Neptune Dark Spot

Hubble Uncovers a Pair of Dark Vortices on Neptune

This Hubble Space Telescope snapshot of the dynamic blue-green planet Neptune reveals a monstrous dark storm [top center] and the emergence of a smaller dark spot nearby [top right].

The giant vortex, which is wider than the Atlantic Ocean, was traveling south toward certain doom by atmospheric forces at the equator when it suddenly made a U-turn and began drifting back northward.

Hubble's Wide Field Camera 3 captured this visible-light image on Jan. 7, 2020, the same time a slightly smaller dark spot mysteriously appeared nearby. That spot then vanished a few months later. The smaller feature may have been a piece of the giant storm that broke off as the larger vortex approached the equator.

Hubble uncovered the giant storm in September 2018 in Neptune's northern hemisphere. The feature is roughly 4,600 miles across. The estimated width of the smaller spot is 3,900 miles.

The large storm is the fourth transient dark spot Hubble has observed since 1993. NASA's Voyager 2 spacecraft first imaged two dark features in Neptune's southern hemisphere in 1989 as Voyager flew by the distant planet. Those storms had disappeared by the time Hubble looked at Neptune in 1994. However, Hubble detected two new dark spots in the planet's northern hemisphere in 1994 and 1996.

It's unclear how these storms form. Their clouds may be rising to higher altitudes, compared to surrounding regions in the gas giant's atmosphere.

Neptune's predominant blue color is due to the absorption of red light by the distant planet's methane-rich atmosphere.