Vagabonds of the Solar System Lecture 27

Main-belt asteroids 2.0 – 3.5 AUs

Distribution of Asteroids Kirkwood gaps were created by repeated gravitational influence by Jupiter

Families of Asteroids Asteroids form “groups or families” and have unique sets of orbits rather than have a continuous range of all orbits. Asteroids form “groups or families” and have unique sets of orbits rather than have a continuous range of all orbits. Most notable family is “Trojan Asteroids” Most notable family is “Trojan Asteroids”

Trojan Asteroids

Various sizes UL: HST image of Ceres (largest asteroid). UR: Radar map of a medium sized asteroid. LL: Flyby spacecraft image of an asteroid (Mathilde, ~50km).

Chicxulub Impact (= dinosaur killer, K-T impact) ~180km in diameter ~180km in diameter Recent discovery (1978) Recent discovery (1978) Equals to the energy of 10,000+ times of all nuclear weapon detonations

Global Iridium layer at the K-T boundary

KT impact  Dinosaur killer Estimated size of 10-20km asteroid

Some recent impacts! Arizona (Barringer Crater) Arizona (Barringer Crater) ~4,000 ft diameter ~4,000 ft diameter 50m size iron meteor collided at a speed of ~20km/sec. 50m size iron meteor collided at a speed of ~20km/sec. ~50,000 yrs ago ~50,000 yrs ago Tunguska (June 30, 1908, Siberia) Burst meteor in the air (~5 miles) About 1,000 times stronger than the Hiroshima bomb. Knocked down about 80 million trees within 15miles

Shoemaker-Levy broken up comet collide Jupiter (1996) broken up comet collide Jupiter (1996)

Happens frequently… A chain of impact craters A chain of impact craters on Ganymede Estimated size distribution of main-belt asteroids

Torino scale A method for categorizing the impact hazard of near-Earth objects (NEOs).  assessing the seriousness of collision predictions by combining probability statistics and known kinetic damage potentials into a single threat value. NASA can't pay for a killer asteroid hunt  cost to find 90% of asteroids, comets (larger than 1km) would be about $1 billion Apophis: Highest ever Torino scale (“4”) Initial calculation of 2.7% chance to hit the Earth in Current calc = 1 in 12.3 million chance to hit the Earth in 2037.

Recent passby of a NEO : 2005 Yu55 0.5km asteroid passed by the Earth in early 2011 November. How small can asteroids be?

Iron meteorites  Widmanstatten pattern Iron meteorites  Widmanstatten pattern Meteors and meteorites. Stony Asteroid Stony Asteroid meteoroid  meteor  meteorite

Comet : Chunk of ice and dust

Comet’s tails Comet Halley

Origin of long-period comets

Cosmic Messengers

Signal from Pioneer A signal from the Pioneer 10 spacecraft, sent from a distance of more than 6 billion kilometers. The spacecraft transmitted the signal with a power of only one watt (about the power of an X-mas tree light)! A signal from the Pioneer 10 spacecraft, sent from a distance of more than 6 billion kilometers. The spacecraft transmitted the signal with a power of only one watt (about the power of an X-mas tree light)!

In summary… Important Concepts K-T impact Different kinds of meteorites Comets (from Kuiper Belt and Oort cloud) Gas and dust tails of comets Important Terms Lagrange point Trojan asteroids Kirkwood gap Widmanstatten pattern Near Earth Objects Torino scale meteoroid, meteor, meteorite Chapter/sections covered in this lecture : Chapter 15