Mike Johnson, age 12, of Butte, Mont., for his question:
IS THERE LIFE ON MARS?
Mars is the fourth closet planet to the sun and the next planet beyond Earth. The diameter of Mars is about 4,200 miles, a little over half that of Earth. Pluto and Mercury are the only planets smaller than Mars. Scientists tell us there is no life on Mars.
The idea that life can or even does exist on Mars has a long history. In 1877, an Italian astronomer named Giovanni Schiaparelli claimed to have seen a planetwide system of channels. And an American astronomer named Percival Lowell then popularized these faint lines as canals and held them out as proof of a vast attempt by intelligent beings to irrigate an arid planet.
Subsequent spacecraft observations have shown there are no canals on the planet, and various other alleged proofs of life on Mars have turned out to be equally illusory.
Not only are there no canals, but dark areas once thought to be oases are not green, and their spectra contain no evidence of organic materials. The seasonal changes in the appearance of these areas are not due to any vegetative cycle, but to seasonal Martian winds blowing sterile sand and dust.
The strongest evidence against the presence of life is the thinness of the atmosphere and the fact that the surface of the planet is exposed not only to lethal doses of ultraviolet radiation, but also to chemical effects of highly oxidizing substances produced by photochemistry.
Perhaps the most fundamental and far reaching result obtained by the Viking landers is that the soil of Mars contains no organic material. The results of the soil analysis for organic molecules carried out by the Viking landers provide no evidence for the existence of life, but rather indicate that Mars is nothing more than a sterile desert.
A more difficult question is whether life ever existed on Mars, given the strong evidence of climatic change and indications of a previously warmer, thicker atmosphere.
The most detailed knowledge of Mars has come from six missions carried out by unpiloted U.S. spacecraft between 1964 and 1976. The first close views of Mars were obtained by Mariner 4 in 1964, and further information was gained by the flyby missions of Mariners 6 and 7 in 1969.
The first Mars orbiter Mariner 9, launched in 1971 studied the planet for almost a year, giving planetary scientists their first comprehensive global view of the planet and the first detailed images of its two moons.
In 1976, two Viking lander crafts touched down successfully on the surface and carried out the first direct investigations of the atmosphere and surface. The second Viking lander ceased operating in April 1980, whi,le the first lander worked until November 1982.
The Viking mission also included two orbiters that studied the planet for almost two full Martian years, transmitting to Earth tens of thousands of high resolution images, as well as temperature and humidity measurements.
Check on latest findings on Mars by going to the JPL web site listed in the main menu of Youaskandy web site.