Transcript Astronomy 1010

Announcements
Brooks Observatory tours (March 16 - 18)
7:30 - 8:30 p.m. – extra credit
Weather permitting
Will look at Saturn, Jupiter, Orion Nebula
Bring back your ticket with your name on the back
Homework: "Temperature and Formation of Our
Solar System" exercise in the tutorial workbook,
pages 57-58. Read chapter 7.
Midterm #2 – March 23
Chapter 10
Remnants of Rock and Ice
• Asteroids
• Meteorites
• Comets
• Pluto and its moon
Remnants of the Solar Nebula
Small bodies remain virtually unchanged since
their formation 4.5 billion years ago
They carry history of the Solar system in their
compositions, locations, and numbers.
Asteroid means starlike, a rocky leftover
Comet means hair (Greek), an icy leftover
Meteor – a thing in the air (falling star)
Meteorite – any piece of rock than fell to the
ground from the sky
Finding Asteroids
Asteroid Vesta
Asteroid Eros
Comet Halley
Comet 1993a Mueller
Comet Hale-Bopp
Nucleus of Comet Borrelli
Meteor
Leonid Meteor Shower
Asteroids
Undetectable to the naked eye (a.k.a. minor planets)
The first asteroid Ceres was discovered by Piazzi in
1800 in an attempt to find the missing planet
between Mars and Jupiter
Ceres has a diameter of ~500 km (half of Pluto)
There are more than 100,000 asteroids larger than 1
km in diameter
The asteroid belt lies between 2.2 and 3.3 A.U.
Missing planet
Origin and evolution of the Belt
The most likely reason for the belt existence is
orbital resonances
A resonance occurs if an object’s orbital period is a
simple ratio of another’s object period (1/2, 1/4,etc.)
Asteroids with resonance periods will be pushed out
of their orbits by large planets (e.g., Jupiter)
Asteroid belt
Evolution of the Belt
Early in the history of the Solar system, the belt
contained enough planetesimals to form a planet.
Gravitational tugs from Jupiter created the gaps.
Some pieces of the unformed planet were kicked
out and either crashed into a planet or left the
system.
Two stable zones (1:1 resonance) along Jupiter’s
orbit host two families of asteroids (Trojans).
Jupiter’s Trojan Asteroids
Meteorites
Meteorites are pieces of rock falling from the sky.
Meteorites are real
Seen as fireballs (sometimes with sound)
May cause damage, but most fall into oceans
Types of Meteorites
Primitive meteorites composed of a random mix
of flakes from the solar nebula.
They contain pure metals, which are bound in
minerals on Earth
Processed meteorites – parts of a larger object.
Younger than primitive ones.
Some resemble the Earth’s core, others are
similar to the Earth’s crust and mantle.
Primitive Meteorites
Processed Meteorites
The Origin of Meteorites
Primitive meteorites may be either rocky or
carbon-rich
These 2 types are formed at different distances
from the Sun
Processed meteorites can be removed from the
surface of a planet by an impact.
There are meteorites from Moon and Mars found
on Earth.
Comets
Comets contain information about the outer solar
system
Most of them visit the inner part only once, a few
are regular guests
One of the most famous comets is Halley’s comet.
It was discovered by Edmund Halley in 1682.
Its orbital period is 76 years. The last appearance in
1986.
Comet Structure
Comets are basically dirty snowballs where ice
mixes with rocky dust.
Their mean size is a few kilometers across.
Comets change appearance when they approach
the Sun.
The comet body is called nucleus.
Sublimating ices create coma.
A tail pointing away from the Sun appears.
There are two tails: plasma tail and dust tail.
Comet Orbits
The Origin of Comets
Comet Hale-Bopp
Sun Grazing Comets
Pluto
Pluto was discovered in 1930 by Claude Tombaugh.
Its radius is 1,195 km and mass is 0.0025 Earth mass.
Its orbital period is 248 years.
It was closer to the Sun than Neptune in 1979 – 1999.
At aphelion it is 50 AU from the Sun.
Its moon Charon was discovered in 1978.
Pluto and Charon
Pluto’s Orbit
Pluto and Charon
Charon, Pluto’s Moon
Pluto has a bump that moved from side to side with
a period of 6.4 days
The discovery of Charon enabled astronomers to
determine Pluto’s mass (Kepler’s 3rd law).
Pluto’s rotation axis is tipped 118o relative to its
orbit  it rotates backwards relative to most of
other planets (except Venus and Uranus)
Charon
Diameter – more than half Pluto’s.
Mass – 1/8 the mass of Pluto.
Average distance from Pluto – 20,000 km.
Charon could have formed by a giant impact.
Charon is visible from only one side of Pluto.
It neither rise nor set in Pluto’s skies.
Cosmic Collisions
Meteor showers – result of the Earth’s passing
through a comet orbit
Meteors are single pieces of comet dust
25 million meteors enter Earth’s atmosphere
every day
Meteor showers get their names after
constellations from which they appear to radiate
Large Impacts
The larger the impactor, the more rare the impact
Meteor crater in Arizona formed 50,000 years ago.
A large impact occurred 65 million years ago
perhaps caused the dinosaur extinction.
In 1908, an unusual explosion occurred in Siberia.
Meteor Crater in Arizona
Tunguska Meteorite
Tunguska Meteorite
Summary
Asteroids and comets are the best evidence of how
the solar system formed
The small bodies are significantly affected by
planets gravity.
Impacts with comets and meteorites are spectacular
events, but may even alter life.
Pluto has more similarities with the Kuiper belt
comets.