 | |
| Discovery[1][2][3] | |
|---|---|
| Discovered by | Brett J. Gladman et al.[b] |
| Discovery site | Mauna Kea Obs. |
| Discovery date | 23 September 2000 |
| Designations | |
Designation | Saturn XXIX |
| Pronunciation | /ˈsiːɑːrnɑːk/ |
Named after | Siarnaq(Inuit mythology) |
| S/2000 S 3 | |
| Adjectives | Siarnaupian, Siarnaqian[c] |
| Orbital characteristics[4][5] | |
| Epoch 17 December 2020 (JD 2459200.5) | |
| 0.1187382 AU (17,763,000 km) | |
| Eccentricity | 0.5293834 |
| +2.42yr (+883.87d) | |
| 35.08520° | |
| Inclination | 43.80073°(toecliptic) |
| 40.96116° | |
| 79.59603° | |
| Satellite of | Saturn |
| Group | Inuit group (Siarnaq) |
| Physical characteristics | |
| 39.3±5.9 km[6] | |
| 10.18785±0.00005 h[7][8] | |
| −23°±15°[8] | |
| 98°±15°[8] | |
| Albedo | 0.050±0.017[6] |
Spectral type | D (reddish)[9] B−V=0.87±0.01[9] V−R=0.48±0.01 V−I=1.03±0.01 |
| 20.1 (visible)[10][11] | |
| 10.9±0.05[6] | |
Siarnaq is the second-largestirregular moon ofSaturn. It was discovered on 23 September 2000 by a team of astronomers led byBrett J. Gladman. It was named after theInuit goddess of the sea, Siarnaq, who is more commonly known asSedna. Siarnaq is the largest member of Saturn'sInuit group ofprograde 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 thecollisional breakup of a larger progenitor moon after it wasgravitationally captured into orbit around Saturn several billion years ago.[12][13] Several other small Inuit group moons share similar orbits to Siarnaq, indicating that the moon had experienced another collision after forming from its progenitor.[12]
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 andJoseph A. Burns.[2] The discovery of Siarnaq formed part of an observational campaign to search for distantirregular satellites around Saturn. The campaign was coordinated by Gladman in late 2000 using variousground-based telescopes equipped with sensitiveCCD cameras to survey Saturn'sHill sphere, the region within which satellites can have stable orbits around the planet.[14][15]
In September 2000, Gladman and collaborators conducted a wide-area survey around Saturn down to aR-bandlimiting magnitude of 24.5 with the 3.6-meterCanada-France-Hawaii Telescope (CFHT) at theMauna Kea Observatory inHawaii.[16] They reobserved their previous irregular satellite discoveries from August 2000 (Ymir andPaaliaq) and identified two new irregular satellite candidates: Siarnaq andTarvos.[17] Siarnaq, the brighter of the two, was detected at anapparent magnitude of 20.[3]
Between 25–29 September 2000, follow-up observations of Siarnaq and other newly-discovered Saturnian irregular satellites were made at various observatories.[18] Preliminary orbit calculations ruled out the possibility that the satellites could be foregroundasteroids and confirmed they were indeed orbiting Saturn.[17] The discovery of Ymir, Paaliaq, Siarnaq, and Tarvos were formally reported by theInternational Astronomical Union on 25 October 2000[3][19] and announced by Gladman's team a day later at a meeting hosted by theAmerican Astronomical Society'sDivision for Planetary Sciences.[15] The discovery of the four satellites raisedSaturn's known moons to 22, surpassingUranus's moon count of 21 at the time.[17]
Although Siarnaq was confirmed as a satellite, the orbit was poorly known due to an insufficient number of observations.[20] The moon was reobserved by theKitt Peak National Observatory in December 2000,[21] and later by thePalomar andLa Palma observatories in early 2001.[18] 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 overtakingJupiter as the planet with the most known moons until 2003.[14][22]
The moon is named after Siarnaq, theInuit seagiantess orgoddess and ruler of the Inuit underworldAdlivun.[23] In other variants ofInuit legend, she is also known by other names such asNuliajuk andSedna. 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.[24][25]
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'sWorking Group for Planetary System Nomenclature in a general assembly held in July 2003.[24] Siarnaq was also assigned theRoman numeral designation Saturn XXIX, the 29th moon of Saturn.[26]
Before Siarnaq was given its name, it was formerly known by theprovisional designation S/2000 S 3 assigned by the IAU in the discovery announcement.[d] The provisional designation indicates that it was the third Saturnian satellite identified in images taken in 2000.[3] Siarnaq is among the first Saturnian irregular satellites discovered sincePhoebe 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.[14][24]
Kavelaars was advised by his colleagues to deviate from the traditionalGreco-Roman mythology theme for Saturnian moons and instead propose names from different cultures. Throughout late 2000, Kavelaars spent several months consultingAmerindian scholars for appropriate name suggestions that were both multicultural andCanadian in origin. In March 2001, he was reading the Inuit taleHide 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 namesKiviuq and Sedna.[27][25] 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.[24] The former name was later used for90377 Sedna, a distanttrans-Neptunian object discovered in 2003.[23]
I sent [Kavelaars] that bit about Siarnaq, or we call her Nuliajuk, that creature that lives under the sea, who's also know [sic] as Sedna. She's got so many names ... sometimes she's simply called the Old Woman Who Lives Down There. Anyway, I was talking about the realm of the shaman in this book, and I said, "And the only person who can go down there and comb her hair and make her feel better is the shaman Paaliaq." And this was just something I made up in my story. So I was really surprised when the final approved list of names of these four moons of Saturn included Paaliaq, because I just made him up. That was fun.
— Michael Kusugak, in aWindspeaker interview[24]
Frominfrared observations by theWide-field Infrared Survey Explorer (WISE) spacecraft, Siarnaq is estimated to be 39.3 km (24.4 mi) in diameter.[6]
Siarnaq is light red in color, and the Siarnaupian (Siarnaqan)[c] spectrum in the infrared is very similar to the Inuit-group satellitesPaaliaq andKiviuq, supporting the thesis of a possible common origin in the break-up of a larger body.[9][28][29]
TheJames Webb Space Telescope obtained the spectrum of Siarnaq over the 0.7-5.3 micron region withNIRSpec, finding a 3.0micron absorption feature associated withhydrated minerals. Water ice was not found to be present in substantial quantities on Siarnaq, in contrast toPhoebe, the largest Saturnian irregular satellite. Additionally,carbon dioxide formed by irradiation oforganic compounds was detected on Siarnaq's surface. Siarnaq appears nearly identical in its composition toAlbiorix, another Saturnian irregular satellite observed by James Webb Space Telescope.[30]
Observations of Siarnaq at differentphase angles show that its brightness stays relatively constant at high phase angles, where it produces a shallowphase curve, but exhibits a strongopposition surge, where it sharply brightens by 0.2 magnitudes atopposition (zero phase).[31]: 14 This phase curve behavior of Siarnaq suggests it has a highlyporous surface likely covered with substantialregolith.[31]: 14
The rotation period of Siarnaq was measured by theCassini spacecraft to be 10.19 hours; this is the shortest rotation period of all prograde irregular moons of Saturn.[7] Siarnaq displays alight curve with three maxima and minima over a full rotation, implying a roughly triangular shape similar to that ofYmir.[8] FromCassini observations of Siarnaq at differentphase angles, the orientation of its north rotational pole has been determined to be pointing toward 98°ecliptic latitude and −23°ecliptic longitude.[e] This corresponds to a sidewaysaxial tilt, indicating that Siarnaq experiences long, extreme seasons similar to the planetUranus.[8]
| Meanorbital elements[32] | |
|---|---|
| Epoch 1 January 2000 12:00 UT (JD 2451545.0) | |
| Semi-major axis | 17,880,800 km (0.119526 AU) |
| Eccentricity | 0.311 |
| Inclination | 48.2°* |
| Orbital period | +2.45 yr (+895.87 d) |
| Apsidal precession period | 567.330 yr |
| Nodal precession period | 401.023 yr |
| |
Siarnaq orbits Saturn at an average distance of 17.9 million km (11.1 million mi) in 896 days (2.45 years).[4] Due to gravitationalperturbations the Sun and other planets, the orbit of Siarnaq varies of time. Over a 200-year period, Siarnaq's semi-major axis fluctuates between 17.5–18.3 million km (10.9–11.4 million mi), eccentricity between 0.089–0.554, and inclination between 41.4°–54.3° with respect to theecliptic.[33]: 8 The moon is in a temporarysecular resonance with Saturn, in which Siarnaq and Saturn have matchingapsidal precession periods.[34][35][f] Siarnaq's high orbital eccentricity and inclination places it close to the threshold forLidov–Kozai resonance.[38]
Siarnaq belongs to Saturn'sInuit group of prograde irregular moons, which have average semi-major axes between 11.2–18.4 million km (7.0–11.4 million mi) and high average inclinations between 45°–50°. The Inuit group is further split into three distinct subgroups at different semi-major axes: theKiviuq group, thePaaliaq group, and the Siarnaq group.[12] 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, andS/2020 S 5.[32] 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.[39]
| Geography | |
|---|---|
| Moons | |
| Astronomy | |
| Exploration | |
| Related | |
