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Do Planets have Weather?

THURSDAY OCTOBER 01, 2009

Sometimes we get very close-focused, believing meteorologists who tell us that weather on earth is created by the air, by temperature differences that come off the ground, by winds created at ocean surfaces and from gases released by cities and farms. The thought doesn't occur to them and us that perhaps the weather got here first, long in forming, traveling and arriving, before impacting on the rest. Tide and sea are pulled by the Moon and so too the air that rests on the water surface. Land surface temperature differences arise from adjacent oceanic temperatures. By the time temperatures, pressures and wind speeds are measured, weather has already happened. A gas released from a chimney or a cow gets dealt-to immediately by the weather that is about at the time. No tail ever wagged a dog.

 

Weather cannot arise from air or anything in air. There is weather on other planets, yet no air. Do other planets have weather like Earth? Do they have storms, rain, hurricanes, lightning, or snow? Does Mercury or the Moon have an atmosphere? Is there wind on the Moon?

Weather is a form of tidal disturbance that is caused, like our sea tides, by outside forces and transmits itself through whatever atmosphere a planet has. Most of the planets as well as a few smaller bodies in our solar system do possess an atmosphere. While weather conditions on Earth may seem violent and extreme at times, even the worst weather on Earth is nothing compared to an average day on most other worlds. Let us take a brief tour through the solar system and describe the atmospheric weather we would encounter.

 

Mercury is the only planet with no real atmosphere to speak of. The world is too small with gravity too weak to hold on to large quantities of atmospheric gas. However, Mercury does maintain a very thin and transitory atmosphere consisting of potassium, sodium, oxygen, helium, hydrogen, and water vapor. The leading theory is that it comes from the solar wind, outgassing due to radioactive decay from the surface, and comet impacts. Mercury does not appear to experience weather.

 

Venus, meanwhile, has the densest and perhaps most hostile atmosphere of any planet in the solar system. Being closer to the Sun, Venus receives considerably more heating than Earth. The atmosphere is almost entirely carbon dioxide with small amounts of nitrogen and numerous other gases. The dense atmosphere gives the planet a surface temperature hot enough to melt lead and a pressure more than 90 times greater than Earth's. Venus is surrounded by thick permament clouds of sulfur dioxide and sulfuric acid that form high in the atmosphere from volcanic eruptions at the planet's surface, blocking most sunlight from reaching the surface. Temperature remains nearly constant at a blistering 460°C. Wind speeds of more than 300 km/h have been measured at the top of the cloud layer.

 

Temperature extremes on Earth vary from a peak of 58°C in Death Valley, California, to -89°C in Antarctica. Wind speeds at the surface can reach nearly 320 m/h (200 mph) in hurricanes or cyclones, the worst storms experienced on the planet. The highest speeds on an average day are high in the atmosphere in a region called the jet stream where sustained winds of 55 to 120 km/h (35 to 75 mph) are typical.

 

Our atmosphere is higher than we think. The 4th layer of Earth's atmosphere, the thermosphere, ends at approximately 62 miles from the Earth’s surface. The whole mantle comprises three quarters nitrogen and a quarter oxygen, with tiny traces of other gases. Very close to ground, between 1-8 miles, water vapor and tiny amounts of natural gases like CO2, less than 5% of the total 'ocean' that sits above earth, move through it with their own cycles like impurities within the sea. As ocean impurities don't change tides these gases don't change weather. But as these are all we see we tend to imagine that they have a greater effect than they actually do. In fact most weather occurs at Boeing 747 level, over systems that cover huge distances, and can be seen from space as giant swirlings orbiting the globe, far enough above Earth so as to have no contact with the ground.

 

The Martian atmosphere is very thin with a surface pressure less than 1% that of Earth. The predominant substance composing the atmosphere is CO2 with small amounts of nitrogen and other gases. Temperatures on Mars average -46°C. Coldest temperatures can be found at the poles during Martian winter when the surface drops to -87°C, so cold that about a quarter of the atmosphere freezes into slabs of dry ice, increasing the size of the polar ice caps. Wind speeds as high as 480 km/h (300 mph) have been measured racing from the Martian poles towards the equator stirring up great clouds of dust and creating wispy clouds of water ice.

 

The atmospheres of all four gas giants, Jupiter, Saturn, Neptune and Uranus are generally similar, dominated by hydrogen and helium. Their atmospheres also contain substances like ammonia, sulfur, and methane that create the colors these planets are known for. These worlds are cold given their distance from the Sun, but all are warmer than the solar energy they receive can account for. The largest single storm ever seen is Jupiter's Great Red Spot that has existed at least as long as humans have been able to observe it. This permanent storm is three times larger than Earth and circles Jupiter's southern hemisphere in just six days. Jupiter is also covered by many smaller storms, some of which appear and disappear within hours while others last for centuries. Similar storms have also been observed on the other gas giants, including Saturn's Great White Spot and Neptune's Great Dark Spot, though these are generally much smaller and less stable than Jupiter's mighty tempests.

 

In addition to the worlds already discussed, several moons circling planets possess atmospheres as well. Most are similar to the virtually nonexistent atmosphere of Mercury. Earth's Moon has a tenuous atmosphere consisting of byproducts from radioactive decay or bombardment of meteorites and the solar wind. The only moon with a fairly thick atmosphere is Saturn's largest satellite Titan. Titan's atmosphere is even denser and produces a greater surface pressure than Earth's. In 2005, NASA successfully dropped the Huygens lander through Titan's atmosphere to touch down on its frozen surface. Huygens detected very little wind on the surface, but speeds as high as 435 km/h (270 mph) were measured at high altitude, similar to our jet streams. The strong winds appear to be generated by tidal forces from Saturn and produce large wind-blown sand dunes forming in parallel west-to-east lines.

 

This suggests a tidal force for all weather on all planets, rather than to local, close-to-ground causes. For, in addition to the planets, the solar system itself experiences ‘weather’ of sorts. This weather results from conditions at the surface of the Sun that generates solar flares and the solar wind. These phenomena can affect atmospheric conditions and weather on the planets and may also produce interference in Earth satellites and communications systems. Only when we can think beyond our farting cows, our hazed-over towns, our borders and our globe, can we begin to understand what really controls and influences weather and climate. Huge cosmic forces are involved. We are simply at the end of their ride.


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