PTYS/ASTR 206Jupiter 4/3/07 Jupiter ← Io. PTYS/ASTR 206Jupiter 4/3/07 Announcements Reading Assignment –Finish Chapter 14 5 th homework now on the course

PTYS/ASTR 206 Jupiter4/3/07

Jupiter

← Io


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.


Second Exam Results

• Average: 70.4• Median: 71.0• High: 107 (3 scores over 99)• Total tests taken: 127

89 and above 18 (14.2%)

78 – 88 30 (23.6%)

67 – 77 28 (22.0%)

56 – 66 27 (21.3%)

55.5 and below 24 (18.9%)


Second mid-term exam grade distribution

0

2

4

6

8

10

12

14

16

18

95-100 90-95 85-90 80-85 75-80 70-75 65-70 60-65 55-60 50-55 45-50 40-45 35-40 30-35 25-30

Series1


Approximate Curve for second midterm exam

> 87 A (15.7%)

75.5 – 86.5 B (25.2%)

61.5 – 73.5 C (29.9%)

45.5 – 61 D (22.8%)

< 45 E (6.3%)


• Which is brighter?– A sunspot– Venus– Mercury– The moon

Exam question: redux


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.


So --- the correct answer is …

• Which is brighter?

– A sunspot– Venus

– Mercury– The moon

Which is second brightest?


Jupiter• Jupiter is the fifth planet

from the Sun and the largest planet within the solar system.

• 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).


Jupiter Basic Facts

• Distance from Sun5.2 AU

• Eccentricity0.05

• Orbital period11.9 years

• Rotation periodAbout 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

• Mass317.8 Earth masses


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


Jupiter is Oblate because of Rapid Rotation


Jupiter’s Orbit

• 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!)


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)

Made by amateur -- Antonio Cidado

Mercury 11

Venus 60

Moon ~1800

Mars 20

Jupiter 45

Saturn 19

Uranus 4

Neptune 2

Pluto 0.1

Planet angular sizes as seen from Earth at closest approach, in arcseconds


Jupiter imaged by theCassini spacecraft


Closeup image of Jupiter by Cassini


Jupiter was struck by a comet in the summer of 1994 – SL9 (Shoemaker-Levy)

It is the only time that we have seen such a collision take place, although we know it has happened countless times in the history of our solar system



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



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)


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.


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.


Brown and white ovals on Jupiter

• Brown ovals are probably “holes” in the upper cloud deck that show warmer regions below

• white ovals are large storm systems, like the GRS, but are smaller. They are high up in the atmosphere→→


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)


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


Liquid Metallic Hydrogen• Under normal conditions,

Hydrogen is not a metal (it does not conduct heat or electricity)

• 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 !


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, we use the magnetic field to measure Jupiter’s rotational rate!


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 association with Jupiter’s moon Io


• Probably thousands of times brighter than any auroral display on Earth

• Linked to its moon Io

Aurora on Jupiter

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PTYS/ASTR 206Jupiter 4/3/07 Jupiter ← Io. PTYS/ASTR 206Jupiter 4/3/07 Announcements Reading Assignment –Finish Chapter 14 5 th homework now on the course