In 2017, a huge rocky formation was spotted moving through space, defying science's understanding of natural motion. Researchers called the rock 'Oumuamua. Two years later, a similar formation was found. Could the rocks have been made by intelligent life? And is this the first time we've seen something out of this world? Space is full of mysteries--and we're here to solve them. Includes 21st Century Skills and Content, sidebars, activity, table of contents, index, and glossary.