Astronomy Picture of the Day

Discover the cosmos! Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer.

November 4, 1995
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.
Neptune's Moon Proteus
Credit: NASA, Voyager 2

Explanation: Proteus is the second largest moon of Neptune behind the mysterious Triton. Proteus was discovered only in 1982 by the Voyager 2 spacecraft. This is unusual since Neptune has a smaller moon - Nereid - which was discovered 33 years earlier from Earth. The reason Proteus was not discovered sooner is that its surface is very dark and it orbits much closer to Neptune. Proteus has an odd box-like shape and were it even slightly more massive, its own gravity would cause it to reform itself into a sphere.

Tomorrow's picture: The Watchers

| Archive | Glossary | Education | About APOD |
Top 5 logo Best pick logo Cool NASA site logo

Authors & editors: Robert Nemiroff (GMU) & Jerry Bonnell (USRA).
NASA Technical Rep.: Sherri Calvo. Specific rights apply.
A service of: LHEA at NASA/ GSFC