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Venus is a planet that was actually rediscovered by spacecrafts. It is difficult to study Venus from Earth through a telescope, as covered by a thick layer of clouds that looks quite homogeneous in the visible spectral range. Venus attracted attention since ancient time, but the beginning of studies was launched in 1610 by Galileo, who observed and described phases of Venus, that looked like the moon shined by reflected sunlight. In 1761, Mikhail Lomonosov discovered presence of the planet's atmosphere during a passage of the planet on the solar disk. However, no clear significant scientific data about Venus had been received until 1932, while astronomers W. Adam and T. Denhem (USA) recorded three bands in the Venus spectrum corresponding to carbon dioxide (CO2). Their intensities indicated a big content of CO2 in the atmosphere. In 1956 american astronomers recorded thermal emission of Venus at 3 cm wave, which corresponds to a temperature above 300 ° C. Further, in 1958, the first radar imaging allowed to determine, in particular, high surface temperature, and in 1961 the planet’s orbital period was measured by radar (243 earth days).
Before the space era it was known that the main component of Venus atmosphere was CO2. Some researchers suggested that under the thick cloud layer there was an ocean. Considering the richness of carbon compounds, it was assumed that the ocean surface might consist of oil. In the radio range high temperatures around 500 C were measured, but there was no confidence if that temperature refered to the surface or to the ionosphere. Venera-7 (1970) was the first station, which landed on the hard surface of Venus, measured temperature and pressure.
Venus is the only planet, which became “hospitable” for all Soviet missions. Ten landings were made; the first orbiter and the first (so far the only one) balloon probe in the cloud layer of Venus were launched.
Soviet space exploration of Venus began in 1961. A series of spacecrafts was called "Venera". For 20 years 16 launches to Venus were made.
The main soviet spacecraft explored Venus.
| Spacecraft | Year | Main results |
|---|---|---|
| "Venera-1" | 1961 | Flyby (contact lost) |
| "Venera-2,3" | 1965 | Magnetic fields, cosmic rays, streams of charged particles of low-energy, solar plasma flows and their energy spectra, cosmic radio waves and micrometeorites |
| “Venera-4”
| 1967 | The first probe entered in the planet atmosphere and transmitted data |
“Venera-5, 6”  | 1969 | Data transmission down to altitude of 11 km over the surface |
“Venera-7
| 1970 | The first successful landing of spacecraft on the other planet |
| “Venera-8”
| 1972 | Landing and transmission of data for 50 minutes |
| “Venera-9, 10”
| 1975 | First orbiters around planet. Transmission of black-and-white photos of the planet surface by means of lander |
| “Venera-11, 12”
| 1978 | Transmission of scientific data from the planet surface up to 110 minutes |
| “Venera-13, 14”
| 1982 | The first colored panoramic photos of the planet surface, soil analysis |
| “Venera-15, 16”
| 1983 | Acquisition of radar images of venus surface |
| “Vega-1, 2”
| 1984 | The first balloon probes in the atmosphere of the other planet, operated about two days and transmitted scientific data directly to the earth |
