Themisto (moon) facts for kids
| Discovery | |
|---|---|
| Discovered by | Charles Kowal (1975) Elizabeth Roemer (1975) |
| Discovery date | September 30, 1975 November 21, 2000 rediscovered |
| Orbital characteristics | |
| Periapsis | 5,909,000 km (0.039 AU) |
| Apoapsis | 8,874,300 km (0.059 AU) |
|
Mean orbit radius
|
7,391,650 km (0.04941 AU) |
| Eccentricity | 0.2006 |
| 129.82761 d (0.3554 a) | |
|
Average orbital speed
|
4.098 km/s |
| Inclination | 45.81° (to the ecliptic) 47.48° (to Jupiter's equator) |
| Satellite of | Jupiter |
| Physical characteristics | |
|
Mean radius
|
4 km |
| Circumference | ~25 km |
| ~200 km² | |
| Volume | ~270 km³ |
| Mass | 6.89×1014 kg |
|
Mean density
|
2.6 g/cm3 assumed |
| ~0.0029 m/s2 (0.0003 g) | |
| ~0.0048 km/s | |
| Albedo | 0.04 assumed |
| Temperature | ~124 K |
Themisto, also known as Jupiter XVIII, is a small moon that orbits the giant planet Jupiter. It is not perfectly round, and it moves around Jupiter in a "prograde" direction. This means it orbits in the same direction that Jupiter spins. Themisto was first found in 1975, but then it was lost! Scientists rediscovered it in 2000.
Contents
Finding and Naming Themisto
Themisto has a unique discovery story. It was first spotted by two astronomers, Charles T. Kowal and Elizabeth Roemer, on September 30, 1975. They called it S/1975 J 1. However, they couldn't observe it enough to figure out its exact path around Jupiter, so it became lost to science.
Rediscovery in 2000
For many years, Themisto was just a note in old astronomy books. Then, in 2000, a team of scientists including Scott S. Sheppard, David C. Jewitt, Yanga R. Fernández, and Eugene A. Magnier found what seemed to be a new moon. They named it S/2000 J 1. Soon after, they realized it was the very same moon that had been lost since 1975! Another team had also seen it earlier that year but hadn't officially announced it.
How Themisto Got Its Name
In October 2002, this special moon was officially named Themisto. This name comes from Greek mythology. Themisto was a daughter of the river god Inachus and was connected to Zeus, who is the Greek version of the Roman god Jupiter.
Themisto's Special Orbit
Themisto's path around Jupiter is quite unusual. Most of Jupiter's many moons orbit in groups or families. But Themisto orbits all by itself! It travels in a space between Jupiter's four largest moons, called the Galilean moons, and another group of moons that orbit in the same direction as Jupiter.
Size of Themisto
Themisto is a very small moon. Scientists believe it is about 8 kilometers across. To give you an idea, that's roughly the length of 80 football fields!
Images for kids
-
Themisto seen by the Canada-France-Hawaii Telescope on August 6, 2000, before its official rediscovery later that year.
See also
In Spanish: Temisto (satélite) para niños
