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Themisto (IPA: /θəˈmɪstoʊ/, the-mis'-toe, Greek Θεμιστώ) (Jupiter XVIII) is a moon of Jupiter. It was first discovered by Charles T. Kowal and Elizabeth Roemer on September 30, 1975, reported on October 3 (IAUC 2845) and designated S/1975 J 1, but not enough observations were made to establish an orbit and it was subsequently lost.

Themisto
Discovery
Discovered by Charles Kowal (1975)

Elizabeth Roemer (1975)
Scott S. Sheppard (2000)
David C. Jewitt (2000)
Yanga R. Fernández (2000)
Eugene A. Magnier (2000)

Discovered on September 30, 1975

November 21, 2000 rediscovered

Orbital characteristics
Mean radius 7,391,650 km (0.04941 AU)
Eccentricity 0.2006
Periastron 5,909,000 km (0.039 AU)
Apastron 8,874,300 km (0.059 AU)
Orbital period 129.82761 d (0.3554 a)
Orbital circumference 45,972,400 km (0.307 AU)
Average orbital speed 4.098 km/s
Max. orbital speed 5.074 km/s
Min. orbital speed 3.379 km/s
Inclination 45.81° (to the ecliptic)
13.865° (to Jupiter's equator)
Is a satellite of Jupiter
Physical characteristics
Mean diameter 8 km
Circumference ~25 km
Surface area ~200 km2
Volume ~270 km³
Mass 6.89×1014 kg
Mean density 2.6 g/cm3
Surface gravity ~0.0029 m/s2 (0.0003 g)
Escape velocity ~0.0048 km/s
Rotation period  ?
Axial tilt  ?°
Albedo 0.04
Surface temp. (K)
min mean max
~124 K
Atmospheric pressure 0 kPa

It appeared as a footnote in astronomy textbooks into the 1980s. Then, in 2000, a seemingly new satellite was discovered by Scott S. Sheppard, David C. Jewitt, Yanga R. Fernández and Eugene A. Magnier, and was designated S/2000 J 1. It was soon confirmed that this was the same as the 1975 object. The Sheppard et al. announcement (IAUC 7525, November 25, 2000) was immediately correlated with an August 6, 2000 observation by the team of Brett J. Gladman, John J. Kavelaars, Jean-Marc Petit, Hans Scholl, Matthew J. Holman, Brian G. Marsden, Philip D. Nicholson and Joseph A. Burns — an observation that was reported to the Minor Planet Center but not published as an IAU Circular (IAUC).

In 2002 it was officially named after Themisto, a lover of Zeus (Jupiter) in Greek mythology. Themisto's orbit is unusual, as it orbits about midway between the Galilean moons and the first group of prograde irregulars.


... | Callisto | Themisto | Leda | ...





























Jupiter's natural satellites

Inner satellites | Galilean moons: Io, Europa, Ganymede, and Callisto | Themisto | Himalia group | Carpo | S/2003 J 12 | Ananke group | Carme group | Pasiphaë group | S/2003 J 2

Astronomy Encyclopedia

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