Friday, April 18, 2014

Jupiter's moon Europa: The Importance of Plumes

Plumes on the closest of the jovian moons, Io, are a common phenomenon. Credit: NASA/JPL

The Hubble Space Telescope is famous for finding black holes.

It can pick out thousands of galaxies in a patch of sky the size of a thumbprint.

The most powerful space telescope ever built, the Hubble provided evidence that the Universe isn't slowing down in its infinite rush into whatever lies beyond.

But the Hubble's cosmic firepower was recently put to a new purpose: searching for a billowing cloud of water vapor on Jupiter's moon Europa.

The plumes are a sign that extraterrestrial life could be lurking within our own Solar System.

Before we head way out there, we need to know a little about the eruptions happening at home.

Plumes: Warm and Nearby
On Earth, the plumes are a hallmark of energy in motion. Here, active geology often takes the form of pyroclastic eruptions. Pyro is Greek for "fire," while "clastic" derives from "broken."

Pyroclastic eruptions feature solid rock, semi-solid fragments and hot gases expelled from the mantle through areas of weakness in the crust.

They create the plumes of ash and smoke we typically associate with volcanos. Even when volcanos are underwater, as many are, they send up steaming columns of lava fragments, bits of rock and heated gas.

These underwater plumes of hot material rise hundreds of meters. The heated underwater plumes that make it to the surface of the ocean can be seen from space.

While these displays are impressive, not all that explodes from the Earth's crust is pyroclastic. Geysers are long columns of water.

Their bases lie close enough to the mantle to be heated by its 1,000° C (1,832 ° F) temperatures.

The heated water expands and rises, forcing its way to the surface. Once the water and steam reach the surface, the pressure falls, as does the plume of vapour, after inertia shoots it briefly into space.

In all of these formations, heated gases escape from the interior and reach the surface. There, they rapidly expand and cool, dissipating the fierce energies that drove them to erupt.

In this way, volcanism reflects the build-up of pressure within a planet or other large body on which it is known to occur.

In March of 2006, geysers were discovered spewing water from the surface of Enceladus, one of Saturn's icy moons.

Thus began a race to explain how a moon with surface temperatures of -330° Fahrenheit (-201° Celsius) could have active geology, and to discover if those geysers could signal a warm core for Enceladus and other icy moons.

More information: "Transient Water Vapour at Europa's South Pole." Lorenz Roth, Joachim Saur, Kurt D. Retherford, Darrell F. Strobel, Paul D. Feldman, Melissa A. McGrath, and Francis Nimmo. Science 10 January 2014: 343 (6167), 171-174.Published online 12 December 2013 [DOI: 10.1126/science.1247051]

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