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% CO 2, 3% N 2, 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 CO 2  Mars has no plate tectonics to return the CO 2 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 CO 2 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 CO 2, atmosphere cools  Lava flows stop 