50 Dollars Neptune

The Marshall Islands began issuing commemorative coinage in the late 1980s under a licensing arrangement that outsourced production entirely to foreign mints, making these coins legal tender in name while functioning almost exclusively as collector pieces. The Neptune issue belongs to a space-themed series tied loosely to NASA's Voyager 2 mission, which had completed its Neptune flyby in August 1989 — the first and, to date, only spacecraft to observe the planet at close range.

Voyager 2's Neptune encounter confirmed the existence of the Great Dark Spot and detected winds exceeding 2,100 kilometers per hour, the fastest recorded in the solar system at the time.