Hippocamp, named for the sea monster from Greek mythology, is only about 21 miles in diameter. By comparison, Neptune is 30,598 miles in diameter.

The average diameter across the planet is 30,598 miles (49,244 km), almost four times the diameter of Earth.

A trip around Neptune's equator would cover 96,129 miles (154,705 km).

The density of Neptune is 1.638 grams per cubic centimeter. The low density indicates that, like Uranus, its atmosphere is made up of more ice than Saturn and Jupiter, causing scientists to call it an "icy giant".