Mars and Venus: Different destinies of terrestrial planets

Abstract

Being insignificantly different in distance from the Sun, the main terrestrial planets—Venus, the Earth, and Mars—fall, with due account for inaccuracies, within the so-called habitable zone, i.e., the range of distances from a parent star within which water on the planets can exist in the liquid state. Most likely, in the process of their formation, the three planets received approximately the same share of water. However, only the Earth’s climate is suitable for the development of life. How did it happen that Mars became cold and water on it froze, while the absolutely dry surface of Venus is red hot, exceeding 460°C? Was this always the situation? Climate changes on Mars and Venus from the beginning of the planets' independent existence to the present day are considered, and parallels are drawn with the changing climate of the Earth. The article also discusses how the particularities of the early climate of Mars are related to its inhabitation, as well as the likelihood of discovering biological activity on that planet. Some of the results presented in this article were obtained using Russian instruments installed on the artificial satellites Mars Express and Venus Express.