Dear Amy: Does Mars or any other planet have life? — Kavya, Kumbakonam, India
Dear Kavya: The only planet that we know has life is Earth, but that won't stop scientists from searching for signs of life elsewhere. One of the things they look for is water, because it is a source of oxygen, which is essential to life on Earth. In addition, water can provide protection from UV rays. Scientists also look at the climate or clues of the past climate on a planet, because life is able to survive only in a small window of temperature. A planet can't be too hot or too cold.
Since the '70s, NASA has been searching Mars for signs of life. So far, there has been no evidence of life, but it's possible that life once existed there. Billions of years ago, the surface of Mars flowed with water and was much warmer. To learn more about the possibility of life on Mars, visit www.nasa.gov/audience/forstudents/postsecondary/features/mars_life_
There are other stars and planets in the universe, so it's possible that life exists somewhere else. Visit Hunt for Alien Worlds, www.pbs.org/wgbh/
nova/worlds, and decide for yourself whether aliens might exist.
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