Answer:
The correct answer is D) There are signs that Mars once had liquid water on its surface.
Explanation:
Researchers have not found life, or evidence of life, on Mars yet. This planet is considered to be a good candidate in the search of extraterrestrial life because, even though it is smaller than the earth, it still is a huge planet with high possibilities of life on it.
There is evidence that more than 3.500 million years ago, Mars was a warmer planet with water on its surface. There are, for example, some dry riverbeds that reflect the presence of rivers on the planet´s surface. They believe that Mars once had an atmosphere with CO², but after losing it, the planet became cold and desertic.
Researchers have found subterranean water, which was detected by radar. There is a lake in the martian south pole, 1.5 km under a thick ice layer, that has at least a meter wide, 20 kilometers long, and is surrounded by high ground. They establish that its origin is the melting of the ice. It is very cold and salty, which makes it difficult to find life on it, but the only ecological niche that could exist for life is underground where there is protection from extreme cold and high radiation levels.
