130 Elektra

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130 Elektra
130 Elektra VLT (2021), deconvolved.pdf
VLT-SPHERE adaptive optics image of Elektra taken on 5 August 2019 [1]
Discovery [2]
Discovered by C. H. F. Peters
Discovery site Litchfield Obs.
Discovery date17 February 1873
Designations
(130) Elektra
Pronunciation /ɪˈlɛktrə/ [3]
Named after
Electra [4]
A873 DA [5]
main-belt [2] [5]  ·(outer) [6]
background [7]
Adjectives Elektrian /ɪˈlɛktriən/ [8]
Orbital characteristics [5]
Epoch 1 July 2021 (JD 2459396.5)
Uncertainty parameter 0
Observation arc 127.53 yr (46,582 d)
Aphelion 3.7808 AU
Perihelion 2.4725 AU
3.1266 AU
Eccentricity 0.20923
5.53 yr (2,019 d)
87.758°
0° 10m 41.79s / day
Inclination 22.782°
145.009°
237.588°
Known satellites 3
Physical characteristics
Dimensionsc/a = 0.57±0.04 [1]
262 × 205 × 164±3% km [9]
Mean diameter
199±2 km [1]
Mass (6.4±0.2)×1018  kg [1]
Mean density
1.55±0.07 g/cm3 [1]
5.224663±0.000001  h [9] [1]
156° [1]
–88° [9]
71° [9]
0.067 (calculated) [1]
0.086±0.015 (NEOWISE) [5] [7]
0.0755±0.0110 (IRAS) [10] [7]
G (Tholen) [5]
Ch (SMASS) [5]
7.21 [5] [2]  ·7.05 [1]

    Elektra (minor planet designation: 130 Elektra) is a large outer main-belt asteroid and quadruple system with three minor-planet moons. It was discovered on 17 February 1873, by astronomer Christian Peters at Litchfield Observatory, New York, and named after Electra, an avenger in Greek mythology.

    Contents

    Description

    Lightcurve-based 3D-model of 130 Elektra 130Elektra (Lightcurve Inversion).png
    Lightcurve-based 3D-model of 130 Elektra

    The spectrum of 130 Elektra is of the G-type; hence it probably has a Ceres-like composition. Spectral signatures of organic compounds have been seen on Elektra's surface [11] and it displays evidence of aqueous alteration. [12]

    In the late 1990s, a network of astronomers worldwide gathered lightcurve data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including (130) Elektra. The light curve of (130) Elektra forms a double sinusoid while the shape model is elongated and the derived rotation axis is perpendicular to the plane of the ecliptic. [13] [14]

    Optical observations have found two satellites of this asteroid. Once the orbits are known, Elektra's mass can be reliably found. The value of 6.6×1018 kg indicates a density of 1.3 ± 0.3 g/cm3. Optical observations have also determined that Elektra's shape is quite irregular, as well as giving indications of albedo differences of 5-15% on its surface. [15] [16] [17]

    Occultations

    Occultation profile of Elektra as observed from Europe on 21 April 2018 20180421-Elektra cbf.gif
    Occultation profile of Elektra as observed from Europe on 21 April 2018

    Elektra has been observed to pass in front of a dozen stars since 2007, most notably on 21 April 2018 when over 30 mostly citizen astronomers spread across five European countries recorded the sudden drop in light of an 11th magnitude star. The sky-plane plot of the chords reveals a peanut-shaped body, possibly the result of a two-body merger early in the history of the Solar System. [18] [19]

    Satellites

    Elektra has three orbiting natural satellites, all of which are unnamed and measure a few kilometres across. Together with the primary body Elektra, they comprise a quadruple system. Given their similar spectra, these satellites are thought to be fragments of Elektra that were created from a disruptive impact. [20] As of November 2021, Elektra has the most satellites of any main-belt asteroid, and is the only known quadruple asteroid system in the Solar System. [21] All three satellites are faint and orbit closely to Elektra, which makes them difficult to observe due to Elektra's bright glare obscuring them. The largest telescopes with adaptive optics systems and advanced image processing techniques are required for detailed study of the satellites' properties. [15] [20]

    Moons of Elektra [20]
    NameDiscoveredAnnouncedDiameter (km)Semi-major axis (km)Orbital period (d)EccentricityInclination (°) [lower-alpha 1] Ascending node (°)Arg. of perihelion (°)Mean anomaly (°)
    third satellite (undesignated) [21] 2014-12-092021-11-061.63450.7
    S/2014 (130) 1 [20] 2014-12-062014-12-162.0±1.5497.63±0.331.256±0.0030.157±0.036165.3±8.2196.6±9.6312.9±11.450.6±12.9
    S/2003 (130) 1 [22] 2003-08-152003-08-176.0±1.51297.58±0.545.287±0.0010.0835±0.0096160.21±1.50176.1±5.7184.4±14.1117.3±11.7

    S/2003 (130) 1

    Orbit diagram of the Elektra quadruple system 130 Elektra system.png
    Orbit diagram of the Elektra quadruple system

    S/2003 (130) 1 is the largest and outermost satellite of Elektra, around 6 km (3.7 mi) in diameter, assuming the same albedo as the primary. [20] It was discovered on 15 August 2003, by a team of astronomers led by W. J. Merline using the Keck II telescope at the Mauna Kea Observatory in Hawaii. The discovery images showed that the satellite appeared to be separated 0.72 arcseconds from the primary, with an apparent magnitude difference of 8.5 in the near-infrared K-band. The team confirmed the existence of the satellite after reobserving it with the Keck II telescope on 17 August 2003. The discovery was announced on that same day and the satellite was given the provisional designation S/2003 (130) 1. [22]

    S/2003 (130) 1 orbits 1,300 km (810 mi) from Elektra with a period of 5.3 days. Its orbit has a moderate eccentricity of 0.08 and an inclination of 160° with respect to the celestial equator. Preliminary simulations of the Elektra system show that S/2003 (130) 1's semi-major axis oscillates less than 1.4 km (0.87 mi) over 20 years. Near-infrared observations from December 2014 show that S/2003 (130) 1 along with S/2014 (130) 1 display a similar spectrum to Elektra, supporting the hypothesis that they are fragments from a disruptive collision. [20]

    S/2014 (130) 1

    Collage of infrared VLT-SPHERE images showing Elektra's resolved shape (brightness muted) and positions of its two moons from 6 to 31 December 2014. S/2003 (130) 1 is the brighter object while S/2014 (130) 1 is the fainter, inner object visible in the second and third images. S-2014 (130) 1 by SPHERE-VLT 2014.jpg
    Collage of infrared VLT-SPHERE images showing Elektra's resolved shape (brightness muted) and positions of its two moons from 6 to 31 December 2014. S/2003 (130) 1 is the brighter object while S/2014 (130) 1 is the fainter, inner object visible in the second and third images.

    S/2014 (130) 1 is the second satellite of Elektra by distance and order of discovery. It was discovered on 6 December 2014, by a team of astronomers led by B. Yang using the SPHERE adaptive optics system on the Very Large Telescope's Melipal (UT3) telescope at Cerro Paranal, Chile. [23] Discovery observations showed that the satellite had a separation distance of 0.38 arcseconds and a magnitude difference of 10, corresponding to a diameter of about 2 km (1.2 mi) if it has the same albedo as the primary. [16] [20] The discovery was announced on 16 December 2014, but the satellite was mistakenly designated S/2014 (130) 2 before being immediately corrected to S/2014 (130) 1. [16]

    S/2014 (130) 1 orbits 500 km (310 mi) from Elektra with a period of 1.3 days; about two and a half times closer and four times quicker than the outer satellite S/2003 (130) 1. Its orbit has an eccentricity of 0.16 and an inclination of 165° with respect to the celestial equator. It is unknown why S/2014 (130) 1 has a significantly higher eccentricity than S/2003 (130) 1; only its short-term orbital evolution has been analyzed so far. Preliminary simulations of the Elektra system show that S/2014 (130) 1's semi-major axis oscillates less than 100 m (330 ft) over 20 years. Near-infrared observations from December 2014 show that S/2014 (130) 1 along with S/2003 (130) 1 display a similar spectrum to Elektra. [20]

    Third satellite

    On 6 November 2021, astronomers A. Berdeu, M. Langlois, and F. Vachier announced the discovery of a third satellite in VLT-SPHERE images taken between 9 and 31 December 2014, making Elektra the first quadruple system discovered and imaged in the main asteroid belt. The discovery images show that its separation from the primary varies from 0.23 to 0.26 arcseconds, suggesting a semi-major axis around 345 km (214 mi) and an orbital period of 0.7 days. The third satellite is the innermost companion of the Elektra system, orbiting roughly one and a half times closer and twice as quickly as S/2014 (130) 1. The third satellite is 10.52±0.50 magnitudes fainter than the primary in the near-infrared YJH-band, implying a diameter of about 1.6 km (0.99 mi). The third satellite of Elektra currently does not have an official designation. [21]

    Notes

    1. With respect to the celestial equator

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