Discovery [1] [2] [3] | |
---|---|
Discovered by | Brett J. Gladman et al. [lower-alpha 2] |
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 [lower-alpha 3] |
Orbital characteristics [4] [5] | |
Epoch 17 December 2020 (JD 2459200.5) | |
0.1187382 AU (17,763,000 km) | |
Eccentricity | 0.5293834 |
+2.42 yr (+883.87 d) | |
35.08520° | |
Inclination | 43.80073° (to ecliptic) |
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] | |
Pole ecliptic latitude | 98°±15° [8] |
Pole ecliptic longitude | −23°±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, 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. [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 and Joseph A. Burns. [2] 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. [14] [15]
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. [16] They reobserved their previous irregular satellite discoveries from August 2000 (Ymir and Paaliaq) and identified two new irregular satellite candidates: Siarnaq and Tarvos. [17] Siarnaq, the brighter of the two, was detected at an apparent 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 foreground asteroids and confirmed they were indeed orbiting Saturn. [17] The discovery of Ymir, Paaliaq, Siarnaq, and Tarvos were formally reported by the International Astronomical Union on 25 October 2000 [3] [19] and announced by Gladman's team a day later at a meeting hosted by the American Astronomical Society's Division for Planetary Sciences. [15] The discovery of the four satellites raised Saturn's known moons to 22, surpassing Uranus'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 the Kitt Peak National Observatory in December 2000, [21] and later by the Palomar and La 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 overtaking Jupiter as the planet with the most known moons until 2003. [14] [22]
The moon is named after Siarnaq, the Inuit sea giantess or goddess and ruler of the Inuit underworld Adlivun. [23] 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. [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's Working Group for Planetary System Nomenclature in a general assembly held in July 2003. [24] Siarnaq was also assigned the Roman numeral designation Saturn XXIX, the 29th moon of Saturn. [26]
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. [lower-alpha 4] 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 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. [14] [24]
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. [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 for 90377 Sedna, a distant trans-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 a Windspeaker interview [24]
From infrared observations by the Wide-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) [lower-alpha 3] 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. [9] [28] [29]
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). [30] : 14 This phase curve behavior of Siarnaq suggests it has a highly porous surface likely covered with substantial regolith. [30] : 14
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. [7] Siarnaq displays a light curve with three maxima and minima over a full rotation, implying a roughly triangular shape similar to that of Ymir. [8] 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. [lower-alpha 5] This corresponds to a sideways axial tilt, indicating that Siarnaq experiences long, extreme seasons similar to the planet Uranus. [8]
Mean orbital elements [31] | |
---|---|
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 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 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 the ecliptic. [32] : 8 The moon is in a temporary secular resonance with Saturn, in which Siarnaq and Saturn have matching apsidal precession periods. [33] [34] [lower-alpha 6] Siarnaq's high orbital eccentricity and inclination places it close to the threshold for Lidov–Kozai resonance. [37]
Siarnaq belongs to Saturn's Inuit 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: the Kiviuq group, the Paaliaq group, and the Siarnaq group. [12] The Siarnaq group is the outermost Inuit subgroup and includes six known members: Siarnaq, Tarqeq, S/2004 S 31, S/2019 S 14, S/2020 S 3, and S/2020 S 5. [31] 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. [38]
Caliban is the second-largest retrograde irregular satellite of Uranus. It was discovered on 6 September 1997 by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the 200-inch Hale Telescope together with Sycorax and given the temporary designation S/1997 U 1.
Ananke is a retrograde irregular moon of Jupiter. It was discovered by Seth Barnes Nicholson at Mount Wilson Observatory in 1951. It is named after the Greek mythological Ananke, the personification of necessity, and the mother of the Moirai (Fates) by Zeus. The adjectival form of the name is Anankean.
Themisto, also known as Jupiter XVIII, is a small prograde irregular satellite of Jupiter. It was discovered in 1975, subsequently lost, and rediscovered in 2000.
Setebos is one of the outermost retrograde irregular satellites of Uranus. It was discovered on 18 July 1999 by John J. Kavelaars et al. and provisionally designated S/1999 U 1.
The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to the enormous Titan, which is larger than the planet Mercury. There are 146 moons with confirmed orbits, the most of any planet in the solar system. This number does not include the many thousands of moonlets embedded within Saturn's dense rings, nor hundreds of possible kilometer-sized distant moons that have been observed on single occasions. Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possibly Rhea, are currently in hydrostatic equilibrium. Three moons are particularly notable. Titan is the second-largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape featuring river networks and hydrocarbon lakes. Enceladus emits jets of ice from its south-polar region and is covered in a deep layer of snow. Iapetus has contrasting black and white hemispheres as well as an extensive ridge of equatorial mountains among the tallest in the solar system.
Kiviuq is a prograde irregular satellite of Saturn. It was discovered by J. J. Kavelaars et al. in 2000, and given the temporary designation S/2000 S 5. It was named after Kiviuq, a hero of Inuit mythology.
Ijiraq, or Saturn XXII (22), is a small prograde irregular satellite of Saturn. It was discovered by the team of Brett Gladman, John J. Kavelaars, et al. in 2000, and given the temporary designation S/2000 S 6. It was named in 2003 after the ijiraq, a creature in Inuit mythology.
Paaliaq is a prograde irregular satellite of Saturn. It was discovered by J. J. Kavelaars, Brett J. Gladman, Jean-Marc Petit, Hans Scholl, Matthew J. Holman, Brian G. Marsden, Philip D. Nicholson and Joseph A. Burns in early October 2000, and given the temporary designation S/2000 S 2. It was named in August 2003 after a fictional shaman in the book The Curse of the Shaman, written by Michael Kusugak, who supplied Kavelaars with the names of giants from Inuit mythology that were used for other Saturnian moons.
Skathi, also named Saturn XXVII and originally spelled Skadi, is a natural satellite of the planet Saturn. Skathi is one of Saturn's irregular moons, in its Norse group of satellites. It was discovered on September 23, 2000, by a team of astronomers led by Brett Gladman. The team announced their discovery on December 7, 2000, along with seven other satellites of Saturn, namely; Tarvos, Ijiraq, Thrymr, Siarnaq, Mundilfari, Erriapus, and Suttungr. The moon was named after Skaði, a figure in Norse mythology, as part of an effort to diversify the largely Greek and Roman names of astronomical objects.
Albiorix is a prograde irregular satellite of Saturn. It was discovered by Holman and colleagues in 2000, and given the temporary designation S/2000 S 11.
Erriapus, or Saturn XXVIII (28), is a prograde irregular satellite of Saturn. It was discovered by Brett Gladman, John J. Kavelaars and colleagues in 2000, and given the temporary designation S/2000 S 10. It was named Erriapo in August 2003 after Erriapus, a giant in Gaulish mythology; the name was changed from dative Erriapo to nominative Erriapus per IAU conventions in late 2007.
Tarvos, or Saturn XXI, is a prograde irregular satellite of Saturn. It was discovered by John J. Kavelaars et al. on September 23, 2000, and given the temporary designation S/2000 S 4. The name, given in August 2003, is after Tarvos, a deity depicted as a bull god carrying three cranes alongside its back from Gaulish mythology.
Mundilfari, or Saturn XXV, is a natural satellite of Saturn. It was discovered by Brett J. Gladman, et al. in 2000, and given the temporary designation S/2000 S 9. Mundilfari is about 7 kilometres in diameter, and orbits Saturn at an average distance of 18,5903 Mm in 952.95 days, at an inclination of 168.4° to the ecliptic, in a retrograde direction and with an eccentricity of 0.210.
The Inuit group is a dynamical grouping of the prograde irregular satellites of Saturn which follow similar orbits. Their semi-major axes range between 11 and 19 Gm, their inclinations between 45° and 50°, and their eccentricities between 0.11 and 0.39. They take an average of 2 years to orbit Saturn.
The Gallic group is a dynamical grouping of the prograde irregular satellites of Saturn following similar orbits. Their semi-major axes range between 16 and 19 Gm, their inclinations between 36° and 41°, and their eccentricities between 0.46 and 0.53. The International Astronomical Union (IAU) reserves names taken from Gallic mythology for these moons.
S/2006 S 3 is a natural satellite of Saturn. Its discovery was announced by Scott S. Sheppard, David C. Jewitt, Jan Kleyna, and Brian G. Marsden on June 26, 2006 from observations taken between January and April 2006.
In astronomy, an irregular moon, irregular satellite, or irregular natural satellite is a natural satellite following a distant, inclined, and often highly elliptical and retrograde orbit. They have been captured by their parent planet, unlike regular satellites, which formed in orbit around them. Irregular moons have a stable orbit, unlike temporary satellites which often have similarly irregular orbits but will eventually depart. The term does not refer to shape; Triton, for example, is a round moon but is considered irregular due to its orbit and origins.
Philip D. Nicholson is an Australian-born professor of astronomy at Cornell University in the Astronomy department specialising in Planetary Sciences. He was editor-in-chief of the journal Icarus between 1998 and 2018.
2013 VZ70 is a centaur on a horseshoe co-orbital configuration with Saturn. It was first observed on 1 November 2013 by the Outer Solar System Origins Survey at Mauna Kea Observatory in Hawaii, United States. The discovery was announced on 23 August 2021.
S/2019 S 1 is a natural satellite of Saturn. Its discovery was announced by Edward Ashton, Brett J. Gladman, Jean-Marc Petit, and Mike Alexandersen on 16 November 2021 from Canada–France–Hawaii Telescope observations taken between 1 July 2019 and 14 June 2021.