what is it composed of?
Salts such as magnesium sulfate, sulfuric acid hydrate or abiotic organic compounds collectively called tholins
Europa (moon)
Spectrographic evidence suggests that the dark, reddish streaks and features on Europa's surface may be rich in salts such as magnesium sulfate, deposited by evaporating water that emerged from within. Sulfuric acid hydrate is another possible explanation for the contaminant observed spectroscopically. In either case, because these materials are colorless or white when pure, some other material must also be present to account for the reddish color, and sulfur compounds are suspected.

Another hypothesis for the colored regions is that they are composed of abiotic organic compounds collectively called tholins
where is europa located in the solar system It is orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter when was it discovered? 1610 by whom? Galileo Galilei state any one of its features? It is the smoothest known object in the Solar System, lacking large-scale features such as mountains and craters
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Europa (moon) [SEP] Composition
Spectrographic evidence suggests that the dark, reddish streaks and features on Europa's surface may be rich in salts such as magnesium sulfate, deposited by evaporating water that emerged from within. Sulfuric acid hydrate is another possible explanation for the contaminant observed spectroscopically. In either case, because these materials are colorless or white when pure, some other material must also be present to account for the reddish color, and sulfur compounds are suspected. Another hypothesis for the colored regions is that they are composed of abiotic organic compounds collectively called tholins. The morphology of Europa's impact craters and ridges is suggestive of fluidized material welling up from the fractures where pyrolysis and radiolysis take place.