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Modern Space Exploration: Neptune

Revitalizing interest and excitement in humankind’s “final frontier”. Assisting students in scientific inquiry, promoting a love of science, and encouraging interest in STEM careers.



Neptune Articles

Significant Events

  • 1612: Galileo incorrectly records Neptune as a fixed star during observations with his small telescope.

  • 1846: Using mathematical calculations, astronomers discover Neptune, increasing the number of known planets to eight. Neptune's largest moon, Triton, is found the same year.

  • 1983: Pioneer 10 crosses the orbit of Neptune and becomes the first human-made object to travel beyond the orbits of the planets of our solar system. The spacecraft remains on a trajectory heading towards the red star Aldebaran (in the constellation Taurus) and is expected to pass by it in about 2,000,000 years.

  • 1984: Astronomers find evidence for the existence of a ring system around Neptune.

  • 1989: Voyager 2 becomes the first and only spacecraft to visit Neptune, passing about 4,800 kilometers (2,983 miles) above the planet's north pole.

  • 2002: Using improved observing techniques, astronomers discover four new moons orbiting Neptune: Laomedia, Neso, Sao and Halimede.

  • 2003: Another moon, Psamathe, is discovered using ground-based telescopes.

  • 2005: Scientists using the Keck Observatory take images of the outer rings and find that some of the ring arcs have deteriorated.

  • 2011: Neptune completes its first 165-year orbit of the sun since its discovery in 1846.

  • 2013: A scientist studying Neptune's ring arcs in archival Hubble Space Telescope images finds a previously unknown 14th moon of Neptune, provisionally designated S/2004 N 1.

  • 2016: Scientists using the Hubble Space Telescope discover a new dark spot on Neptune, the first new atmospheric vortex seen in the 21st century.

“Exploration.” NASA, NASA, 26 June 2019,


Neptune Quick Facts

Quick Facts

16 hours

165 Earth years

15,299.4 miles | 24,622 kilometers

Planet Type
Ice Giant


“In Depth.” NASA, NASA, 23 June 2020,