Europa: Ice World - Life on Europa

Europa
 
 
Europa has a very different surface from its rocky neighbor, Io. Galileo images hint at the possibility of liquid water beneath the icy crust of this moon. The bright white and bluish parts of Europa's surface are composed almost completely of water ice. In contrast, the brownish mottled regions on the right side of the image may be covered by salts (such as hydrated magnesium-sulfate) and an unknown red component. The yellowish mottled terrain on the left side of the image is caused by some other, unknown contaminant.

This global view was obtained in June 1997 when Galileo was 1.25 million kilometers from Europa; the finest details that can be discerned are 25 kilometers across.


 Europa's Ionosphere

 
NASA's Galileo spacecraft has found an ionosphere on Jupiter's moon Europa, an indication that the icy moon also has an atmosphere, Galileo scientists reported today.

"While this discovery does not relate to the question of possible life on Europa, it does show us there is a surface process occurring there, and Europa is not just some dead hunk of material," said lead investigator Dr. Arvydas Kliore of NASA's Jet Propulsion Laboratory, Pasadena, CA. Kliore reports his findings in the July 18 issue of Science magazine.

The ionosphere was detected through a series of six occultation experiments performed during Galileo's encounters with Europa in December 1996 and February 1997. During occultation, Europa was positioned between the spacecraft and Earth, causing interruption in the radio signal. Measurements of the Galileo radio signal received at the Deep Space Network stations in Goldstone, CA, and Canberra, Australia, showed that the radio beam was refracted by a layer of electrons, or charged particles, in Europa's ionosphere.

An ionosphere is a layer of charged particles (ions and electrons) found in the upper levels of an atmosphere, created when gas molecules in the atmosphere are ionized. On Europa, this ionized layer can be caused either by the Sun's ultraviolet radiation or by energetic particles trapped in Jupiter's magnetic field, known as the magnetosphere. Europa and the other Jovian satellites are immersed in this magnetosphere. "Most likely the charged particles in Jupiter's magnetosphere are hitting Europa's icy surface with great energy, knocking atoms of water molecules off the moon's surface," Kliore said.

 

 Submarine Volcanism?
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Europa is one of the four large Galilean satellites of Jupiter. Data and theory have suggested (though not proven) that Europa has an ocean of liquid water beneath its icy crust. Europa undergoes tidal heating similar to that driving the spectacular volcanism on the Jovian moon Io, and this heating may have been sufficient to melt the ice and maintain an ocean. Among the topics the conference will address are geologic and geophysical evidence concerning an ocean, and what its physical state might be.

If an ocean exists on Europa, the question of whether it could support life immediately arises. The first detailed examination of Europa by the Voyager spacecraft (in 1979) coincided very closely with the first detailed investigation by oceanographers of volcano-hydrothermal sites on the Earth's seafloor. That work has shown that in the presence of liquid water, volcanoes can sustain life without energy from the sun. Submarine volcanism is also a possibility on Europa.


  ice burgs
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http://www.jpl.nasa.gov/galileo/mess43/ocndscvd.html

Carr was visibly impressed with the way these enormous, 3-to-6-km-wide blocks, scarred with ridges, were tipped and rotated. This motion, he explained, could not be accounted for by wind or slope, but could be caused only by the traction of currents in a liquid medium.

Paul Geissler from the University of Arizona, and also new to the panel, concurred. The tilted bergs, he explained, showed just how thin the surface here was--perhaps only 1- or 2-km thick! [Thin indeed compared to a 100-km (60 mi.) deep ocean.] Geissler also explained that convection in solid ice (suspected on Ganymede) could not account for all the observed movement. And the lack of any feature higher or deeper than a few hundred meters would be consistent with a 1- or 2-km layer of floating ice [remember, icebergs are 90 percent below the surface].

Max Coon of the Northwest Research Association displayed a picture of pack ice in the open water of the Earth's own Arctic Ocean for comparison. Such floes, he explained, frozen in a winter sea, would resemble Europa's bergs even more closely. Open water on Europa would boil and freeze at the same time; the rapid freezing would seal in further loss; the water vapor released into space would settle as snow and help color the whitest, brightest surface in the solar system.


Life on Europa