May 18, 2019 : There Are Storms On Titan And On The Earth Like On Many Other Worlds In The Solar System

Clouds of water are widespread on our planet. Most of the surface of the Earth is covered by liquid water. There are rivers, lakes, seas as well as oceans on the Blue Planet. A meteorological cycle involving liquid water can be observed. That meteorological cycle is characterized by evaporation processes, condensation processes and precipitation processes. Sunlight, environmental heat or seasonal factors play a key role in the dynamics of our meteorology. Thanks to the Cassini-Huygens probe, we have been in a position to determine that there is also a meteorological cycle on Saturn's largest moon Titan. That meteorological cycle appears particularly exotic since it is based on methane rather than water. The environmental temperature at the level of the surface on Titan is so low that methane can appear in its liquid form on the surface. Radar data as well as infrared or near-infrared data acquired from the Cassini orbiter during its long mission in the System of Saturn and its numerous moons have clearly shown that there are lakes, seas and rivers on Titan.

In the first half of the Cassini-Huygens mission in the Saturn System, the eyes of the Cassini orbiter have clearly revealed dynamic cloud systems in the south polar region of the Opaque Moon. That region was experiencing the Summer season. The first body of surface liquid clearly identified on Titan was Ontario Lacus, a large pool of liquid composed of methane and ethane. Later in the Cassini mission, a giant vortex or cyclone engulfing the north polar region was identified from the orbiter. Radar data obtained from the Radar Mapper of the Cassini spacecraft have clearly shown that the most humid areas on Titan are found in the high latitudes of the northern hemisphere. Cirrus-like clouds evolving at a high latitude around the north polar region have been clearly identified at the end of the Cassini mission in the Saturn System. Large cloud systems developing above the low or mid-latitudes of the giant moon have been observed in 2010, at the start of the Autumn season in the southern hemisphere and of the Spring season in the northern hemisphere. In 2012, a vortex evolving above the south polar region of Titan was clearly identified from the Cassini probe. Titan and the Earth appear to be paradises for the study of storms or cyclones but several other worlds in the Solar System unveil a dynamic atmosphere.

Most moons in the Solar System are devoid of any atmosphere. Therefore, there are no hurricanes, cyclones, vortices or tornadoes above those worlds. Mercury which is the nearest planet to the Sun is devoid of any significant atmosphere. However, in that world where daytime temperatures can be around 800 degrees Fahrenheit or 450 degrees Celsius, micrometeoroid showers as well as magnetic tornadoes can take shape. The micrometeoroids which are tiny dust particles can be encountered in the morning on that cratered world. The Messenger spacecraft proposed by NASA had revealed, during its mission around Mercury, magnetic  tornadoes  on that relatively dense world. Magnetic  tornadoes  represent twisted bundles of magnetic fields that connect the magnetic field of the globe to space. The magnetic twisters had been identified during the second flyby of the Messenger spacecraft performed on October 6, 2008. Venus which is the second closest planet to the Sun is very different from Mercury since it reveals a completely opaque atmosphere dominated by carbon dioxide.

Venus is much heavier than Mercury and is a little bit smaller than the Earth. The atmosphere of the twin of the Earth is rich in sulfuric acid clouds. The atmospheric pressure and the environmental temperature on the Venusian surface are incredibly high. The mean environmental temperature on the surface of Venus is around 462 degrees Celsius ( approximately 864 degrees Fahrenheit) and the atmospheric pressure is around 93 Bar. One can imagine rain of sulfuric acid in the atmosphere of Venus. Venus experiences lightning as well. Lightning on Venus may even be more frequent than on Earth. Christopher Russell who is a NASA-sponsored researcher on the European Space Agency's Venus Express mission pointed out :  Not a very good place to vacation, that is for sure.  A vortex above the south polar region had been clearly identified by the Venus Express orbiter. Recently, Japanese planetologists identified a huge streak-like structure in the Venusian clouds on the basis of data acquired from the Akatsuki orbiter.

Like on the Gas Giants or on the Ice Giants of the Solar System, giant vortices or cyclones can take shape on Earth, in the ocean where the environmental temperature is sufficiently high for the development of that type of meteorological phenomenon. Hurricanes can devastate some areas along the coastline of the United States from time to time. Tornadoes are regularly encountered inside the United States. In tornadoes, winds can be over 300 miles per hour or 480 kilometers per hour. That's why the tornadoes often destroy houses or make cars fly. Hurricanes, cyclones or typhoons can be really impressive from observation satellites above the Earth. They are bigger than storms and they can last for days until they lose their strength in the land. Those vortices produce strong winds extending outward for 675 miles or 1,100 kilometers. The Hurricane Michael which turned out to be one of the most powerful hurricanes in the recent past and which reached an area near Mexico Beach in Florida on October 10, 2018 was characterized by winds of 160 miles per hour or 257 kilometers per hour. That hurricane belonged to the Category 5 of hurricanes, the category of the most powerful hurricanes.

Mars, the Red Planet, contains a thin atmosphere where clouds are relatively rare. The meteorology of Mars is very different from the meteorology of the Earth since there are no oceans of liquid water on the Red Planet. However, intense dust storms can take shape from time to time on Mars like on Titan for instance. Those huge dust storms can become global like in the year 2018. Due to the giant dust storm of 2018, we lost contact with the Opportunity rover. That rover proposed by NASA had been studying the Red Planet for about 15 years. The relatively high concentration of dust in the air of Mars, dominated by carbon dioxide, makes the atmosphere hazy or reddish. The environmental temperature of Mars is particularly cold. The combination of atmospheric pressure and environmental temperature on the Red Planet prevents the potential development of storms of water or cyclones of water. The main problem is dust. We have to take that problem into account for future missions since dust can affect electronics and mechanical systems. The InSight lander proposed by NASA brings us meteorological data on a daily basis from Elysium Planitia close to the equator of the Red Planet.

The Gas Giant Jupiter which is the largest planet in the Solar System contains a myriad of cyclones or vortices. We all know the Great Red Spot of Jupiter, a giant vortex much bigger than the Earth. It has been observed or monitored for at least 300 years. The size of that vortex has been progressively diminishing for a century and a half. Why is it decreasing in size ? That is a good question ! The Great Red Spot may be about to disappear. The data obtained from the Juno spacecraft which is currently orbiting Jupiter are likely to bring us key information regarding the nature, the origin or the dynamics of that remarkable atmospheric feature. Scott Bolton who is Juno's principal investigator pointed out :  Juno data indicate that the solar system's most famous storm is almost one-and-a-half Earths wide, and has roots that penetrate about 200 miles (300 kilometers) into the planet's atmosphere.  During the 20th century, three smaller vortices with an oval shape merged to produce the Little Red Spot, a vortex approximately half the size of the Great Red Spot. The giant vortices of Jupiter can persist or develop for many years due to the absence of solid surface likely to slow them down.

The Gas Giant Saturn is also filled with storms, vortices, cyclones or hurricanes. One of the most remarkable features on the Ringed Planet is undoubtedly the hexagon-shaped cloud pattern found in the north polar region of Saturn. That unique hexagon represents a six-sided jet stream characterized by winds which blow at about 200 miles per hour or about 322 kilometers per hour. Each segment is a bit wider than our planet and multiple Earths could be put inside. A giant vortex which looks like a hurricane can be found in the middle of that surprising structure. The southern hemisphere of the Gas Giant is also rich in storms, cyclones or vortices. A portion of that area had been dubbed  Storm Alley  by researchers of the Cassini mission. The storm can persist or develop over time. An impressive storm had been clearly observed and monitored in 2010 and 2011. That bright storm had evolved like a tadpole in the atmosphere and it eventually ran into its own tail and disintegrated.

Uranus and Neptune are also Gas Giants where strong storms, vortices or hurricanes can take shape. The Voyager 2 spacecraft had identified few clouds on Uranus at the time of its historic flyby. The environmental haze of Uranus had prevented us from discerning atmospheric features below the external atmospheric layer. However, in 2018, an image captured by the Hubble Space Telescope, in the infrared spectrum, revealed a huge and bright stormy cloud cap evolving above the north polar region of Uranus. During the same year, astronomers resorting to the Gemini North telescope on Hawaii's Mauna Kea managed to determine that clouds on that Gas Giant are composed of hydrogen sulfide. Neptune, which is the farthest Gas Giant from the Sun, is known to be the windiest world in the Solar System. Winds on that blue planet can blow at speeds of more than 1,200 miles per hour or 2,000 kilometers per hour. Thus, winds on Neptune blow approximately nine times faster than winds on our planet.

Neptune unveils clouds of frozen methane. The Voyager 2 spacecraft had identified, during its flyby of Neptune in 1989, two giant storms or cyclones. Those cyclones are known as  The Great Dark Spot  and  Dark Spot 2 . The images of the farthest Gas Giant obtained from the Hubble Space Telescope in 1994 led planetologists to conclude that the major storms observed in 1989 had vanished. Therefore, now, researchers believe that new storms can emerge every four to six years. Those storms or cyclones may last up to six years. We have identified many exoplanets which may look like Jupiter, Saturn, Uranus or Neptune. There are many extreme worlds beyond our Solar System. There are Gas Giants evolving very close to their star for instance. WASP-43b is part of those extreme worlds since it unveils winds which blow at the speed of sound from a day side where environmental temperatures can reach 1,600 degrees Celsius or 3,000 degrees Fahrenheit to a night side where environmental temperatures can go down below 500 degrees Celsius or 1,000 degrees Fahrenheit.

The image in the upper part of this table reveals the disk of Titan unveiling a multitude of clouds at a relatively low latitude on the Opaque Moon. The image was produced on the basis of data obtained from the Narrow-Angle Camera of the Cassini orbiter on October 18, 2010. The view is the outcome of data acquired using a filter sensitive to near-infrared radiation centered at 938 nanometers as well as data obtained using a filter sensitive to visible radiation centered at 619 nanometers. The relatively high level of cloud activity at low latitudes or mid-latitudes on Titan is completely unusual and may be closely related to seasonal changes.
The image in the lower part of this table unveils a portion of the Great White Spot of Saturn. That bright spot appeared in the northern hemisphere of the Gas Giant. That remarkable storm may be closely related to seasonal changes. The original view of Saturn shown in natural color was produced on the basis of data acquired on February 25, 2011 with the Wide-Angle Camera of the Cassini orbiter. Images captured using red, green and blue spectral filters were combined to generate the final view. Each view in this table is at about the same scale.

Credit for the view of Titan's disk: NASA/JPL/Space Science Institute.
Credit for the original view of Saturn: NASA/JPL-Caltech/Space Science Institute.
Montage credit for the scale of the portion of the Great White Spot of Saturn: Marc Lafferre, 2019.

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