Salt from an underground sea on Jupiter's moon Europa may be seeping onto the surface, then darkening as it is exposed to radiation, a new study shows.
"That would be a simple and elegant solution for what the dark, mysterious material is," planetary scientist Kevin Hand, with NASA's Jet Propulsion Laboratory in Pasadena, California, said in a press release.
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Scientists have been trying to figure out the source and composition of dark material found along cracks and other relatively young geologic features on Europa. Complicating the picture is the harsh radiation environment on Europa, which is blasted by particles whipped around by Jupiter's powerful magnetic field.
In a report to be published in the journal Geophysical Research Letters, Hand and co-author Robert Carlson, also at JPL, describe laboratory tests on simulated Europa terrain that attempt to match the colors of various irradiated substances with the spectrum of colors found in the cracks on Europa by NASA's now-defunct Galileo spacecraft and several telescopes.
In addition to previous studies showing sulfur and magnesium are potential matches, the new experiment reveals plain old salt - sodium chloride - is a candidate material too.
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The scientists tested salt as well as mixtures of salt and water in a vacuum chamber set at an Europa-like temperature of minus 280 degrees Fahrenheit. They then used an electron beam to blast the materials, simulating the radiation environment on the moon.
The white salt turned yellowish-brown, a color similar to what has been found inside fractures on the moon's surface.
"The chemical signature of radiation-baked sodium chloride is a compelling match to spacecraft data for Europa's mystery material," Hand said.
Scientists are trying to piece together enough information to figure out if Europa has conditions that are suitable for life.