Herse, a Small Moon of Jupiter

Carme group (Photo credit: Wikipedia)

Carme group – core members (Photo credit: Wikipedia)

     Herse is also known as Jupiter L because it was the fiftieth moon of Jupiter to be discovered. The discovery was made on February, 2003 by a team of astronomers that included Brett Gladman, John Kavelaars, and others. It was provisionally called S/2003 J 17.

     The provisional name looks exotic, but it actually is quite easy to interpret. The capital “S” shows that the object is a satellite. Next comes 2003, the year of its discovery. The capital “J” shows that the satellite is a moon of Jupiter, and the number 17 reveals that it was the seventeenth moon of Jupiter to be discovered in 2003.

     The International Astronomical Union does not give an official name to a newly discovered moon until it is sure that the claimed discovery is valid. It sometimes happens that some astronomer thinks that he has discovered a new satellite, but it is later found to be identical with a satellite that has been sighted previously. Sometimes a newly discovered satellite mysteriously disappears. For these reasons, a satellite does not receive an official name until the discovery is confirmed and its orbit has been established with reasonable certainty.

     By 2009, the International Astronomical Union was satisfied that Jupiter L was a legitimate addition to the growing list of Jovian satellites. Herse became its permanent name.

     The word “herse” means “dew” in the ancient Greek language. Two mythological figures bore this name. One was a daughter of Cecrops. Cecrops was the founder of the city of Athens. His nether extremities were serpentine. This particular Herse had sisters named Aglauros and Pandrosos. The other Herse was the daughter of Zeus and Selene. Selene was the daughter of the Titans Hyperion and Thea, according to Hesiod, and one of the Greek goddesses associated with the moon.

     Since Jupiter is the Roman equivalent of the Greek Zeus, astronomers want to name the moons of Jupiter after mythological figures associated with Zeus. The daughter of Cecrops does not fulfill this requirement very satisfactorily, so it was the daughter of Zeus and Selene who gave her name to this Jovian satellite.

     Since the ancient Greeks had many different dialects, Herse’s name was sometimes spelled “Hersa.” However, the satellite Herse revolves around Jupiter from east to west, while Jupiter rotates on its axis from west to east. For this reason, Herse exhibits retrograde motion. Since any newly discovered retrograde moon of Jupiter is supposed to receive a name that ends in the letter “e,” astronomers called this satellite “Herse” instead of “Hersa.”

     Selene is a small satellite. It does not have a neat spherical shape like some of the larger moons of Jupiter. According to NASA, its estimated mean radius is only one kilometer.

     Herse belongs to the Carme group of Jovian moons, all of which may have originally been an asteroid that broke apart, according to NASA. To support this theory, NASA points out that Herse and other members of the Carme group have eccentric retrograde orbits with steep angles between the plane of their respective orbits and the plane of Jupiter’s equator. Their surfaces have similar colors, except that the surface of one of them (Kalyke) is redder.

     The orbit of Herse is closer to Jupiter than the orbit of the other moons of the Carme group. According to NASA, Herse is 17,570,134 kilometers from the center of Jupiter when closest to the mother planet and 29,239,867 kilometers from Jupiter’s center when farthest away.

References:

NASA: Herse

http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_S2003_J17

USGS: Jupiter L Named Herse

http://astrogeology.usgs.gov/news/page/8/item/jupiter-l-named-herse

Wikipedia: Herse (Moon)

http://en.wikipedia.org/wiki/Herse_(moon)

Theoi: Herse

http://www.theoi.com/Titan/Herse.html

Theoi: Selene

http://www.theoi.com/Titan/Selene.html

“Theogony” by Hesiod; translated by M.L. West