• noun a species that is one of the first to begin to grow in a previously unoccupied site, e.g. a moss growing on a scree slope
  • (written as Pioneer)
    Series of US spacecraft. The Pioneers launched between 1958 and 1969 were mainly designed for experiments in Earth orbit, to do with the Earth’s particles and fields, and for solar observations, apart from some Pioneers intended, without much success, for lunar orbit. In 1973 Pioneer 10 was the first spacecraft to visit Jupiter, and has since become the first spacecraft to leave the solar system. Pioneer 11 passed near Jupiter and Saturn. Later members of the series are Pioneer Venus 1 and 2, large probes sent to Venus to make observations from above the atmosphere of Venus and to send probes to the planet’s surface. Pioneer Venus 1, the orbiter, arrived at Venus in 1978 and Pioneer Venus 2, the landers, in 1979. The orbiter made radar maps of the Venusian surface and observed its cloud cover while the five landers from the sent short-lived probes to investigate the planet’s atmosphere and surface.

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