AnnouncementsBrooks Observatory tours (March 16 - 18)

7:30 - 8:30 p.m. – extra creditWeather permitting

Will look at Saturn, Jupiter, Orion NebulaBring back your ticket with your name on the back

Midterm #2 – March 23

Homework: "Temperature and Formation of Our

Solar System" exercise in the tutorial workbook, pages 57-58.  Read chapter 7.

Chapter 10Remnants 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 leftoverComet means hair (Greek), an icy leftoverMeteor – 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

AsteroidsUndetectable 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

SummaryAsteroids 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.