Beyond the asteroid belt are the four largest planets of the Solar System. All of them are gaseous worlds with deep atmospheres where tremendous pressure deep down gradually compresses it into a metallic slush. None of them have solid surfaces and all of them have radiation, thunderstorms, powerful winds, and rings. Even though they share these characteristics, there are unique, defining features among them.

Jupiter: The largest planet is a world with powerful winds over 400 miles per hour, hurricanes lasting centuries, lightning that can span continents, and the fastest rotation with its day lasting just under ten hours. Jupiter also has the most intense radiation of all the planets. This radiation is so nasty that it can disable spacecraft and kill a person instantly. As a result, Jupiter has massive displays of auroras. Much of the radiation belt is powered by the large moon, Io, interacting with Jupiter’s metallic core. Io, the most volcanic world in the Solar System, spews tons of sulfur dioxide from its volcanoes, which escapes Io’s gravity and gets trapped in orbit around Jupiter. The sulfur atoms become ionized by the intense radiation thereby charging the huge radiation belt around Jupiter that is often referred to as the Io Torus. Radiation is invisible, but a visible feature of Jupiter is an icon all to its own, the Great Red Spot.

The Great Red Spot is the signature trademark of Jupiter. Anyone drawing the planet, especially children, almost always include it. This giant red eye is over two times the diameter of Earth and is actually a giant hurricane with winds over 400 miles per hour that has raged since before the invention of the telescope 400 years ago. It is an eddy in the atmosphere that is being held in place and held together by opposing jet streams that help keep it spinning. Huge thunderstorms are created by the internal heat within Jupiter that is still being generated by the continual slow contraction of the planet’s core since its creation. Unlike the hurricanes on Earth that eventually die when they pass over land, the Great Red Spot cannot readily die as there is no solid surface beneath it to rip it apart. The distinctive reddish color may be due to certain phosphorus compounds that are dredged up from far below and then frozen high up at the tops of the clouds. The clouds that make up the Great Red Spot are the tallest and the highest on Jupiter and may be critical in creating the reddish color as there is no place colder. Lethal radiation and the Great Red Spot are two distinguishing features that set Jupiter apart from the other planets.

Saturn: The very mention of this planet conjures up images of a golden globe surrounded by icy white rings. Easily the symbol of the solar system and outer space, Saturn is a planet of beauty. The beautiful golden color is due mainly to hydrogen sulfide compounds deep within its atmosphere. Saturn rotates only a little slower than Jupiter, but the winds howl at nearly 1000 miles per hour. Internal heat within Saturn fuels thunderstorms similar to Jupiter and sometimes these storms are intense enough to appear as white spots, but it is farther from the Sun and colder. Therefore a persistent haze covers the planet giving it a more uniform appearance than Jupiter. The golden globe of Saturn would be interesting to observe if it were not upstaged by the huge ring system that surrounds it.

The rings are so big and bright that they can be seen from Earth with a magnification of only 20 times. The rings are primarily composed of tiny icy particles that are no bigger than grains of sand, although there may be icy stones and boulders. The rings may have been created by either moons that grew too close to Saturn and were torn apart or are the remains of moons that never formed. The rings have gaps caused by the gravitational pull of existing larger moons, especially Mimas and Titan. As large as the rings appear, they are amazingly thin. They are probably no more than a mile thick and most likely not more than several hundred feet thick, yet they have probably existed for hundreds of millions of years. They may last several hundred million years more, but it is obvious that we are living in a time where they exist and can enjoy their beauty. A golden globe and intricate rings are two distinguishing features that set Saturn apart from the other planets.

Uranus: Often considered a dull, boring planet and badly misunderstood, Uranus really does have personality. The bland, hazy atmosphere is due to the fact that Uranus does not give off as much internal heat as Jupiter, Saturn, and Neptune; therefore it does not have the riot of spots and belts. The winds are slower and the intense cold creates a thick methane haze that obscures the clouds below. It is the methane that gives Uranus its turquoise color as methane absorbs the red component of sunlight and scatters the blue. A defining feature of Uranus is its rings. Unlike Saturn’s icy white rings, Uranus has rings as dark as coal and are very thin, nearly rope-like. They may be the remains of an asteroid or small moon that came too close to Uranus and was torn apart. The rings are made of carbon compounds and have no ice indicating that they are relatively new and will probably not last long. They were accidentally discovered on March 10, 1977 while scientists were watching Uranus occult a star in order to study its atmosphere. Before the occultation began the star winked out five times, then after the occultation, the star winked out five more times in reverse pattern. The reason became obvious; Uranus had rings and joined Saturn as a ringed planet. Unfortunately they are too dark to see from Earth unless it is the Hubble Space Telescope observing it. The rings show up very well in infrared as their dark color absorbs heat efficiently.

The signature feature of Uranus is that it is tipped over on its side at 98º so it practically rolls around as it orbits the Sun. It is possible that a huge collision knocked Uranus over early in its creation. This odd tilt also makes for strange seasons during the 84 years it takes for Uranus to orbit the Sun. Each pole alternately experiences up to 42 years of continuous darkness or daylight, possibly a factor in the bland characteristics of Uranus. The moons orbit along Uranus’ equator, which makes it appear as if they are shuffling up and down, or going around, similar to viewing a Ferris wheel at different angles. Although often overlooked, especially when planning for future planetary missions, Uranus is truly an interesting world worthy of further exploration. Dark rings and a sideways tilt are two distinguishing features that set Uranus apart from the other planets.

Neptune: As the farthest planet from the Sun and the coldest at around -350ºF, Neptune is a beautiful blue planet that owes its color to the same gas as Uranus, methane. The methane concentration is slightly higher and the haze is much less, therefore Neptune is bluer than Uranus. The deeper the clouds are, the darker and bluer they appear since we are looking deeper into the atmosphere where the methane concentration is higher. The dark spots and belts are clearings in the atmosphere that allow a peek into Neptune’s depths. Higher clouds are brighter and the highest clouds are white since they are above the bulk of the methane.

Neptune generates far more heat than Uranus and Saturn and it rivals Jupiter. The result is a blue version of Jupiter complete with thunderstorms and howling jet streams. Neptune has the fastest winds of all the planets reaching 1200 miles per hour, which creates banding and multiple spots. It is so dynamic that recent surveillance of Neptune has noted changes in the banding, new spots have formed and others have disappeared. The Great Dark Spot dominated Neptune’s visage in 1989 when Voyager 2 flew by. The Hubble Space Telescope searched for it in 1994, but could not find it; instead, it had been replaced by a smaller dark spot in the northern hemisphere. Blue clouds and fierce winds are two distinguishing features that set Neptune apart from the other planets.

Though similar, the outer planets are as different as possible due to the many factors that helped shaped them during their creation and that continue to affect them today. In a similar comparison, there are smaller worlds that are similar, but dramatically different, such as Pluto, asteroids, and planetary moons. There will be stunning revelations in part 3 of Planetary Personalities.