Reports - 2013

Pictures from the Hubble Site

Astronomy Benalla  Meeting Presentations - Wednesday 17th April 2013 Presenter: Patrick Watson Small Solar System Bodies We looked at some of the objects which come under the IAU Classification of Small Solar System Bodies - specifically Asteroids. MOST asteroids are found in the main asteroid belt, which lies between Mars and Jupiter. An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. Orbital Inclination The members of the families are thought to be fragments of past asteroid collisions. An asteroid family is a more specific term than asteroid group whose members, while sharing some broad orbital characteristics, may be otherwise unrelated to each other. Large prominent families contain several hundred recognized asteroids . e.g. Eos family (≈480);  Eunomia family (≈370). A small percentage of asteroids orbit outside the main asteroid belt: Amor Group asteroids – cross the orbit of Mars. Apollo and Aten Group asteroids cross the orbit of Earth. These three groups are collectively termed near Earth asteroids. TROJAN ASTEROIDS The term "Trojan asteroid" is normally understood to specifically mean the Jupiter Trojans  (Trojans refer to the Trojan Wars of Greek mythology ) Lagrangian Points The Lagrangian Points are five equilibrium points in the orbit of one body around another. THE SUN-EARTH LAGRANGIAN POINTS They are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be part of a constant-shape pattern with two larger objects. The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required by an object to orbit with them. Trojan asteroids in the L₄ group are named after Greek heroes (the "Greek node or camp" or "Achilles group"). Those at the L₅ point are named after the heroes of Troy (the "Trojan node or camp") The Hilda or Hildian asteroids Asteroids in a 3:2 orbital resonance with Jupiter. Hildas move in their elliptical orbits so that their aphelia (furthest distance from the Sun) put them opposite Jupiter, or 60 degrees ahead of or behind Jupiter at the L₄ and L₅ Lagrangian points.  Over three successive orbits each Hilda asteroid passes through all of these three points in sequence. While the term "Trojan asteroid" is normally understood to specifically mean the Jupiter Trojans, the term “Trojan”  has come to be used more generally to refer to other small solar system bodies with similar relationships to larger bodies: • Mars Trojans • Neptune Trojans • Saturnian Trojans   In October 2010 the first Earth Trojan asteroid was discovered. TK₇ has a diameter of about 300 meters. Its path oscillates about the Sun–Earth L₄ Lagrangian point (60 degrees ahead of Earth), shuttling between its closest approach to Earth and its closest approach to the L₃ point (180 degrees from Earth) about every 400 years. There many other objects which fall into the Small Solar System Bodies classification which are of interest: Trans-Neptunian Object (TNO) • Scattered Disc Objects • Kuiper Belt Objects (KBOs) • Classical KBOs  or “cubewanos” • Plutinos • Plutoid Detached Objects Centaurs Damacloids Eris has been classified as a minor planet, is a TNO and also a scattered disc object. Eris and its moon Dysnomia