_Itha.png) Modelled shape of Itha from itslightcurve | |
| Discovery[1] | |
|---|---|
| Discovered by | K. Reinmuth |
| Discovery site | Heidelberg Obs. |
| Discovery date | 22 August 1919 |
| Designations | |
| (918) Itha | |
Named after | Name picked from the almanac Lahrer Hinkender Bote[2][3] |
| A919 QD · 1919 FR A907 CA · 1907 CA 1943 PB | |
| main-belt[1][4] · (outer) Itha[5] | |
| Orbital characteristics[4] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 99.72yr (36,421 d) |
| Aphelion | 3.4078AU |
| Perihelion | 2.3197 AU |
| 2.8637 AU | |
| Eccentricity | 0.1900 |
| 4.85 yr (1,770 d) | |
| 273.51° | |
| 0° 12m 12.24s / day | |
| Inclination | 12.070° |
| 330.46° | |
| 15.565° | |
| Physical characteristics | |
| 3.47393±0.00006 h[9] | |
| S(SMASS-I; Xu)[10] | |
| 10.6[1][4] | |
918 Itha (prov. designation:A919 QDor1919 FR) is a stonyasteroid and the namesake as well as the principal body of theItha family, located in the outer region of theasteroid belt. It was discovered by German astronomerKarl Reinmuth at theHeidelberg Observatory on 22 August 1919.[1] TheS-type asteroid has a notably shortrotation period of only 3.5 hours and measures approximately 21 kilometers (13 miles) in diameter. It was named "Itha", a female name taken from the almanacLahrer Hinkender Bote, unrelated to the discoverer's contemporaries.[2][3]
When applying the synthetichierarchical clustering method (HCM) byNesvorný, Itha is the principal body and namesake of theItha family (633),[5] a smallfamily of stony asteroids with only a few dozen known members.[11]: 23 Other larger and low-numbered members of this family include968 Petunia,1067 Lunaria,3787 Aivazovskij,4119 Miles and5232 Jordaens. However, according to another HCM-analysis byMilani andKnežević (AstDys), Itha is abackground asteroid as it is not a legitimate family in their analysis.[12] It orbits the Sun in theouter asteroid belt at a distance of 2.3–3.4 AU once every 4 years and 10 months (1,770 days;semi-major axis of 2.86 AU). Its orbit has aneccentricity of 0.19 and aninclination of 12° with respect to theecliptic.[4] Itha was first observed asA907 CA (1907 CA) at the U.S. Taunton Observatory (803) in Massachusetts. The body'sobservation arc begins atHeidelberg Observatory on 23 August 1919, the night after its official discovery observation.[1]
Thisminor planet was named "Itha", picked from theLahrer Hinkender Bote, analmanac which was published inLahr, southern Germany.[2][3] Especially in theAlemannic-speaking region, aHinkender Bote (lit. "limping messenger") was very popular from the late 17th throughout the early 20th century. Thecalendar section containsfeast days, the dates of important fairs andastronomical ephemerides. For 15 January, the calendar gives "Itha" as the Germanname day analogue next toMaurus andHabakuk, the protestant and catholic entries in thecalendar of saints, likely referring toSaint Maurus and prophetHabakkuk.[13]
As with 22 other asteroids – starting with913 Otila, and ending with1144 Oda – Reinmuth selected names from this calendar due to his many asteroid discoveries that he had trouble thinking of proper names. These names are not related to the discoverer's contemporaries.Lutz Schmadel, the author of theDictionary of Minor Planet Names learned about Reinmuth's source of inspiration from private communications with Dutch astronomerIngrid van Houten-Groeneveld, who worked as a young astronomer at Heidelberg.[2]
Itha is anS-type asteroid in the SMASS-I classification by Xu (1995).[10] This agrees with the overallspectral type for members of the Itha family.[11]: 23
In June 2011, a rotationallightcurve of Itha was obtained fromphotometric observations byJulian Oey at Kingsgrove Observatory (E19), Australia, in collaboration with three Argentinian astronomers. Lightcurve analysis gave a well-definedrotation period of3.47393±0.00006 hours with a brightness variation of0.30±0.03magnitude (U=3).[9] Two modeled lightcurves using photometric data from theLowell Photometric Database and from the BlueEye600 robotic telescope (L36) atOndřejov Observatory gave a sidereal period of3.473810±0.000001 and3.473808±0.000002, respectively. The modelling of the former gave twopoles at (59.0°, −59.0°) and (249.0°, −72.0°), while that of the latter gave only one pole at (72.0°, −54.0°) inecliptic coordinates (λ, β).[14][15]
According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite, and theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer (WISE), Itha measures (20.44±1.9), (21.37±0.84) and (21.561±0.106) kilometers in diameter, and its surface has analbedo of (0.2220±0.048), (0.203±0.018) and (0.224±0.034), respectively.[6][7][8] TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.2412 and a diameter of 20.53 km based on anabsolute magnitude of 10.6.[16] Other published mean-diameters by the WISE team include (20.335±0.281 km) and (23.715±0.094 km) with corresponding albedos of (0.224±0.034) and (0.1672±0.0333).[16][10]
