The closest planet to the Sun is Mercury. It’s a tiny world, even smaller than Saturn’s moon Titan and Jupiter’s moon Ganymede. That’s unusual for a planetary system. Most star systems have a large world between the size of Earth and…

The closest planet to the Sun is Mercury. It’s a tiny world, even smaller than Saturn’s moon Titan and Jupiter’s moon Ganymede. That’s unusual for a planetary system. Most star systems have a large world between the size of Earth and…