Call it the comeback kid. A massive cloud of gas crashing into the Milky Way probably started its life in our galaxy, according to new observations from the Hubble Space Telescope. Located 40,000 light years from Earth, Smith's Cloud is 11,000 light years long, 2500 light years across and has a mass millions of times that of our sun. If we could see it, it would span 30 times the diameter of the full moon from tip to tail. But because it is made mostly of hydrogen gas, it is nearly invisible. It was discovered in the early 1960s when astronomer Gail Smith detected radio waves emitted by its hydrogen atoms. In 2008, other astronomers reported that the cloud is moving towards the Milky Way and will crash into its disc in 27 million years.
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