The lack of craters on Europa told scientists that Europa's surface was very changed. That meant that it might be young and active like that of the Earth! Moreover, as they examined each new picture, Europa's surface seemed to get younger and younger. First scientists thought it was 3 billions years old, then they guessed it was only 1 million years old, then 10,000 years old, and finally they guessed that it might be currently active!
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