough for collisions to have destroyed most of the smaller moons.<ref name="Ashton2021"/>

NotesEdit

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ReferencesEdit

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External linksEdit

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Natural Satellites Ephemeris Service, Minor Planet Center
Siarnaq In Depth, NASA Solar System Exploration, updated 19 December 2019
Siarnaq (S/2000 S 3), Tilmann Denk, updated 19 May 2023
Four more moons for Saturn, David Adam, Nature, 26 October 2000
New moons: not standing alone, David Adam, Nature, 26 October 2000
The Irregular Satellites of Saturn, Brett Gladman, Observatoire de la Cote d'Azur, October 2000

Template:Moons of Saturn Template:Saturn