Europa: Facts About Jupiter's Icy Moon and Its Ocean
So far, more than 60 moons of various sizes have been discovered around the planet Jupiter. The four largest moons of Jupiter are Io, Ganymede, Callisto, and Europa. The surface of Europa is frozen, covered with a layer of ice, leading scientists to believe there is a very active ocean beneath the surface of this intriguing moon.
Facts about Europa
Age: Europa is estimated to be about 4.5 billion years old, about the same age of Jupiter.
Distance from the sun: On average, Europa's distance from the sun is about 485 million miles (or 780 million kilometers).
Distance from Jupiter: Europa is Jupiter's sixth satellite. Its orbital distance from Jupiter is 414,000 miles (670,900 km). It takes Europa three and a half days to orbit Jupiter. The same side of the Europa faces Jupiter at all times.
Size: Europa is 1,900 miles (3,100 km) in diameter, making it smaller than the Earth's moon, but larger than Pluto. It is the 15th largest body in the solar system, and the smallest of the Galilean moons.
Temperature: Europa's surface temperature at the equator never rises above minus 260 degrees Fahrenheit (minus 160 degrees Celsius). At the poles of the moon, the temperature never rises above minus 370 degrees Fahrenheit (minus 220 degrees Celsius).
The Discovery of Europa Galileo Galilei discovered Europa on Jan. 8, 1610. It is possible that German astronomer Simon Marius (1573-1624)also discovered the moon at the same time. However, it is Galileo who is most often credited with the discovery. For this reason, Europa and Jupiter's other three largest moons are often called the Galilean moons. Galileo, however, called the moons the Medicean planets in honor of the Medici family.
It is possible Galileo actually observed Europa a day earlier, on Jan. 7, 1610. However, because he was using a low-powered telescope, he couldn't differentiate Europa from Io, another of Jupiter's moons. It wasn't until later that Galileo realized they were two separate bodies.
The discovery of the Galilean moons orbiting Jupiter helped scientists realize that the planets in our solar system, including Earth, revolved around the sun and not the Earth.
Exploration of Europa
Europa in 1979 by Voyager 1
Exploration of Europa began in the 1973 with the Jupiter flybys of Pioneer 10 and 11 in 1973 and 1974 respectively. The first closeup photos were of low resolution compared to later missions.
The two Voyager probes traveled through the Jovian system in 1979 providing more detailed images of Europa's icy surface. The images caused many scientists to speculate about the possibility of a liquid ocean underneath.
The Galileo mission, launched by NASA in 1989, is responsible for much of the information we have on Jupiter and the bodies surrounding it. It took more than six years for the unmanned Galileo spacecraft to reach its destination. The craft stayed in orbit of Jupiter from December 8, 1995 until Sept. 21, 2003.
Characteristics of Europa
A prominent feature of Europa is its high degree of reflectivity. Europa's icy crust gives it an albedo—light reflectivity—of 0.64, one of the highest of all of the moons in the entire solar system.
Scientists estimate that Europa’s surface is about 20 million to 180 million years old, which makes it fairly young.
Observing pictures taken by the Galileo spacecraft, scientists believe Europa is made of silicate rock, and has an iron core and rocky mantle, much like the Earth does. Unlike the interior of Earth, however, the rocky interior of Europa is surrounded by a layer of ice that is approximately 62 miles (or 100 km) thick.
Experts also believe there is an ocean deep beneath the surface of the moon, and that it is possible this ocean contains some form of life. The possibility that there is extraterrestrial life on the Europa has sparked the imaginations of many, and is one of the reasons interest in Europa remains high. In fact, recent studies have given new life to the theory that Europa can support life.
The surface of the moon is covered by a salt water ocean. And, because the moon is so far from the sun, this ocean is frozen across the surface of the moon.
The surface of Europa is covered with cracks. Many believe these cracks are the result of tidal forces on the ocean beneath the surface. It's possible that, when Europa's orbit takes it close to Jupiter, the tide of the sea beneath the ice rises higher than normal. If this is so, the constant raising and lowering of the sea caused many of the cracks observed on the surface of the moon.
It is also believed that the ocean beneath the surface sometimes erupts through the surface (much like lava erupts from a volcano) and then freezes. Icebergs observed on the surface of the moon may support this theory.
Europa's Atmosphere Europa has a tenuous oxygen atmosphere, likely the result of charged particles from the sun hitting water molecules on the moon's surface, breaking the molecules into oxygen and hydrogen atoms. While the hydrogen escapes the moon's surface, oxygen is left behind.