Download Lecture 11

Lecture 11:
The Solar System’s biggest (Jovian
planets) and smallest (dwarf planets and
smaller bodies)
Astronomy 111
Wednesday October 5, 2016
Reminders
• Online homework #5 due Monday at
3pm
ASTR111 Lecture11
Jovian Planets
ASTR111 Lecture 11
Jovian Planets and Other Solar
System Constituents
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The Solar System:
List of Ingredients
Ingredient
Percent of total mass
Sun
Jupiter
other planets
everything else
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99.8%
0.1%
0.05%
0.05%
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Jupiter and Saturn
Jupiter and Saturn consist mainly of hydrogen
and helium.
Jupiter:
Escape speed = 60 km/sec
Air temperature = 165 K (-160o F)
Saturn:
Escape speed = 35 km/sec
Air temperature = 93 K (-290o F)
Earth:
Escape speed = 11 km/sec
Air temperature = 290 K (60o F)
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Jupiter and Saturn
Atmospheres of Jupiter and Saturn retain H, He.
Because Jupiter and Saturn are cold and have high
escape speed, they hang onto hydrogen and
helium.
Jupiter’s atmosphere is 75% hydrogen, 24% helium.
Saturn’s atmosphere is 92% hydrogen, 6% helium.
Question: Where is Saturn’s helium?
Answer: Saturn is so cold, its helium condenses and
rains downward.
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Jupiter and Saturn
Jupiter and Saturn radiate away more energy
than they receive from the Sun.
What is the source of the extra energy?
Mostly, it is heat left over from when the planets
formed. (Big objects cool more slowly).
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Jupiter and Saturn
Jupiter and Saturn have belts and zones of clouds, plus
circular storms.
Air heated from
above by the
Sun, from below
by internal heat:
Strong winds and
large storms.
We see clouds of
ammonia (NH3),
colored by
complex
compounds.
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Jupiter’s
atmosphere is
divided into
light-colored
zones and
dark-colored
belts.
High-speed
winds blow
eats or west at
the boundaries
between them.
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Saturn has a similar pattern of zones and belts.
They are less dramatic than Jupiter’s: Saturn’s clouds
are buried deep in its atmosphere and are blurred by
haze.
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The Great
Red Spot
of Jupiter
An enormous
circular storm
(up to 40,000
km across) in
the southern
hemisphere of
Jupiter.
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Clouds are usually made of different stuff from the
“air” they float in.
Venus: carbon dioxide atmosphere, sulfuric acid
clouds.
Earth: nitrogen atmosphere, water clouds.
Mars: carbon dioxide atmosphere, water & carbon
dioxide clouds.
Jupiter & Saturn: hydrogen atmosphere, ammonia
clouds.
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Jupiter and
Saturn are
differentiated.
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Moons of Jupiter and Saturn
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Jupiter’s moons
Jupiter has ~70 known moons.
~60 are small (<300 km
across) and irregular
(similar to Phobos
and Deimos).
Many of the outer
moons have
retrograde orbits;
they are probably
captured asteroids.
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Moons
of
Jupiter:
orbits.
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4 of the moons of Jupiter are large (> 3000
km across) and spherical (like our Moon).
These are the four Galilean moons:
Io, Europa, Ganymede, Callisto
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Galilean Moons:
A miniature analog to the Solar System
Revolution
counterclockwise,
on nearly circular
orbits, in nearly
the same plane.
Io and Europa:
mostly rock
Ganymede and Callisto: rock and ice
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Terrestrial planets: Internal heat
determined by size of planet.
Galilean moons: Internal heat determined
by proximity of Jupiter.
Near Jupiter (Io): lots of tidal activity, much
volcanic activity, no ice.
Far from Jupiter (Callisto): little tidal
heating, no volcanic activity, lots of ice.
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Saturn has 56 known moons
49 are small (<300 km across) and irregular (like
small moons of Jupiter).
6 are mid-sized (400--1500 km in diameter) and
spherical.
One of Saturn’s moons is the giant moon Titan.
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Moons
of
Saturn:
orbits.
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Uranus and Neptune
• Uranus was discovered in
1781 by William Herschel
• Neptune discovered in
1846 (Urbain Le Verrier
using Newton’s Laws to
explain perturbations of
Uranus’s orbit and infer
Neptune’s existence)
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Uranus and Neptune
Uranus and Neptune are planetary ―twins‖,
like Earth and Venus. Uranus is 3% larger
in radius but 15% smaller in mass than
Neptune.
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1)
2)
3)
4)
Interiors of Uranus and Neptune
Gaseous atmosphere: hydrogen, helium,
methane
Liquid outer layer: hydrogen, helium
Liquid or slushy mantle: water, ammonia
Solid core: rock, metal
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The rotation axis of Uranus
is tilted by about 90o, causing
extreme seasons.
Axis tilts:
• Jupiter = 3o
• Saturn = 27o, Neptune = 30o
• Uranus = 98o
The seasons of Uranus
Winter solstice (AD 1985):
north – perpetual dark, south – perpetual sun.
Vernal equinox (2007): sun rises once every 17 hours.
And so forth …
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Near the winter solstice (1986), the atmosphere
of Uranus was boring:
(left: visible light)
(right: ultraviolet)
No storms; very faint belts & zones.
Heat flow from summery south to wintery north
smeared out storms.
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At the vernal
equinox (in
2007), Uranus
got stormier:
Heating of
northern
hemisphere
produces
storms, made
visible by clouds
of methane.
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Uranus has 27 known moons.
22 are small (< 200 km across) and irregular.
5 are mid-sized (400 => 1600 km in diameter) and
spherical. No giant moons.
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Neptune
Neptune has surprisingly strong storms, driven by
internal heat.
Temperature at
Neptune’s cloud
level is 55 Kelvin
(-360o F).
This is as warm as
Uranus,
although
Neptune is
much further
from the Sun.
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Neptune’s
atmosphere
is being
warmed
from
below by
internal
heat.
This extra heat drives large circular storms,
like the “Great Dark Spot” seen above.
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Neptune has 13 known moons.
12 are small (< 500 km across) and irregular.
One is the giant moon Triton.
Proteus
Triton
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Nereid
Dwarf planet Pluto
Jan. 23, 1930
Jan 29. 1930
Discovered in 1930 by Clyde Tombaugh,
while searching for Planet X.
Orbital period = 248 years
Rotation period = 6.4 days
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Pluto and Charon
Pluto’s moon,
CHARON, was
discovered in 1978.
From the ground,
Charon looked
like a ―lump‖
on Pluto’s side.
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New Horizons
At last, a mission to Pluto! (Too little, too late)
Launch:
January 2006
Jupiter flyby:
February 2007
Pluto flyby:
July 2015
Then onward into
the outer solar
system.
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Dwarf planet Eris
(a.k.a. “Xena”)
Oct. 21, 2003
Discovered in 2005, systematic search.
Orbital period = 557 years
Rotation period = 26 hours
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Eris (“Xena”), the troublemaker
Discovered in 2005
by Mike Brown
and
collaborators.
It has a moon.
It is BIGGER than
Pluto!
Trouble!
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Orbits of Jovian planets, Pluto and Eris
(Will not collide—
orbits are not
in
the
same
plane)
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Are Pluto and Eris planets?
That depends on how you define ―planet‖.
As of August 2006, new category of
―dwarf planet‖.
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IAU: definition of “planet”
The International Astronomical Union
defines “planet" as a celestial body that,
within the Solar System,
(a) is in orbit around the Sun;
(b) has sufficient mass for its self-gravity to
overcome rigid body forces so that it
assumes a hydrostatic equilibrium (nearly
round) shape; and
(c) has cleared the neighborhood
Planets: Mercury, Venus, Earth, Mars,
Jupiter, Saturn, Uranus, Neptune
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IAU: “dwarf planet”
The International Astronomical Union defines a
"dwarf planet" as a celestial body that, within the
Solar System,
(a) is in orbit around the Sun;
(b) has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a
hydrostatic equilibrium shape;
(c) has NOT cleared the neighborhood around its
orbit; and
(d) is not a satellite
Dwarf Planets (so far): Eris, Pluto, Haumea,
Makemake, Ceres
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IAU: “dwarf planet”
The International Astronomical Union defines a
"dwarf planet" as a celestial body that, within the
Solar System,
(a) is in orbit around the Sun;
(b) has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a
hydrostatic equilibrium shape;
(c) has NOT cleared the neighborhood around its
orbit; and
(d) is not a satellite
Dwarf Planets (so far): Eris, Pluto, Haumea,
Makemake, Ceres
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More dwarf planets?
More objects like Pluto and Eris (or even
bigger) might exist. They are hard to find:
• Very dim
• Very slow moving
Perhaps more easily detected from their
gravitational influence?
From studies of Neptune’s orbit: No more
Jovian (massive) planets within 200 A.U.
of the Sun.
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Many smaller bodies
Many rocky
asteroids & icy
comets
populate the
solar system.
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Asteroids
• The asteroid belt lies
between Mars &
Jupiter
• Leftover remnants
from planet formation
• >90,000 named
asteroids
• Asteroids move in the
sky relative to the
stars, so they are
easy to find.
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Asteroids
https://www.youtube.com/watch?v=BKKg
4lZ_o-Y
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Kuiper belt
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Kuiper belt
The Kuiper belt, beyond Neptune,
contains small, icy, Pluto-like objects.
The Kuiper belt lies close to the ecliptic
plane, and stretches from 30 A.U. to 50
A.U. from the Sun.
Named after Gerard Kuiper, who predicted it
should be full of planetesimals.
Over 1,000 Kuiper belt objects (a subset of
trans-Neptunian objects) have been found
in the belt since its discovery in 1992.
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Kuiper belt
The icy Kuiper Belt Objects (KBOs)
are leftover planetesimals.
Kuiper Belt Objects have colors (and
spectra) consistent with them being icy.
They are probably planetesimals that
formed within the Kuiper belt.
The Kuiper Belt Objects are scattered too
thinly for them to have accreted into a
larger body.
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Comets
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Comets: “dirty snowballs”
Strip away their tails, and comets are just
snowballs several km across.
A comet contains:
frozen water,
frozen carbon dioxide,
ammonia,
dust & rocks,
carbon,
complex carbon compounds
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Comets are big, dusty
snowballs. If a comet
comes close to the
Sun, the ice is
vaporized, and the
dust is freed.
Thus, comets in the
inner
Solar System are
surrounded by dust
clouds.
If the Earth passes
through
the dust, a meteor
shower results.
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Kuiper belt vs. Oort cloud
Most comets are in the Kuiper belt or the
Oort cloud, far from the Sun.
Comets with short orbital periods come
from the Kuiper belt,
30-50 A.U.
from the Sun.
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Comets with long
orbital periods come
from the Oort cloud,
500-50,000 A.U.
from the Sun.
Oort cloud is a swarm
of comets that
stretches one-fifth
the way to the
nearest
neighboring star.
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A comet or asteroid packs a
punch
An object 10 kilometers
across, traveling at
10 km/sec, will upon
impact release as much
energy as a million
100 megaton bombs.
It will blast out a crater
at least 100 kilometers
across.
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A comet or asteroid impact
probably caused the extinction of
the dinosaurs
In the Cretaceous mass extinction (65
million years ago), 70% of all species
were killed off … including all dinosaurs.
The extinction was rapid, geologically
speaking.
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The Chicxulub impact crater, 180 km across,
buried under thick sediment. Estimated
age: 64.98 million years.
The impactor was only
10 km across!
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