Space

Voyager 2 confirms Neptune’s rings this date in 1989

Neptune's rings: Overexposed crescent planet with two distinct narrow white rings around it against black background.
Neptune’s rings are faint and continuous. This Voyager 2 image displays an increased brightness to bring out fainter features. Image via NASA/ JPL.

Neptune’s rings confirmed August 22, 1989

By the late 1980s, astronomers suspected that planet Neptune – now categorized as the outermost major planet – had rings. After all, the next planet inward, Uranus had rings (found 1977). So did Jupiter (found 1979) and Saturn (first glimpsed through early telescopes in the 1600s). Watching from Earth in 1984, astronomers recorded extra blinks before and after Neptune passed in front of a distant star. They were caused by the ring material, blocking the star’s light. But it was NASA’s Voyager 2 spacecraft that provided the first photographic proof of the existence of Neptune’s rings on August 22, 1989.

At the time, the spacecraft was a few days out from its closest encounter with the planet on August 25, 1989. As Neptune began looming large in Voyager’s cameras, the spacecraft photographed a faint but continuous ring system encircling the planet. The images of Neptune’s rings confirmed astronomers’ long-held suspicions.

Names for Neptunian rings

Today, Voyager 2 remains the only earthly spacecraft to have encountered Neptune. But since Voyager’s 1989 flyby, the Hubble Space Telescope and Earth-based telescopes have imaged the two brightest rings of Neptune. Astronomers named those two Neptunian rings Adams and Le Verrier. They’re named for John Couch Adams and Urbain Jean Joseph Le Verrier, whose independent calculations helped find Neptune’s position in the sky – and thus led to its discovery – in 1846.

NASA Solar System Exploration explained that there are also names for three more rings of Neptune:

Starting near the planet and moving outward, the main rings are named Galle, Leverrier, Lassell, Arago, and Adams. The rings are thought to be relatively young and short-lived.

Peculiar ring arcs

So, today, we know that Neptune has at least five main rings. Plus it has four prominent ring arcs. The arcs are peculiar clumps of dust. Astronomers struggled to understand their existence, because the laws of motion predict these arcs should spread out into a uniform ring over short timescales. Scientists now believe the gravitational effects of Galatea, a moon just inward from the ring, confine the arcs.

Four prominent arcs have names, too. Astronomers call them Liberté (Liberty), Egalité (Equality), Fraternité (Fraternity), and Courage. They’re located in the outermost ring, Adams.

Several faint rings around Neptune. Dark vertical bar blocks view of the planet.
An overexposed Neptune is blocked out in this image and the backlit rings shine through. Voyager 2’s wide-angle camera made this image from two 591-second exposures of the rings taken on August 26, 1989, from a distance of 175,000 miles (280,000 km). Image via NASA/ JPL.

Bottom line: NASA’s Voyager 2 spacecraft confirmed the discovery of Neptune’s rings on August 22, 1989, when it took images of a faint, continuous ring system around the planet.

Posted 
August 22, 2021
 in 
Space

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