The Small Dark Spot, sometimes also called Dark Spot 2 or The Wizard's Eye, was an

extraterrestrial vortex An extraterrestrial vortex is a vortex that occurs on planets and natural satellites other than Earth that have sufficient atmospheres. Most observed extraterrestrial vortices have been seen in large cyclones, or anticyclones. However, occasional d ...

on the

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...

. It was the second largest southern

cyclonic storm In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anti ...

on the planet in 1989, when ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, '' Voyager 1'', ...

'' flew by the planet. When the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

observed Neptune in 1994, the storm had disappeared.

Observation history

The Small Dark Spot was discovered in 1989 by the Voyager 2 spacecraft along with the

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' ...

and Scooter (a bright fast moving cloud located between the two giant storms). The Small Dark Spot was found at a latitude of 54° South while rotating East around Neptune with a period of 16.1 hours. Unlike the Great Dark Spot (which has some of the highest measured wind speeds in the Solar System), wind speed data was not taken for the Small Dark Spot. The spot was also observed without any white "companion clouds" present around its edges, again in contrast to the Great Dark Spot. When

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

pointed the Hubble Space Telescope toward Neptune in 1994, both giant spots were no longer present.

Physical characteristics

The nickname "Wizard's Eye" given to this storm comes from its distinct features which create a striking eye-like appearance. Overall the Small Dark Spot is significantly smaller but on the same order of magnitude as the Great Dark Spot and rotates about 30° further south and with a period about 2 hours shorter than the larger storm. The dark oval of this storm which created the overall outline for the eye-like shape was formed by a clockwise rotating vortex which sucked atmosphere inward toward the planet center. This action of pulling atmosphere downward created a hole in the upper methane cloud deck of Neptune and gave the storm its darker blue tone. Also present within the dark region of the storm were sharp band-lines potentially indicating unseen high winds, despite exact measurements having never been taken. The bright central region representing the pupil of the eye-like shape was formed by white methane-ice clouds upwelling from the center of the storm. Within the chaos of these central clouds are some larger structures, including a distinct V-shape on the East side of the storm indicating the storm's believed clockwise rotation. These clouds are composed of the same methane-ice that forms similar clouds called "companion clouds" present near the edges of other large storms on the planet; however, the Small Dark Spot did not have any of these companion clouds apparent in its 1989 observation. Additionally, no companion clouds were observed in the region of the spot in the 1994 observation of the planet.

Disappearance

After being observed by Voyager 2 in 1989, the planet would not be observed in high resolution again until the Hubble Space Telescope turned its view to it in 1994. In 1994 and subsequent observations, both major storms had apparently vanished. The storm causing the Great Dark Spot; however, may have continued at a lower altitude as evidenced by the persistence of the storm's companion clouds. The Small Dark Spot did not have any companion clouds by which to judge survival of the storm causing the spot. While a conjectured mechanism for decay and death of large vortexes on Neptune is their approach to the equator where the planet has 400 meter per second jet streams, this storm (as well as others) could have also decayed from unexplained mechanisms of Neptune's atmosphere.

Observation history

Physical characteristics

Disappearance

See also

References

Further reading