CHAPTER 1 AmAzing Asteroids Asteroids are small rocky bodies that orbit or travel around the Sun In general they are materials left over from the formation of planets or are created when other bodies in space collide and break apart Most of the rocky asteroids move around the Sun in elliptical orbits in the same direction of the Sun’s rotation rotation Such motion is termed prograde Looking down on the solar system from a vantage point above Earth’s North Pole an observer would find that prograde orbits are counterclockwise Orbits in a clockwise direction are called retrograde Between the orbits of Mars and Jupiter are a host of asteroids about 1,000 km 600 miles or less in diameter that orbit in the nearby ring called the asteroid belt Many astronomers consider the asteroid belt a demarcation point between the inner solar system consisting mainly of the terrestrial planets and the outer solar system It is because of their small size and large numbers relative 10
AMAzing Asteroids to the major planets that asteroids are also called minor planets The two designations have been used inter changeably though the term asteroid is more widely recognized by the general public Among scientists those who study individual objects with dynamically interesting orbits or groups of objects with similar orbital characteristics generally use the term minor planet whereas those who study the physical properties of such objects usually refer to them as asteroids EARLY OBSERVATIONS The first asteroid was discovered on January 1 1801 by the astronomer Giuseppe Piazzi at Palermo Italy At first Piazzi thought that he had discovered a comet However after the orbital elements of the object had been computed it became clear that the object moved in a planetlike orbit between the orbits of Mars and Jupiter Owing to illness Piazzi was able to observe the object only until February 11 Although the discovery was reported in the press Piazzi only shared details of his observations with a few astronomers at first and did not publish a complete set of his observations until months later The short arc of observations observations did not allow computation of an orbit of sufficient accuracy to predict where the object would reappear when it moved back into the night sky 11
Asteroids Meteors Meteorites And CoMets Giuseppe Piazzi
AMAzing Asteroids There matters might have stood were it not for astronomers astronomers searching for a missing planet between Mars and Jupiter during an astronomical conference in 1796 Unfortunately Unfortunately Piazzi was not a party to this attempt to locate the missing planet In 1801 German mathematician Carl Friedrich Gauss developed a method for computing the orbit of an asteroid from only a few observations Using Gauss’s predictions the German Hungarian astronomer Franz von Zach rediscovered Piazzi’s lost object on January 1 1802 Piazzi named this object Ceres after the ancient Roman grain goddess and patron goddess of Sicily thereby initiating a tradition that continues to the present day asteroids are named by their discoverers The discovery of three more faint objects at least when compared with Mars and Jupiter in similar orbits over the next six years Pallas Juno and Vesta complicated complicated this elegant solution to the missing-planet problem and gave rise to the surprisingly long-lived though no longer accepted idea that the asteroids were remnants of a planet that had exploded Following this flurry of activity the search for the planet appears to have been abandoned until 1830 when Karl L Hencke renewed it In 1845 he discovered a fifth asteroid which he named Astraea There were 88 known asteroids by 1866 when the next major discovery was made Daniel Kirkwood an American astronomer noted that there were gaps now 13
