Neptune was named by the astronomer who discovered the planet, Urbain Le Verrier. It is named after the Roman god of the sea, which was in keeping with the theme of naming the planets after gods from Greek and Roman mythology. Other proposed names included Janus, Oceanus and Le Verrier.
Neptune was discovered by Le Verrier in 1846. The earliest observation of the planet was recorded in the early 17th century by Galileo, who mistook it for a fixed star. It is the farthest planet from the sun and the fourth largest planet by diameter. It is the most dense planet, with a mass 17 times that of Earth.