Transcript Chapter 3: Near-Earth Objects Chevy Asteroid (not Chevy Astro) 1992: A football-sized meteorite crashed through the trunk of Michelle Knapp’s Chevrolet Malibu Classic.

Chapter 3: Near-Earth Objects
Chevy Asteroid (not Chevy Astro)
1992: A football-sized meteorite crashed through the trunk of
Michelle Knapp’s Chevrolet Malibu Classic in Peekskill,
New York
Near-Earth objects
(NEOs) are
asteroids or comets
that approach Earth
What are the
chances that a
larger space object
will crash into Earth
in the near future?
The Good Earth, Chapter 3: Near-Earth Objects
Chevy Asteroid (not Chevy Astro)
Earth carries the
scars of past impacts
with asteroids and
comets
Barringer (Meteor) Crater, Arizona formed
approximately 50,000 years ago when a 50-meter
diameter meteorite crashed to Earth.
A devastating
collision with a 10-km
wide asteroid is
hypothesized to have
caused a global
extinction event 66
million years ago
Russia Chelyabinsk 2/15/2013
http://www.wimp.com/meteorexplodes/
40,000-43,000 miles per hour
Exploded at 98,000 feet (18 miles) altitude
1,500 injured, 7,200 building damaged, 14,000 tons
Volcanic Shock Wave
http://www.wimp.com/volcanicmount/
Characteristics of Near-Earth Objects
Most NEOs do not come close to Earth
but occasionally one may approach
within the moon’s orbit
In 2029, the asteroid Apophis is
expected to come within 36,000
km of Earth . . . about here.
Characteristics of Near-Earth Objects
Few asteroids were
recognized in the inner solar
system 100 years ago.
Today, more than 90,000
asteroids have been identified.
(Red squares = NEOs)
Characteristics of Near-Earth Objects
Asteroids
• Size – space pebbles to
940 km in diameter
(Ceres)
• Travel at ~16 km/s
(36,000 mph)
• Composed of rock
and/or metals
− Meteor – asteroids that
burn in atmosphere
Asteroid 433 Eros
− Meteorite – an asteroid
that strikes Earth’s
surface
Characteristics of Near-Earth Objects
Comets
• Size – generally larger
than asteroids
Comet “tail” forms as heat
from sun causes ice to change
from solid to a gas. The “tail”
points away from the sun
− Many are 100s km across
• Travel faster than
asteroids
− ~50 km/s (112,000 mph)
• Composed of dust and
ice with a rocky core
− “icy dirtballs”
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Comets
• Analysis of light from
explosion on Tempel 1
revealed information on
comet composition
• Common compounds
present including
− Cyanide
− Carbon dioxide
Collision of “impactor” spacecraft with
comet Temple 1, July 4, 2005
− Water – scientists are
investigating if comets
could have supplied water
in Earth’s early oceans
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Comets
• 1908 Explosion of a comet in the atmosphere over
Tunguska, Russia, destroyed forest over an area the
size of a major city (2,100 km2)
Trees knocked down by a comet exploding in the atmosphere over Tunguska
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Two types of comets
• Short-period comets
− originate in Kuiper Belt
beyond Neptune
− Return to inner solar
system every few years
• Long-period comets
Kuiper Belt
Oort Cloud
− Originate in the Oort
Cloud at the outer limits of
the heliosphere
− Return orbits over
decades to thousands of
years
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
• Long-period comets
− Travel toward the sun with
irregular orbits that may be at
a high angle to planets
• Short-period comets
− Orbit sun with similar
paths to outer planets
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
• NEO collisions with rocky
planets and moons formed
2 types of impact craters
− Simple craters
− Complex craters
1,200 meters
Barringer (Meteor) Crater, Arizona, a simple
crater formed 50,000 years ago. This was the
first meteorite crater recognized on Earth.
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
• Craters all feature
− Broken rocks (breccia)
− Ejecta thrown from crater
− Melt rocks
− Altered minerals
• Simple Craters
− Bowl-shaped
− Few kilometers wide
• Complex Craters
− More than 4 km diameter
− Central peak, ring
structures
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
Simple crater
• Unnamed
crater on Mars
Bowl-shaped
2,600 meters
Ejecta blanket
surrounding
the crater
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
Complex crater
Ejecta blanket
surrounding crater
• Eratosthenes crater
on the moon
• 58 km diameter
Central peak
Ring-structures
around edge of crater
Small simple craters
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
• Crater vs. NEO size
− An impact crater is 10-20
times larger than the
colliding NEO
− Example: Manicouagan
Crater, Canada
 ~100 km wide crater
 NEO was 5-10 km in
diameter
Remains of the 200 million year-old
Manicouagan Crater, Canada.
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
• Craters on Earth
− More than 150 impact
craters identified on
continents
− Few impact sites
identified in oceans
 Why?
Sites of the 10 largest impact craters on Earth.
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
• The impact of an NEO with
a diameter equivalent to
− the Lincoln Memorial (~50
meters) would destroy a large
city
− the National Mall (~1 km)
collides with Earth every
100,000 years and would
devastate most nations
Key buildings of Washington, D.C.
− Washington, D.C., (~10 km)
collides with Earth every 100
million years and would
produce global-scale
destruction
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
• Large NEO impacts
are infrequent
− Impacts of relatively
small NEOs (~50
meters) occur at
intervals of hundreds
to thousands of years
− Large NEO (10+ km)
impacts occur on time
scales measured in
hundreds of millions
of years
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
What would happen if a 10 km NEO collided with Earth?
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
What would happen if a 10 km NEO collided with Earth?
1. Fireball racing through atmosphere
2. People at impact site, seconds to live
3. Air blast would flatten everything for hundreds of
kilometers in all directions
4. Massive earthquake at collision
5. Ocean impact would produce giant tsunami hundreds of
meters high
6. Molten rock from collision would rain down, start massive
wildfires
7. Huge cloud of dust blocks sunlight, cools planet for
months, kills off most vegetation
8. Gases from impact – sulfur dioxide, water vapor – added
to atmosphere
The Good Earth, Chapter 3: Near-Earth Objects
Beware Flying Rocks
• NEO impacts are the only major natural
hazards that we have the potential to prevent
− Can’t stop volcanic eruptions
− Can’t stop earthquakes
− Can’t stop hurricanes
• With fore-warning, NEOs could potentially be
deflected off-course or destroyed
• Scientists have already hit a comet with a
spacecraft and landed a spacecraft on an asteroid
The Good Earth, Chapter 3: Near-Earth Objects
Beware Flying Rocks
NEO Detection
• Current NEO search programs focus on the
approximately 1,000 objects with diameter of
more than 1 km
− Search programs are looking for fast-moving dark
objects against the backdrop of space
− Largest NEOs pose the greatest risk and are
easiest to find
− Scientists map position of specific NEOs over time
to chart their course relative to Earth
The Good Earth, Chapter 3: Near-Earth Objects
Beware Flying Rocks
• The Torino Scale
− 0 = NEO will miss Earth or
burn up in atmosphere.
− 1 (green) = will pass near
Earth but extremely unlikely
to impact.
− 2-4 (yellow) = NEO with
minor chance of impact.
− 5-7 (orange) = serious threat
of impact, planning may be
warranted.
− 8-10 (red) = certain collision,
number corresponds to size
of NEO.
The Good Earth, Chapter 3: Near-Earth Objects