Jupiter’s 11 new moons

To ancient Romans and Greeks, he was the lover of the goddesses Metis, Themis, Mnemosyne and Demeter; and to mortal women Semele, Io, Europa, Danae, Leda, Leto and Ganymede.

He was the father of Helen and Pollux , Perseus, Britomartis, Adrastea, Tityus and many more, all from different women.

To modern man, he is Jupiter, the mightiest and the king of all the planets.

In 1610, Galileo saw four tiny dots orbiting the planet through his telescope. Collectively known as the Galilean moons, they are the largest satellites of Jupiter – Ganymede, the largest satellite in the solar system; Callisto, Jupiter’s second largest; Europa, a moon covered with thick layers of water ice; and Io, the most volcanically active object in the solar system.

On Jan. 5, 2001, a team of astronomers from the University of Hawaii’s Institute of Astronomy announced the discovery of 11 new moons orbiting Jupiter. The team is composed of Scott Sheppard who led the research; David Jewitt, Yan Fernandez and Gene Magnier.

Using the university’s 2.2-meter telescope on Mauna Kea, they discovered the first nine satellites between Nov. 23 and 26, 2000 and officially designated them as S/2000 J2 to J11. The tenth satellite, S/2000 J11, was discovered on Dec. 5, 2000. The team also discovered the long-lost satellite of Jupiter dubbed as S/1975 J1 on Nov. 21, 2000.

The discovery of the 11 satellites ranked Jupiter second with the most number of moons at 28, with Saturn, first with 30 known satellites.

On May 16, 2002, the International Astronomical Union announced the discovery of 11 more satellites of Jupiter. When added to the previously known satellites, this brings to 39 the total number, toppling Saturn’s.

The researchers were astronomers from the University of Hawaii’s Institute of Astronomy headed by Scott Sheppard and David Jewit and Jan Kleyna of Cambridge University of England. The team used the Canada-France-Hawaii’s 3.6-meter telescope attached with one of the largest and most advanced digital camera in the world called "12K."

The newly discovered satellites are considered "irregular satellites," meaning they have large, elongated and highly inclined orbits. Of the 39 moons of Jupiter, 31 are irregular. The remaining eight are regular satellites which include the four Galilean moons discovered by Galileo.

The new satellites orbit in the direction opposite to the rotation of Jupiter. This is called "retrograde motion." They move around Jupiter once every 557 to 773 Earth-days.

They are relatively small, only about two to four kilometers in diameter. The researchers have not yet established the properties of their surfaces, compositions or densities but they suspect that the satellites are mostly rocky objects.

The scientists are not yet sure how Jupiter acquired the satellites. But two hypotheses are being considered – the gas drag hypothesis and the mass growth hypothesis. Any of the two might have occurred during the early years of the formation of the Solar System millions of years ago.

Jupiter can be observed after sunset until the first week of July. The next time Jupiter reappears is before sunrise on the first days of September 2002.

Watch the beautiful Jupiter-Venus conjunction on June 2-4 at 7 p.m. in the western sky.

The four Galilean moons can be observed using a 10x50 binocular.

(The author is a member of the Philippine Astronomical Society. He can be contacted at 0919-8558080. The PAS website is at http://www.geocities.com/philastrosoc.)