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Space exploration
Probes to Venus


mariner probes

Space exploration
Probes to Venus

The Soviet Union launched the first probes toward Venus in 1961, but these attempts failed. The first successful probe to fly past Venus and return data was the U.S. Mariner 2, on Dec. 14, 1962. Mariner 5 flew past Venus in 1967 and returned important data. Mariner 10 passed Venus and then made three passes near Mercury in 1974 and 1975.

Soviet attempts to obtain data from Venus finally succeeded in 1967. Venera 4 dropped a probe by parachute, and it transmitted data from the planet's extremely dense atmosphere. In 1970, Venera 7 reached the surface of the planet, still functioning. Between 1975 and 1985, several other probes landed and conducted observations for up to 110 minutes before the temperature and pressure destroyed them. In 1978, the United States sent two probes to Venus, Pioneer Venus 1 and 2. Pioneer Venus 1 was an orbiter. Pioneer Venus 2 dropped four probes into the planet's atmosphere.

Probes that orbited Venus generated rough maps of its surface by bouncing radio waves off the ground. Pioneer Venus 1 mapped most of the surface to a resolution of about 50 miles (80 kilometers). This means that objects at least 50 miles apart showed distinctly on the map. In 1983, two Soviet probes carried radar systems that mapped most of the planet's northern hemisphere to a resolution of 0.9 mile (1.5 kilometers). In 1990, the U.S. probe Magellan mapped almost the entire surface to a resolution of about 330 feet (100 meters).

Probes to Jupiter and beyond must meet special challenges. Radiation belts near Jupiter are so intense that computer circuits must be shielded. The dim sunlight at the outer planets requires lengthy camera exposures. And the vast distances mean that radio commands take hours to reach the probes. Probes have visited Jupiter, Saturn, Uranus, and Neptune. Only Pluto has not been visited.


U.S. probes Pioneer 10 and Pioneer 11 were sent to Jupiter in 1972 and 1973. After observing Jupiter, Pioneer 11 was redirected toward Saturn, arriving there in 1979. It was renamed Pioneer-Saturn. From 1979 to 1981, sophisticated Voyager probes provided much more detailed data on Jupiter and Saturn. They still explore space. Voyager 2 flew past Uranus in January 1986 and Neptune in August 1989. The probes sent back spectacular photos of the outer planets and their rings and moons, and recorded a great deal of scientific data. Active volcanoes were found on Io, a moon of Jupiter, and geysers were discovered on Triton, a moon of Neptune. Other moons exhibited bizarre ice and rock formations.

The Galileo space probe, launched on a mission to Jupiter by the United States in 1989, was far more sophisticated than earlier planetary probes. It consisted of two parts-an atmosphere probe and a larger orbiting spacecraft. On the way to Jupiter, Galileo flew past the asteroids Gaspra and Ida. In July 1995, the atmosphere probe separated from the spacecraft. Both parts reached Jupiter five months later. As planned, the probe plunged into Jupiter's atmosphere, and the spacecraft went on to explore Jupiter, its satellites, and its rings.

In 1997, the United States launched the Cassini probe to investigate Saturn, its rings, and satellites. Cassini carried a separate probe built by the ESA to explore the satellite Titan. Cassini was due to reach Saturn in 2004.

Probes to comets. Two Soviet probes flew past Venus and dropped instruments into its atmosphere, then intercepted Halley's Comet as it passed by the sun in 1986. In 1985, the ESA launched its first interplanetary probe, called Giotto. It passed closer to the comet's nucleus than any other probe and returned dramatic close-up images. Japan also sent two small probes. After several years of inactivity, Giotto was reactivated to fly past the comet Grigg-Skjellerup in July 1992.

The United States did not send a probe to Halley's Comet due to budget limitations. But NASA scientists used a small probe already in space to explore another comet. The International Sun-Earth Explorer 3 satellite had spent several years between Earth and the sun. In 1983, its course was shifted into interplanetary space, and it was renamed the International Cometary Explorer. On Sept. 11, 1985, it passed a comet named Giacobini-Zinner, becoming the first probe to reach a comet.

Probes to asteroids. NASA launched the Near Earth Asteroid Rendezvous (NEAR) probe in February 1996. In June 1997, the probe flew within 753 miles (1,216 kilometers) of the asteroid Mathilde. Images produced from NEAR data show that the asteroid is about 40 miles (65 kilometers) wide. Other data indicate that Mathilde is only about as dense as water. Astronomers suspect that the asteroid is so light because it is full of tiny holes.

NEAR flew past the asteroid Eros at a distance of 2,378 miles (3,829 kilometers) in December 1998. Eros is slightly smaller than Mathilde, but about twice as dense as that asteroid. Eros appears to be made of solid rock. NEAR went into orbit around Eros in February 2000. In March 2000, the probe was renamed Near Earth Asteroid Rendezvous-Shoemaker (NEAR-Shoemaker) in honor of American astronomer Eugene Shoemaker. NEAR-Shoemaker landed on Eros in February 2001.

In October 1998, NASA launched a probe called Deep Space 1 (DS1). The probe flew within only about 16 miles (26 kilometers) of the asteroid Braille in July 1999. DS1 failed to return clear images of Braille, which scientists believe is between 0.6 and 3 miles (1 and 5 kilometers) across. However, the flight successfully tested several new types of equipment for space probes. This equipment included a navigation system that operates automatically, rather than under the direction of people and computers on Earth. Also included was an ion rocket, which operates by shooting electrically charged particles called ions out of its nozzle.

Contributor: James Oberg, M.S., Spaceflight Engineer; author, UFOs and Outer Space Mysteries.
Source : World Book 2005

Space exploration
What is space?
Getting into space and back
Living in space
Meeting basic needs in space
Communicating with Earth
The dawn of the space age
Space probes
Probes to Venus
Probes to Jupiter and beyond
Probes to comets
Human beings enter space
Apollo: Mission to the moon
Exploring the moon
Returning to Earth
The International Space Station
Space shuttles
Types of shuttle missions