Venus is an inner, or telluric, planet; the second from the Sun. It is the third brightest object in the sky, after the Sun and the Moon. It is of similar size to the Earth and, according to observations, does not have a magnetic field. Venus rotates very slowly in a retrograde direction. The surface temperature is 470°C, due to an extreme greenhouse effect. The planet is completely surrounded by clouds composed of sulphuric acid.
Venus is a prime target for space missions and the first were sent by both the Soviets and the Americans at the start of the 60s: in fact, Venus is twice as close to Earth as Mars is and celestial mechanics calculations are easier for a planet without a moon. Since the dawn of the space age, a total of 23 missions (American and Soviet) have successfully travelled to Venus, out of 41 that were launched (counting all of those that flew past Venus without being dedicated to studying it). This success rate is much higher than that of Mars missions.
Here comes a description of the research associated to Venus