130 Elektra

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Template:Nowrap
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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.

DescriptionEdit

File:130Elektra (Lightcurve Inversion).png

Lightcurve-based 3D-model of (130) Elektra

(130) Elektra has the spectrum of a G-type asteroid; hence it probably has a Ceres-like surface. Spectral signatures of organic compounds have been seen on Elektra's surface<ref name=CruBro87>Template:Cite journal</ref> and it displays evidence of aqueous alteration.<ref name=Fornasier1999>Template:Cite journal</ref>

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.<ref name="Durech2007"/><ref>Template:Cite journal</ref>

Optical observations have found three satellites of this asteroid. Once the orbits are known, Elektra's mass can be reliably found. The value of 6.6 × Template:10^ kg indicates a density of Template:Nobr. 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.<ref name="Marchis2006"/><ref name="Johnston"/><ref name="Marchis2008"/>

OccultationsEdit

File: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.<ref name="Miles2018"/><ref name="JOA2019-1"/>

SatellitesEdit

Template:Update 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.<ref name="Yang2016"/> Template:As of, Elektra has the most satellites of any main-belt asteroid, and is the only known quadruple asteroid system in the Solar System.<ref name="CBET5066"/> 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.<ref name="Marchis2006"/><ref name="Yang2016"/>

Moons of Elektra<ref name="Yang2016"/><ref name="Berdeu2022"/>
Name	Discovered	Announced	Diameter (km)	Semi-major axis (km)	Orbital period (d)	Eccentricity	Inclination (°)Template:Efn	Ascending node (°)	Arg. of perihelion (°)	Mean anomaly (°)
NA<ref name="jpldata"/><ref name="CBET5066"/>	2014-12-09	2021-11-06	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	—
Template:Mp<ref name="Yang2016"/>	2014-12-06	2014-12-16	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	—
Template:Mp<ref name="IAUC8183"/>	2003-08-15	2003-08-17	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val	Template:Val

S/2003 (130) 1Edit

Template:Mp is the largest and outermost satellite of Elektra, around Template:Cvt in diameter, assuming the same albedo as the primary.<ref name="Yang2016"/> 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 had 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 Template:Mp.<ref name="IAUC8183"/>

Template:Mp orbits Template:Cvt 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 Template:Mp's semi-major axis oscillates less than Template:Cvt over 20 years. Near-infrared observations from December 2014 show that Template:Mp along with Template:Mp display a similar spectrum to Elektra, supporting the hypothesis that they are fragments from a disruptive collision.<ref name="Yang2016"/>

S/2014 (130) 1Edit

File: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. Template:Mp is the brighter object while Template:Mp is the fainter, inner object visible in the second and third images.<ref name="ESO"/>

Template:Mp 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.<ref name="ESO"/> Discovery observations showed that the satellite had a near-infrared magnitude difference of 10, corresponding to a diameter of about Template:Cvt if it has the same albedo as the primary.<ref name="Johnston"/><ref name="Yang2016"/> The discovery was announced on 16 December 2014, but the satellite was mistakenly designated Template:Mp before being immediately corrected to Template:Mp.<ref name="Johnston"/>

Template:Mp orbits Template:Cvt from Elektra with a period of 1.2 days—about two and a half times closer and four times quicker than the outer satellite Template:Mp Its roughly-circular orbit is inclined 156° with respect to the celestial equator. Preliminary simulations of the Elektra system show that Template:Mp's semi-major axis oscillates less than Template:Cvt over 20 years. Near-infrared observations from December 2014 show that Template:Mp along with Template:Mp display a similar spectrum to Elektra.<ref name="Yang2016"/>

Inner satelliteEdit

On 6 November 2021, astronomers A. Berdeu, M. Langlois, and F. Vachier reported the discovery of a third, closer-in satellite in archival VLT-SPHERE images taken between 9 and 31 December 2014, making Elektra the first quadruple system discovered and imaged in the main asteroid belt.<ref name="CBET5066"/> This third satellite, which remains undesignated,<ref name="jpldata"/> had eluded discovery when the images were taken, due to its faintness and close proximity to Elektra's bright glare. For these reasons, it had to be measured through image subtraction of Elektra's glare. The satellite measures roughly Template:Cvt in diameter, based on a near-infrared magnitude difference of 10.5.<ref name="Berdeu2022"/> The satellite has been identified in later VLT images from February 2016 and July–August 2019.<ref name="Berdeu2022"/>

With a semi-major axis of Template:Cvt and an orbital period of Template:Convert, it is the innermost companion of the Elektra system. In contrast to the two outer satellites, its orbit is remarkably eccentric and inclined; it has a high eccentricity of 0.33 and an inclination about 38° with respect to Elektra's spin axis (129° with respect to the celestial equator). The satellite's close proximity to Elektra makes its orbit subject to perturbations by shape-induced irregularities in Elektra's gravitational field (see geopotential model), which may account for most of the uncertainties in its Keplerian orbit.<ref name="Berdeu2022"/>

NotesEdit

Template:Notelist

ReferencesEdit

Template:Reflist

External linksEdit

First observation of a quadruple asteroid - Detection of a third moon around (130) Elektra, Anthony Berdeu, YouTube, 10 February 2022 (video presentation on the third satellite discovery)
130 Elektra and S/2003 (130) 1, orbit data website maintained by F. Marchis. Includes adaptive optics image of primary, and satellite orbit diagram.
Data on (130) Elektra from Johnston's archive (maintained by W. R. Johnston)
Occultation Prediction Software (David Herald)
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