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- Jupiter is the largest planet in the Solar System and has at least 16 large moons and even more very small ones.
- Four of Jupiter’s moons, or satellites, can be seen using a small telescope or even a pair of binoculars.
- The four moons were first seen and described by Galileo four hundred years ago, in 1610.
- They were later given the names, Io, Europa, Ganymede and Callisto, all of which are names taken from Greek mythology.
- They cannot be seen with the naked eye.
Figure 1. Jupiter and the 4 Galilean moons seen through a small telescope
- Of these four moons Io is the moon which is closest to Jupiter and, like all the other moons, orbits around the planet.
- “Moon” is another word for “satellite”, which means a body in outer space which revolves, or turns around another body.
- Io is a little larger than our own moon, with a diameter of about 2262 miles (3643 kilometres) and is made of rock.
- Io orbits Jupiter at a distance of about 262,094 miles (421,800 kilometres) from the planet.
- Io orbits round Jupiter at a speed of 38,764 miles(62,423 kilometres) per hour which is faster than the other moons. The speed of its orbit is due to both Europa and Ganymede exerting a pull of gravity on Io.
- Io orbits Jupiter four times for every single orbit that Ganymede makes and every two orbits that Europa makes.
- She travels 1645,796 miles (2650,236 kilometres)in her orbit and takes only 1.7 of our earth days to complete a single orbit.
- As Io turns round the planet, she keeps the same face turned towards Jupiter, so in the course of one orbit, Io only turns once on her axis.
- Several NASA space missions to Jupiter have given close up photographs and information about these “Galilean moons”, such as this photograph taken from Apollo Mission 4.
Figure 2. Images of the four Galilean moons from the Apollo spacecraft.
- The edge of Jupiter can be seen in the bottom right. Io is the large moon in the bottom left, closest to Jupiter.
- Io is so close to Jupiter that the pull of Jupiter’s gravity causes continual disturbance to the moon’s surface.
- Volcanic eruptions constantly cover the surface of Io with new coatings of sulphuric lava.
- Io is the most volcanically active body in the whole solar system.
- The volcanoes are driven by silicate magma.
- With volcanoes constantly erupting and spilling out hot lava, Io’s surface is so hot that any moisture is driven off it.
- Because of the constant volcanic eruptions, the appearance of Io is constantly changing.
- NASA describes Io as “Looking like a giant pizza covered with melted cheese and splotches of tomato and ripe olives”.
Figure 3. A NASA image of Io's surface
- Io, in Greek mythology, was a Princess of Argos. She was loved by Zeus, the sky god of the Greeks (known to the Romans as Jupiter).
- Zeus’ wife, Hera (known to the Romans as Juno) was jealous of Io, so Zeus turned Io into a young cow to escape from Hera, but Hera set Argus, a herdsman with 100 eyes, to watch Io.
- Zeus (Jupiter) killed Argus and Hera (Juno) then sent a gadfly, an insect that stings cattle, to drive Io away.
- In the heavens, however, the moon Io no
Really nice overview of the moon
Lots of pictures