Download the outer planets, their satellites and the plutoids

UNIT
18
UNIT 18
THE OUTER PLANETS, THEIR SATELLITES AND THE PLUTOIDS
Goals
After mastery of this unit, you should:
a. be aware of the current observational data and theories of the structure of the outer planets, their
satellites and the plutoids.
➤Text
➤
References
7.2; 10.1 through 10.6; 13.1
See the Online Text Guide to DOSC to find the links to the listing by Objectives.
➤Mastery
➤
will be evaluated by a 15-question multiple-choice evaluation (13 correct responses for
mastery) on the following:
➤Objectives
➤
You should be able to recognize:
1. the general common features of the first four outer planets:
(a) low densities
(c) massive atmospheres
(b)large size
(d)well-developed satellite systems
2. the following features (if they are visible), given a photograph of Jupiter or Saturn
similar to Figures DOSC 10-1, 10-4 through 10-6:
(a) polar regions
(d)Great Red Spot (Jupiter only)
(b)belts
(c) zones
+(e) limb darkening
(f) Cassini division (Saturn only)
3. the following related to Jupiter and Saturn:
(a) the two major gases present in their atmospheres
(b)the temperature of their upper atmospheres
(c) the atmospheric conditions believed to exist 60 km below the cloud tops
(d)a description of and the probable explanation for the Great Red Spot
4. a description and explanation of the source of the following radiation from Jupiter
and Saturn:
(a) infrared thermal radiation
(b)short-wave radio radiation (decimeter)
(c) the description of terms such as synchrotron radiation, Wien’s law, and magnetic poles
(d)that Jupiter and Saturn radiate more heat then they receive from the Sun
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5. the following descriptions of the structure and surfaces of Jupiter and Saturn:
(a) Earth-sized rocky core
(b) high-pressure metallic hydrogen
(c) high surface gravity and pressure
6. a description of the following properties of Saturn’s rings:
(a) discovery year and name of the astronomer who discovered them
(b) that the thickness is less than 100 m
(c) that there are several gaps, Cassini’s division being the most prominent
(d)the detailed structure discovered by the Voyagers
(e) Shepherd satellites
(f) the three probable origins of the rings
7. a description of the following properties of Jupiter’s rings:
(a) the approximate discovery year and method of discovery
(b) that the rings are composed mostly of dark dust-like material
8. a description of the following properties of planetary rings:
(a) they are within the Roche limit
(b) that their structure is determined by the satellites of the planet
(c) that their structure may be modified by electrical forces
9. the following general properties of the satellite systems of the giant planets:
(a) the meaning of the term “sphere of gravitational influence”
(b) a description of the typical size distribution with distance
(c) the four causes of active geological processes for the satellites
(d)the two basic materials from which the satellites are constructed
10. the following about Jupiter’s satellites:
(a) the names and descriptions of the Galilean satellites
(b) that Io is sometimes surrounded by a yellow glow and the explanation for this
(c) that Europa is covered by ice over a liquid layer and how the liquid layer can exist
(d)the difference between prograde and retrograde motion
(e) that Jupiter’s outer moons are captured interplanetary bodies
11. the following about Saturn’s satellites:
(a) a description of the properties of Titan and its atmosphere
(b) a description and explanation of the properties of Iapetus and Enceladus
(c) why we believe that Phoebe is a captured moon
12. You should be able to recognize a description of the following about Uranus and
Neptune:
(a) the accidental discovery of Uranus
(b) the prediction and discovery of Neptune
(c) the similarities and differences in these planet’s atmospheres and the reasons
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THE OUTER PLANETS, THEIR SATELLITES AND THE PLUTOIDS
UNIT
18
(d)a description of the Great Dark Spot and its cause
(e) the similarities in the structures of these planets
13. the following about the typical velocities of atoms and molecules in an atmosphere:
(a) recognize the equation and use it to predict gas velocities
(b)why (a) predicts that the gas giants will have more atmospheres than the
smaller planets
14. You should be able to recognize a description of:
(a) obliquity, and the obliquity of Uranus
(b)the rotation of Uranus
(c) the ring systems of Uranus and Neptune and shepherd satellites
(d)the arc-rings of Neptune
(e) the explanation given for the structure of Miranda (Uranus)
(f) the orbital and surface properties of Triton (Neptune)
15. the following about Pluto:
(a) the five reasons for questioning the planetary status of Pluto and that it is no
­longer considered a planet. It and other similar objects are called Plutoids
(b)a description of the probable origin of Pluto
+(c)that Pluto was discovered by luck, even though astronomers were looking for
another planet using the method that worked for Neptune
+(d)the year of the discovery of the satellite of Pluto and the effect of this discovery
on our ideas about Pluto
+(e)that optical searches have shown that no other rocky planet can be near the
plane of the ecliptic, be as large as Neptune, and be within 100 AU of the Sun.
➤Streaming
➤
Video — Unit 18
Recent information on planetary probes and new discoveries can be found at: http://www
.planetary.org/news. Choose your object and the current year and work backwards in time.
NOTES – If there are no notes, all the information is in the relevant sections of the text.
Obj. 2e. Examine photos of Jupiter and Saturn as well as other planets with an
atmosphere. They show an image that is darker at the limb (apparent edge) of the planet’s
image. This limb darkening is caused by absorption of light in the planet’s atmosphere. The
light from the limb must pass through more of the planet’s atmosphere to reach us than
light from the center of the planet’s image.
Obj. 4c. See DOSC Chapter 13 (Section 1).
Obj. 11. The Cassini-Huygens mission has further analysis issued in late 2008. There are
mountains, some of which are about 2 km high. The atmosphere has a structure which
mirrors the Earth in its density distribution, but not in its actual density (much higher than
the Earth’s atmospheric density) or its composition. The troposphere has summer methane
cumulus clouds in the summer and stratospheric polar winter ethane clouds. There is also
a general polar hood of haze. The surface has torrential methane rains between centuries of
little or no methane rain. There is a strong indication that the entire surface is drifting on a
subsurface ocean.
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Obj. 11c. Although Newton’s laws, applied to the motions of Neptune and Uranus,
predicted Pluto’s position, the object that was found was not what was predicted.
Astronomers had predicted a large gas giant. In retrospect, astronomers realize that there
were too many uncertainties in the data, to make any prediction at all. It was purely luck
that Pluto was in the region of the sky that was being searched. Perturbations still seem
to exist in Neptune’s orbit but no planet to account for them has been discovered. Other
astronomers think that there is no need for another planet to explain the motions of the
other planets. They believe that the remaining errors in Neptune’s orbit are only the result
of uncertainties in the observational data. In 2006, the IAU reduced Pluto to the status to a
minor planet (see Unit 20).
Obj. 13. The Maxwell-Boltzmann law relates the mean kinetic energy of a molecule or
atom in a gas to the temperature of the gas. If m is the mass of the molecule or atom and v is
the velocity of the molecule or atom, the kinetic energy is given, as described in Unit 3, as
Kinetic Energy = __
​ 1 ​  mv 2.
2
The Maxwell-Boltzmann law tells us that the mean (average) kinetic energy is proportional
to the Kelvin temperature, T, by the rule:
2
1  ​ m__
Mean kinetic energy = ​ __
v​ ​ 3 ​  kT,
​   = __
2
2
2
−23
−1
where the bar over the v denotes an average of the squared velocity, and k = 1.38 × 10 J-K
The letter “J” is the symbol for the SI (metric) unit of energy, the Joule, the energy 1 kg has
when moving 1 m/s. The Maxwell-Boltzmann equation can be rewritten to become
____
__
__ 2
average speed = ​√v​ ​ ​   = ​ ____
​ 3kT
 
. 
m ​ ​ 
√
In Unit 13, Obj. 7, we discussed escape velocity and its relation to the mass and size of the
gravitating body.
_____
√
​ 2GM
 
   
​ ​ 
,
escape velocity = ​ _____
R
where G is Newton’s gravitational constant, M is the mass of the planet or satellite, or other
body, and R is the radius of the body. Whenever the average velocity of a molecule or atom
in a planet’s atmosphere comes close to the escape velocity, the molecule will escape. For
Jupiter the escape velocity is much larger than for Earth and the average velocity is much
lower than for the Earth, so the hydrogen is retained as part of Jupiter.
Obj. 15a–d. Is Pluto a planet and is Charon the satellite of a planet? In 2006 the IAU
(International Astronomical Union) defined the word planet.
1. The orbit must be circular enough not to cross the orbit of another planet.
2. A planet must also have enough mass to become nearly spherical.
3. And a planet must be able to sweep other small astronomical objects out of its
orbital path.
4. The object must have a maximum magnitude larger than 1+. Such objects will be
called Plutoids or trans-Neptunian Objects. Satellites of Plutoids are not Plutoids.
In order of size (large to small) the Plutoids discovered by mid-2010 are Eris, Pluto
(2 satellites), Makemake, Humea (2 satellites), Sedna (2 satellites), Orcus, 2007 OR10
and Quaoar. The IAU has only made an official designation for the first three listed.
The IAU met in August 2009 and no action was taken on this matter.
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THE OUTER PLANETS, THEIR SATELLITES AND THE PLUTOIDS
UNIT
18
➤Concepts
➤
from Unit 18 Objectives, Notes, and Text
giant planet
belts
zones
Great Red Spot
atmospheric
composition of Jupiter
and Saturn
temperature of Jupiter
and Saturn
carbonaceous
material
dirty ice
Jupiter’s Galilean
satellites
Io and its tidal heating
Europa, Ganymede,
Callisto
Jupiter’s captured moons
thermal infrared
radiation
prograde and retrograde
motion
synchroton radiation
Saturn’s inner satellites
internal structures of
Jupiter and Saturn
Saturn’s satellite Titan
metallic hydrogen
ring systems of Jupiter
and Saturn
Cassini’s division
Roche’s limit
shepherd satellites
resonance
Saturn’s other major
satellites: Iapetus and
Phoebe
Features common to all
four giant planets
Uranus
Neptune
atmospheric properties
of Uranus and
Neptune
Great Dark Spot
internal structures
of Uranus and
Neptune
obliquity
retrograde rotation
ring systems of Uranus
and Neptune
shepherd satellites
arc-rings
Uranus’ satellites
Miranda
Neptune’s satellite
Triton
Pluto
Charon
“Planet X”
Plutoids
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UNIT 18
THE OUTER PLANETS, THEIR SATELLITES AND THE PLUTOIDS
➤Word
➤
Practice
1. __________ __________ is emitted when very fast electrons move through a magnetic field.
2. __________ rotation is east to west.
3. The __________ __________ of Jupiter is a long-lived storm.
4. The four large satellites of Jupiter are called the __________ satellites.
5. Jupiter’s __________ thermal radiation is due to the planet’s heat.
6. Jupiter’s __________ is about 133 K.
7. The great Red Spot is often visible on the disk of __________.
8. A sodium cloud often surrounds Jupiter’s satellite __________.
9. Much of Jupiter’s interior is__________ __________.
10. Within __________ limit a large natural satellite will be tidally torn apart.
11. The opposite of prograde is __________.
12. The outer planets are characterized by __________ __________ and large size.
13. Jupiter’s __________ radiation is synchrotron radiation.
14. Jupiter’s infrared radiation is __________ radiation.
15. The __________ __________ __________ is an atmospheric feature of Neptune
­discovered on Voyager 2 photographs.
16. Jupiter is such that it may be hard to say where the surface divides the planet from
its __________.
17. Satellites that revolve about their parent body in the same sense as the planets
revolve about the Sun are said to revolve __________.
18. __________ is the term used to refer to a possible planet in orbit beyond Pluto.
19. __________ satellites revolve counter to the planet’s revolution.
20. __________ is the only known satellite of Pluto.
21. The dark lines across the disk of Jupiter are called __________.
22. Jupiter’s outermost moons are __________ moons that were previously
­interplanetary bodies.
23. The bright cloud bands parallel to Jupiter’s equator are called __________.
24. Jupiter’s__________ is about 60% hydrogen.
25. The rocky matter making up the moons of Jupiter is a black __________ material.
26. The Galilean satellite covered with ice is __________.
27. __________ has rings easily visible through a telescope.
28. __________ division is a prominent gap in the rings of Saturn.
29. __________ __________ system is very thin and composed of many small particles.
30. __________ atmosphere is similar to Jupiter’s.
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THE OUTER PLANETS, THEIR SATELLITES AND THE PLUTOIDS
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31. __________ __________ __________ begins at the edge of the rings with five small
satellites.
32. __________ occurs when a periodic force applied to a system has the same
­frequency as one of the natural frequencies of the system.
33. Saturn’s satellite __________ seems to have a structure intermediate between
Europa and Ganymede.
34. __________, __________, and __________ are three small moons of Saturn just inside
the orbit of Titan.
35. The moon __________ of Saturn has an atmosphere.
36. __________ __________ is a term used to describe a mixture of ice and carbonaceous
dirt
37. __________ is a satellite of Saturn with one light and one dark side.
38. Saturn’s satellite __________ is a small black-surfaced object in retrograde orbit.
39. __________ __________ can help confine rings to a narrow zone.
40. The planet __________ was discovered by its gravitational effects on the orbit of
Uranus.
41. An axial rotation from East to West is termed __________ rotation.
42. __________ was called a planet until 2006. It is now defined as a minor planet.
43. In addition to rings about Uranus, the space probes showed that there were rings
around __________.
44. Ring systems that contain thicker segments are called __________ systems.
45. __________ __________ or its orbit may be related to the peculiar orbit of Triton.
46. The first planet discovered in recorded history is __________.
47. __________ is the largest satellite of Neptune. It may have a thin atmosphere.
48. The __________ of a planet is the deviation of the axis of rotation from the
­perpendicular to the orbital plane.
49. Uranus’ __________ were discovered only in 1977 when they passed in front of a
star.
50. __________ satellites were mostly discovered by Voyager.
51. __________ is the innermost of the five largest satellites of Uranus. It has a highly
fractured surface.
52. __________ is the satellite of Pluto.
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