/puy'euh near"/, n.1. a person who is among those who first enter or settle a region, thus opening it for occupation and development by others.2. one who is first or among the earliest in any field of inquiry, enterprise, or progress: pioneers in cancer research.3. one of a group of foot soldiers detailed to make roads, dig intrenchments, etc., in advance of the main body.4. Ecol. an organism that successfully establishes itself in a barren area, thus starting an ecological cycle of life.5. (cap.) Aerospace. one of a series of U.S. space probes that explored the solar system and transmitted scientific information to earth.6. (cap.) (formerly) a member of a Communist organization in the Soviet Union for children ranging in age from 10 to 16. Cf. Komsomol, Octobrist.v.i.7. to act as a pioneer.v.t.8. to be the first to open or prepare (a way, settlement, etc.).9. to take part in the beginnings of; initiate: to pioneer an aid program.10. to lead the way for (a group); guide.adj.11. being the earliest, original, first of a particular kind, etc.: a pioneer method of adult education.12. of, pertaining to, or characteristic of pioneers: pioneer justice.13. being a pioneer: a pioneer fur trader.[1515-25; < MF pionier, OF peonier foot soldier. See PEON, -EER]Syn. 2. leader, trailblazer, forerunner, pathfinder.
* * *First series of unmanned U.S. deep-space probes.Pioneers 0–4 were all intended to be lunar missions, but only Pioneer 4 succeeded in escaping Earth's gravity (1964). Pioneer 1 was the first spacecraft launched by NASA (1958). Pioneers 6–9 were successfully launched into solar orbits (1965–68) to study the solar wind, solar magnetic field, and cosmic rays. Pioneer 10, launched in 1972, was the first space probe to traverse the asteroid belt and the first to fly by Jupiter (1973), where it discovered Jupiter's huge magnetic tail. It then became the first man-made object to exit the solar system. Pioneer 11's data and photographs (1979) enabled scientists to identify two previously undiscovered moons and an additional ring around Saturn and radiation belts in its magnetosphere. Two Pioneer Venus spacecraft, the Orbiter and the Multiprobe (Pioneer 12 and 13, respectively), reached Venus in 1978. The Orbiter observed the planet's clouds and atmosphere and mapped its surface by radar; the Multiprobe released four instrument packages into the atmosphere at different locations.
* * *▪ space probesany of the first series of unmanned U.S. space probes designed chiefly for interplanetary study. Whereas the first five Pioneers (0–4) were intended to explore the vicinity of the moon, all other probes in the series were sent to investigate planetary bodies or to measure various interplanetary-particle and magnetic-field effects. Pioneer 6 (launched 1965), for example, was injected into solar orbit to determine space conditions between Earth and Venus. It transmitted much data on the solar wind and solar cosmic rays (cosmic ray) in addition to measuring the Sun's (Sun) corona and the tail of Comet Kohoutek. Pioneer 10 (1972) flew by Jupiter in December 1973, the first space probe to do so, and discovered its huge magnetic tail, an extension of the planet's magnetosphere. Pioneer 11 (1973), also called Pioneer- Saturn, passed by Jupiter in December 1974 and flew within about 20,900 km (13,000 miles) of Saturn in September 1979. It transmitted data and photographs that enabled scientists on Earth to identify two additional rings around the planet and the presence of radiation belts within its magnetosphere. Pioneers 10 and 11 each carried a gold plaque inscribed with a pictorial message in the event that extraterrestrial beings ever found the spacecraft. Two complementary Pioneer Venus spacecraft (Pioneer 12 and 13; 1978) reached their destination at the end of 1978. The first, called the Orbiter, studied Venus's clouds and atmosphere and mapped more than 90 percent of its surface by radar. The second spacecraft, the Multiprobe, dropped one large and three small instrument packages into the planet's atmosphere at different locations to measure various physical and chemical properties.
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