_Sorga.png) Modelled shape ofSorga from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | A. Massinger |
| Discovery site | Heidelberg Obs. |
| Discovery date | 15 April 1912 |
| Designations | |
| (731) Sorga | |
Named after | "the heavens"[2] (Indonesian language) |
| A912 GH · 1940 WP 1912 OQ | |
| Orbital characteristics[3] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 104.24yr (38,075 d) |
| Aphelion | 3.4090AU |
| Perihelion | 2.5656 AU |
| 2.9873 AU | |
| Eccentricity | 0.1412 |
| 5.16 yr (1,886 d) | |
| 201.03° | |
| 0° 11m 27.24s / day | |
| Inclination | 10.689° |
| 46.136° | |
| 288.62° | |
| Physical characteristics | |
| 8.184±0.005 h[11] | |
731 Sorga (prov. designation:A912 GHor1912 OQ) is a highly elongatedbackground asteroid from the outer regions of theasteroid belt, approximately 38 kilometers (24 miles) in diameter. It was discovered on 15 April 1912, by German astronomerAdam Massinger at theHeidelberg-Königstuhl State Observatory in southwest Germany.[1] TheC-type (CD) andX-type asteroid (Xe) has arotation period of 8.2 hours. It was namedSorga, meaning "the heavens" in theIndonesian language.[2]
Sorga is a non-family asteroid of the main belt'sbackground population when applying thehierarchical clustering method to itsproper orbital elements.[4][5][6] It orbits the Sun in theouter asteroid belt at a distance of 2.6–3.4 AU once every 5 years and 2 months (1,886 days;semi-major axis of 2.99 AU). Its orbit has aneccentricity of 0.14 and aninclination of 11° with respect to theecliptic.[3] The body'sobservation arc begins atHeidelberg Observatory on 21 October 1919, more than seven years after its official discovery observation.[1]
Thisminor planet was namedSorga, the word for "the heavens" in theIndonesian language, also transliterated as "surga". Thenaming was not mentioned inThe Names of the Minor Planets byPaul Herget.[2]
In theTholen classification,Sorga is closest to a common, carbonaceousC-type asteroid and somewhat similar to a darkD-type asteroid (CD), while in the Bus–BinzelSMASS classification, it is an Xe-subtype which transitions from theX-type to the brightE-type.[3][5]Sorga has also been classified as a metallicM-type asteroid.[12]
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In April 2005, a rotationallightcurve ofSorga was obtained fromphotometric observations byBrian Warner at hisPalmer Divide Observatory (716) in Colorado. Analysis gave a classically shaped bimodal lightcurve with a well-definedrotation period of (8.184±0.005) hours and a high brightness variation of (0.52±0.02)magnitude, indicative of its elongated shape (U=3).[11] In February 2009, Warner revisitedSorga and determined a very similar period of (8.192±0.002) hours though with a much lower amplitude of (0.19±0.02) magnitude (U=3).[13][a]
In January 2010, astronomers at thePalomar Transient Factory measured a period of8.188±0.0023 hours with an amplitude of0.72 magnitude (U=2).[12][14] Additional observations byChristophe Demeautis in September 2017, and by Bruno Christmann in April 2020, gave a period of (8.186±0.003) and (8.1865±0.0003) hours with an amplitude of0.54±0.02 and0.57±0.02 magnitude, respectively (U=3–/3).[15]
In 2016, a modeled lightcurve rendered a concurring sidereal period of8.18633±0.00002 hours using data from the Uppsala Asteroid Photometric Catalogue, the Palomar Transient Factory survey, and individual observers, as well as sparse-in-time photometry from theNOFS, theCatalina Sky Survey, and the La Palma surveys (950). The study also determined twospin axes of (83.0°, 40.0°) and (275.0°, 21.0°) inecliptic coordinates (λ, β).[16]
According to the surveys carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer (WISE), the JapaneseAkari satellite, and the Infrared Astronomical SatelliteIRAS,Sorga measures (34.597±0.409), (38.93±0.44) and (41.78±2.0) kilometers in diameter and its surface has analbedo of (0.209±0.042), (0.173±0.005) and (0.1436±0.015), respectively.[7][8][9][10] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.1339 and a diameter of 41.70 kilometers based on anabsolute magnitude of 9.7.[12] The WISE team also published an alternative mean-diameter of (31.955±0.293 km) with an albedo of (0.2605±0.0759).[12]
Twoasteroid occultations on 24 October 2007, and on 31 October 2012, gave a best-fit ellipse dimension of (45.7 km × 45.7 km) and (38.0 km × 38.0 km), with an intermediate and low quality rating of 2 and 1, respectively.[5] These timed observations are taken when the asteroid passes in front of a distant star.[5]
