Transcript martianmeteorites1s

Martian Meteorites
Astronomy 315
Professor Lee Carkner
Special Lecture
Roys Lecture Tomorrow Night
Dr. Ralph Harvey:
“Written In Stone: What the Martian
meteorites are trying to tell us about Mars”
7:30 pm, Thursday, May 12, Olin
Auditorium
5 points extra credit on observing
project if you go
See me there to sign in
Rocks in Space
Asteroid --
Meteoroid -- a small piece of rock in space
Meteor -caused by friction

Meteorite -- a meteoroid that hits the
ground
Types of Meteorites
Meteorites are classified based on their
composition
Iron Meteorites

Iron and some nickel
Stony Meteorites

Silicates (silicon and oxygen)

Contain small round glassy inclusions called
chondrules
What are the properties of chondrites and
irons and how can you identify them?
Iron Meteorites

Have small depressions on surface caused by
heat of passage through atmosphere

These are a particular type of crystal that forms
only by very slow cooling (millions of years)
Helps to distinguish true meteorites from
terrestrial rocks
Chondrite (Stony) Meteorites

One distinguishing feature is a fusion crust
where the outer layers are heated by friction
with the atmosphere

Origin uncertain, but indicate that chondrites
have never been strongly heated

Carbonaceous chondrites also contain
volatiles (water and carbon compounds) and
thus represent unprocessed material from the
early solar nebula
Selection Effect
Chondrites are the most common type of
meteorite

However, chondrites look a lot like normal
Earth rocks

Irons are rare

2/3 of finds are iron
Example of a selection effect

It is an artifact of the way we do our search
Impacts
Most meteoroids are small enough to burn up
completely in the atmosphere

Most of the craters are eroded away, only the recent
(~100,000 years) one are still visible

In fossil records we see evidence of mass extinction
(where most of Earth’s species are wiped out)
Is this due to impacts?
Formation of Meteoroids
Some asteroids became large enough to
differentiate

decay of radioactive materials provided the heat
These asteroids were then broken up by collisions

Fragments of the crust form stonys
Asteroids that never differentiated formed
chondrites
The Canals of Mars
The red color of Mars led the Greeks and Romans to
name it after the god of war

In 1877 G. Schiaparelli thought that he saw
intersecting straight lines on Mars

This was translated to English as “canals” implying that
somebody built them
Percival Lowell built an observatory near Flagstaff,
AZ and published elaborate maps of a network of
canals and oasis on Mars
Mars was thought to be very dry, so naturally the
inhabitants needed to carefully manage water
Mars Facts
Size:
smallest planet with an atmosphere

Orbit:
most distant terrestrial planet from the Sun
Rotation Period:
almost the same day length as Earth
Mean Temperature:
about -80 F
Spacecraft to Mars

Viking 1 and 2 (1975) extensively imaged
Mars and also sent landers to the surface
Current missions:

Mars Odyssey (2001, orbiter)

Pathfinder/Sojourner (1997, rover)
Spirit and Opportunity (2003, rover)
Surface Features
Volcanoes -- Mars has many shield volcanoes,
but they are not active today

Canyons -- Mars shows deep canyons, the
result of volcanic activity stressing the crust

Craters --The northern hemisphere is less
heavily cratered than the southern
Why?


Dust storms alter the Martian craters
The Surface of Mars
Mars is red due to iron oxide (rust) in the soil

Dust storms sometimes cover large fractions of the
surface

Mars is cold


Mars has seasons due to the tilt of its axis
Mars’s Atmosphere
Composition: 95% CO2, 3% N2, trace
amounts of water vapor and oxygen

About 140 times less pressure than the
Earth’s atmosphere

As the water rained out it removed the
CO2
Mars has no plate tectonics to return the
CO2 to the atmosphere
Water on Mars
Mars is now a very dry world

A pan of water left out on Mars would boil

Frost is seen on the surface composed of
frozen water and CO2 that condensed out of
the atmosphere
It is possible that water exists underground
Was Mars Wet?
Surface features indicate that water once flowed
freely on the Martian surface

Due to:

Spot flooding (water frozen underground and sometimes
comes to the surface)?
Mars may have been warmer with a thicker
atmosphere in the past

Where is the water now?

In the polar caps?
Mars may warm up periodically allowing water to form
(Mars may now be in an ice age)
Life on Mars?
Mars shows evidence for liquid water and
higher temperatures in the past

Could that life have survived?

We do have a few meteors that were blasted
off the surface of Mars

AH84001 shows some features that look a little like the
remains of life-forms, but evidence is not very strong
A Possible History of Mars
Mars forms
Mars is cratered
Volcanism creates
volcanoes and lava
flows

Mars losses internal
heat, crust cools

Atmosphere loses
CO2, atmosphere
cools
Lava flows stop
