This has required many space missions with orbiters and probes to gather information to increase understanding of our "sister planet." Since Venus exploration began, there have been 41 planned missions to study that planet, though many of them failed at launch or lost communication before reaching their destination. In all, 26 missions have successfully reached the planet and returned scientific data. As many as 4 more missions are planned to launch for Venus by 2009. Several missions returned important information that has led to our current understanding of Venus' climate and composition, and as such, should be mentioned.
In late 1962, the United States' Mariner 2 mission sent back the first scientific data about Venus, showing that its surface was about 425aC (800aF). In 1967, the USSR's Venera 4 mission became the first to be placed directly in Venus' atmosphere and return atmospheric data; it showed that the atmosphere was 90-95% CO2 and no N2 was detected. The pressure was measured at 75 bar (or 75 times stronger than that on Earth), and the surface temperature was read at 500aC. Venera 4 was crushed by Venus' atmosphere before it reached the surface. One day after Venera 4 visited Venus, the United States' Mariner 5 atmospheric probe arrived at the planet and returned data that the atmosphere was 85-99% CO2. The 1969 USSR Venera 5 and Venera 6 atmospheric probes both returned data indicating an atmosphere composed of 93-97% CO2, 2-5% N2, and less than 4% O2. In late 1970, the USSR attained the first successful landing of a spacecraft on another planet (which was Venus), and measured the surface temperature at 475aC and the surface pressure at 90 bar. .
With the next Venera mission (Venera 8), the first measures of wind speed in Venus' atmosphere were gathered. This mission measured wind speeds to be 100 m/s above 48 km, 40-47 m/s at 42-48 km, and 1 m/s below 10 km.
