Asteroids Astronomy 311 Professor Lee Carkner Lecture 15

Where is the water on Mars? a)Underground b)In the atmosphere c)In the polar caps d)a and b only e)a and c only

What is currently the principle resurfacing agent on Mars? a)Water b)Volcanism c)Wind and dust d)Glaciers e)Impacts

Which of the following correctly orders Mars missions from oldest to most recent? a)Phoenix, Spirit, Viking, Mariner 4 b)Viking, Spirit, Phoenix, Mariner 4 c)Mariner 4, Viking, Spirit, Phoenix d)Mariner 4, Spirit, Phoenix, Viking e)Spirit, Mariner 4, Viking, Phoenix

What two compounds likely make up the ice caps of Mars? a)Water and methane b)Carbon dioxide and water c)Carbon dioxide and ammonia d)Ammonia and methane e)Water and methane

Temperature of Mars  Temp of Mars from radiation balance  T M = [R S /(2 D S )] ½ T S  T M = [6.96X10 8 / (2)(1.5)(1.496X10 11 )] ½ (5778)  T M = K  T F = 1.8T K -460 = (1.8)(227.7)-460 = F  How good is this estimate?  Principle source of error is that we have ignored the effects of Mars’s atmosphere  Since atmosphere is very thin, error is small  How hot must Sun be for liquid water on Mars?  T M = [R S /(2 D S )] ½ T S  T S = T M /{[R S /(2 D S )] ½ }  T S =(227.7) / {[6.96X10 8 / (2)(1.5)(1.496X10 11 )] ½ }  T S = K

Quiz #2 Friday  Quiz 2 similar format as Quiz 1  ~20 multiple choice/matching  ~4 short answer  Covers lectures 9-15  bring pencil and calculator

Rocks in Space  Asteroid --  Meteoroid -- a small piece of rock in space  Meteor -- the flash of light when a meteoroid hits the Earth’s atmosphere   sometimes called a falling or shooting star  Meteorite -- a meteoroid that hits the ground

Types of Meteorites  Meteorites are classified based on their composition   Irons are composed of metal  Chondrites are composed of silicates (rock)   Irons make up only ~5% of falls  But, irons are much easier to find   Chondrites look a lot like normal Earth rocks  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   Often show Widmanstatten patterns when etched with acid   Helps to distinguish true meteorites from terrestrial rocks

Widmanstatten Patterns

Chondrite (Stony) Meteorites  Composed of silicates   Contain chondrules, small glassy inclusions of material that were heated and quickly cooled   Chondrites are old  Carbonaceous chondrites also contain volatiles (water and carbon compounds) and thus represent unprocessed material from the very early solar nebula

Chondrules

The Missing Planet  In the 18th century astronomers noticed that there was a gap between Mars and Jupiter with no planets   This turned out to be a small planet (diameter 918 km) which he named Ceres   This is the asteroid belt

The Asteroid Belt

Asteroid Myths  Are the asteroids debris from a planet that exploded?   Is the asteroid belt dangerous to travel through?   There is on average about one million kilometers between asteroids

Asteroid Facts  Size: Ceres (918 km), Pallas (522 km), about 200 larger than 100 km, most are less than 1 km  Orbit:  Description: very small, irregularly shaped, cratered

Formation of the Asteroid Belt   Jupiter’s gravity:  Ejected most near-by planetesimals   Alters the orbits of the remaining asteroids

Studying Asteroids  Several asteroids have been observed at close range   In 2005 the Japanese mission Hayabusa studied asteroid Itokawa and tried to collect a sample for return to Earth

Asteroid Features  Only Ceres, Pallas and Vesta (the 3 largest asteroids) have enough gravity to form a sphere   Asteroids show many craters   During the heavy bombardment period asteroid collisions must have been frequent

Composition of Asteroids  Asteroids are divided into three major groups based on composition  S Type   C Type   M type  composed of iron and nickel

Formation of Asteroids   C type asteroids are found in the outer belt where temperatures are lower  Need low temperatures to keep volatiles

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 achondritic stonys  Asteroids that never differentiated formed chondrites

NEOs  Some asteroids cross the Earth’s orbit and are called Near Earth Objects (NEO)   About 1 big one every few hundred years  Consequences of impacts  Local damage and small climate change   Very large tidal waves   Mass extinctions 

What Use is an Asteroid?  Mining   Space Habitats   Spaceships  Put engines on the space colony  Providing Material for Life in Space 

Summary  Asteroids are small bodies that orbit the Sun  Most are in the asteroid belt between Mars and Jupiter (2-3.5 AU)  Jupiter’s gravity prevented the asteroids from forming a planet  Description:  Small (most less than 1 km)  Max size is few hundred km  Irregularly shaped  Heavily cratered

Summary: Meteoroids  Iron  made of metal  formed from core of asteroids (M type)  Achondrites (Stony)  made of rock with no inclusions  made from crust of asteroids (S type)  Chondrites (Stony)  made of rock with small inclusions  made from undifferentiated asteroids (S and C type)