Transcript Understanding Orbits

Asteroids and Kuiper Belt Objects
 Know about Pluto
 Know about the
Asteroids
 Know about Comets
 Comprehend the Oort
Cloud and Kuiper Belt
The Discovery of Pluto
 Percival Lowell predicted the existence of an additional
planet in 1905
 Clyde Tombaugh used a device called a blink comparator,
spotting the “jump” of a tiny dot on a photograph on 18
Feb 1930
Pluto’s Orbit and Atmosphere
 Pluto’s orbit is eccentric
 Averages 40 Aus from the Sun, but it
ranges from 30 units to 50 units
 An Astronomical Unit, or AU, is the
mean distance between the Earth and the
Sun, about 93 million miles
 A Parsec is also a measure of distance,
roughly (3.26 LY or 19 Trillion Miles)
Pluto’s Orbit and Atmosphere
 Pluto has an atmosphere, but not year-round
 At perigee it “warms up”
 At apogee it receives so little solar energy that its surface is
below the temperature at which methane freezes
So Why is Pluto Not a Planet?
 August 24, 2006, the International Astronomical Union (IAU), an organization of
professional astronomers, passed two resolutions that collectively revoked Pluto's
planetary status
 By definition, a planet:
 Orbits around the Sun
 Has sufficient mass for its self-gravity to overcome rigid body forces so that it
assumes a hydrostatic equilibrium (nearly round) shape
 Has cleared the neighborhood around its orbit
Asteroids
 The asteroid belt – the region between Mars and Jupiter
where most asteroids orbit
 Jupiter’s gravitational pull has created gaps in the asteroid
belt at 2.50 AU and 3.28 AU
The Origins of Asteroids
 Astronomers once thought that
asteroids were the remains of a planet
that had exploded
 Explanation that seems more plausible
today: asteroids are simply primordial
material that never formed into a
planet
 Jupiter’s gravity keeps pulling
on objects in the asteroid belt
and stirring them up
Project Dawn
Comets’ Predictable Orbits Around the Sun
 In 1705 Halley boldly predicted the comet’s return in 1758


On Christmas night of 1758, Comet Halley appeared in the sky
Scientists have traced Halley sightings back to 239 BC
Halley's Comet's last appearance was in 1986,
and its average period of revolution around
the Sun is 76 years. But it turns out that the
gravitational pull of the giant planets creates
variations in that period of up to a few years
(so the time between successive appearances
isn't always exactly 76 years). Its next
appearance should be in 2061.
A Comet’s Three Main Parts
A comet consists of a head and a tail
1.
Head is made up of a nucleus—the solid core of a comet—and a coma
2.
A coma is the part of a comet’s head made up of diffuse gas and dust
3.
The tail of a comet is the gas and/or dust swept away from the comet’s
head
The Shell of Comets Surrounding the Solar
System
 In 1950 Oort revived an idea
that in a space far beyond
Neptune’s orbit, a great
number of comets orbit the
Earth
 Oort cloud - a theoretical
sphere, between 10,000 AU
and 100,000 AU from the Sun,
containing billions of comet
nuclei
The Small Band of Comets That Make Up
the Kuiper Belt
 In 1951 Kuiper proposed a
second, smaller band of comets
within the Oort cloud
 The Kuiper belt is a disk-
shaped region beyond Neptune’s
orbit, 30 AU to 1,000 AU from
the Sun and the presumed
source of short-period comets
Meteors vs. Meteorites
• Meteor – a streak of light in the
sky caused when a rock particle
falling to Earth is so heated by
friction with the atmosphere that it
emits light
• Fireball – an extremely bright
meteor
• Object that causes the meteor is a
meteoroid
• Meteorite is an interplanetary
chunk of matter that has struck a
planet or a moon
Asteroids and Kuiper Belt Objects
 Know about Pluto
 Know about the
Asteroids
 Know about Comets
 Comprehend the Oort
Cloud and Kuiper Belt