Transcript Lec20-040307

← Io
Jupiter
PTYS/ASTR 206
Jupiter
4/3/07
Announcements
• Reading Assignment
– Finish Chapter 14
• 5th homework now on the course website -- due
Thursday, April 12.
• Reminder about term paper – due April 17.
• Next study-group session is Wednesday, April
11, from 10:30AM-12:00Noon – in room 330.
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Second Exam Results
•
•
•
•
Average: 70.4
Median: 71.0
High: 107 (3 scores over 99)
Total tests taken: 127
89 and above
78 – 88
67 – 77
56 – 66
55.5 and below
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18
30
28
27
24
(14.2%)
(23.6%)
(22.0%)
(21.3%)
(18.9%)
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Second mid-term exam grade distribution
18
16
14
12
10
Series1
8
6
4
2
0
95-100 90-95
85-90
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80-85
75-80
70-75
65-70
60-65
55-60
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50-55
45-50
40-45
35-40
30-35
25-30
Approximate Curve for second midterm exam
> 87
75.5 – 86.5
61.5 – 73.5
45.5 – 61
< 45
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A
B
C
D
E
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(15.7%)
(25.2%)
(29.9%)
(22.8%)
(6.3%)
Exam question: redux
• Which is brighter?
– A sunspot
– Venus
– Mercury
– The moon
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Sunspots are cooler than the surrounding photosphere and,
hence, they are darker. But … they extremely bright !!!
They only appear dark because of the contrast with the
surrounding, brighter, and hotter, material.
If they were isolated from the surrounding photosphere they
would be brighter than an electric arc.
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So --- the correct answer is …
• Which is brighter?
– A sunspot
– Venus
– Mercury
– The moon
Which is second brightest?
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• Jupiter is the fifth planet
from the Sun and the
largest planet within the
solar system.
Jupiter
• It is two and a half times as
massive as all of the other
planets in our solar system
combined.
• Jupiter, along with Saturn,
Uranus, and Neptune, are
gas giants (also called
Jovian planets).
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• Distance from Sun
5.2 AU
• Eccentricity
0.05
• Orbital period
11.9 years
• Rotation period
About 10 hours
The most rapidly
rotating planet in the
solar system!
• Diameter
10.4-11.2 Earth diameters
It is noticeably oblate
• Density
– 1.38 g/cm3
• Mass
317.8
Earth masses
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Jupiter Basic Facts
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Jupiter’s composition
• Jupiter’s atmosphere is
composed of about 75% H, 24%
He, and 1% other
– It is slightly depleted in He
relative to solar abundances
(Saturn’s atmosphere is
significantly depleted in He
as we will discuss on
Thursday)
• These proportions change
slightly in Jupiter’s much denser
interior
• It rotates so rapidly that it is
noticeably flattened
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Jupiter is Oblate because of Rapid Rotation
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•
Jupiter’s orbital period of about 12 years
means that it moves very slowly relative to
the background stars.
•
It moves 1/12th of its orbit during the same
time that Earth has moved once around its
orbit. Hence, it appears at opposition about
every 13 months.
– The next opposition is June, 5 this year
– It will be fairly low in the midnight (even
at its highest point in the evening) sky
between the constellations Scorpio and
Sagittarius
– Currently, it rises about 10:30PM in the
southeast and is best viewed in the early
morning through a telescope
•
One of a handful of objects that are truly
amazing through a telescope
– It is the 4th brightest object in the sky
(barring a supernovae!)
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Jupiter’s Orbit
Planet angular sizes as seen
from Earth at closest
approach, in arcseconds
Jupiter as seen
from Earth
• Even through binoculars it appears as
a disk rather than a point-like star
• The 4 Galilean satellites are easily
seen
• Can see cloud belts and zones
• Moon transits and occultations
• Giant red spot
• Brown and white ovals (in good seeing)
Mercury
11
Venus
60
Moon
~1800
Mars
20
Jupiter
45
Saturn
19
Uranus
4
Neptune
2
Pluto
0.1
Made by amateur -- Antonio Cidado
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Jupiter imaged by the
Cassini spacecraft
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Closeup image of Jupiter by Cassini
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Jupiter was struck by a comet in the summer
of 1994 – SL9 (Shoemaker-Levy)
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It is the only time that we have
seen such a collision take place,
although we know it has
happened countless times in the
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history of our solar system
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Jupiter’s Atmosphere
• The visible “surface” is actually the
tops of its clouds
– Mostly H and He, with trace
amounts of methane, water vapor,
and ammonia
• The rapid rotation of the planet twists
the clouds into separate latitudinal
bands
– “Belts” -- dark bands
– “Zones” – light bands
– These bands blow in opposite
directions
– Spacecraft images show vortices
and storms between the bands
• The outer layers show differential
rotation
– Equator rotates faster than pole
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Zones and Belts
• Zones are high in the atmosphere – cooler (dark regions in
the image at the right)
• Belts are low in the atmosphere – warmer (brighter in IR)
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What causes the color of
Jupiter’s cloud tops ?
• Should be colorless!
– i.e. mostly composed of H and
He, ammonia (ammonium
hydrosulfide), and water, which
are colorless
• Probably phosphorous and sulfur
compounds are present in trace
amounts in the atmosphere that tint
the cloud tops.
• The colors indicate the clouds'
altitudes,
– blue is lowest and red as highest.
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The Giant Red Spot
• The “perfect storm”
– Has lasted at least
400 years and
possibly longer
• It is dark in IR, which
means that it is cooler and
HIGH in the atmosphere
• But … it is brownish like
the belts, which are lower
in the atmosphere. SO, it
has similarities to both
belts and zones.
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Brown and white ovals on Jupiter
• Brown ovals are probably
“holes” in the upper cloud
deck that show warmer
regions below
→
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• white ovals are large storm
systems, like the GRS, but
are smaller. They are high
up in the atmosphere
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Jupiter’s Internal Heat
• Jupiter radiates 1.6 times a much
energy as falls on it from the Sun.
– It has an internal heat source !
– Probably residual heat left over
from the original collapse of the
solar nebula
– possibly slow thermal
contraction
• This internal heat source probably
drives the complex weather pattern
in its atmosphere
– (note that the solar energy drives
Earth’s weather)
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Jupiter’s Interior
• Jupiter probably has a rocky
core several times more
massive than the Earth
• The core is surrounded by a
layer of liquid water, ammonia,
methane, and associated
compounds
• On top of this is a layer of
helium and liquid metallic
hydrogen and an outermost
layer composed primarily of
ordinary hydrogen and helium
– A Liquid Giant!
• Beyond this is normal molecular
hydrogen and helium
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• Under normal conditions,
Hydrogen is not a metal (it does
not conduct heat or electricity)
Liquid Metallic Hydrogen
• Under extreme pressures found
deep in Jupiter, electrons move
freely from nucleus to nucleus
– Excellent conductor of
electricity !
• The intense magnetic field of
Jupiter is thought to result from
electrical currents in this region of
metallic hydrogen that is spinning
rapidly
• Never produced on Earth in the
laboratory !
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Jupiter’s Magnetic Field is ~14 times bigger than
Earth’s and produces an enormous magnetosphere
(largest in the solar system)
Jupiter’s magnetic field is anchored into the interior – hence,
PTYS/ASTR
206 magnetic field to measure
Jupiter
we
use the
Jupiter’s rotational rate!
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Synchrotron Radiation from Jupiter
Charged particles in the densest portions of Jupiter’s
magnetosphere emit synchrotron radiation at radio
wavelengths (electrons spiraling along magnetic field lines)
Close
moon Io
PTYS/ASTR
206 association with Jupiter’s
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Aurora on Jupiter
• Probably thousands of
times brighter than any
auroral display on Earth
• PTYS/ASTR
Linked
to its moon Io
206
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