Aside from my last lecture: my solar cooker! Don’t forget to turn in homework. Bring star wheel on Wed! Remember, no class next Monday, Nov 11, Veteran’s day Wed Nov 13: second Kitt Peak trip: many more details on Wednesday!

Small objects in the Solar System Meteors, Comets, : we see them without a telescope Asteroids: small rocky objects mostly between Mars and Jupiter – too faint to see without a telescope Kuiper belt objects: even fainter objects beyond Pluto, debris left over from solar system formation Image of comet Wild 2, visited by Stardust mission, return Jan 2006

Moving objects we see in the sky Planes at night: move many degrees/second Satellites: slower than planes, often N-S or S-N Iridium flares: near sunset or sunrise: streak that lasts for a few seconds – move more slowly than “shooting star” Man-made: Natural : Meteors ( misnamed “shooting stars”) Comets – they do NOT flash across the sky! Asteroids: small objects in orbit around the sun between Mars and Jupiter, seen only with telescopes Kuiper Belt Objects (KBOs): small objects orbiting on the outer fringe of solar system

Meteors (shooting stars) can appear at any time, from any direction. Those associated with a particular meteor shower appear to come from a particular direction. None last longer than an “ooh..” They are no larger than a grain of sand – or perhaps a pea for this one! Meteors: debris from comets, chips of asteroids

Meteor showers: remnants of comets Many more per hour: a picture over several hours would show that they all seem to come from one direction in the sky Showers occur on the same dates every year: Perseids, Aug Leonids, Nov 16-17

If a meteor does not burn up completely, and reaches the ground it is a meteorite Samples to examine: Most of these are probably remnants of asteroids Most common are iron Less common: stony (easily missed, more fragile)

Campo de Cielo, Argentina – fell ~5800 yrs ago, crater noted in 1576 Canyon Dieblo, from Meteor crater, fell ~50,000 yrs ago Stony meteorite, fell Mar 5, 1960, Burkina, Africa Some samples:

Tektites: thought to be melted terrestrial rocks, the results of impacts by large meteors

And last Feb 15, over Russia, an meteor (about half ton), exploded, and the blast wave injured 1200 people, shattered windows over large area Lots of meteorite pieces recovered, including big chunk from lake

The first, named C e r e s, d i s c o v e r e d i n i n s e a r c h f o r p r e s u m e d p l a n e t b e t w e e n M a r s a n d J u p i t e r Asteroids: small bodies that orbit the sun between the orbit of Mars and Jupiter – largest about 500 miles diameter

Largest asteroids The smallest asteroids: a few km in diameter and smaller Statistics: we estimate there are as many as a million larger than 1 km diameter And a subset (1,000)have orbits that cross the orbit of earth

Motion in the solar system: a review Stars – motion due to earth’s rotation. Position of stars do not change significantly over history, although astronomy can measure their motion Planets: “wander” along the path called the zodiac, or ecliptic in the sky. (review retrograde motion vrs inner planets). Asteroids: also move mainly along the ecliptic

Last Feb 16 was an interesting day: tracking a near asteroid at 2.1 meter on Kitt Peak This field is about 1/3 the full moon, or 10 arc minutes. Multiples images show the asteroid moving across. But several hours before this close pass, a meteor exploded over Russia

Ida (about 58 km long) and its moon Dactyl: from NASA Galileo mission to Jupiter in 1993

Asteroid, or rubble pile? A few years ago, A Japanese probe took these images. Probe lowered itself to the surface to capture a sample to be returned to earth.

Asteroids: remains of a planet that did not coalesce? Small rocky or iron objects (a few 100 to a few km in diameter) mostly in orbit between Mars and Jupiter

The dangers from earth crossing orbits: Spacewatch, Kitt Peak: mapping orbits of dangerous ones

Asteroids and Dinosaurs What did you learn from the homework reading?

Frequency of Earth Impacts 1 meter sized: every few weeks… 5 meters size: once a year 100 meters sized: every thousand years (Meteor crater impactor about 50 meters in diameter) 1 km size: every million years( crater that probably killed dinosaurs was probably km in diameter, and left a crater that is about 200 km in diameter)

Collisions on other planets: In 1994 a comet (or rubble pile) collided with Jupiter Resulting scars lasted many weeks

Reminder: How did the moon form? (Colette’s class Oct 21).

Lunar Highlands: Rugged, bright terrain caused by collisions, early in history of solar system

Comets: their orbits around the sun are very elliptical Some have short periods ( years) like Comet Halley Others have periods of thousands of years, such as Comet ISON, in a sky near you now… Comets; they appear in the sky for days or weeks – do not flash across the sky!

Comets: Large ( many km diameter) dirty snowballs, orbiting the sun in highly elliptical orbits. So where do we see them? We only see them when they come close to the sun and evaporation and sublimation creates a long tail. The tail always points away from the sun, even when comet moving away from sun They move among the stars, fastest when closest to the sun. (Why?)

Comet orbit leaves debris of meteor showers: Comet Temple-Tuttle responsible for Leonid meteors (November)

Coming soon to a sky near you: Comet ISON ISON:” International Scientific & Optical Network”, devoted to monitoring the sky ISON will be closest to the sun on Nov 28, closest to earth Dec 26

Earth (Reminder, from Colette’s class Oct 21) And at the outer edge of solar system, the Kuiper Belt Objects (KBOs)

The Kuiper belt is composed of small bodies, and a reservoir of short period comets: best known KBO is… Pluto!

Take away In addition to the 8 planets there are many small objects down to dust grain size, orbiting the sun with us: meteors, asteroids, comets, KBO’s We detect each in different ways: They are clues to the formation of the solar system