Pasiphae was discovered on Jan. 27, 1908, by Philibert Jacques Melotte with the Greenwich Observatory's 30-inch Cassegrain telescope.
With a mean radius of 18.6 miles (30 kilometers), Pasiphae is the largest member of the Pasiphae group, a family of Jovian satellites which have similar orbits and are therefore thought to have a common origin. Pasiphae was probably an asteroid that was captured by Jupiter's gravity and then suffered a collision which broke off a number of pieces. Those pieces became at least some, and perhaps all, of the other moons commonly categorized as members of the Pasiphae group.
All of the Pasiphae moons are retrograde, which means they orbit Jupiter in the opposite direction from the planet's rotation. Their orbits are also eccentric (elliptical rather than circular) and highly inclined with respect to Jupiter's equatorial plane. All of these characteristics support the idea that the Pasiphae satellites began as one or more captured asteroids, rather than forming as part of the original Jupiter system.
Compared to Jupiter's other satellite groups, confidence is lower that all the moons in the Pasiphae group originated in a single collision. This is due to differences in color (varying from red to gray), and differences in orbital eccentricity and inclination among the members of the Pasiphae group. Sinope, in particular, is suspected of starting out as an independent asteroid.
However, both Pasiphae and Sinope are locked in secular resonances with Jupiter, which means that Jupiter's gravity tugs at them at regular intervals in a way that can modify their orbits over time. This could account for the differences in their orbits compared to each other and to other presumed members of the Pasiphae group.
If Sinope does not belong in the Pasiphae group, then the individual moon called Pasiphae retains 99 percent of the mass of the original asteroid. If Sinope is included, Pasiphae still retains the lion's share: 87 percent of the original mass. None of the Pasiphae members is massive enough to pull itself into a sphere, so they are probably all irregularly shaped.
Pasiphae has a mean radius of 18.6 miles (30 kilometers), assuming an albedo of 0.04. At a mean distance of about 14.6 million miles (23.6 million kilometers) from Jupiter, the satellite takes about 744 Earth days to complete one orbit.
How Pasiphae Got Its Name
Pasiphae was named for the wife of Minos, who was king of Crete. According to one account, she was the mother of Ammon (king of the Egyptian gods) by Zeus, the Greek equivalent of the Roman god Jupiter. But she is probably best known for the legend in which Poseidon makes her fall in love with a bull (which was either sent by Zeus or was Zeus in disguise). She crawls inside a cowhide-covered wooden cow, has intercourse with the bull and subsequently gives birth to the Minotaur, a human-flesh-eating monster with the body of a man and the head of a bull, who winds up imprisoned in a labyrinth.
A name ending in "e" was chosen for this moon in accordance with the International Astronomical Union's policy for designating outer moons with retrograde orbits.