Are We Alone

20 Pages 4930 Words

ller scale it seems that there really are canali (or at least their dried-out remnants) on the surface of Mars.
Today, of course, no liquid water flows on Mars. The planet is around 80 million kilometres further from the Sun than the Earth is, and has a climate comparable to that of Antarctica. Worst of all, the existence of liquid water requires not just suitable temperatures, but also suitable pressures; when the pressure is too low there is nothing to stop molecules from simply flying away from a liquid's surface, causing it to boil furiously. The carbon dioxide atmosphere that envelops Mars is vanishingly thin, and the two Viking spacecraft that landed there in 1976 recorded an atmospheric pressure more than a hundred times lower than on Earth. Even at the planet's equator, where temperatures can rise to quite a comfortable 20°C, any liquid water would evaporate almost instantly into the rarified Martian air.
Nonetheless, the presence of ancient riverbeds and channels suggest that Mars once had a warmer climate, and a much thicker atmo...