How Jupiter Moon Europa's Underground Ocean Was Discovered - NBC Right Now/KNDO/KNDU Tri-Cities, Yakima, WA |

How Jupiter Moon Europa's Underground Ocean Was Discovered

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YAHOO.COM - This is Part 4 of a six-part series telling the story of humankind's efforts to understand the origins of life, by looking for it in extreme environments where life thrives without relying on the sun as an energy source.

It follows an oceanographic expedition to the Mid-Cayman Rise led by Chris German of the Woods Hole Oceanographic Institution, and NASA's efforts to plan a future mission to Jupiter's moon Europa. By understanding how life can live without the sun, we may discover how life began on our planet, and whether or not Earth is the only place in the universe capable of supporting a biosphere.

Nineteen seventy-seven was the kind of year that only comes around once every 176 years. That's how often the outer planets of our solar system (Jupiter, Saturn, Uranus and Neptune — sorry, Pluto) line up just right in their orbits around the sun to allow for a spacecraft to slingshot past all four of them.

Rather than wait until 2153, NASA decided to take advantage of the opportunity of ‘77. The space agency launched the twin 1-ton space probe emissaries, Voyager 1 and Voyager 2, from Florida's Cape Canaveral in September and August of that year, respectively. [Voyager: Humanity's Farthest Journey (Video)]

The Voyager mission was only supposed to last for four years, and technically, both spacecraft were only heading to Jupiter and Saturn. Mission designers had planned Voyager 2's trajectory so it could continue on toward Uranus and Neptune if Voyager 1 (which launched second but took a faster route) succeeded at Jupiter and Saturn. Fifty-two worlds and 12 years later, the Volkswagen Beetle-size probes brought new meaning to success in planetary science.

Their journeys to the outer planets gave humanity a front-row seat to see half the solar system up close in great detail for the first time (NASA's Pioneer 10 and 11 spacecraft had zipped past Jupiter in 1973 and 1974, but they were far less capable and yielded significantly less data).

The Voyager probes sent back stunning images of the Great Red Spot on Jupiter that revealed it to be a raging storm the size of two Earths. Saturn's rings —thought to be smooth and ordered — were revealed to be oddly intertwining and kinked. The mission further discovered that Uranus orbits on its side and Neptune sports the fastest winds in the solar system.

And that was just the planets. The 48 moons captured by the Voyager craft were arguably even more striking than their parent planets.

Jupiter's Galilean moons

The largest of Jupiter's satellites are the four Galilean moons — Io, Ganymede, Callisto, and Europa — which are named for their discoverer, Italian astronomer Galileo Galilee.

Galileo spotted them in 1610 after tweaking his telescope to reach a magnifying capability of 20x (20 times better than the naked eye). These four worlds were the first moons discovered orbiting a planet other than Earth. (Since our own moon is awfully hard to miss, we'll never know who was the first person to look up and say, "What's that?" Thus, it's probably safe to credit Galileo with discovering moons.)

The Galilean moons proved to be full of surprises at close range. An active volcano was spotted on the innermost of the Galilean moons, Io, spouting ash and gases a whopping 174 miles (280 kilometers) in height — the first evidence of active volcanism beyond Earth.

The mission team would find half a dozen more erupting volcanoes on Io over the course of the mission. Team leader Brad Smith said this made Io look like a pizza. Later, astronomers would identify more than 400 active volcanoes there, making Io the most geologically active world in our solar system.

You'd think such a world might be a hot one, but you'd be wrong. Most of Io's surface is minus 238 degrees Fahrenheit (minus 150 degrees Celsius). Colossal eruptions of gases condense and fall back to the surface as pastel yellow, orange and bluish-white sulfur dioxide snow.

This makes Io a surrealist's dream: fiery hell plus winter wonderland with an everything-on-it sulfuric pizza surface and the churning clouds of Jupiter looming above hazy skies.

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