Orgueil Meteorite

The Orgueil meteorite fell on the village of Orgueil, near Toulouse, Fr., in May 1864 and is often used to infer the relative proportions of elements in the solar system (cosmic abundances). Like the Allende and Murchison meteorites, it is classified as a carbonaceous chondrite, a type that comprises the most primitive meteorites—ones having a chemical composition much like that of the Sun and thus of the solid material that formed at the birth of the solar system.

About 20 fragments of the Orgueil meteorite were recovered. Their analysis soon after the fall revealed the presence of hydrogen, carbon, and oxygen and that its substance resembled peat and coal. Subsequent examination showed that hydrocarbons were present. The meteorite was once at the centre of a dispute about extraterrestrial life, prompted by similarities between its organic matter and hydrocarbons of biological origin on Earth. Determination of the optical properties of the organic material, however, indicated that its origin was not associated with biological processes. Later, small objects found in the meteorite were suggested to be the decayed or fossilized remains of organisms. These were later shown to be pollen and starch grains resulting from terrestrial contamination.

Jupiter

Beyond the asteroid belt is Jupiter, the most massive planet of the solar system and the fifth in distance from the Sun. It is one of the brightest objects in the night sky; only the Moon, Venus, and sometimes Mars are more brilliant. Jupiter is designated by the symbol

When ancient astronomers named the planet Jupiter for the Roman ruler of the gods and heavens (also known as Jove), they had no idea of the planet's true dimensions, but the name is appropriate, for Jupiter is larger than all the other planets combined. It takes nearly 12 Earth years to orbit the Sun, and the planet rotates once about every 10 hours, more than twice as fast as Earth. Its colourful cloud bands can be seen with even a small telescope.

Jupiter has a narrow system of rings and more than 60 known moons, one larger than the planet Mercury and three larger than Earth's Moon. Some astronomers speculate that Jupiter's moon Europa may be hiding an ocean of warm water—and possibly even some kind of life—beneath an icy crust.

Jupiter has an internal heat source; it emits more energy than it receives from the Sun. The pressure in its deep interior is so high that the hydrogen there exists in a fluid metallic state. This giant has the strongest magnetic field of any planet, with a magnetosphere so large that, if it could be seen from Earth, its apparent diameter would exceed that of the

Jupiter

Photograph of Jupiter taken by Voyager 1 on February 1, 1979, at a range of 32.7 million km (20.3 million miles). Prominent are the planet's pastel-shaded cloud bands and Great Red Spot (lower centre). NASA/JPL

Moon. Jupiter's system is also the source of intense bursts of radio noise, at some frequencies occasionally radiating more energy than the Sun. Despite all its superlatives, however, Jupiter is made almost entirely of only two elements, hydrogen and helium, and its mean density is not much more than the density of water.

Knowledge about the Jovian system grew dramatically after the mid-1970s as a result of explorations by three spacecraft missions—Pioneers 10 and 11 in 1973-74, Voyagers 1 and 2 in 1979, and the Galileo orbiter and probe, which arrived at Jupiter in December 1995- The Pioneer spacecraft served as scouts for the Voyagers, showing that the radiation environment of Jupiter was tolerable and mapping out the main characteristics of the planet and its environment. The greater number and increased sophistication of the Voyager instruments provided so much new information that it was still being analyzed when the Galileo mission began. The previous missions had all been flybys, but Galileo released a probe into Jupiter's atmosphere and then went into orbit about the planet for intensive investigations of the entire system over several years. Yet another view of the Jovian system was provided in 2000 by the flyby of the Cassini spacecraft on its way to Saturn and in 2007 by the flyby of the New Horizons spacecraft on its way to Pluto. Observations of the impacts of the fragmented nucleus of Comet Shoemaker-Levy 9 with Jupiter's atmosphere in 1994 also yielded information about its composition and structure.

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