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July 16, 2000 Surprise on Mars! http://www.thursdaysclassroom.com/22jun00/article1.html
Water on Mars is not really a new discovery. We've known for years that there is a small amount of frozen water near Mars' polar caps. There is also a small amount of water vapor in martian air. But no one has ever seen liquid water on Mars. Spacecraft pictures taken 28 years ago showed there are dried-up river beds and channels, but those were eroded by water that flowed billions of years ago. There may have even been an ocean covering much of Mars' northern hemisphere in the distant past. But today, Mars seems very, very dry. Scientist's wonder 'Where did the water go?' These new pictures show us that some of the water went underground. The reason there is no water on the surface is that there is very little atmosphere on Mars. On Earth, there is air pressure from the gases in our atmosphere; if you go up a high mountain, there is less air pressure. Water is cooler when it boils up on that mountain top and you must cook your food longer. The atmospheric pressure on Mars is about 100 times smaller than the air pressure at Earth's sea level. This means that on Mars, water would boil immediately when it came to the surface, even if it was not hot. Strange planet isn't it? If liquid water did exist on Mars, scientists expected that it would be deep inside the planet. Mars is so cold, that any water near the surface would have to be frozen. The average temperature on Earth is 60 degrees Fahrenheit (16 degrees Celsius); the average temperature on Mars is -80 degrees Fahrenheit (-60 degrees Celsius). In these new pictures, it looks like water has been flowing recently on Mars. The photographs show gullies that run over the edges of older craters. These craters, caused by the impacts of meteorites on the surface of Mars, are useful for figuring out the ages of things we see. If there were craters on top of the gullies, we would know that the gullies are older than the craters. Since the gullies are on top of the craters, we know that the gullies are newer than the craters. They even have pictures of gullies flowing across young sand dunes. There are also pictures of a large gully that shows rocky areas without dust. Dust is everywhere on Mars. Rocks without dust could mean that water has cleaned them off recently. What else could cause a gully to form on Mars? Volcanic lava flows can look like gullies. However, most of these gullies have not been found near the volcanic areas of Mars. Also, these gullies are clean, like those in a desert on Earth, as though water flowed through them. It might be possible that heavy gases, a mixture of water vapor and carbon dioxide, flowed down these gullies. These possible water spots are found in mysterious places. They are located on slopes that face away from the Sun. These are places where you would expect water to be frozen and not liquid. There are also no gullies near the planet's equator where temperatures might be high enough for liquid water. Scientists also looked for gullies near martian volcanoes -- another possible warm spot for liquid water -- but they aren't there either. The gullies are just where scientists expected them not to be. The possibility of water on the surface of Mars is exciting. Water is an important ingredient for life. On our planet, wherever there is water (even boiling hot springs water) there is life. Does this mean there is life on Mars? No. It only means that there might be some form of life there. Any life that exists would have to be small -- too small to see in more than 65,000 close-up pictures taken by the Mars Global Surveyor spacecraft. There is no hope for a community of movie-style green Martians that go to school and study Earthlings. There may be microscopic critters such as those that live in extreme areas on our Earth. This discovery is also exciting because it would make it much easier for humans to explore Mars. Water would be used for drinking, to make Earth-like air to breathe, and to make hydrogen and oxygen for rocket fuel. If humans were to go to Mars, they would need to stay for a long time. Since both planets travel around the Sun on different orbital paths, a Mars visitor would need to stay for 18 months until the planets were close enough again for the trip home. Before humans can go to Mars, we need to know lots more. We need to know more about how the human body responds to long term life in space. We need to know more about the level of radiation on the surface of Mars. We need to know more about the resources for supporting human life on Mars, because it would be difficult to ship everything we need there. Many more robotic missions to Mars are needed just to find the best landing site! What are scientists planning for the future? NASA wants to send a mission to Mars in 2003. They need to decide whether they will send a mission that lands a robot on the surface or a mission that orbits the planet and takes pictures and measurements. The United States will work with other nations to gather more information about Mars. The surprise on Mars is that there are gullies on the planet's surface. Scientists have formed a hypothesis that the gullies were made by flowing water. They have a second hypothesis that water has been flowing recently. Now they have lots of work to do to test these ideas. What we do know for sure is that Mars is an interesting planet with many mysteries. |