Venus was the first planet to be tracked by spacecraft. Mariner 2, an unmanned United States spacecraft that passed within 21,600 miles (34,760 km) of Venus on December 14, 1962, over 3 12 months after leaving Earth. It measured various conditions like temperatures on and near Venus. In 1966, Venera 2 reached a point 15,000 miles (24,000 km) near the planet on February 27, and Venera 3 crashed into it on March 1. Both were unmanned Soviet spacecrafts.
On October 18, 1967, Venera 4, a Soviet spacecraft, dropped a container of instruments into Venus's atmosphere by parachute. On October 19, the United States spacecraft Mariner 5 flew within 2,480 miles (3,990 km) of the planet. No magnetic field was mapped, but both probes charted much atmospheric carbon dioxide. On December 15, 1970, the Soviet spacecraft Venera 7 landed on the planet. The United States planetary probe Mariner 10 flew nearby on February 5, 1974, and took the first photographs from close up.
On October 22, 1975, the unmanned Soviet spacecraft Venera 9 landed and took the first photographs of Venus's surface from close up. Three days later, another Soviet space vehicle, Venera 10, reached Venus's surface and took photographs, measured the atmospheric pressure, and analyzed the structure of rocks.
In December, 1978, four unmanned spacecrafts reached the planet. The United States craft Pioneer Venus 1 went into orbit on December 4, during which it measured the temperature at the top of the planet's clouds, drew and produced a map of the surface, and sent back radar images. On December 9, the United States Pioneer Venus 2 entered and calculated the atmosphere's density and chemical composition. Data on the lower atmosphere were sent back by Venera 12, which landed on December 21, and also by Venera 11, which reached the planet's surface on December 25.
In 1982, two more Soviet spacecrafts landed on Venus, examined samples of the soil, and took photographs—Venera 13 on March 1 and Venera 14 on March 5. In October, 1983, Venera 15 and Venera 16 began tracking the area of Venus north of 30 north latitude by radar, and sent back detailed photographs of features as small as 0.9 mile (1.5 km) wide. Venera 15 finished its mapping in July, 1984; Venera 16, in April, 1984.
On August 10, 1990, the United States spacecraft Magellan began its orbit and imaged features as small as 330 feet (100 m) wide on its radar. Scientists in charge lowered the craft into Venus's atmosphere on October 11, 1994 so that it could chart conditions there before crashing.
The Venus Express probe, designed by the European Space Agency to scrutinize all aspects of the planet's atmosphere and volcanic activity on the surface was launched on November 9, 2005 and sent into orbit on April 11, 2006. The craft found evidence of lightning in the planet's clouds and also corroborated earlier data suggesting that there was once more water vapor in Venus's atmosphere. Venus Express has also detected infrared light coming from the night sky of the planet, called nightglow. Since 2007, the probe has identified three of the chemicals responsible for the glow: oxygen (O2), hydroxyl (OH), and nitric oxide (NO). However, the nature of the chemical reactions that cause nightglow is still unknown.