1. Forty-five of these moons were discovered only recently, from 2000–2003. 2. Nine new moons were announced in June 2006: S/2004 S19 and S/2006 S1 through S/2006 S8. 3. S/2001 U2 and S/2003 U3 were announced in Fall 2003. 4. S/2003 N1 was announced in Fall 2003. 5. In 2006, the IAU declared Pluto to be a dwarf planet. 6. Two new moons were sighted by the Hubble Space Telescope in Oct. 2005 and confirmed in Feb. 2006. Source: Basic NASA data and other sources. The Moon's Phases The Solar System Mercury
Jupiter takes nearly 12 Earth years to orbit the Sun, and it rotates once about every 10 hours, more than twice as fast as Earth. The existence of Jupiter's ring was first suggested in 1974, as a result of findings from the Pioneer 10 spacecraft as it approached the planet. The ring was verified in 1979 by the first Voyager spacecraft when it crossed the planet’s equatorial plane. Jupiter is the most massive planet in the solar system. It has an equatorial diameter of about 143,000 km (88,900 miles). Jupiter is composed primarily of hydrogen and helium. Under equilibrium conditions, the abundant chemically active elements are all expected to combine with hydrogen.Thus, during earlier study of Jupiter, it was surmised that methane, ammonia, water, and hydrogen sulfide would be present. Except for hydrogen sulfide, all these compounds have been found by spectroscopic observations from Earth. photo of Jupiter taken by Voyager 1 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 it 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. It has a narrow system of rings and 79 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 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 until September 2003. In July 2016, the Juno orbiter arrived at Jupiter for a mission expected to last two years. Other looks at the Jovian system were provided in late 2000 and early 2001 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.
What astronomer suggested that the Sun was at the center of the solar system? What do most asteroids orbit? From comets and planets to stars and moons, test your knowledge of astronomy in this quiz. |