Transcript Powers of ten notation

Brief history of the universe
Atoms
Atoms – consist of a dense nucleus of
positively charged protons and uncharged
neutrons surrounded by a cloud of
negatively charged electrons.
Atoms typically have equal numbers of
protons and electrons, but may lose
electrons to become ionized.
The atom
Elements and isotopes
The element is determined by the number of
protons in the nucleus
The isotope is determined by the number of
neutrons
Opposite charges attract
Positively charged protons attract negatively
charged electrons due to the electric force.
Think of static cling.
Like charges repel
Two electrons or two protons will exert a
repulsive force, pushing each other away.
Discussion
If positive charges repel each other, how can
all those positively charged protons get
packed so tightly in the nucleus of an atom?
Why don’t atoms just blow themselves up?
The Strong Nuclear force
The nucleus is held together against the
repulsive electric force of the protons by the
strong nuclear force.
The strong nuclear force is exerted only over
short distances between protons and
neutrons.
Discussion
If the strong force is the same between two
protons as between a proton and a neutron, are
protons more strongly attracted to other
protons, or neutrons, or are they equally
attracted to both?
Protons bind more tightly with the
electrically neutral neutrons, because they
do not need to overcome the repulsive force
between to protons.
Thus the more protons you stuff into an
atomic nucleus, the more neutrons are
needed to keep it stable.
Neutrons, Protons and electrons
Neutrons – decay into a proton and electron
Neutrons – proton/electron pair bound together
Temperature
Nucleosynthesis
Hydrogen and Helium
The early universe contained about 75%
hydrogen, 25% helium and trace amounts of
lithium and beryllium.
opaque
transparent
CMBR temperature map
Dark matter simulation
Star Formation
The nebular hypothesis
A star, like the Sun and planets, formed from
the gravitational collapse of a single,
spherical, slowly rotating cloud of cold
interstellar gas and dust.
Consequence
Planet formation is a natural outcome of
star formation.
Planetary systems should be common.
Discussion
Why do you think a collapsing rotating cloud
of gas forms a disk?
The Planetesimal Hypothesis
Fluffy dust grains condensing out of the solar
nebula stick together as a result of low-speed
collisions, building up to small bodies called
planetesimals.
Cassiopeia A
Did a supernova trigger the
collapse of the Solar nebula?
Xenon-129 is found in some meteorites
Gaseous even at extremely low temperatures
Could only get there by decay of iodine-129
with a half life of 17 million years
Iodine-129 created in a supernova explosion
was injected into solar system within a few
tens of millions of year before its formation.
Protoplanets
As the protoplanets grow by accretion of
planetesimals, their gravity increases
spurring more accretion.
Two classes of planets
Terrestrial – mostly silicates and iron, smaller
in mass, have solid surfaces, close to Sun
Jovian – mostly made of lighter elements such
as hydrogen and helium, higher mass, far
from Sun
Discussion
What’s a silicate? Give and example of a
silicate.
Solar nebula composition
We expect that the solar nebula from which
the Sun formed, had the same composition as
the current solar surface.
98% hydrogen and helium
1.4% hydrogen compounds – CH4, NH3, H2O
0.4% silicate rocks
0.2% metals
Discussion
Given the composition of the solar nebula,
why do you think all the terrestrial planets
have smaller masses than the Jovian
planets?
Discussion
Why do you think the Jovian planets which are
rich in hydrogen compounds, formed far the
Sun, while the rocky terrestrial planets formed
close to the Sun?
Discussion
Why do you think Uranus and Neptune
didn’t get as big as Jupiter and Saturn?
Discussion
Can the Earth hold hydrogen and helium
gas in its atmosphere? Explain.
Discussion
Can any of the other terrestrial planets hold
hydrogen and helium gas? Explain.
Discussion
The Jovian planets all appear to have cores of
rock and icy materials with a mass of about
10 times that of the Earth. What happens
when a protoplanet gets to be about 10
times the mass of the Earth?
Terrestrial Planets
All the terrestrial planets are more or less
differentiated, i.e. the densest materials have
sunk to the core and the lighter materials have
floated to the surface.
Discussion
If the planets grew by being bombarded with
planetesimals, why do you think the most
dense material ended up in the cores of the
terrestrial planets?
Discussion
Why do you think all the terrestrial planets
were so hot in the past? Isn’t space rather
cold?
How the planets got hot
1) Heat of accretion
2) Heat of differentiation
3) Heat from radioactive decay
Terrestrial planets interior
structure
Core – highest density material, mostly iron
and nickel
Mantle – high density silicate rocks
Crust – lower density silicate rocks, granite
and basalt.
Heat and planets
All the terrestrial planets started out hot
and have been losing heat over time by
radiating it into space from their surfaces.
Planetary size and heat loss
Larger planets lose heat more slowly than
do smaller planets.
Discussion
Don’t larger planets have larger surface
areas, and with a larger surface area
shouldn’t larger planets be able to radiate
more energy into space? So shouldn’t larger
planets cool faster? Why doesn’t this work?
Volume and heat
The greater the surface area, the faster heat
will be radiated. But, it is the volume that
stores the heat. The greater the volume of a
planet the more internal heat it can retain.
Also, more massive planets have more
radiative material.
It’s geometry
The surface area increases as the square of
the radius. But the volume increases as
the cube of the radius. Thus, a larger
sphere has less square miles to radiate the
heat per cubic mile of material.
This is why people get fat!
Geologic activity
Internal heat drives geologic activity on the
planets’ surfaces.
Discussion
How does the heat from the interior of the
planet get to the surface?
Lithosphere
The convective cells in the planets do not
make it to the surface, but are stopped at the
base of the lithosphere. The lithosphere
includes the crust and the upper mantel
region of cooler, stronger rock which does
not flow as easily as the warmer, lower
mantel rock.
Plate Tectonics