ASTR-1010 Planetary Astronomy Day - 37

Titan and Dione

Course Announcements Next Lab: 51 Pegasi: Discovery of a New Planet51 Pegasi: Discovery of a New Planet Homework Chapter 11: Due Friday April 23. Homework Chapter 12: Due Wednesday April 28. Homework Chapter 21: Due Wednesday April 28. -this is extra credit. The last 1 st Quarter moon observing night is: Thursday (April 22) - 8:00. Exam 4 and “Final”: Friday, April 30 – 1030 am

Orbits of Asteroids Most are in the asteroid belt between Mars and Jupiter. Orbits are prograde, in the same direction as the planets orbit. Orbits have small tilts from the plane of the Solar System. Orbits are circular or somewhat elongated. Near-Earth asteroids have orbits that cross that of the Earth.

Asteroid Orbits

Concept Quiz  Asteroids Asteroids are made of A.dust and gas. B.ices and dust. C.rock and metal. D.frozen carbon dioxide (“dry” ice).

Comets Nucleus is an ice/rock mix. Size of nucleus is typically ~ 5 km. When near Sun, comets are “active”: –Nucleus –Coma (head) –Ion tail –Dust tail Comet tails point away from the Sun.

Active Comets © Terry Acomb

Comet Nuclei NASA/JPL/CaltechNASA/JPL-Caltech/UMD

Orbits of Comets Orbits are large and often elongated. Short-period comets: –Periods < few centuries. –Near ecliptic plane. –Prograde orbits, circular or somewhat elongated. Long-period comets: –Periods 1000 to above 100,000 years. –Prograde or retrograde orbits. –Large tilts from the ecliptic, very elongated orbits.

Comet Families Short-period comets come from the Kuiper Belt. – AU from the Sun. –Many planetesimals orbit there (< 50 AU). –These are called Kuiper Belt Objects (KBOs). Long period comets are from the Oort Cloud (100s to 1000s AU).

Many comets come from the Kuiper Belt

Some comets come from the Oort Cloud

Concept Quiz – Short-period Comets Short-period comets are associated with what class of objects? A.Kuiper Belt objects B.Terrestrial planets C.The Oort Cloud D.The giant planets

Concept Quiz – Distant Comets A distant comet at its farthest point from the Sun would have which of the following? A.Dust tail B.Ion tail C.Nucleus D.Coma

Comets and Dust Comets lose dust and gas near the Sun. Small grains make most meteors. Material left behind by a comet makes meteor showers. Dust in the plane of the Solar System makes the zodiacal light.

Comets are the debris of the Outer Solar System

When a comet approaches the inner solar system the ice evaporates

The gas and flaked off dust form a coma and tail

A comet’s tail always points away from the sun

Comet tails can be millions of kilometers long

The tail can break off due to “gusts” in the solar wind

Comet orbits are tilted from the ecliptic and very eccentric

Comets “die” in one of three ways 1: They fall in to the sun

2: They break-up and fizzle out

3: They collide with a planet or moon

Collisions with the Earth Small collisions (dust grains) are frequent. Large collisions (comets, asteroids) less so. Large collisions can be devastating. The biggest collisions have caused mass extinctions.

The Tunguska Event Courtesy of the Wolbach Library, Harvard- Smithsonian Center for Astrophysics, Cambridge, MA

Big rocks DO fall from the sky!

A bad day for the dinosaurs

Chicxulub Impact Site

The Dinosaur Killer! The crater is buried several hundred meters under the surface and is over 200 km in diameter

Wells Creek Impact Basin

Meteor Shows are the result of Earth passing through a debris trail left by a comet

A Meteor Shower Tony Hallas/Science Faction

Meteor Showers come at regular times of the year

Meteorites are classified as Stones, Irons or Stony-irons

The most common meteorite, stones look like ordinary rocks with burnt crust

The most common “find” is an iron meteorite

Widmanstätten Patterns are iron crystals that take millions of years to form

Stony-Irons are intermediate between stones and irons

Carbonaceous chondrites are from the earliest age of the solar system

The Zodiacal Light Courtesy of Joe Orman