Asteroids (minor planets)

• Bode’s Law suggests a planet between Mars and Jup. at 2.8 AU:– 1801 – Piazzi (It.)

discovers Ceres– 1804 – Juno disc.– 1807 – Vesta disc.

(these are the largest asteroids)

• Now, many thousands are known to exist near 2.8 AU, ranging in size from a few km up to 1000km

• Known as the Asteroid Belt

The Kirkwood Gaps and Resonances

Diversity of Asteroids

Asteroid Composition

C - carbonaceous P - dirty iceS - silicate D - very dark iceM - metal

Spectra of Asteroids depends on composition

Ida and Dactyl: Example of an asteroid with a

moon

Phobos, Moon of Mars: Likely a captured

asteroid

Asteroid Light Curves: Effects of shape and surface patchiness

SHAPE EFFECT MATERIAL EFFECT

Share Question

Holga and Hilda are 2 asteroids. They have the same size and shape and are at the same distance from Sun. Holga is icy with an albedo of 0.9. Hilda is rocky with and albedo of 0.1. Which is brighter in visible light?

a) Holga b) Hilda c) Both same

Which is brighter in infrared light?

a) Holga b) Hilda c) Both same

Asteroid Groups

• Earth crossing– Atens– Apollos

• Mars crossing– Amors

• Asteroid Belt• Trojans - near Jupiter• Centaurs• Kuiper Belt

CentaursTemporary orbits at 20-50 AU, from Saturn to Neptune

Kuipers • Stable region• Around 35,000 objects

of size 100-300 km around Neptune and Pluto (30-50 AU)

• Belt extends to 400 AU• A flattened belt!

Kuiper Belt Objects

Outer orbit isPluto

Impacts

Evidence points to the idea that impacts havesignificantly influenced planets and moons.

Tunguska Event

• Siberia, 1908• June 30, 7:17 am• Explosion of large meteorite at 6km altitude -

deafening bangs and a fiery cloud

• With relevance to today, what should be the criteria for informing/warning/alarming the public of “near” collisions?

• How much should be invested toward defending planet Earth against impacts?

Tunguskan Destruction

End of the Dinosaurs

Asteroid Detected Hours Before Impact• A routine search revealed a

small asteroid hurtling toward Earth

• Rapid international observations predicted the object’s impact 19 hours later over Sudan

• The fireball from the asteroid breaking up in the atmosphere was observed by passing aircraft, satellites and residents of Sudan

• This small impact tested NASA warning procedures developed for more ominous impact events

Image of F class asteroid 2008 TC3 in the hours before it impacted Earth. Exposure time was 6 minutes, so the asteroid appears as a streak. Image from La Sagra Sky Survey, Spain.

2008 TC3

• The small asteroid was expected to vaporize in the atmosphere but a joint NASA-Sudanese team undertook a search for fragments

• Surprisingly, ~280 fresh-looking meteorites have been found spread along TC3’s predicted ground track

• Analysis of the collected samples enabled scientists to determine the asteroid’s composition and type

• Meteorite composition and density suggest TC3 was ejected from the surface of a larger asteroid of rare type

Meteorites Found from Asteroid

A meteorite from 2008 TC3 is discovered in the Nubian Desert of Sudan by staff and students of the University of Khartoum.

meteorite

Connecting Samples with Sources• 2008 TC3 was the first

asteroid observed from space to the ground

• For the first time, scientists can study meteorite samples knowing where the meteorites came from

• Global cooperation and increasingly widespread technology may make these fortuitous events more common

Clockwise from top left: Telescope of the Catalina Sky Survey where TC3 was discovered; Detection image of 2008 TC3; Cell-phone image of luminous trails left in the atmosphere when TC3 disintegrated into dust; TC3 meteorite in the Nubian Desert of northern Sudan

Protecting the Earth, Informing People, Preventing Panic

Destructive Potential