Themisto (moon)

Infobox Planet
name = Themisto


caption = artist's impression
bgcolour = #ffc0c0
width = 200
discovery = yes
discoverer = Charles Kowal (1975)
Elizabeth Roemer (1975)
Scott S. Sheppard (2000)
David C. Jewitt (2000)
Yanga R. Fernández (2000)
Eugene A. Magnier (2000)
discovered = September 30, 1975
November 21, 2000 rediscovered
mean_orbit_radius = 7,391,650 km (0.04941 AU)
eccentricity = 0.2006
periapsis = 5,909,000 km (0.039 AU)
apoapsis = 8,874,300 km (0.059 AU)
period = 129.82761 d (0.3554 a)
avg_speed = 4.098 km/s
inclination = 45.81° (to the ecliptic) 47.48° (to Jupiter's equator)
satellite_of = Jupiter
physical_characteristics = yes
mean_radius = 4 kmSheppard, S. S.; Jewitt, D. C.; [http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf "An abundant population of small irregular satellites around Jupiter"] , Nature, 423 (May 2003), pp. 261-263 ]
circumference = ~25 km
surface_area = ~200 km²
volume = ~270 km³
mass = 6.89e|14 kg
density = 2.6 g/cm³ "assumed"Physical parameters [http://ssd.jpl.nasa.gov/?sat_phys_par from JPL] ]
surface_grav = ~0.0029 m/s² (0.0003 g)
escape_velocity = ~0.0048 km/s
albedo = 0.04 "assumed"
single_temperature = ~124 K

Themisto (pron-en|θɨˈmɪstoʊ "thə-MIS-toe," or as in Greek "Θεμιστώ)," also known as nowrap|Jupiter XVIII, is a small prograde irregular satellite of Jupiter. It was discovered in 1975, lost, and then rediscovered in 2000.

Discovery and naming

Themisto was first discovered by Charles T. Kowal and Elizabeth Roemer on September 30, 1975, reported on October 3, 1975 [ [http://cfa-www.harvard.edu/iauc/02800/02845.html IAUC 2845: "Probable New Satellite of Jupiter"] 1975 October 3 (discovery)] and designated nowrap|S/1975 J 1. However, not enough observations were made to establish an orbit and it was subsequently lost.

Themisto 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 nowrap|S/2000 J 1. It was soon confirmed that this was the same as the 1975 object. The Sheppard et al. announcement [ [http://cfa-www.harvard.edu/iauc/07500/07525.html IAUC 7525: "S/1975 J 1 = S/2000 J 1"] 2000 November 25 (recovery)] 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). [ [http://cfa-www.harvard.edu/mpec/K00/K00Y16.html MPEC 2000-Y16: "S/1975 J 1 = S/2000 J 1, S/1999 J 1"] 2000 December 19 (recovery and ephemeris)]

In October 2002 it was officially named after Themisto [ [http://cfa-www.harvard.edu/iauc/07900/07998.html IAUC 7998: "Satellites of Jupiter"] 2002 October 22 (naming the moon)] , daughter of the river god Inachus by Zeus (Jupiter) in Greek mythology.

Characteristics

Themisto's orbit is unusual. Unlike most of Jupiter's moons, which orbit in distinct groups, Themisto orbits alone, midway between the Galilean moons and the first group of prograde irregulars.

Themisto is about 8 kilometers in diameter (assuming an albedo of 0.04)

ee also

*Irregular satellites

References

#

Ephemeris [http://cfa-www.harvard.edu/iau/NatSats/NaturalSatellites.html IAU-MPC NSES]
#Mean orbital parameters [http://ssd.jpl.nasa.gov/?sat_elem NASA JPL]

External links

* [http://www.ifa.hawaii.edu/~jewitt/irregulars.html David Jewitt's pages]
* [http://www.dtm.ciw.edu/sheppard/satellites/jupsatdata.html Jupiter's Known Satellites] (by Scott S. Sheppard)