Although present-day Mars is extremely cold and barren, NASA has discovered evidence that it was once a warmer planet. Some believe that water may still exist in a frozen state on Mars and if we could warm up the atmosphere significantly, it would be possible to create human-friendly living conditions there. In addition, scientists have discovered that the current atmosphere on Mars resembles Earth's atmosphere a billion years ago. They speculate that the process that warmed up Earth's atmosphere to allow plant and animal life to exist can be repeated on Mars. Furthermore, Earth and Mars share the basic elements needed for life to exist (carbon, oxygen and nitrogen), albeit in different amounts.
The question of whether there is life on Mars has fascinated mankind for some time -- even long before the first mapping of the red planet in 1877. And it seems that we're no closer to a conclusive answer today. While authors, scientists, astronomers and even Hollywood have long grappled with this question -- each proposing a suggested life-form on Mars ranging from scientifically likely to sci-fi imaginary -- we have continued to explore Mars in the ever-increasing quest to find evidence of life there. To date, samples of Martian soil have suggested only chemical, but not biological, activity. It seems that the closest we're going to get to an answer about life on Mars is that there may be bacteria lying dormant there, perhaps in the regions of Mars' icy polar caps.
When NASA sent several exploratory vehicles to Mars' surface in 2004, they found even more similarities between Earth and our neighbor. Our land surface areas are about the same size and so are both planets' atmospheric chemistries. Both planets also tilt on their axes in similar manners, which means both have marked seasonal variations. We also have differences, however. Mars does not have the same magnetic field as Earth, but the red planet may have once had some sort of magnetic field that changed or flipped for unknown reasons [source: NASA].
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