Transcript Goal: To know about asteroids and their relations to us.

Goal: To know about asteroids
and their relations to us.
Objectives:
1) To learn where asteroids are located and
what the asteroid belt is actually like.
2) To learn about the Sizes and
compositions of asteroids
3) To learn about how asteroids are
distributed in our solar system
4) To understand the evolution of asteroids.
5) How could we prevent an asteroid
impact?
Map
• 2-3.5 AU
Courtesy of
Wikipedia
What is the asteroid belt like?
(USNO images of POSS I)
• A
B
Hollywood myth
• It is just a myth created by Hollywood that
asteroid belts are difficult to navigate.
• They are in actually pretty wide open, and
to get close to an asteroid, you have to
pretty much make a trip with an encounter
planned!
• If it was like Hollywood wants you to
believe, the asteroid belt would appear as
a bright ring across the night sky.
How do we know about asteroids?
• In the early 1800s astronomers started
noticing that there were starts that would
move from night to night with respect to
the background stars.
• These objects were far too dim (and
therefore too small) to be planets.
• They had discovered asteroids.
• The largest asteroid is < 1/3 the diameter
of the moon!
Today we know:
• There are millions of asteroids in the
asteroid belt down to the size of about 1
km.
• Are we safe from these asteroids? How
many of these asteroids do we expect to
hit the earth in the next 100 million years?
Why is there an asteroid belt?
• The asteroid belt exists because that is a region
where the gravitational influences from Jupiter
would not allow a full planet to form (in fact
Jupiter caused Mars to be so small for the same
reason).
• This is a debris field left over from the formation
of the solar system.
• As expected, asteroids are made of the same
stuff as the entire earth (well, what the earth
would be made of if the heavier stuff didn’t sink
into the core).
Compared to crust of the earth
• Asteroids have materials such as gold,
silver, and other precious metals.
• Earth has the same % as asteroids, but
most of our gold and silver are in the core!
• Asteroids contain a LOT of iron.
• Asteroids also have some elements very
rare on the surface of the earth – like
Iridium. Where are they on Earth?
Distribution
Resonance: object orbits a specific # of times every time Jupiter orbits another
specific # of times. This means they meet up at the same place every few orbits!
Below courtesy of Wikipedia
What are the densities of
asteroids?
•
•
•
•
A) 0.25 that of water
B) about that of water
C) 3X that of water
D) all of the above.
What are the densities of
asteroids?
•
•
•
•
Complete bodies vs “rubble piles”.
Gaspra
(from Galileo)
20 km long
Ida + Dactyl
• Ida = 36 miles X
14 miles
• Dactyl = 1 mile
• Images from
Galileo craft
• Dactyl is first
moon
discovered
around an
asteroid
Some bigger ones
• Ceres – largest asteroid – round. Maybe
have frozen water! (image from Hubble)
• Vesta – 2nd or 3rd largest (from Hubble)
Vesta
closer
up
South
Pole
Not all are in main belt
• Other asteroid groups:
• Trojans – 60 degrees in from of and
behind Jupiter. This are gravitationally
stable regions called “Lagrange Points”.
• Mars crossing asteroids (Eros)
Eros - NEAT
Eros - closer
Near Earth Asteroids - NEOs
• There are many which cross the path of
the earth.
• Some of these will someday hit the earth!
• It is not a question of if, but when.
Asteroid impacts:
• 10 km and larger – global extinctions!
• This obliterates an region with a radius of 1000
km. The crater would have a radius of 100 km!
• Enough dust and Sulfur would be added to the
atmosphere to drop global temperatures by 1020 F for 5-10 years.
• The loss of sunlight would kill plants and
plankton.
• After that, the extra Carbon Dioxide would raise
temperatures to 5-10 F above the average for
the next 50-100 years.
• I call this the TV dinner effect.
10 km impacts cont.
• Luckily these impacts are rare.
• The last known one was 65 million years
ago.
• Yes, that caused the extinction of the
dinosaurs.
• Impacts like this occur once every 100
million years.
1 km
• 1 km impacts create craters 10 km in radius and
obliterate a radius of 100 km (so an entire state
or small country).
• If it hits an ocean, this would cause a giant
Tsunami.
• This would create a few years without summer.
• A billion lives would probably be lost all told, and
would make life difficult for years to come, but
would not cause an extinction.
• Impacts like this occur every 100,000 years.
Narrated Video:
• www.physics.iupui.edu/Astronomy/Rhoads
Astro/A100/DSCN2730.avi
100 m
• Occur every 100-300 years.
• Create a crater 1-2 miles in diameter and
obliterate a 10-20 mile radius (similar to
Mt. St. Helens eruption of 1980).
• Only local effects unless it is a water
landing – then potential Tsunami.
• Closest to last event – 1908 Tunguska
event.
Tunguska
• In 1908 an object about 50 m in diameter
exploded in mid air (never hit the ground,
and never left a crater) – 5 miles up.
• It leveled 2000 square kilometers of forest
land.
• It this had been over a city, the entire city
would be wiped out!
Smaller objects
• Objects the size of a basketball hit the
earth about once a month.
• When they hit are they hot or cold?
Smaller objects
• When smaller objects hit, they are
decelerated to terminal velocity (so the
same speed as a rock dropped from the
top of a skyscraper).
• They impact at about 100 miles per hour.
• As a result, they stay in the sky a long
time.
• So, they have cooled off, and are actually
COLD!
Meteoroids, meteors, and
meteorites
• Meteoroids are rocks in space. Usually it
refers to the objects < 100 m in size.
• Meteors are objects in our atmosphere.
• Shooting stars are meteors.
• Shooting stars are objects the size of a
grain of sand that burn up very quickly.
Meteorites
• Meteorites hit the ground.
• Meteorites are usually very dense and
very heavy if a decent size (such as the
size of my fist).
• Since they have a lot of iron, they are
highly magnetic, even if they look like a
common stone.
• Many look highly rusted.
Meteorites in all shapes/sizes
• There are many types of meteorites:
• Most are made of tiny melted spheres
called Chondrules.
• 8% are similar to rocks on earth formed by
volcanoes.
• 5% are mostly iron.
• 1% look like stones.
You go to your parked car…
• But alas something has crushed it!
• Unhappy, you go to see your car has been
hit by a meteorite! This is very rare.
• You turn to your friend and exclaim what?
Where to find asteroids
• As you can imagine, they are fairly rare on
Earth, but there are places to look…
• Antarctica – ice flows tend to dump rocks,
including accumulated meteorites, and small
areas.
• Australia – desert, so little erosion. The
limestone below causes small amounts of rocks,
makes it easier to find meteorites.
• Sahara desert – arid, so little erosion, so any
rocky area (not all of the desert is sand) can
reveal meteorites (just look for rocks which are
magnetic…).
Easiest place to find them:
• Ebay.
• They sell for about $1 - $500 a gram
(more for very special ones).
• So, they are worth more than silver, and
sometimes as much as GOLD!
Prevention
• If we find one headed our way, how can
we prevent an impact?
Prevention
• If we find one headed our way, how can
we prevent an impact?
• Blow it up! Sorry Hollywood, VERY bad
idea. You just make things worse! You
get a LOT of impacts.
• Best way is to nudge the orbit (to either
miss the earth, or to avoid the orbit of the
earth completely).
Conclusion
• We have learned about what asteroids are
and where to find them.
• We have explored what they are made out
of.
• We have seen their damage potential, and
the possibilities for preventing it, and for
capitalizing on the smaller events when
they do occur.