Did Mars long ago develop far enough for life to arise? If so, does anything still live within Mars' dusty plains, beneath its ice caps, or somewhere underground?
In 1964 the Mariner Four spacecraft flew by Mars and got a good look. What it saw looked more like the Moon than the Earth. Then, in the mid-1970's, two lander-orbiter robot teams, named Viking, went in for an even closer look. The landers tested the soil for the chemical residues of life. All the evidence from Viking told us: Mars is dead. And extremely harsh.
The mission recorded Martian surface temperatures from -17 degrees Celsius down to -107. We now know it can get even colder than that at the poles. The atmosphere is 95% carbon dioxide, with only traces of oxygen. And it's extremely thin, with less than one percent the surface pressure of Earth's atmosphere.
And it's bone dry. In fact, the Sahara Desert is a rainforest compared to Mars, where water vapor is a trace gas in the atmosphere. On Earth, impact craters erode over time from wind and water... and even volcanic activity. On Mars, they can linger for billions of years.