Portal:Solar System/Did you know/4

• ...that the passing of the Great Comet of 1577 (pictured) caused almost century-long debate, during which Galileo argued that comets were merely optical illusions?

• ...that systematic mapping of the Michelangelo quadrangle on Mercury has revealed the presence of four nearly obliterated multi-ring impact basins, possibly the oldest features in the mapped areas of the planet?

• ...that there have been several proposals for space advertising projects, including a giant, 1km² billboard visible from Earth?

• ...that some astrologers claim Earth has a second moon they call Lilith?