Mariner - astronomy.

Mariner - astronomy. I INTRODUCTION Mariner, name of a series of ten United States space probes, launched from 1962 to 1973, designed to explore Mercury, Venus, and Mars, the three planets of the inner solar system. Mariner 2, which flew past Venus, was the first probe to reach another planet. Mariner 4 was the first probe to relay data from Mars. Mariner 10 was the first probe to fly past two planets--Venus and Mercury (see Space Exploration). II SPACECRAFT All Mariner spacecraft were launched by an Atlas Agena rocket, a military intercontinental ballistic missile. The probes used four solar panels to gather sunlight for electrical power. The orientation and trajectory of the craft were aligned to the positions of either the sun and the earth, or the sun and the bright star Canopus. The probes communicated with scientists and engineers on the earth by continuous radio transmissions. To measure the temperatures, atmospheric pressures, and chemical compositions of the planets they flew past, the Mariner spacecraft used on-board radiometers, spectrometers, and magnetometers. Television cameras radioed back to scientists on the earth the first close-up photos of these neighboring planets. III MISSIONS Mariner 1 was launched on the first mission to Venus on July 22, 1962. Its rocket veered off course shortly after launch, however, and the probe had to be destroyed. About one month later, on August 26, 1962, Mariner 2 was launched toward Venus. It weighed 203 kg (446 lb). On December 14 it flew past the planet at a distance of 41,000 km (25,475 mi). Heat-sensing radiometers measured temperatures of more than 427° C (800° F) and an atmospheric pressure 100 times greater than that on Earth. Mariner 3 was launched toward Mars on November 5, 1964. The mission ended prematurely, however, after the probe's protective shroud failed to open and transmission was lost. Later that month, on November 28, Mariner 4 was launched. It flew past Mars on July 14, 1965, at a distance of 9846 km (6118 mi). No radiation belts or magnetic field were detected around the planet, indicating that Mars does not have a metallic core. Mariner 4 monitors also found that the pressure of the planet's carbon dioxide atmosphere is only one-hundredth that of Earth's atmosphere. The probe relayed 21 photos of meteorite craters on Mars. By the time that Mariner 5 was launched, on June 14, 1967, the design of the Mariner spacecraft had been slightly modified. Mariner 5 was somewhat larger and heavier than the earlier probes, weighing about 245 kg (about 540 lb). It was 2.89 m (9.5 ft) high and its solar panels spanned 5.48 m (18 ft). The probe was equipped with a host of new instruments, including a central computer that controlled the other on-board instruments. Mariner 5 flew within 3990 km (2480 mi) of Venus on October 19, 1967, and provided additional information about the planet's atmosphere. Mariner 6 and Mariner 7 were identical spacecraft, each weighing about 412 kg (about 906 lb). These probes were fully automatic, although they could be reprogrammed remotely from Earth. On February 24, 1969, Mariner 6 was launched toward Mars and passed by the planet at a distance of 3431 km (2132 mi) on July 31. The probe transmitted television images of Mars and analyzed the planet's surface and atmosphere with radio, ultraviolet, and infrared signals. Mariner 7 was launched on March 27, 1969, and flew within 3534 km (2190 mi) of Mars on August 5. The probe studied the Martian atmosphere and relayed 126 photos of the planet's surface, particularly the southern polar region. On May 30, 1971, 22 days after Mariner 8 failed to launch, Mariner 9 was launched toward Mars. The largest of the Mariner probes, it weighed 998 kg (2200 lb) and was equipped with rocket engines that would give the craft the needed boost to jump into the orbit of Mars. On November 13, 1971, Mariner 9 entered into orbit around Mars, becoming the first artificial satellite of another planet. The probe relayed more than 7000 photos of the dramatic landforms of Mars, including an equatorial canyon 3700 km (2300 miles) long that is larger than the Grand Canyon of Earth, a dormant volcano as large as the state of Arizona, and countless features that resemble dry river beds. By the time of the launch of Mariner 10 on November 3, 1973, the design of the Mariner spacecraft had become quite complex in order to render the probes capable of more extensive scientific research over longer periods. Mariner 10 was relatively small, with a weight only half that of Mariner 9. On February 5, 1974, Mariner 10 passed Venus at a distance of 4200 km (2600 mi). Using the planet's gravity as a slingshot, the probe was catapulted toward Mercury without having to resort to additional on-board propulsion systems. On March 29, 1974, Mariner 10 flew within 704 km (437 mi) of Mercury, circled back a second time on September 21, and passed the planet a third time on March 16, 1975, at only 327 km (203 mi) above the surface. The data relayed by Mariner 10 revealed Mercury to be a heavily cratered, sun-baked planet with an iron core similar to that of Earth, a thin hydrogen atmosphere, and a weak magnetic field. The Mariner program provided much information about the planets of the inner solar system. The program also provided an opportunity for scientists to learn how to use robotic spacecraft to study planets. The knowledge gained from the Mariner program was applied directly to the Voyager program, in which two spacecraft were launched in 1977 to explore the gaseous outer planets of the solar system--Jupiter, Saturn, Uranus, and Neptune. Contributed By: Dennis L. Mammana Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.