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 asteroids3) To learn about how asteroids are

distributed in our solar system4) 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?

DistributionResonance: 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 10-20 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/RhoadsAstro/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.