Transcript A105 Stars and Galaxies

A100
Survey of the
Solar System
Read Chapter 7 – Survey of the SS
Homework 6 – Impact Craters, due on
Friday
Kirkwood Obs. open Wednesday
This week’s Quiz via Oncourse T&S
Today’s APOD
The Sun Today
EARLY VOTING
 WHERE? Curry Building (7th & Morton, one block west
of College Ave)
 EVERY day until November 3rd
 Monday – Saturday: 8:30am – 6:00pm
 Sunday: 1:00pm – 5:30pm
 November 3rd: 8:30am – 12:00
 TRANSPORTATION: Students may take a free early
vote shuttle any weekday between the hours of
11:00am – 5:30pm. The shuttle leaves every 15 minutes
from the IMU circle drive and the 10th street side of
the Wells library.
 Voters MUST present their Indiana drivers license,
student id, or passport when they go to vote.
Another possible activity:
Close Encounters at Ivy Tech
Bloomington
An academic panel discussion will
explore how different academic
disciplines might aid in welcoming
extraterrestrial visitors
Thursday, Oct. 30, 6 PM, Ivy Tech 4th
floor Auditorium, Room 438
Use general activity worksheet
The Solar System
A diversity of objects – The Sun, planets, dwarf
planets, asteroids, comets, dust, gas
An underlying order in the dynamics of their
movements
Two main families of planets:
solid rocky inner planets
gaseous/liquid outer planets
The Sun
The Sun is a star
A ball of hot,
incandescent gas
Energy comes from
nuclear reactions in
its core
Composed mainly of
hydrogen (71%)
helium (27%)
Plus traces of nearly all
the other chemical
elements
The Sun
The Sun is the
most massive
object in the
Solar System
700 times the
mass of the
rest of the
Solar System
combined
The Sun’s mass provides
the gravitational force to
hold all the Solar System
bodies in their orbits
around the Sun
The Planets
Orbits are almost
circular and lie in
nearly the same
plane
Plutoids do not lie
in the plane of the
planets’ orbits
Pluto’s orbit has an
inclination of 17°
Rotational axes are
not lined up
Revolution
and
Rotation
All of the planets travel counterclockwise around
the Sun (as seen from high above the Earth’s
north pole)
Six planets rotate counterclockwise; Venus
rotates clockwise (retrograde rotation), and
Uranus and Pluto appear to rotate on their sides
Mercury
Venus
Earth
Mars
Inner (“Terrestrial”) Planets
 Small “rocky” bodies
 Differentiated crust, mantle, core
 Mainly silicon and oxygen crust and mantle
 Iron/nickel cores
 Relatively thin or no atmospheres
 Large differences in surface structures and processes
Outer
“Gas Giant”
“Jovian”
Planets
Jovian planets are much larger than terrestrial
planets
Jupiter’s radius is 11 times larger than Earth’s
No well-defined surface
Gaseous, liquid, or “icy” (H2O, CO2, CH4, NH3)
What is a
surface?
Terrestrial planets – the surface is the hard
boundary between the crust and the
atmosphere
Jovian planets (and the
Sun!) – the “surface” is the
top layer we can see
Jovian planets don’t have a
real surface – we see the
tops of the clouds
Dwarf
Planets
&
Plutoids
 Pluto and similar objects don’t fit either planet family
 Astronomers have discovered more than 200 objects like
Pluto orbiting the Sun
 In 2006, a new family was introduced – the dwarf planets
 Massive enough to pull themselves spherical
 Orbits have not been swept clear of debris
Lots of
Moons!
 Jupiter > 62
 Saturn > 31
 Uranus > 27
 Neptune > 13
 Mars - 2
 Earth - 1
 Mercury, Venus have
no (known) moons
 Plutoids and asteroids
have moons
More and more moons
of the outer planets
are still being
discovered!
Comets and Asteroids
 Comets are icy bodies about 10 km or less across
 Comets can grow very long tails of gas and dust as they near
the Sun and are vaporized by its heat
 Asteroids are rocky or metallic bodies ranging in size
from a few meters to 1000 km across (about 1/10 the
Earth’s diameter)
Where are
Asteroids
Found?
Most asteroids
orbit the Sun in a
band between
Mars and Jupiter
 Asteroids may be the failed building-blocks of a planet
 Some asteroids lead or trail Jupiter around its orbit
 known as “Trojan Asteroids”
Where Are
Comets Found?
 Most comets orbit the Sun far beyond Pluto in the Oort
cloud, a spherical shell extending from 40,000 to
100,000 AU from the Sun
 Some comets may also come from a disk-like swarm of
icy objects that lies beyond Neptune and extends to
perhaps 1000 AU, a region called the Kuiper Belt
How Do We
Determine the
Composition of
the Planets?
 Since the inner and outer planets differ dramatically in
composition, it is important to understand how
composition is determined
 A planet’s reflection spectrum can reveal a planet’s
atmospheric contents and the nature of surface rocks
 Seismic activity has only been measured on Earth for
the purposes of determining interior composition
Density tells us about composition
A planet’s average density is determined
by dividing a planet’s mass by its volume
Mass determined from the planet’s moons
using Kepler’s modified third law
Volume derived from a planet’s measured
radius
Composition
from
Density
 Once average density known, the following factors are
taken into account to determine a planet’s interior
composition and structure:
 Densities of abundant, candidate materials
 Variation of these densities as a result of compression due to
gravity
 Surface composition determined from reflection spectra
 Material separation by density differentiation
 Mathematical analysis of equatorial bulges
Densities of Terrestrial Planets
Average densities ranging from 3.9 to 5.5 g/cm3
Largely rock and iron
Iron cores
Relative element ratios similar to the Sun except for
deficiencies in lightweight gasses (hydrogen and
helium)
Densities of Jovian Planets
Average densities from 0.71 to 1.67 g/cm3
Compositions similar to the Sun – with hydrogen
and helium
Contain Earth-sized rocky cores
Atmospheres
Interiors
Dates
to
ASSIGNMENTS
Remember
this week
 Chapter 7
 Homework and quiz on Friday
 Kirkwood Obs. open on Weds.