Impact Craters

1
Impact Craters
2
There Are Lots of Craters!

• Craters can be seen on nearly every rocky body in
  the solar system
• Not all of them are left over from formation
  there are still collisions going on

3
Two Kinds of Craters

• There are two kinds of craters impact craters
  and volcanic craters
• Craters on the moon were once thought to be
  volcanic, but have since been determined to be
  impact craters

4
Types of Impact Craters
5
Origins of Impact Craters

• Comets, meteorites, asteroids, hit planets and
  moons to create impact craters
• Earth-crossing asteroids cross Earths orbit,
  could be potentially hazardous
• Tracking NEOs is important, but still small
  chance of collision

6
Why Are Craters Important?

• Craters dominate many bodies in the solar system
• common process that tells us something about the
  evolution of solar system
• Most impacts happened early in the solar systems
  life
• played a large role in the formation of Mercury,
  Venus, Earth, the moon, and Mars, which formed by
  accretion
• Can sometimes give us an idea of a bodys age

7
A History of Cratering on Earth

• Earths oldest surviving crater is 3.47 billion
  years old (Earth is 4.55 billion years old)
• Chicxulub (10km) hit 65 million years ago and is
  possibly related to dinosaurs extinction
• Tunguska impact happened recently 1908 in Siberia

8
Why Doesnt Earth Have More Craters?

• Weathering on Earth erodes craters more quickly
  than on bodies without atmospheres
• Other examples Io, Europa are being constantly
  resurfaced

9
Comet Shoemaker-Levy 9

• String of cometary fragments
• Hit Jupiter in July, 1994
• NO craters on Jupiter its made of gas!

10
A Few Physics Things

• Potential Energy PE mgh (gEarth -9.8 m/s2)
• m mass g gravitational acceleration, h
  height
• Energy of the object before you drop it
• Kinetic Energy KE ½ mv2
• m mass v velocity
• Energy of the object while its falling
• ETotal PE KE

11
Errors Measurements

• Every measurement will not be the same ? ERRORS
• Measurements will scatter around a mean value
• Mean M S m / n
• m measurement value n of measurements

12
Errors Standard Deviation

• There is also a standard deviation from that mean
• Each measurement will differ from the mean by a
  deviation D M - m
• Standard Deviation s Ö (SD2 / (n-1))

13
Where Do Errors Come From?

• Even if you repeat the same experiment many
  times, the results will not always be exactly the
  same
• Can you really drop the ball from the EXACT SAME
• Height
• Angle
• Is the sand surface ALWAYS constant?

14
Scale Factors

• Scale Actual Size / Measured Size
• Meteor Crater actual size 1.186km
• Size in image 267 pixels
• Image scale 1.186km / 267pixels
  0.004 km/pixel
• See pg. A.8 of your lab manual for reference

15
Basic Lab Procedure

• Get a pan filled with sand, a container of
  impactors, and a meterstick
• Follow the procedures in the manual for each of
  the three different experiments
• Also complete the exercise in the manual with the
  picture by figure out the scale of the image