Earth or Europa: Name this Ocean World

Certain features make it hard to distinguish between the two—can you tell them apart?

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Artist's illustration of Jupiter and Europa with the Galileo spacecraft after its pass through a plume.

This ocean world is 93 million miles away from the Sun.

Artist's illustration of Jupiter and Europa with the Galileo spacecraft after its pass through a plume.
Earth is approximately 93 million miles (or 150 million kilometers) away from the Sun. Europa is more than five times that distance—it’s way out there in our solar system at 485 million miles (or 780 million kilometers) from the Sun.
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NASA astronaut Reid Wiseman tweeted this photo from the International Space Station on Tuesday morning, Sept. 2, 2014. "My favorite views from #space – just past #sunrise over the ocean," the Expedition 40 astronaut tweeted.

Approximately 70 percent of this ocean world is covered in water.

NASA astronaut Reid Wiseman tweeted this photo from the International Space Station on Tuesday morning, Sept. 2, 2014. "My favorite views from #space – just past #sunrise over the ocean," the Expedition 40 astronaut tweeted.
The ocean covers approximately 70 percent of the Earth's surface. Europa’s entire surface, on the other hand, is covered with ice. And scientists believe that beneath that icy surface is an ocean containing more than twice as much water as Earth.
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Two views of the trailing hemisphere of Europa. The right is a false-color composite combining violet, green and infrared images to enhance color differences in the predominantly water-ice crust of Europa.

This ocean world has an ocean depth of between 40 to 100 miles (60 to 150 kilometers).

Two views of the trailing hemisphere of Europa. The right is a false-color composite combining violet, green and infrared images to enhance color differences in the predominantly water-ice crust of Europa.
Europa’s ocean lies below a shell of ice probably 10 to 15 miles (15 to 25 kilometers) thick and has an estimated depth of 40 to 100 miles (60 to 150 kilometers). Earth’s ocean, on the other hand, has an average depth of about 2.5 miles (4 kilometers).
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This “blue marble” image is the most detailed true-color image of the Earth to date.

The core of this ocean world is iron.

This “blue marble” image is the most detailed true-color image of the Earth to date.
Like our planet, Europa is believed to have an iron core.
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Color view of Europa made from images taken by NASA's Galileo spacecraft in the late 1990s.

This ocean world has its own moon.

Color view of Europa made from images taken by NASA's Galileo spacecraft in the late 1990s.
Europa has no moons and is actually one of Jupiter’s 53 named moons. It’s about 65 percent of the size of our Moon.
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This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on Monday morning, July 9, 1979.

The surface of this ocean world has glaciers, ridges and valleys, and tides that stretch and relax across its surface.

This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on Monday morning, July 9, 1979.
Europa and Earth both share similar geologic features, although Europa’s surface is mostly made up of solid ice in contrast to Earth’s rocky surface. Europa’s ocean might also have volcanic or hydrothermal activity on the seafloor—similar to Earth’s—that could make the ocean suitable for living things.
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This space-based view of Earth’s city lights is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite.

This ocean world has been studied by more than ten NASA missions.

This space-based view of Earth’s city lights is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite.
Earth actually has the highest number of NASA missions to date—153 supported by aircraft, ships and ground observations measuring aspects of the environment that touch the lives of every person around the world. Europa, on the other hand, has been studied by eight missions so far: Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini and New Horizons took images of Europa either as a flyby or from Jupiter orbit. From Earth orbit, the Hubble Space Telescope has also studied Europa.
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