Nate Hill, age 12, of Chester, Penn., for his question:
IS THERE LIFE ON MARS?
Mars is the fourth closest planet to the sun and the next planet beyond the earth. Although the surface conditions on Mars are more like the earth's than those of any other planet, scientists agree that the plants and animals of the earth could not live on Mars. A few scientists, however, say that some form of life may indeed exist on the planet.
A number of unmanned United States spacecraft have landed on Mars. The probes transmitted high quality, closeup photographs of the planet's surface features. The spacecrafts' instruments also analyzed Mars' atmosphere and soil to seek signs of life.
In spite of all the experiments to date, scientists have not been able to determine whether life exists on Mars.
The average temperature for the entire planet is about minus 80 degrees Fahrenheit. There is a wide variation between daytime and nighttime temperatures. In areas near Mars' equator, daytime temperatures may rise to as high as 70 degrees Fahrenheit. But the average nighttime temperature on Mars is about minus 150 degrees Fahrenheit.
Atmosphere on Mars is thinner and contains fewer gases than that surrounding the earth. It consists chiefly of carbon dioxide, with small amounts of nitrogen, argon and oxygen. The planet's atmosphere also contains extremely small traces of water vapor.
The diameter of Mars is about 4,200 miles, a little over half that of the planet earth.
Mars travels around the sun in an elliptical, or oval shaped, orbit. Its distance from the sun varies from about 155 million miles at its farthest point to about 128 million miles at its closest point. Mars takes about 687 earth days to go around the sun, compared with about 365 days, or one year, for the earth.
The planet seems to have had large amounts of surface water millions of years ago, but almost none exists today. Scientists think that water now may be frozen in large polar ice caps.
The polar ice caps of Mars cover small areas located at the planet's north and south poles. The polar caps appear white from the earth and may contain large amounts of frozen water.
Each cap grows and shrinks with the Martian seasons. A cap appears to evaporate and become smaller when it is tilted toward the sun, and then freezes and gets larger when it is tilted away from the sun. The evaporating polar caps may provide some of the water vapor that is thought to be present in the atmosphere of the planet.
Much of the surface of Mars seems to contain a brick colored mineral called limonite which is found in various deserts on the earth. Two thirds of the surface is in this reddish rust brown bright area color.
About one third of the planet's surface has dark areas. The dark areas form irregular patterns and generally appear greenish or bluish gray in color. These areas are called "maria" or seas, eventhough they do not have any measurable amounts of water. For further information on Mars to to: http://marsrovers.nasa.gov/home/