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REMINDERS:
• Homework
#1 due Thursday (day after tomorrow!) at the
beginning of class (10:30 AM)
• Homework
• Office
Tuesday, July 15, 2014
#2 will be available after class tomorrow (noon)
Hours today will be 2-3 PM in Watanabe 401
UNDERSTANDING ORBITS
• https://kerbalspaceprogram.com/
Tuesday, July 15, 2014
PLANETS AND SOLAR SYSTEM
DEBRIS
Tuesday, July 15, 2014
OPINION POLL!
• Do
you think Pluto is (or should be) a planet?
• (A)
Yes! How could you kill Pluto, you
heartless monster?
Tuesday, July 15, 2014
• (B)
No, of course not, don’t be silly.
• (C)
I really don’t know. Maybe?
• (D)
Depends on how you define ‘planet.’
THE 8 PLANETS
• In
order: Mercury,
Venus, Earth, Mars,
Jupiter, Saturn, Uranus,
Neptune
• Usually
grouped based
on size and
composition
Tuesday, July 15, 2014
DEBRIS: ASTEROIDS, COMETS,
AND DWARF PLANETS
• Everywhere
in the solar
system: billions of objects
• Sizes
varying from a few
meters to 1000s of km across
• Mostly
composed of rocks,
dust, and ice
• Similar
to the building blocks
for planets
Tuesday, July 15, 2014
THE SHAPE OF THE SOLAR
SYSTEM
•
Mostly flattened into a disk shape
•
The plane of this disk is called the ecliptic
•
An orbit’s angle to the ecliptic is called the inclination
Tuesday, July 15, 2014
ROTATION IN THE SOLAR
SYSTEM
• Most
objects rotate in the same direction around the Sun
• Most
planets (but not all!) spin in the exact same direction
• This
is a consequence of the planet formation process
• Planet
spin (spin, not the orbital rotation) is determined by the
history of the planet
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Tuesday, July 15, 2014
WHAT MAKES SOMETHING A
PLANET?
• IAU
official definition:
• 1)
Orbits the sun
• 2)
Has enough mass to pull itself into a spherical shape
• 3)
Has ‘cleared the neighborhood’ around its orbit
Tuesday, July 15, 2014
WHAT MAKES SOMETHING A
PLANET?
• More
intuitive requirements:
• 1)
Specific formation history (planetesimals + gas
accretion)
• 2)
Smaller than a Brown Dwarf star, but big enough to be
spherical
• 3)
Gravitationally dominates its orbital region, is by far the
largest object in its orbit
• 4)
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Only orbits a star (not, say, another planet)
CLASS ACTION!
Tuesday, July 15, 2014
TO BE A PLANET, AN OBJECT
MUST MEET 3 CRITERIA
• Which
of these three does the
moon not meet, causing it not to be
classified as a planet?
• (A)
Only orbits the Sun
• (B)
Is spherical
• (C)
Cleared the
neighborhood of other
objects
Tuesday, July 15, 2014
TO BE A PLANET, AN OBJECT
MUST MEET 3 CRITERIA
• Which
of these three does the
moon not meet, causing it not to be
classified as a planet?
• (A)
Only orbits the Sun
• (B)
Is spherical
• (C)
Cleared the
neighborhood of other
objects
Tuesday, July 15, 2014
ROCKY PLANETS
•
Formed as clumps of dust grains,
which stick to each other and
build to bigger sizes
•
At some point, the dust clumps
stop sticking, but can start merging
•
Some survive to become large
(100s of kilometers in size), called
planetesimals
•
These gather smaller objects and
grow into planets
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GIANT PLANETS
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•
Form first, typically further out
from the star
•
Collections of dust grains grow
and stick with the help of ices
•
When the rocky part is big
enough, it starts collecting gas
•
The more gas a planet collects,
the more it can collect
•
Stops when all the gas around it
is gone
MERCURY
• Radius: 2439
• Mass:
6.08 ×1023 kg (0.06 Earths)
• Semi-major
• Axial
axis: 0.39 AU
tilt: 2’.11
• Year: 88
Earth days
• Day: 176
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km (0.38 Earths)
Earth days
MERCURY FACTS
• Smallest
planet, but also very
dense (large iron core)
• No
atmosphere
• May
still have water (frozen)
at the poles, hidden in
shadows
• Surface
similar to the far size
of the Moon: craters, no
geologic activity
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VENUS
• Radius: 6052
• Mass:
4.87 ×1024 kg (0.82 Earths)
• Semi-major
• Axial
km (0.95 Earths)
axis: 0.72 AU
tilt: 177°
• Year: 225
Earth days
• Day: 243
Earth days, retrograde
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VENUS
• Almost
a twin of Earth
• Huge, dense
atmosphere of
CO2 (96%) and Nitrogen (3%)
• Thick
sulfuric acid clouds block
view of surface
• Evidence
of ancient volcanoes
on surface
• Extremely
hot due to
greenhouse effect
Tuesday, July 15, 2014
EARTH
• Radius: 6371
• Mass:
5.97 ×1024 kg (1 Earths)
• Semi-major
• Axial
axis: 1 AU
tilt: 23°
• Year: 365
• Day: 1
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km (1 Earths)
Earth days
Earth day
EARTH
• One
large moon
• Atmosphere
of Nitrogen
(78%) and Oxygen (21%)
• Significant
surface water,
possibly more inside
• Only
planet in universe
known to support life
• Very
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geologically active
MARS
• Radius: 3396
• Mass:
6.42 ×1023 kg (0.11 Earths)
• Semi-major
• Axial
km (0.54 Earths)
axis: 1. 66 AU
tilt: 25°
• Year: 780
Earth days
• Day: 24.6
hours (1 day + 36 minutes)
Tuesday, July 15, 2014
MARS
• Two
small moons
• Thin
atmosphere of CO2
(95%) and Nitrogen (3%)
• Evidence
of past water &
geologic activity
• Has
polar ice caps and subsurface ice
• Currently
hosts 5 active
spacecraft from Earth
Tuesday, July 15, 2014
ASTEROID BELT
• Millions
of objects ranging
in size from 1000 km to a
grain of dust
• Regarded
as the remnants
of a small failed planet
• ‘Sculpted’ by
Jupiter
• Asteroids
the gravity of
are mostly
rocky, some are metallic
Tuesday, July 15, 2014
CERES
• Largest
across
asteroid: 950 km
• 1/3
the mass of the whole
asteroid belt
• Composed
• May
of ice and rock
harbor an ocean of
liquid water under its
surface
Tuesday, July 15, 2014
OPINION POLL!
Tuesday, July 15, 2014
WHEN IT WAS DISCOVERED,
CERES WAS CALLED A PLANET
• Do
you think it still qualifies as a
planet, now that we know more
about it?
• (A)
Yes
• (B)
No
• (C) Yes, but
a different kind of
planet than the others we
know
Tuesday, July 15, 2014
JUPITER
• Radius: 71492
km (11.2 Earths)
• Mass:
1.89 ×1027 kg (317.8
Earths)
• Semi-major
• Axial
axis: 5.2 AU
tilt: 3°
• Year: 11.86
• Day: 9.93
Tuesday, July 15, 2014
Earth years
hours
JUPITER’S MOONS
• Jupiter
has over 67 moons of varying size
• Mostly
ice/rock mixtures
• May
have warm, salty subsurface oceans
Io
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Europa
Ganymede Callisto
JUPITER AND THE ASTEROIDS
• Jupiter
sculpts the shape of
the asteroid belt, clearing out
gaps at integer orbital
resonances
• Jupiter
also has asteroids
following and leading it in its
orbit
Tuesday, July 15, 2014
CLASS ACTION!
Tuesday, July 15, 2014
THE ASTEROID BELT IS
BETWEEN MARS AND JUPITER
•A
typical asteroid should have an
orbital period of about:
Tuesday, July 15, 2014
• (A)
A year
• (B)
50 days
• (C)
5 years
• (D)
50 years
THE ASTEROID BELT IS
BETWEEN MARS AND JUPITER
•A
typical asteroid should have an
orbital period of about:
Tuesday, July 15, 2014
• (A)
A year
• (B)
50 days
• (C)
5 years
• (D)
50 years
SATURN
• Radius: 60268
km (9.45 Earths)
• Mass:
5.68 ×1026 kg (95.15
Earths)
• Semi-major
• Axial
axis: 9.58 AU
tilt: 27°
• Year: 29.46
• Day: 10.5
Tuesday, July 15, 2014
Earth years
hours
Tuesday, July 15, 2014
Tuesday, July 15, 2014
SATURN’S MOONS
• Saturn
has 62 moons
• Many
are like Jupiter’s moons: ice and rock
• Titan
is the main exception: thick atmosphere, rocky surface
Tuesday, July 15, 2014
TITAN
• Larger
than Mercury
• Has
a thick atmosphere
of Nitrogen (95%) and
methane (4%)
• Has
lakes of liquid
methane on the surface
• Atmospheric
haze makes
surface difficult to see
Tuesday, July 15, 2014
RING SYSTEMS
• All
four of the giant planets have rings, Saturn’s are the largest
• Made
• May
of rocks, chunks of ice, and dust
have formed from bits of collided moons
• Inner
Tuesday, July 15, 2014
planets may once have had rings too...
URANUS
• Radius: 25559
• Mass:
8.68 ×1025 kg (14.54 Earths)
• Semi-major
• Axial
axis: 19.29 AU
tilt: 97°
• Year: 84.32
• Day: 17.2
Tuesday, July 15, 2014
km (4.01 Earths)
Earth years
hours, retrograde
URANUS
• Composed
of Hydrogen
(83%), Helium (15%), and
methane (2%)
• Atmosphere
has ammonia,
water, and methane ice clouds
• Highly
tilted, possibly from
interactions with other planets
• 27
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known moons
NEPTUNE
• Radius: 24764
km (3.88 Earths)
• Mass:
1.02 ×1026 kg (17.15
Earths)
• Semi-major
• Axial
axis: 30.1 AU
tilt: 28°
• Year: 165
Earth years
• Day: 16.1
hours
Tuesday, July 15, 2014
NEPTUNE
• Composed
of Hydrogen
(80%), Helium (19%), and
methane (1%)
• Has
• 13
ice clouds like Uranus
known moons
• First
planet found by
mathematical predictions
Tuesday, July 15, 2014
COMETS
• ‘Dirty
dust
snowballs:’ ice and
• Mostly
live far away from
the sun, beyond Neptune
• Can
be perturbed and fall
in towards the Sun
• When
they heat up, they
leave behind tails of
evaporated material
Tuesday, July 15, 2014
COMET TAILS
• Comets
and dust
have two tails: gas
• Gas
tail always points
directly away from the Sun
• Dust
tail is left behind in the
orbit path
Tuesday, July 15, 2014
THE KUIPER BELT
• Like
the asteroid belt, but
outside the orbit of
Neptune
• Many
comets live here
• Other
objects like Pluto,
Eris, Haumea, etc.
• Mostly
Tuesday, July 15, 2014
icy bodies
PLUTO
• Radius: 1153
km (0.18 Earths)
• Mass:
1.31 ×1022 kg (0.002
Earths)
• Semi-major
• Axial
axis: 39 AU
tilt: 119°
• Year: 246
Earth years
• Day: 6.39
Earth days
Tuesday, July 15, 2014
PLUTO
• Composed
mostly of Nitrogen
ice with traces of methane and
CO
• Has
at least 5 moons, one of
which is 11% as massive as Pluto
• Has
a highly inclined (17°) and
eccentric (e = 0.25) orbit
• May
Tuesday, July 15, 2014
have a core of ice and rock
TRANS-NEPTUNIAN OBJECTS
Tuesday, July 15, 2014
THE OORT CLOUD
• Composed
of comets
of many billions
• Extends
to thousands of
times farther from the sun
than Neptune
• Scattered
remnants of
planet formation
• May
be the source of longperiod comets
Tuesday, July 15, 2014
THE EDGE OF THE SOLAR
SYSTEM
• Interstellar
space ‘starts’ between 100
and 200 AU from the Sun
• This
region is called the heliopause and
corresponds to the edge of the Sun’s
dominant effect on the surrounding
environment
• Spacecraft Voyager
1 is reported to
have crossed the boundary, is currently
at ~128 AU from the Sun
Tuesday, July 15, 2014
SPACE...
THE FINAL FRONTIER
Tuesday, July 15, 2014