The Galilean Moons Trivia Quiz

Answer: 1610

Galileo Galilei lived from 1564 until 1642 and was a big influence in the Renaissance. According to Wikipedia, Galileo has earned a few pretty significant monikers: the "father of modern observational astronomy", the "father of modern physics", the "father of science", and the "father of modern science".

Finding moons orbiting Jupiter essentially disproved geocentrism (all planetary bodies orbiting the Earth), and Galileo became a proponent of the heliocentric model (the planets orbit the sun, and moons orbit the planets). It didn't sit well with many people, and especially not with the Church.

Answer: Medici

Galileo was the tutor of Cosimo de' Medici between 1605 and 1608, when Cosimo was a teenager (he was born in 1590). His father's death in 1609 vaulted Cosimo to the position of Grand Duke of Tuscany, a position he held for 11 years.

Galileo made his discovery only a year into Cosimo's reign, and he wanted to curry favour with his former pupil to hopefully gain a patron. The Grand Duke's secretary, however, thought it might be better to honour the whole family, so Galileo settled on the name Medicea Sidera (the Medician stars) instead.

Answer: True

Simon Marius, a contemporary of Galileo's, was the one to suggest the names Callisto, Europa, Ganymede and Io. However, the two of them did not get along well. Marius published his observations of Jupiter and its moons in 1814, claiming to have discovered the moons before Galileo had. As a result of their dispute, Galileo stubbornly refused to acknowledge Marius' names for the moons, and in all his published works, he only ever referred to the moons as Jupiter I, II, III, and IV.

As it happens, the names suggested by Marius did not come into common use by astronomers until the mid-20th century.

Answer: Ganymede

Ganymede is not only the largest Galilean moon, it is the largest moon in the entire solar system. It has a diameter of 5,262.4 km (3,269.9 miles), which makes it approximately half again as large as our own moon (a ratio of 3:2).

Ganymede (Jupiter III) makes its orbit around Jupiter in approximately 7.15 days, meaning that it travels at a speed of 10.88 km/s, ten times faster than Earth's moon.

Answer: Io

Io (Jupiter I) is the innermost of the four Galilean moons, and with a diameter of 3,636 km (2,259 miles), is the fourth largest moon in the solar system, after Ganymede, Titan (of Saturn), and Callisto.

Io is the most volcanically active object in the solar system, with over 400 active volcanoes. Some of the volcanoes are so violent that they erupt to a height of 500 km (300 miles)! This geological instability arises from being between the gravitational forces of Jupiter on one side and the other Galilean moons on the other side.

Answer: Europa

Europa (Jupiter II) is the smallest of the Galilean moons with a mere 3,121.6 km (1,940 miles) diameter, which also makes it just slightly smaller than our own moon.

Europa's surface is primarily water ice, and it is believed that there may be an ocean underneath the ice that is about 100 km (60 miles) thick. For this reason, scientists surmise that there may be life on Europa.

Answer: Callisto

In order from inner to outer, the four Galilean moons are Io, Europa, Ganymede and Callisto. The inner three (Io, Europa and Ganymede) orbit Jupiter in the aforementioned 1:2:4 ratio. That means that in the time it takes Ganymede to orbit Jupiter once, Europa manages it twice, and Io does it four times.

Io orbit: 1.769137786 days
Europa orbit: 3.551181 days
Ganymede orbit: 7.15455296 days

(stats from Wikipedia)

Callisto is the second largest of the Galilean moons with a diameter of 4,820.6 km (2,995 miles), and the third largest moon in the solar system. Callisto takes 16.6890184 days to orbit Jupiter.

Answer: True

Mercury's diameter is 4,879 km (3,032 miles), putting it between Callisto and Ganymede for size. It hardly seems fair that Mercury has planetary status, while the Galilean moons are just moons.

Answer: Galileo

There have been a number of spacecraft that have been sent to Jupiter over the years, but Galileo was the first that was designed to stay and observe for a longer period of time (the others were all flybys). The first one was Pioneer 10, which was launched in 1972, flying past Jupiter a year later in 1973.

Galileo (launched in 1989) entered Jupiter's orbit on December 7, 1995, and stayed there until it was crashed into Jupiter's atmosphere on September 21, 2003, to protect the local moons from possible contamination with terrestrial bacteria.

Answer: False

Juno was launched to establish a polar orbit around Jupiter, to more closely study the gas giant and try to learn details of its formation (amongst many other things).

There *was* a planned Europa orbiter, but that was cancelled in 2002. Then there was the Jupiter Icy Moons orbiter (JIMO) that was cancelled in 2005. It will happen eventually, but as of 2014, nothing is set in stone for the Galilean moons.