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Transcript
2.1a describe the location and nature of the main constituents of our Solar System, including planets, dwarf planets, asteroids, comets, centaurs and Trans Neptunian Objects (TNOs) ASTEROID BELT TRANS NEPTUNIAN OBJECTS CENTAUR REGION CERES ROCKY DWARF PLANETS PLUTO COMET PATH ERIS MERCURY VENUS EARTH MARS JUPITER ROCKY INNER PLANETS SATURN URANUS NEPTUNE GAS OUTER PLANETS OUR SOLAR SYSTEM NOT TO SCALE Picture credit : (Sun) SOHO-ESA&NASA The 8 planets of the Solar System are clearly divided between the 4 inner, smaller, rocky planets and the 4 outer, much larger, gas planets. The inner planets orbit the Sun at faster speeds and within a two year period. Temperatures are warmer, being closer to the Sun and there are few moons (only three). All the outer planets have ring systems, are very cold and have large numbers of moons in orbit around them. There is a gap where a planet had been thought to orbit the Sun between the orbits of Mars and Jupiter. This planet is now known not to have ever existed. In the early Solar System, small pieces of rock would have collided and merged together (ACCRETION). These rocks, coming close to the gravity of Jupiter, speeded up so when they collided with others, they were broken apart to create smaller pieces. These lumps of rock make up the asteroid belt, formed in an orbit between Mars and Jupiter. Collisions with other celestial objects caused some to fly off in new directions and cross Earth’s orbit. Satellite views of asteroids Picture credit : Galileo Project, JPL and NASA The asteroid Ida shown with a small asteroid Dactyl which acts as its moon Picture credit : NASA/JPL Views of the asteroid Kleopatra (217 km long) If all the material so far discovered in the asteroid belt was packed together, a planet with a diameter no bigger than 1,500 km would be formed. When Pluto was found to be smaller than some of the objects being discovered in the Kuiper Belt, the classification of a dwarf planet was given to objects of substantial size, but not big enough to be labelled a planet (on 24th August 2006). Pluto is substantially smaller than Mercury and objects of the order of size of Pluto were therefore named as dwarf planets. This left the largest asteroid Ceres as a dwarf planet as it was big enough (974 km long and 909 km wide) to fit the new classification. The Kuiper Belt object that led to the downgrading of Pluto was originally named Xena, but is now officially called Eris. Eris has a diameter exactly half that of Mercury and is the biggest dwarf planet so far discovered. The dwarf planet is found well beyond the orbit of Pluto. One of the 3 co-discoverers of Eris, Mike Brown, has produced an excellent piece of information about his work, with moving images showing the way that Eris was first discovered. This can be viewed from the following link:The Discovery of Eris http://www.gps.caltech.edu/~mbrown/planetlila/ Web credit : Mike Brown and Caltech There are many icy/rock objects (planetesimals) in the Kuiper Belt and an area called the Scattered Disc. If one of these has an orbit that crosses inside the orbit of Neptune, the object becomes classified as a Trans Neptunian Object (TNO). Pluto is the biggest TNO. Some of the Kuiper Belt Objects (KBOs) have been dislodged from their orbits and have ended up wandering in variable orbits where the objects (called Centaurs) can cross the orbits of Saturn and Uranus – not quite reaching inwards to Jupiter, or outwards to Neptune. The first Centaur, discovered in 1977, was Chiron. This was thought to be an asteroid, but has since developed the coma of a comet. Half asteroid/half comet gave the link to the new group of objects in the Solar System (the Centaur, in Greek mythology, was half man/half horse). Chiron and other Centaurs may become short period comets. The shortest period for all comets is comet Encke, with a period of 3.3 years. The orbit of the comet around the Sun is so short that it only reaches out into the Asteroid Belt. Most short period comets (returning within 200 years) fly out to the Kuiper Belt before returning. This type of comet usually flies close to the plane of the Solar System. Long period comets appear from any direction as they started life amongst the Oort Cloud, about 2 l.y. away. These, as with the short period comets, are made of ice and dust.