WEATHER IN SPACE
Do other planets in our solar system experience weather?
Many planets and even moons in our solar system have atmospheres and, therefore, weather. The gas giants—Jupiter, Saturn, Uranus, and Neptune—all have very thick atmospheres which include storms and even lightning. Lightning has been observed on Jupiter, Saturn, Io, and Titan, and is speculated to exist on Venus. Jupiter, of course, is famous for the huge swirling "Great Red Spot," which is a wind storm 8,500 miles (14,000 kilometers) wide and 16,000 miles (26,000 kilometers) long that astronomers estimate has been ongoing for at least 400 years. Saturn, too, has a thick atmosphere topped by crystallized ammonia clouds; it also has a "Great White Spot," but this storm lasts for about a month and then fades, recurring at intervals. Uranus has a distinctive, blue-green atmosphere made mostly of hydrogen (83 percent) and helium (15 percent); Neptune also has a blue color (which is why it is named after the Roman god of the sea), with a hydrogen-helium-methane atmosphere. Below this upper atmosphere, astronomers believe Neptune has a lower atmosphere made of ammonia, crystallized methane, and ionized water; even deeper may be a layer of hydrogen sulfide. The winds on all of these planets are believed to be very powerful. Neptune, for instance, has winds reaching 700 miles (1,100 kilometers) per hour; the planet has a "Great Dark Spot," that is an ongoing storm about the size of Earth's Moon, and a smaller, white storm that has the whimsical name of "Scooter."
Not counting Earth, the inner planets—Mars, Venus, and Mercury—all have atmospheres. The atmosphere on Mars is very thin, and it has an air pressure about one percent that of Earth's. Theories abound as to why Mars lost its atmosphere, ranging from giant asteroids smashing into the planet and ripping away its air, to the lack of plate tectonics providing sufficient heat, to the idea that the planet somehow lost its magnetosphere. Without much atmosphere, Mars does not have much weather. Mercury, similarly, has virtually no atmosphere and is essentially a big rock in space. Venus is far more interesting than either Mars or Mercury, in terms of atmosphere. It is a planet with an atmosphere too rich in carbon dioxide, and consequently it experiences a "runaway greenhouse effect" that heats the surface to 900°F (500°C), which is hot enough to melt metals like lead, tin, and zinc.
Poor Pluto, which has been downgraded in status from planet to planetoid, has a thin atmosphere containing nitrogen, methane, and carbon monoxide. Several moons in our solar system also have atmospheres. Of these, Saturn's Titan is perhaps the most interesting. Its dense atmosphere (50 percent denser than Earth's) contains 98.4 percent nitrogen and 1.6 percent methane. Astronomers believe that Titan has lakes and seas composed of liquid methane and nitrogen, and that it experiences rain showers made of methane. A smoggy, orange haze made of hydrocarbons envelopes the atmosphere. Some other moons have thin atmospheres, such as Neptune's Triton, and Ganymede, which is another moon circling Jupiter, is believed to have a water ocean beneath a layer of ice.
The Cassini spacecraft took this image of Titan's atmosphere, with Saturn's south pole in the background, in December 2005. (NASA/JPL/Space Science Institute)
Is there weather outside the solar system?
In recent years there has been a flurry of activity among astronomers who are discovering more and more exoplanets. Over 200 have thus far been found, and most of these are gas giants. The reason for this is because gas giants, being very large, exert a greater gravitational pull. The most successful technique for finding exoplanets has been to observe how stars move; observatories such as the Hubble Telescope are sensitive enough to detect if a star has a slight wobble to it, which indicates the presence of planets and a solar system. Combining this method with infrared spectroscopy, it is possible to detect the molecular composition of distant planets. Carbon dioxide and monoxide, hydrogen, neon gas, water, and hydrocarbons have all been detected. Astronomers are quite confident that they are seeing planets outside our solar system that have atmospheres, and they speculate that some may have life-supporting liquids and gasses.