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= Extraterrestrial Storms = An extraterrestrial storm is a storm that occurs on planets and natural satellites other than Earth that have sufficient atmospheres. Most observed extraterrestrial storms have been large cyclones, or anticyclones. However, occasional dust storms have been known to occur on Mars and Titan. Various spacecraft missions have recorded evidence of past and present extraterrestrial storms. The largest extraterrestrial storms are found on the gas giants, Jupiter and Saturn, and the ice giants, Uranus and Neptune.

Mercury
Due to Mercury's thin atmosphere, it does not experience weather-like storms or other atmospheric weather phenomena such as clouds, winds, or rain. Rather unusually, Mercury has magnetic 'tornadoes' that were observed by NASA's Mercury MESSENGER during a flyby in 2008. The tornadoes are twisted bundles of magnetic fields that connect Mercury's magnetic field to Space.

Venus
Venus Express observed two large shape-shifting vortices on Venus' poles (polar vortices) in 2006 on one of its close-up flybys of the planet. The south pole was seen to have a large, constantly changing, double-eye vortex through high-resolution infrared measurements obtained by the VIRTIS instrument on Venus Express. The cause of the double-eyed vortex is unknown but the polar vortices are caused by the Hadley Cell atmospheric circulation of the lower atmosphere. Unusually, neither of the double vortices at the south pole ever line up and are located at slightly different altitudes. The southern pole's cyclone-like storm is roughly the size of Europe. In addition, the southern polar vortex is constantly changing shape but the cause is unknown.

In 1979, NASA's Pioneer Venus observed a double vortex cyclone at the north pole. There haven't been many more close-up observations of the north pole since Pioneer Venus.

Since most of the planet's water has escaped to space, Venus does not experience rain like Earth does. However, there has been evidence of lightning on Venus as confirmed by data from Venus Express. The lightning on Venus is different than the lightning on all other planets as it is associated with sulfuric acid clouds instead of water clouds. The magnetometer instrument on Venus Express detected electrical discharges when the spacecraft was orbiting close to the upper atmosphere of Venus. Most storms form high up in the atmosphere about 25 miles from the surface and all precipitation evaporates about 20 miles above the surface.

Mars
Most of the atmospheric events observed on Mars are dust storms which can sometimes disrupt enough dust to be seen from Earth. Many large dust storms occur every year on Mars but even more rare are the global dust storms that Mars experiences on average every 6 Earth years. NASA has observed global dust storms in 1971, 1977, 1982, 1994, 2001, 2007, and 2018. While these massive dust storms do cause problems for rovers and spacecraft operating on solar power, the winds on Mars top out at 97 km/h (60 mph), less than half as strong as hurricane-force winds on Earth, which is not enough to rip apart mechanical equipment.

While Mars is most known for its recurring dust storms, it still experiences cyclone-like storms and polar vortices similar to Earth.

On April 27, 1999, a rare cyclone 1,100 miles in diameter was detected by the Hubble Space Telescope in the northern polar region of Mars. It consisted of three cloud bands wrapped around a massive 200-mile-diameter (320 km) eye, and contained features similar to storms that have been detected in the poles of Earth (see: polar low). It was only observed briefly, as it seemed to be dissipating when it was imaged six hours later, and was not seen on later imaging passes. Several other cyclones were imaged in about the same area: the March 2, 2001 cyclone, January 19, 2003 cyclone, and the November 27, 2004 cyclone.

In addition, NASA's 2001 Mars Odyssey Spacecraft observed a cold, low density, polar vortex in the planet's atmosphere above latitudes 70 degrees north and higher. NASA determined that every winter a polar vortex forms over the north pole above the atmosphere. The vortex and atmosphere are separated by a transition zone where strong winds encircle the pole and terrestrial jet stream-like characteristics. The stability of these annular polar vortices are still being researched as scientists believe Martian dust may play a role in the formation of these vortices.

Jupiter
The Great Red Spot on Jupiter is, by far, the largest extraterrestrial anticyclone (or cyclone) known. It is so large that about 2 to 3 Earths could fit inside it. The Great Red Spot has existed on Jupiter for at least 340 years. In the image to the left, the Great Red Spot can be seen near the top center. The Great Red Spot has turned dull pink to bright red, but has not yet dissipated and is not likely to do so in the near future.

Oval BA (or Red Spot Jr.) is a remnant formed from the merger of multiple white ovals. It is located just to the south of the Great Red Spot and has been increasing in strength.

The Great Dark Spot is a feature observed near Jupiter's north pole in 2000 by the Cassini–Huygens spacecraft. A feature in the atmosphere of Neptune was also called the Great Dark Spot. The latter feature, imaged by Voyager 2 in 1989, may have been an atmospheric hole rather than a storm. It was no longer present in 1994, although a similar spot had appeared farther to the north.

Saturn
On October 11, 2006, the Cassini-Huygens spacecraft took images of a storm with a well-defined distinct eyewall over the south pole of Saturn. It was 8,000 kilometres (5,000 mi) across, with storms in the eyewall reaching 70 km (40 mi) high. The storm had windspeeds of 550 km/h (340 mph) and appeared to be stationary over Saturn's south pole.

In addition, several storms like the Great White Spot occasionally appear on Saturn's northern latitudes, becoming large enough to be spotted by telescopes on Earth every 28 and a half years.

There is also a long-lived storm known as the Dragon Storm, which flares occasionally on Saturn's southern latitudes.

A hexagonal cyclone in Saturn's north pole has been spotted since the passage of Voyager 1 and 2, and was first imaged by Cassini on January 3, 2009. It is just under 15,000 miles (25,000 km) in diameter, with a depth of about 60 miles (100 km), and encircles the north pole of the ringed planet at roughly 78° N latitude.

Titan
On June 27, 2012, before a distant flyby of Titan, Saturn's largest moon, the Cassini–Huygens spacecraft took images of a vortex over Titan's south pole.

Titan has a visible hood high above the north pole consisting of denser high altitude haze compared to the rest of the moon's atmosphere. The formation of the vortex at Titan's south pole may be related to the coming southern winter and the start of what will be a south polar hood.

Scientists think the images obtained in this flyby show open cell convection. In open cells, air sinks in the center of the cell and rises at the edge, forming clouds at cell edges. However, because the scientists cannot see the layer underneath the vortex, they don't know what mechanisms may be at work.

A more recent observation of the south polar vortex led scientists to conclude that it has formed at a much higher altitude than previously thought.

Uranus
Starting in 2006, dark spots like those on Neptune were observed on Uranus as the planet approached its solstice in 2007.

Great Dark Spot[ edit]
The Great Dark Spot on Neptune is a series of anticyclones (possibly atmospheric holes, similar to the ozone hole) first discovered by Voyager 2 in 1989. It was then approximately the same size as Eurasia.

Small Dark Spot[ edit]
The Wizard's Eye (sometimes called Great Dark Spot 2) is another cyclone on Neptune. It is about one-third the diameter of the Great Dark Spot. It received the name "Wizard's Eye" because it looks like an eye. This appearance is caused by a white cloud in the middle of the Wizard's Eye.