Mars had an oxygen-rich atmosphere around 4 billion years ago
13
The density of Saturn is so low that if you were to put it in a giant glass of water it would float.
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There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
15
Some asteroids have other asteroids orbiting them.
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The population of the Earth has more than doubled since 1950.
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There are approximately 3,500 astronomers in the U.S. - but over 15,000 astrologers.
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