Mars - is there water on mars? are there aliens on mars?
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Mars

Mars from space
Mars from space

The closest planet to Earth is Mars, and Mars is also the planet that seems most likely to have life on it besides our own Earth. It's the next planet further away from the Sun after Earth.

The planet Mars formed about 4.5 billion years ago (4,500,000,000 years ago), about the same time as our Sun and the Earth and the other planets that go around the Sun.

Mars is a lot like Earth in some ways. Mars is not too far from the Sun to be solid (as Jupiter is), and it's not so close to the Sun that it is very hot (like Mercury). Like Earth, Mars rotates so that it has regular short days and nights, seasons, and a year more or less the same length as our year. But Mars is only about half as big as Earth - about 1000 miles (1500 kilometers) across, so Mars has less gravity than Earth does.

The atmosphere - the air - on Mars is thinner than on Earth, because there is less gravity. The air is mostly carbon dioxide and hardly any oxygen. This probably means that there are no plants on Mars that can photosynthesize using sunlight.

Probably there is no liquid water on Mars now, because the temperature is usually below freezing there, and the air is too thin. The air pressure is so low that water would just evaporate. There is ice made out of water though.

Learn by doing - Mars

Bibliography and further reading about planets:

Planets
Stars
Space
Physics
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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