1. Asteroids Astronomy 311 Professor Lee Carkner Lecture 15

2. 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 = 227.7 K  T F = 1.8T K -460 = (1.8)(227.7)-460 = -50.1 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 =(273) / {[6.96X10 8 / (2)(1.5)(1.496X10 11 )] ½ }  T S = 6926.2 K

3. Rocks in Space  Asteroid --  Meteoroid -- a small piece of rock in space  Meteor --  caused by friction   Meteorite -- a meteoroid that hits the ground

4. Types of Meteorites   Two major types are iron and chondrite   Chondrites are composed of silicates (rock)  Chondrites are the most common type of meteorite   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?

5. Iron Meteorites  Composed of iron and nickel   Called regmaglypts   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

6. Widmanstatten Patterns

7. 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 very early solar nebula

8. Chondrules

9. The Missing Planet   In 1801 G. Piazzi found a faint moving star in the gap   Ceres was too small to be the missing planet, but soon many more smaller objects were found  This is the asteroid belt

10. The Asteroid Belt

11. 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

12. Asteroid Facts  Size: Ceres (918 km), Pallas (544 km), Vesta (529 km), about 200 larger than 100 km, most are less than 1 km   Orbit:  Description: very small, irregularly shaped, cratered

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

14. 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   Scheduled to move to Ceres in 2015

15. Asteroid Types  S Type   M type   C Type  composed of carbonaceous chondrite material  C type asteroids tend to be found in the outer asteroid belt where temperatures are lower

16. Formation of Meteoroids   heavier materials (like iron) sank to the core, while lighter elements (silicates) formed the crust  decay of radioactive materials provided the heat   Fragments of the core form iron meteoroids   Asteroids that never differentiated formed chondrites

17. NEOs   NEO’s can hit the Earth  About 1 big one every few hundred years  Consequences of impacts   ~50 m diameter   ~100 m diameter costal hit  Mass extinctions  ~1 km diameter

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

19. 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

20. 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)