Planet weather

Q:  Do other planets have weather? If so, what kind, what planets?  Natalie, Somewhere, USA

Jupiter's Great Red Spot, a gigantic storm, persisting for hundreds of years. The white oval storm below the Red Spot has about the same diameter as Earth.   1979. Courtesy of NASA and Wikipedia.

A: Yes, other planets endure such weather that Earth's worst seems balmy.  All planets, except Mercury, in our solar system have an atmosphere and, therefore, weather.  Mercury is the exception. 

"I'm not sure it's fair to describe Mercury as having 'weather'.  With virtually no atmosphere, the planet's temperature change is driven entirely by the (extremely slow 176-Earth-days from one sunrise to the next) rotation of the planet beneath the near Sun," says astronomer Robert Massey of the Royal Observatory Greenwich in London. 

For the rest, let me mention a few weather extremes.  Pluto, for instance, turns into a planet frostball every so often.  A red-tinted frost probably covers Pluto — a methane-nitrogen-carbon-monoxide frost.  Pluto moves in a greatly elongated orbit about the Sun in 248 years.  During the 20 years she is closest to the Sun, temperatures rise, and ice turns to gas.  Moreover, when Pluto orbits away from the Sun, and the gases freeze, her atmosphere may collapse, and a planet-wide frost ensues: a frostball Pluto.

Venus, on the other hand, has a surface literally hot enough to melt lead:  860° F (460° C).  The closer Sun shines more intensely on Venus than on Earth, but thick clouds high in the atmosphere reflect much of the light.  The surface converts the sunlight filtering through the clouds into thermal energy, which heats the surface, which then emits infrared radiation.  The atmosphere absorbs this infra-red radiation, transforms it again, radiates mostly in the infrared and heats the surface below, even more.  Furthermore, the enormous amount of carbon dioxide in Venus' extraordinarily thick atmosphere generates more heating through this atmospheric heating process than on any other planet in our solar system.  That is why Venus is so hot, say physicist Craig Bohren, author of Clouds in a glass of beer, and atmospheric scientist Peter Pilewskie of the University of Colorado, Boulder.

Her atmosphere is so thick it exerts a surface pressure about 90 times Earth's.  She's covered with sulphuric-acid clouds whose tops race across her skies at triple Earth hurricane speed, while surface zephyrs waft at only a couple of miles an hour.

We've been watching what may be the solar system's longest lasting storm — Jupiter's Great Red Spot — on and off for 340 years, since Cassini first discovered it in 1665, shortly after Hans Lippershey invented the telescope in 1608.  The high-pressure storm gyrates (in the opposite direction from low-pressure Earth hurricanes) due to Coriolis effects (just as on Earth) making a complete rotation every 6 days (2.5 times faster than storms rotate on Earth).  Click for animation of the swirling storm, courtesy of Wikipedia and the  American Museum of Natural History. 

Jupiter's extremely rapid rotation rate (a 10-hour day) helps drive the large storms, says Massey.  For example, consider a point on our equator — Quito, Ecuador.  A corresponding point on Juniper's equator whips around 27 times faster than Quito does. 

The windiest spot under the Sun may be Neptune.  We've clocked blasts over 1500 mph (2400 km/h). 

Scientists have been making a "big thing" about the analogies of Titan's weather (Saturn's biggest moon) to Earth's, says James F. Kasting of  Pennsylvania State University, Distinguished Professor of Geosciences.   It rains methane on Titan instead of water but otherwise has Earthlike weather processes, smog, for example.  The Sun's ultraviolet light breaks up methane in Titan's atmosphere, which produces the orange haze: a smog worse than LA's on its worst day.

If you and I could land on Titan, we would descend through a colorful nitrogen atmosphere denser than Earth's:  a violet outer layer, next, a thin blue layer, a yellow band, and finally deepening shades of orange until we settled on her cold (-290° F, -180° C) surface — perhaps a sticky, cold sand made from ice grains.  Scattered clouds would float above in the orange hazy distance. 

Martian dust devils can tower to five miles (8 km) above its terrain, dwarfing our half-mile high tornados.  Global-wide dust storms can last for several months.  The major factor driving dust storms, says Massey, is the small dust-particle size.  Even Mars' thin atmosphere can lift these tiny motes.

Immense (1000-miles across) hurricane gyrating just off the Martian North Pole, 1999.  Courtesy of J. Bell (Cornell), S. Lee (Univ. Colorado), M. Wolff (SSI), et al., NASA.  Drawing modified by author.

Total darkness shrouds the Martian winter pole, creating such cold that up to 25% of Mars' atmosphere condenses into thick slabs of dry ice.  When summer comes, the dry ice sublimates, and generates vast hurricanes.

Unlike Earth, Mars' changing distance from the Sun affects its seasons, especially in the southern hemisphere.  Mars is closest to the Sun in the southern summer and farthest away in the southern winter.  Consequently the south has more extreme seasons than the north.

"The very fact that we can see planetary weather is a testament to the technological advances of the last four centuries. We've moved from seeing planets as bright dots to being able to see storms brewing on Jupiter, find out which gases surround Pluto and watch the Martian ice caps sublime. So much of this can even be seen using telescopes on or near the Earth — although, too often, they just whet our appetite for further space missions," says Massey.

Further Reading:

Planets, Royal Observatory Greenwich

The Weather Centre, planets:  BBC

The Great Red Spot, Wikipedia

Perfect storm on Mars, Hubble space telescope site

Hans Lippershey, The Galileo Project, Rice University

Titan, Royal Observatory Greenwich    

Titan, Wikipedia

(Answered July 4, 2006; updated Aug. 20, 2007)