Great Dark Spot

The Great Dark Spot (also known as GDS-89, for Great Dark Spot, 1989) was one of a series of dark spots on Neptune similar in appearance to Jupiter's Great Red Spot. In 1989, GDS-89 was the first Great Dark Spot on Neptune to be observed by NASA's Voyager 2 space probe. Like Jupiter's spot, the Great Dark Spots are anticyclonic storms.

However, their interiors are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be shorter, forming and dissipating once every few years or so. Based on observations taken with Voyager 2 and since then with the Hubble Space Telescope, Neptune appears to spend somewhat more than half its time with a Great Dark Spot. Little is known about the origins, movement, and disappearance of the dark spots observed on the planet since 1989.

Characteristics

The Great Dark Spot was seen by NASA's Voyager 2 probe in the southern part of Neptune. This dark area was shaped like an oval and was about as big as Earth. It looked similar to Jupiter’s Great Red Spot, but it could move north and south over time, unlike Jupiter’s spot.

Around the edges of this storm, winds blew very fast—up to 2,100 kilometers per hour! Scientists think the Great Dark Spot might be a gap in Neptune’s methane clouds. It also made large white clouds made of frozen methane, located high above the main cloud layer. These clouds stayed for a long time, unlike regular clouds on Earth.

Disappearance

When scientists took new pictures of the Great Dark Spot in November 1994 using the Hubble Space Telescope, they found that it had vanished. This made astronomers think that the spot might have been hidden or simply disappeared. Even though the Great Dark Spot was no longer visible, some clouds that moved with it stayed, showing that these storms might still exist in some form. Scientists believe these dark spots might fade away when they move too close to Neptune's equator, or perhaps for other reasons that we do not yet understand.

Other dark spots observed

After the Great Dark Spot was discovered, scientists found more dark spots on Neptune. In 1989, when the Voyager 2 space probe saw the Great Dark Spot, it also found another dark spot called Dark Spot 2. This spot disappeared before 1994.

Since then, the Hubble Space Telescope has been watching Neptune and finding more dark spots. In 1994, a dark spot appeared in the northern part of the planet and vanished between 1998 and 2000. Another one showed up in 1996 and disappeared before 1998.

In 2015, a dark spot was found in the southern part of Neptune by the Hubble Outer Planet Atmosphere Legacy program. It moved toward the pole before disappearing in 2017. In 2016, a new spot similar to the Great Dark Spot appeared in the northern part and has been visible for several years.

In 2018, Hubble watched a new dark spot form from the very beginning. This spot was smaller than the one found by Voyager 2 but was still bigger than the Atlantic Ocean, about 4,600 miles across. In 2020, this dark spot changed direction and started moving north instead of south. Scientists think this happened because of natural forces that keep storms stable in the northern part of the planet.

Nearby, a smaller spot called "Dark Spot Jr." was found but later disappeared. Scientists are still learning how these dark spots form and why they move the way they do.

Proposed missions

Two ideas for space trips to Neptune were suggested to NASA recently. One idea, called Trident, was proposed in 2021 to visit Neptune and its moon Triton, but two missions to Venus called DAVINCI+ and VERITAS were chosen instead. Another idea, Neptune Odyssey, plans to send a spacecraft around Neptune and is aimed for a launch in 2033. These missions want to learn more about Neptune’s moon Triton and its atmosphere. The China National Space Administration also studied a way to travel to Neptune using special engine technology.