Vagabonds of theSolar 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.

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 diameterRecent 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)~4,000 ft diameter50m size iron meteor collided at a

speed of ~20km/sec. ~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)

Happens frequently… A chain of impact craters

on Ganymede

Estimated size distribution of main-belt asteroids

Torino scaleA 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 2029. •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

Meteors and meteorites.

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)!

In summary…

Important ConceptsK-T impactDifferent kinds of meteoritesComets (from Kuiper Belt and Oort

cloud)Gas and dust tails of comets

Important TermsLagrange pointTrojan asteroidsKirkwood gapWidmanstatten patternNear Earth ObjectsTorino scalemeteoroid, meteor, meteorite

Chapter/sections covered in this lecture : Chapter 15