How did galileo's observations of jupiter and venus support copernicus's model?

Before Copernicus most people were thinking that the Earth is at center of universe. In 1609 Galileo observed sky through his home made telescope.
He found 4 moons orbiting Jupiter..It was a proof that bodies are orbiting other planets and not earth alone. He found the crescent shape of Venus through his telescope and this could happen only if Sun is at center.

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A. to determine if humans can explore mars safely