Download Comets…

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
Man-made:
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”
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: debris
from comets, chips
of asteroids
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!
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. 11-2
Leonids, Nov 16-17
If a meteor does not burn up completely, and
reaches the ground it is a meteorite
Most of these are
probably remnants of
asteroids
Most common are iron
Samples to examine:
Less common: stony
(easily missed, more
fragile)
Some samples:
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
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
• 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 10-20 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; they appear
in the sky for days
or weeks – do not
flash across the sky!
Comets: their orbits around the sun are very elliptical
Some have short periods (10 -100 years) like Comet
Halley
Others have periods of thousands of years, such as
Comet ISON, in a sky near you now…
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
And at the outer edge of solar system,
the Kuiper Belt Objects (KBOs)
(Reminder, from Colette’s class Oct 21)
Earth
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