Jupiter has 53 named moons. Fourteen more have been discovered but not given official status or names. Combined, scientists now think 67 moons revolve around Jupiter in unison. Jupiter's four largest moons are called the Galilean satellites after Italian astronomer Galileo Galilei, who first observed them in 1610. They are Io, Europa, Ganymede, and Callisto.
Io is the most volcanically active body in the solar system. Io's surface is covered by sulfur in different colorful forms. The scorching temperature on the moon's surface generates enough heat for volcanic activity and to drive off any water.
Europa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice beneath. Europa is thought to have twice as much water as Earth. This aspect of Europa intrigues astrobiologists because of its potential for having a "habitable zone."
Ganymede is the largest moon in the solar system (larger than the planet Mercury) and is the only moon known to have its own internally generated magnetic field.
Callisto's surface is heavily cratered and ancient — a visible record of events from the early history of the solar system. However, the very few small craters on Callisto indicate a small degree of current surface activity.
Although the space between the moons seems void and inactive, three of the moons influence each other in an interesting way. Io is in a tug-of-war with Ganymede and Europa, and Europa's orbital period (time to go around Jupiter once) is twice Io's period, and Ganymede's period is twice that of Europa. In other words, every time Ganymede goes around Jupiter once, Europa makes two orbits and Io makes four orbits. The moons all keep the same face towards Jupiter as they orbit, meaning that each moon turns once on its axis for every orbit around Jupiter.
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What does the word aspect mean as used in the passage?
A.
a particular characteristic or feature of something
B.
the positioning of a structure in a particular direction
C.
a relationship between celestial bodies in a particular horoscope
D.
the way in which time is indicated by a particular verb