Both Mars and Venus have been objects of scientific and popular speculation since at least the beginning of the 20th century, and since the 1960s spacefaring nations have been sending robotic probes to explore these two planets. Nevertheless, Mars has drawn far more attention. Since 2002 no fewer than two Mars probes have been actively gathering data during any given year. There were actually seven used in 2015 alone. This is plausible because Mars is far more hospitable than Venus, where surface temperatures can reach 480 °C, surface pressure is 92 times that of the Earth and the planet is permanently surrounded by thick clouds of sulfuric acid. We have direct evidence that water once flowed and pooled on Mars. So, it can be assumed that life once existed there and may exist at present. Venus is far more Earth-like than Mars in its size, composition and surface gravity, but due to its harsh environment, it could never host life.