Astronomy 241: Foundations of Astrophysics I 19. Near-Earth Objects Chelyabinsk Meteor: 2013 ~0.5 megaton airburst ~1500 people injured (C) Don Davis Asteroids 101 — B612 Foundation Great Daylight Fireball: 1972 Earthgrazer: The Great Daylight Fireball of 1972 Tunguska Meteor: 1908 Asteroid or comet: D ~ 40 m ~10 megaton airburst ~40 km destruction radius The Tunguska Impact Tunguska: The Largest Recent Impact Event Barringer Crater: ~50 ky BP M-type asteroid: D ~ 50 m ~10 megaton impact 1.2 km crater diameter Meteor Crater — Wikipedia Chicxulub Crater: ~65 My BP Asteroid: D ~ 10 km 180 km crater diameter Chicxulub Crater— Wikipedia Comets and Meteor Showers Comets shed dust and debris which slowly spread out as they move along the comet’s orbit. If the Earth encounters one of these trails, we get a Breakup of a Comet meteor shower. Meteor Stream Perseid Meteor Shower Raining Perseids Major Meteor Showers Forty Thousand Meteor Origins Across the Sky Known Potentially-Hazardous Objects Near-Earth object — Wikipedia Near-Earth object — Wikipedia Origin of Near-Earth Objects (NEOs) ! WHAM Mars Some fragments wind up on orbits which are resonant with Jupiter. Their orbits grow more elliptical, finally entering the inner solar system. Wikipedia: Asteroid belt Asteroid Families Many asteroids are members of families; they have similar orbits and compositions (indicated by colors). Asteroid Belt Populations Inner belt asteroids (left) and families (right). Origin of Key Stages in the Evolution of the Asteroid Vesta Processed Family Members Crust Surface Magnesium-Sliicate Lavas Meteorites Mantle (Olivine) Iron-Nickle Core Stony Irons? As smaller bodies in the early Solar System Heavier elements sink to the Occasional impacts with other bodies fall together, the asteroid agglomerates. center as the asteroid heats. break off pieces of the crust, exposing This forms a separate core, the mantle. mantle, and outer crust. Lava from the interior flows to the surface. Hubble Maps the Ancient Surface of Vesta PR95-20 • ST ScI OPO • April 19, 1995 • B. Zellner (GA Southern Univ.), NASA A fragment of Vesta Hubble Maps the Ancient Surface of Vesta Chicxulub Impactor: A Possible Timeline 1. Baptistina parent body (170 km diameter) smashed ~160 Myr ago. Large Asteroid Breakup — Don Davis 2. Fragment hits Moon, forming Tycho crater (110 Myr ago). 3. Fragment hits Earth, forming Chixulub (65 Myr ago)..