1. 03 Oct 2000ASTR103, GMU, Dr. Correll1 Ch 8--Asteroids, Meteors, Comets

2. 03 Oct 2000ASTR103, GMU, Dr. Correll2 What do you think? Are the asteroids a planet that was somehow destroyed? How far apart are the asteroids on average? Why do comets have tails? In which direction does a comet tail point? What is a shooting star?

3. 03 Oct 2000ASTR103, GMU, Dr. Correll3 Early Solar System From studying cratering on the Moon and the planets –First half-billion year had many collisions between planetesimals –More recently the collisions are much less frequent, but do occur!

4. 03 Oct 2000ASTR103, GMU, Dr. Correll4 Asteroids Asteroids: –remnant planetesimals also known as “minor planets” –mainly concentrated in the asteroid belt between Mars and Jupiter--about 10 million miles average separation –Mostly stony or metallic in composition

5. 03 Oct 2000ASTR103, GMU, Dr. Correll5 Asteroids 1801--Piazza discovers Ceres--the first asteroid

6. 03 Oct 2000ASTR103, GMU, Dr. Correll6 Asteroids--Origins A destroyed planet? –Probably not Jupiter’s gravity creates “resonances” which create bands of stable orbits and gaps of unstable orbits –Kirkwood gaps discovered 1867

7. 03 Oct 2000ASTR103, GMU, Dr. Correll7 Asteroids outside the belt Gravitational perturbations eject comets from the belt into elliptical orbits –Some approach the inner planets –“Apollo” asteroids cross the Earth’s orbit Near-Earth Objects (NEOs) Near-Earth Asteroids (NEAs) Potentially Hazardous Objects (PHOs)

8. 03 Oct 2000ASTR103, GMU, Dr. Correll8 Comets Comets--best thought of as “dirty snowballs” orbiting the Sun which evaporate due to solar heating

9. 03 Oct 2000ASTR103, GMU, Dr. Correll9 Comets Origins Primordial gas, dust, and ice frozen in clumps at the outer limits of the solar system –Kuiper belt--out to 500 AU –Oort Cloud--50,000 AU Occasionally perturbed into elliptical orbits approaching the Sun

10. 03 Oct 2000ASTR103, GMU, Dr. Correll10 Parts of a Comet Coma--spherical cloud of vaporized gas around the frozen nucleus Tails--trail of debris –dust tail--dust particles blown away by solar radiation –ion tail--ions carried away by solar wind

11. 03 Oct 2000ASTR103, GMU, Dr. Correll11 Parts of a Comet Tails always point away from the Sun!

12. 03 Oct 2000ASTR103, GMU, Dr. Correll12 Comets Demise Comets eventually –breakup into smaller fragments (Comet West below) –evaporate –collide with the sun –collide with other planets

13. 03 Oct 2000ASTR103, GMU, Dr. Correll13 Comets Demise

14. 03 Oct 2000ASTR103, GMU, Dr. Correll14 Comets Demise

15. 03 Oct 2000ASTR103, GMU, Dr. Correll15 Meteoroids, Meteors, Meteorites Meteoroids--small rocky or metallic particles throughout the solar system Meteors--upon entering Earth’s atmosphere, friction causes heat and disintegration--shooting stars Meteorites--remnants surviving on the ground

16. 03 Oct 2000ASTR103, GMU, Dr. Correll16 UWO Meteor Group Earth’sLocationevery Nov 17 Meteor Showers/Storms--Earth occasionally passes through cometary debris streams leading meteor showers! Leonid Meteor Shower (Comet Temple-Tuttle stream)

17. 03 Oct 2000ASTR103, GMU, Dr. Correll17 Meteorites Meteorites--remnants surviving on the ground –Mostly remnants of asteroids (to have survived entry into Earth’s atmosphere) Stony meteorites Iron meteorites –Show melting and wearing patterns from processing in asteroids –Carbonaceous Chondrites show no melting may be primordial components of solar system contain organic material!

18. 03 Oct 2000ASTR103, GMU, Dr. Correll18 Dino Killers? Evidence for large impact 65 Million years ago Alvarez theory of K-T boundary Impact crater evidence found off north shore Yucatan at Chixulub

19. 03 Oct 2000ASTR103, GMU, Dr. Correll19 More Recent Events Peekskill 1993 –~1m size Tunguska 1908 –~ 1/2 km size –2200 sq km area Meteor Crater –30,000 BCE –1.2 km crater –30 m meteor

20. 03 Oct 2000ASTR103, GMU, Dr. Correll20 Planetary Defense? Easy to study; expensive to carry out!

21. 03 Oct 2000ASTR103, GMU, Dr. Correll21 What do you think? Are the asteroids a planet that was somehow destroyed? –No, the gravitational pull of Jupiter prevented the planetesimal in the asteroid belt to coalesce into planet How far apart are the asteroids on average? –The distance between asteroids averages about 10 million miles Why do comets have tails? –Gas and dust evaporated from the comet nucleus are blow away by the solar wind and solar radiation pressure, respectively In which direction does a comet tail point? –Gas tails point directly away from the Sun; Dust tails point indirectly away from the sun in arcs What is a shooting star? –A piece of space debris plunging white hot into the Earth’s atmosphere--a meteor, not a star

22. 03 Oct 2000ASTR103, GMU, Dr. Correll22 Questions for Thought Explain the origins of comets and describe the various features seen when near the Sun.