Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. What appears to be a caricature of a complex highway system on Earth is actually a system of ridges and cracks on the icy surface of Jupiter 's moon Europa . The distance between parallel ridges in the above photograph is typically about 1 kilometer. One noteworthy feature is the overall white sheen, possibly indicating the presence of frost. Another is the dark centers between parallel ridges, which might indicate that dirty water from an underground ocean recently welled up in the cracks and froze.
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