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Transcript
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
resonances are when two periods are a ratio of integers
Diversity of Asteroids
Ceres is a dwarf planet
Vesta is largest asteroid
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
Vesta, as seen with Dawn (2011-12)
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
Centaurs
Temporary orbits at 20-50 AU, from
Saturn to Neptune
Kuipers
• Stable region
• Around 35,000 objects of size 100300 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.
Example crater in the Sahara
of Northern Chad
Tunguska Event
• Siberia, 1908
• June 30, 7:17 am
• Explosion of large meteorite at 6km altitude - deafening bangs and a
fiery cloud
• With relevance for 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
Destructive Potential