Transcript Lecture

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 ice
S - silicate
D - very dark ice
M - 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
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Asteroid Belt
Trojans - near Jupiter
Centaurs
Kuiper Belt
Centaurs
Temporary 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 is
Pluto
Impacts
Evidence points to the
idea that impacts have
significantly 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
2008 TC3
• 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.
Meteorites Found from Asteroid
• 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
meteorite
A meteorite from 2008 TC3 is discovered
in the Nubian Desert of Sudan by staff
and students of the University of
Khartoum.
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