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Clearly, because of the great overlap of the NH<sub>3</sub> and PH<sub>3</sub> photolysis regions, products such as PH<sub>2</sub>NH<sub>2</sub> may be produced. Also, the atomic hydrogen atoms produced by photolysis of any hydride by photons with a large excess of energy are fired off with substantial kinetic energy. ... | {
"Header 1": "Photochemistry and Aeronomy",
"token_count": 2021,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
[If all H atoms were thermalized before reacting, only sulfur would be produced, but with a yield of 1.5 to 2 sulfur atoms per photon absorbed because of Reaction (V.196).] In fact, Khare found that a reddish brown polymer was produced in copious amounts. Analysis of the product shows it to be 96% sulfur and only 4% of... | {
"Header 1": "Photochemistry and Aeronomy",
"token_count": 2031,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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The rate of energy generation by $^{40}$ K decay is $3 \times 10^{-10}$ erg per second per gram of total mass, or $6 \times 10^{20}$ erg s<sup>-1</sup> for the entire planet. This provides a mean energy flux of $1 \, \text{erg cm}^{-2} \, \text{s}^{-1}$ . Assuming $16 \, \text{eV}$ is needed to produce an ion p... | {
"Header 1": "Photochemistry and Aeronomy",
"token_count": 1990,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The moral of this story is very simple: organisms and environments have evolved to fit one another like key and lock, and expecting a random terrestrial population of microorganisms to make it on their own on Jupiter is like assuming that your front door key from home will start a randomly selected Moscovitch. There ... | {
"Header 1": "Photochemistry and Aeronomy",
"token_count": 2046,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
In 1955, in the course of radio observations of the supernova remnant called the Crab Nebula, Burke and Franklin of M.I.T. were surprised to observe short, intense bursts of 22-MHz radio noise. Because of the limited spatial (angular) resolution of their receiver antenna, about $2.5^{\circ}$ , short runs of data could... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 2013,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
In a *uniform* magnetic field, moving ions and electrons of charge *q* experience a deflection force (called the Lorentz force) orthogonal to both the *B* and the *v* directions:
$$\vec{F} = q\vec{v} \times \vec{B}. \tag{V.210}$$
Because of the constant bending of the $\nu$ direction by the deflection force, the ... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 2030,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
We need now to consider two other major factors: the effect of gradients in the strength of the *B* field in the "radial" direction (i.e., in the plane of motion of cycling particles) and the effect of injection of particles whose motions are not confined to the plane of the magnetic equator.
We shall define the comp... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 2013,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Particles with pitch angles will work their way poleward slowly and will be mirrored at low latitudes, whereas particles with small pitch angles will travel far more rapidly in latitude and have a longer trip between mirror points. It is amusing to evaluate the times taken for particles to travel from one mirror point ... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 2053,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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These spacecraft encountered Jupiter's bow shock (where the solar wind becomes disrupted by the planetary magnetosphere) at over 100 Jupiter radii from the planet, and the spacecraft passed in and out through the bow shock and the magnetopause several times. As Jupiter rotated, the magnetosphere, which as we have seen ... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 2043,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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Perhaps the most attractive is that due to Peter Goldreich and Donald Lynden-Bell, who pointed out that, as the magnetosphere flows past Io, the huge $(\vec{v} \times \vec{B})$ forces developed between the sub-Jupiter and anti-Jupiter points on Io may short out if Io is a good enough electrical conductor. Then curren... | {
"Header 1": "Radiophysics and Magnetospheres of Jupiter and Saturn",
"token_count": 1613,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Because of the small angular diameters of Uranus and Neptune (3:7<sup>00</sup> and 2:3<sup>00</sup>, respectively, at opposition), it is extremely difficult to make useful observations of their properties from Earth. With respect to the firstorder variables defining the properties of their interiors, mass, radius, rota... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2040,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The ''true'' rotation period of the planet is not that observed for any small and moving sample of the outer millionth of the planetary mass, but that of the planetary interior.
232 V. The Major Planets
Figure V.60 Voyager 2 views of the polar region of Uranus. The image at the left ... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2007,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
"Cometary" ices far from the Sun, bearing clathrate hydrates of the heavy noble gases, are the likely source, but require tens of Earth masses of very cold ice in Jupiter, probably too cold to have ever been stable at Jupiter's present distance from the Sun. Scenarios involving inward migration of the Jovian planets du... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2002,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
We may imagine either a high mutual solubility of rocky and icy materials with a distinct atmosphere or, more probably, a rocky core with a deep ocean of supercritical water that merges gradually into the hydrogen- and helium-rich envelope, with polar gases such as ammonia and water fractionated into the denser fluid a... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2003,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The tilt of the equivalent dipole was found to be 46.8°, almost as large as that of Uranus, with the center of the equivalent dipole offset by an astonishing $0.55 R_N$ from the center of the planet, placing it well within the expected aqueous mantle. At the surface the higherorder terms in the field are larger than t... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2044,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Similarly, the column V. The Major Planets
density of hydrogen above the $NH_3$ cloud base is 1240 km agt. Methane, with 10 times its solar abundance (now at H:C=280), would have a column abundance of 9 km agt above the ammonia cloud base and less than 0.6 km agt in and above the solid-methane clouds. The infrared ... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2038,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Here $\phi_{\odot, U}$ is the solar radiant flux at Uranus' distance from the Sun. Thus, over the 42-year-long polar night of Uranus, the temperature of the atmosphere down to the 8-bar level at the most changes by $42 \times 10/70 = 6$ K. We see that thermal emission at 57 K is so feeble that it cannot cool a larg... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2016,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
An upper limit on the radioactive decay flux would be to assign the heavy element cores to rocky matter exclusively, which would yield a flux of $100\,\text{erg}\,\text{cm}^{-2}\,\text{s}^{-1}$ (and cause serious problems with the rotational moment of inertia and figure of the planet). We then apply Prandtl mixing le... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 2045,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Merging of the magnetospheric field with the solar wind field *must* occur over a substantial region, and solar wind ions will be efficiently funneled into the magnetosphere.
Even for weak planetary dipole moments, the bow shock can lie very far from the planet. The dynamic pressure of the solar wind at the orbit of ... | {
"Header 1": "The Interiors of Uranus and Neptune",
"token_count": 603,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
So far in this chapter we have treated the Jovian planets as independent bodies. There are two important extensions of this discussion that are needed to place them in their context within the Solar System.
The first point is that these planets form a sequence of compositions with increasing heliocentric distance: th... | {
"Header 1": "The Interiors of Uranus and Neptune",
"Header 3": "Perspectives",
"token_count": 1984,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
(*Hint*: Treat the atmosphere as plane-parallel, and neglect the curvature of the planet.)
- V.12 An isothermal layer of pure "snow" (a solid atmospheric condensate of unspecified composition) initially consists mostly of 0.1- $\mu$ m particles for which $p/p_0 = 1.20$ . After a time, this layer will recrystallize int... | {
"Header 1": "The Interiors of Uranus and Neptune",
"Header 3": "Perspectives",
"token_count": 1839,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
- V.28 a. Suppose that an M-class MS star with a luminosity of 10<sup>-4</sup> Suns has a photospheric temperature of 3000 K and an even cooler chromosphere. How would you expect the electron density in the ionosphere of a Jupiter-like planet 5.2 AU from that star to differ from that in Jupiter's ionosphere?
- b. Durin... | {
"Header 1": "The Interiors of Uranus and Neptune",
"Header 3": "The Jovian Thermosphere",
"token_count": 1448,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Our close study of the Jovian planets has presented us with clear evidence that their compositions range from nearly solar (Jupiter) to nearly the composition of a solar-proportion mixture of the condensible ice-forming and rock-forming elements (Neptune and Uranus). We earlier saw, in Chapter III, that the satellites ... | {
"Header 1": "Introduction",
"token_count": 516,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
All of our knowledge of the composition, structure, and history of the surfaces of icy satellites is based on remote observations of the reflection and emission of electromagnetic radiation. A certain body of terminology must be mastered before these data can be interpreted usefully.
Consider a surface irradiated by ... | {
"Header 1": "Surfaces of Icy Satellites",
"token_count": 2019,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
For example, the UBV magnitudes (and hence both the geometric albedos and the color) of the Galilean satellites vary systematically and reproducibly with orbital phase. It was concluded long ago from this evidence that these satellites must be rotationally locked on to Jupiter, each keeping one face perpetually pointed... | {
"Header 1": "Surfaces of Icy Satellites",
"token_count": 1768,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
As we have seen, spectroscopic and polarimetric data combine to give us reliable information about the presence of a very few constituents of satellite surfaces. Some information about the physical state of these surfaces on the scale of 1 m can be deduced as well, because the depths of absorption bands in transparent ... | {
"Header 1": "Eclipse Radiometry",
"token_count": 764,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
In general, the temperature at the surface of an airless body within the Solar System is dominated by the absorption and reemission of sunlight. Imagine a unit element of surface area on the surface of a sphere, illuminated by the Sun. We define $\zeta$ as the zenith angle of the Sun, measured as the Sun–surface–zeni... | {
"Header 1": "Eclipse Radiometry",
"Header 2": "Surface Temperatures",
"token_count": 2023,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The surfaces of the satellites of Saturn, Uranus, and Neptune were studied by the Voyager mission, and the satellite of Pluto has yet to be imaged by a spacecraft flyby. The satellites of Saturn, studied by the Voyager spacecraft, are generally quite heavily cratered, although there is also evidence of other processes ... | {
"Header 1": "Eclipse Radiometry",
"Header 2": "Surface Temperatures",
"token_count": 2041,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The simplest interpretation is that there is a conducting ocean beneath the ice. Thus we are left with
Figure VI.7 Callisto as seen by Voyager 2. The contrast in this black-and-white mosaic has been computer-enhanced to bring out surface details. Note the universal heavy cratering. The... | {
"Header 1": "Eclipse Radiometry",
"Header 2": "Surface Temperatures",
"token_count": 673,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The diameters of many of the icy satellites have been determined by spacecraft occultation measurements or by high-resolution photographic mapping by the Voyager 1 and 2 flyby missions to Jupiter and Saturn and the Voyager 2 flybys of Uranus and Neptune. These diameters were summarized in Table III.5.
The masses of m... | {
"Header 1": "Density and Composition of Icy Satellites",
"token_count": 2039,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The upper curves in b are for solar-proportion mixtures of ice and rock.
causes it to approach the density of the liquid state; indeed, compression of ice that is well below its normal freezing point by concentrating a large force on a small area causes the phenomenon called regelation. The most familiar example of r... | {
"Header 1": "Density and Composition of Icy Satellites",
"token_count": 1205,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
A mixture of water ice and rocky solids with the same elemental proportions as those in solar material will have the composition given in Table VI.2, roughly
Figure VI.11 Phase diagram of water. The stability fields of liquid water, ordinary ice (I), and a number of high-density forms o... | {
"Header 1": "Internal Thermal Structure of Galilean Satellites",
"token_count": 1004,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
To heat the mixture
Table VI.2 Compositions of Condensates in Low-Temperature Solar Material
| | Abundance | | | | | Mass % | |
|-------------|------------|-----------|----------------|----------|----------|----------|------------|
| Element |... | {
"Header 1": "Internal Thermal Structure of Galilean Satellites",
"token_count": 2042,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Depending on the Bond albedo and the heliocentric distance, this temperature will usually lie in the range from 40 to 110 K. With such low surface temperatures, the crust must be frozen to a substantial depth.
In general, for a spherical body in radiative steady state, with only solar and radiogenic heating at work, ... | {
"Header 1": "Internal Thermal Structure of Galilean Satellites",
"token_count": 2043,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
\tag{VI.32}$$
Recall that, in general, the heat capacity at constant pressure, Cp, is (dq/dT)P (see Appendix I), and dqrev ¼ TdS, whence dq/dT ¼ T(dS/dT)P. Then
$$(\partial S/\partial T)_{\rm P} = C_{\rm P}/T.$$
(VI.33)
Also, from the Maxwell relations (Appendix I),
$$(\partial S/\partial P)_{\rm T} = -(\partia... | {
"Header 1": "Internal Thermal Structure of Galilean Satellites",
"token_count": 1548,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The first natural satellite studied, Earth's Moon, always keeps the same face toward Earth. The Moon rotates at a constant rate, but, because of its orbital eccentricity of 0.0549, it does not revolve around the Earth at a constant rate: as seen from Earth, the Moon ''rocks'' back and forth on its axis once every month... | {
"Header 1": "Dynamical Interactions of the Galilean Satellites",
"token_count": 2005,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Satellites S and s are in resonant orbits, which means that the exact configuration of the system repeats at regular intervals; the orbital periods of the two satellites are in a ratio of small whole numbers, such as 2:1 or 3:5. The more massive satellite, S, is taken to be in a circular orbit, and the orbit of s is as... | {
"Header 1": "Dynamical Interactions of the Galilean Satellites",
"token_count": 755,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
To trace the thermal history of a satellite from the time of its formation to its present state and to determine whether a particular ice-plus-rock body has differentiated into a dense rocky core and an ice envelope, we need to have a substantial amount of information about the conditions under which the satellite orig... | {
"Header 1": "Thermal and Tectonic Evolution of Icy Satellites",
"token_count": 2025,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Convective instability inverts the interior structure, liberating energy that may complete the differentiation process (e). In general, the larger the body, the farther it can progress along this evolutionary path.
demonstrated a fascinating ability to produce diverse and biochemically significant organic products. S... | {
"Header 1": "Thermal and Tectonic Evolution of Icy Satellites",
"token_count": 1375,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The minor Jovian satellites fall naturally into three families. One family, orbiting well inside the realm of the Galilean satellites, consists of Amalthea (JV, read Minor Satellites of Jupiter 279
''Jupiter five'') and its smaller sisters Metis (JXVI), Thebe (JXIV), and Adrastea (JXV). Of these, only Amalthea is wid... | {
"Header 1": "Minor Satellites of Jupiter",
"token_count": 1910,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Jupiter. The last members of the Jovian system awaiting our description are the myriad of small objects that make up the modest, rather simple ring that lies between about 1.72 and 1.80 R<sup>J</sup> from the center of the planet (Fig. VI.18). The ring was unknown before the arrival of the first planetary spacecraft at... | {
"Header 1": "Planetary Rings",
"token_count": 1966,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Some source of energy must be available to ''stir up'' the rings and keep them from total collapse Planetary Rings 283
Table VI.4 Saturn's Rings and Ring Satellites
| | Dis | stance |
|------------------------|----------------|------------------|
| Feature ... | {
"Header 1": "Planetary Rings",
"token_count": 2031,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
But the synchronous rotation altitude (at which the ring particle Keplerian orbital frequency equals the rotation frequency of the planet and its attached magnetic field) occurs within the B ring. The spokes usually show a distinctive wedge shape with the apex of the wedge located at or near synchronous orbit, where th... | {
"Header 1": "Planetary Rings",
"token_count": 2017,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Longitudinally continuous dense rings are incompatible with this evidence, but tenuous or very clumpy ringlike features, perhaps better described as arcs than rings, are indicated. The Voyager 2 Neptune encounter in 1989 shed considerable light on this issue: an outer, extremely clumpy ring (imaginatively named 1989N1R... | {
"Header 1": "Planetary Rings",
"token_count": 361,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The Solar System contains seven very large satellites, with masses on the order of 10<sup>26</sup> g. These are Earth's Moon, the four Galilean satellites of Jupiter (J1, Io; J2, Europa: J3, Ganymede; and J4, Callisto), Saturn's largest moon (S6, Titan), and Neptune's large and strange moon (N1, Triton). They span a ra... | {
"Header 1": "Titan",
"token_count": 1998,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Any source of oxygen, such as infall of "meteoritic" ice from collisional debris orbiting within the Saturnian satellite system or outgassing of primordial carbon oxides from solid hydrates, would provide the observed proportions of CO and CO<sub>2</sub> through photochemical reactions in the upper atmosphere.
The fa... | {
"Header 1": "Titan",
"token_count": 2002,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Our study of Jupiter's system was somewhat hindered by the absence of satellites with masses below 48 10<sup>24</sup> g but above 0:012 10<sup>24</sup> g. None of the Jovian satellites are close to the critical size for melting, and none are in the transition region between the ''small satellites'' with radii less than... | {
"Header 1": "The Intermediate-Sized Saturnian Satellites",
"token_count": 2033,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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We shall for convenience define the small satellites as those with radii less than that of Mimas (about 200 km). We shall treat these in several groups in the order of their distance from Saturn. All of these satellites are irregular in shape, too small for internal thermal activity to permit them to relax into spheres... | {
"Header 1": "Minor Satellites of Saturn",
"token_count": 2029,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The orbital period of the most distant of these bodies, S/2000 S1, is 3.59 Earth years.
Dynamically, the outermost satellite family of Saturn is apparently volatile, with capture and loss events occurring from time to time. The two outer families of satellites, prograde and retrograde, almost overlap in semimajor axi... | {
"Header 1": "Minor Satellites of Saturn",
"token_count": 435,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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The orbits of the five largest satellites of Uranus were rather well characterized before the Voyager 2 flyby in January 1986, but almost nothing was known of the intrinsic properties of the satellites. Because of the difficulties inherent in observing the faint and distant Uranian system from Earth, Voyager's contribu... | {
"Header 1": "Satellites of Uranus",
"token_count": 2000,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Our pre-Voyager knowledge of the orbits of Nereid and Triton, the two ''classical'' satellites of Neptune, was fairly good, but the intrinsic properties of the satellites remained very poorly known. A renaissance in our
Figure VI.35 Shepherds watch the rings by day. The two small satel... | {
"Header 1": "Satellites of Neptune",
"token_count": 1994,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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At Triton's distance of 30 AU from the Sun (vs 9.5 AU for Titan) the rate of methane photolysis is limited to $4 \times 10^{-13} \times (9.5/30.0)^2 = 4 \times 10^{-14} \, \text{g cm}^{-2} \, \text{s}^{-1}$ if the atmosphere is optically thick (or less if most photons are reflected from or absorbed by the surface). ... | {
"Header 1": "Satellites of Neptune",
"token_count": 2011,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Pluto was discovered by Clyde Tombaugh at Lowell Observatory in Flagstaff, Arizona, in 1930, and its satellite Charon was discovered in 1978. Pluto and Charon orbit closely about their common center of gravity in circular orbits. Charon is, relative to its primary, the largest satellite in the Solar System. The two con... | {
"Header 1": "The Pluto–Charon System",
"token_count": 2008,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The image of two planets with crossing orbits raises the prospect of a planetary collision. Is it possible for Pluto to collide with Neptune? If so, how soon might it happen? If not, how can they avoid collision?
The semimajor axis of Neptune's orbit is 30.058 AU, and that of Pluto is 39.440 AU. The ratio of their or... | {
"Header 1": "The Neptune–Pluto Resonance",
"token_count": 825,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Five spacecraft, including Pioneer 10 and 11, Voyager 1 and 2, and Ulysses, have flown through the outer Solar System. Voyager 2 completed the planetary phase of its mission in 1989. The Galileo Orbiter and Probe missions have, despite daunting technical obstacles and equipment failures, successfully completed their in... | {
"Header 1": "Spacecraft Exploration",
"token_count": 430,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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#### Introduction
VI.1 Using the elemental abundances tabulated in Table II.4, calculate the density of (a) dry rock and (b) cometary rock-plus-ice solids. Use the equilibrium condensation model as outlined down to step 12 (step 4 for dry rock) in Table IV.7 and mineral densities from the Handbook of Chemistry and Ph... | {
"Header 1": "Exercises",
"token_count": 2004,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Do the same for warming to the ammonia– water eutectic temperature.
- VI.20 Compare the amount of heat needed to warm 1 g of ice from 60 to 273 K to the amount of heat needed to melt the ice. Because the heat capacity of ice varies greatly over this temperature range, use the equation for the heat capacity given in Exe... | {
"Header 1": "Exercises",
"token_count": 746,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
- VI.25 What are the surface acceleration of gravity and escape velocity of Titan?
- VI.26 What are the thermal speeds of H2, methane, and nitrogen at 100 K?
- VI.27 What is the mass of the atmosphere of Titan?
- VI.28 What would be the scale height of the lower atmosphere of Titan if it were made of hydrogen? Of pure ... | {
"Header 1": "Exercises",
"Header 2": "Titan",
"token_count": 1913,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Comets are among the most spectacular andmemorable phenomena of nature. Several times per century a Great Comet arrives, appearing almost anywhere in the heavens, brightening to outshine any star or planet, and growing a luminous tail that may stretch more than 90 across the sky. After a few weeks the comet fades and d... | {
"Header 1": "Historical Perspectives",
"token_count": 2026,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
A comet is a small ice-rich body, rarely larger than a few kilometers in diameter, in an eccentric orbit about the Sun. The phenomena that may make the comet spectacular (and indeed, that make it observable) are associated with the progressively rapid evaporation of ices from its solid nucleus during its precipitous fa... | {
"Header 1": "Nature and Nomenclature of Comets",
"token_count": 1366,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The orbits of the short-period comets are ellipses of moderate eccentricity and inclination (Fig. VII.2). Almost all have inclinations of less than 20 relative to the ecliptic plane. Their orbital eccentricities lie mostly between 0.2 and 0.7. Only four of 113 short-period comets with well-known orbits have periods ove... | {
"Header 1": "Cometary Orbits",
"token_count": 2033,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Those that depart significantly from parabolic motion are clearly in elliptical orbits, and none are found to have velocities large enough to suggest that they are interstellar "wanderers."
salient features are that there is a strong peak in the distribution of observed long-period comets at 1/a=0 (parabolic heliocen... | {
"Header 1": "Cometary Orbits",
"token_count": 2022,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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Subtracted from the comet's speed, it would leave the comet in an orbit with a semimajor axis of less than 13 AU and an orbital period of 47 years. This is typical of a short-period comet. Subsequent encounters with the Jovian planets are unavoidable.
Our study of the icy satellites and Pluto in Chapter VI suggested ... | {
"Header 1": "Cometary Orbits",
"token_count": 2045,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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Thus any comet that gets close enough to an M star to be significantly heated will certainly be ejected from the Solar System.
For a high-luminosity early Main Sequence star the distance out to which comets can be heated to 30 K is about $100L*^{1/2}$ AU, which, for a mass-luminosity relation of $L*=M*^{3.5}$ , im... | {
"Header 1": "Cometary Orbits",
"token_count": 2032,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Taking a mean speed of $50\,\mathrm{km\,s^{-1}}$ and a typical chord length of $2\,\mathrm{AU}$ ( $3\times10^{13}\,\mathrm{cm}$ ) for the comet's passage through the inner Solar System, the time ( $\tau$ ) over which this acceleration is acting is $6\times10^6\,\mathrm{s}$ , and the total velocity change is $\Del... | {
"Header 1": "Cometary Orbits",
"token_count": 644,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The nucleus of P/Halley was imaged at close range by the European Space Agency's Giotto mission in 1986 (Fig. VII.6). The shape of the nucleus is extremely irregular, due either to gentle accretion of large bodies or to collisional erosion. Strong internal heating would tend to reduce the nucleus to near-spherical shap... | {
"Header 1": "Cometary Orbits",
"Header 2": "The Nucleus and Coma of P/Halley",
"token_count": 581,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Without doubt the principal volatile constituent of cometary nuclei is water ice. For many comets, it seems likely that water ice makes up more than 50% of the total mass, perhaps even reaching 80% in some rare cases. This underscores the importance of water ice evaporation in regulating the temperature of the nucleus ... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2023,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Supposing, as a crude approximation, that the molecular cross-section is about $4 \times 10^{-17}$ cm<sup>2</sup> over the entire wavelength range in which photodissociation and photoionization occurs, we can calculate how far from the nucleus a primary water vapor molecule can travel before being photolyzed or ioniz... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2018,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
It is obvious that comas are dominated by photodissociated fragments of molecules and thermally dissociated vapors of minerals, not by the molecular species that actually compose the solid nucleus. It is even more obvious that the species in the plasma tail are derived from further processing of the coma species (pri... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2000,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
This problem was first studied by David Brin and Asoka Mendis of the University of California at San Diego (UCSD) and has been modeled in greater detail by Fraser Fanale and James Salvail of the University of
Hawaii, Harry Houpis of UCSD, Paul Weissman of the Jet Propulsion Laboratory (JPL), Hugh Kieffer of the Unite... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2042,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Thus the emitted thermal flux will be strongly anisotropic. For prograde rotators with modest axial tilts, more momentum will be radiated in the trailing hemisphere than in the leading hemisphere. These larger bodies may then actually be accelerated in their orbital motion, causing them to retreat slowly from the Sun. ... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 1701,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
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By contrast, an older
Table VII.1 Prominent Meteor Showers
| | | | Radiant | | | |
|-----------------|---------------------|----|-------------|--------|------------|---------------|
| Date/peak | Shower name | | RA (h, min) ... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2032,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The displays in 1900 and 1933 were bright but not overwhelming, and it appeared that the orbit of the Leonid swarm may be shifting slightly away from its point of intersection with Earth's orbit.
On the evening of November 16, 1966, observers all over western North America were frustrated in their attempts to observe... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2014,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
It seems that any attempt to capture these particles intact on an Earthorbiting spacecraft would be a dismal failure: the instantaneous deceleration of the dust particle from speeds of tens of kilometers per second at the moment of impact with the spacecraft would lead to complete vaporization of the dust particle (and... | {
"Header 1": "Cometary Orbits",
"Header 2": "Chemistry and Photochemistry of Water",
"token_count": 2045,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Fireballs are extremely brilliant meteors with peak magnitudes < -4, often comparable in brightness to the full Moon, which has an apparent magnitude of about -12.5. They are produced by meteors with masses of at least 100 g and rarely as high as $10^6$ g (1 Mg = 1 tonne). Fireballs exhibit a wide range of behavior d... | {
"Header 1": "Cometary Orbits",
"Header 2": "Cometary Fireballs",
"token_count": 1865,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
One of the strangest discoveries in the recent study of the Solar System occurred on March 24, 1993, when Carolyn and Gene Shoemaker and David Levy, who have together discovered numerous comets, found a very peculiar comet-like blur of light on a photographic plate. The image showed what looked like a string of pearls ... | {
"Header 1": "Cometary Impacts on Jupiter",
"token_count": 2025,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The only other species seen was CO, which could be made by oxidation of Jovian atmospheric methane by oxygen from the projectile, and methane and ammonia. Theoretical calculations by Kevin Zahnle of NASA Ames Research Center show that, in addition to CO, a very water-rich fireball should also contain detectable traces ... | {
"Header 1": "Cometary Impacts on Jupiter",
"token_count": 2021,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Suppose that many of these bodies are so far from the Sun that solar heating is negligible compared to their internal source of heat [see Eq. (VI.22)]. Thus the surface temperatures of these bodies may be dominated by the heat released by internal decay of radioactive heat production is the same as for Ganymede $(1.6 ... | {
"Header 1": "Cometary Impacts on Jupiter",
"token_count": 1342,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The recognition of meteorites as genuine extraterrestrial material and the discovery of the asteroid belt both date from the first decade of the 19th century. From then until as recently as the 1960s the only samples of extraterrestrial material available on Earth were meteorites. Meteoritics, the laboratory study of m... | {
"Header 1": "Introduction",
"token_count": 290,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Meteorites are solid objects of extraterrestrial origin, commonly between a gram and 10 tonnes in mass, that have been found or observed to fall upon the surface of the Earth. They have been subjected to severe selection effects during atmospheric entry on the basis of their mechanical strength. Smaller samples of extr... | {
"Header 1": "Introduction to Meteorites",
"token_count": 2047,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
However, the absence of nickel is proof of the nonmeteoritic nature of the sample and can save the finder further disappointment and wasted effort. Any rock that looks like a metal-bearing meteorite and also contains nickel should be taken to a museum or university geology department for further study. Objects with app... | {
"Header 1": "Introduction to Meteorites",
"token_count": 1622,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Accurate orbit determinations on meteorites are potentially of great value in establishing where the members of particular meteorite classes come from. Unfortunately, the difficulties surrounding this effort are immense. The principal difficulty is that meteorite falls are not very frequent, and the entire process of e... | {
"Header 1": "Meteorite Orbits",
"token_count": 2032,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
In practice, only a small proportion of the observed fireballs have speeds over $40 \text{ km s}^{-1}$ .
A body entering at the maximum speed carries a kinetic energy density of $2.6 \times 10^{13}\,\mathrm{erg}\,\mathrm{g}^{-1}$ . By comparison, the energy required to heat a gram of typical rock from room temperat... | {
"Header 1": "Meteorite Orbits",
"token_count": 2008,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Traveling at a modest 20 km s<sup>1</sup> , this is 8 10<sup>25</sup> erg of kinetic energy. Equating the chemical potential energy of 1 Mt of high explosive to 4:185 10<sup>22</sup> erg, this energy content translates into a 2000 Mt (2 Gt) explosion. For comparison, the largest man-made explosion in history, a Soviet ... | {
"Header 1": "Meteorite Orbits",
"token_count": 1573,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
There is good reason to believe that the frequency of meteorite falls diminishes smoothly with increasing mass. Irons and stones have very different crushing strengths, which biases our meteorite collections in the direction of overrepresenting the stronger irons, and favoring the survival of iron meteorites that are s... | {
"Header 1": "Physical Properties of Meteorites",
"token_count": 2031,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Transverse (shear-wave, or S-wave) speeds of 600 to 1200 m s<sup>1</sup> were measured in six chondritic stones, and longitudinal (pressure-wave, or P-wave) speeds ranging from 2000 to 4200 m s<sup>1</sup> were found in eight ordinary chondrites. These speeds are generally well below the range found for terrestrial ign... | {
"Header 1": "Physical Properties of Meteorites",
"token_count": 2035,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The thermal evolution of meteorite parent bodies will be explored later in this chapter.
The issue of porosity has arisen in our discussions of meteorite densities and thermal conductivities. Since 1997 several researchers have carried out porosity measurements on about 100 meteorites. Guy Consolmagno of the Vatican ... | {
"Header 1": "Physical Properties of Meteorites",
"token_count": 411,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The minerals present in meteorites reflect both the relative abundances of the elements and the conditions under which these minerals formed. Based on our understanding of the cosmic abundances of the elements (Chapter II) and the chemistry of solar material (Chapter IV), it should come as no surprise that the principa... | {
"Header 1": "Meteorite Minerals",
"token_count": 448,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
| | R | Hydroxyl silicates | | |
| Spinel | MgAl2O4 | | Serpentine | (Mg, Fe)6Si4O10(OH)8 | C |
| Hercynite | (Fe, Mg)Al2O4 | | Chamosite ... | {
"Header 1": "Taxonomy and Composition of Chondrites",
"token_count": 2029,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Note that, although almost all the FeO in an ordinary chondrite is in the pyroxene and olivine phases, the concentration of FeO is not the same in both phases: there are differences in the Gibbs free energy of formation of Fe2SiO4 and FeSiO3 (the latter is actually unstable as a pure phase), and olivine is unusual in... | {
"Header 1": "Taxonomy and Composition of Chondrites",
"token_count": 1622,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
It is nowreasonable to ask whether volatile elements might behave similarly to one another, while metallic elements vary coherently as a second group, refractories vary as a third, and so on. Is there any evidence for covariation of such geochemically coherent groups of elements? If so, howmany such groups can be ident... | {
"Header 1": "Metamorphic Grades of Chondrites",
"token_count": 2017,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
It is quite impossible to accept that all these very diverse elements condense at the same temperature, and very difficult to believe that they all reside in the same mineral. The abundances of these elements are highest in the CI matrix material, and lowest in chondrites of petrologic grade 6. Within each group there ... | {
"Header 1": "Metamorphic Grades of Chondrites",
"token_count": 444,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The igneous stony meteorites, called achondrites, are those that have experienced such high temperatures that they have at least partially melted, and as a result have undergone extensive geochemical differentiation. They represent material that has progressed beyond chondritic petrologic grade 6. With fewexceptions, t... | {
"Header 1": "Taxonomy and Composition of Achondrites",
"token_count": 2007,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
However, three of these sparse classes, the shergottites (notably Shergotty and Zagami), nakhlites (Nakhla and Lafayette), and the unique chassignite (Chassigny), share a number of features in common and are almost certainly genetically related. Among the more astonishing features of the shergottite/nakhlite/chassign... | {
"Header 1": "Taxonomy and Composition of Achondrites",
"token_count": 241,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The overwhelming majority of the known stony irons belong to two distinct groups with very different internal structures. The larger group, the pallasites, have a continuous matrix of metal surrounding centimeter-size grains of olivine. The fayalite content of the olivine lies between 11 and 20%. The pallasites are dom... | {
"Header 1": "Taxonomy and Composition of Stony-Irons",
"token_count": 948,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
The two principal minerals in the iron meteorites are the iron–nickel alloys kamacite ( iron, with low Ni content) and taenite ( iron, with high Ni content). The three principal structural classes of irons are determined by the relative abundances of these two minerals, which are in turn determined by the bulk Fe:Ni ra... | {
"Header 1": "Taxonomy and Composition of Irons",
"token_count": 2028,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
But these groups, representing perhaps 13 distinct parent bodies, are far from the whole story. There are in fact 95 analyzed irons that fall into none of these groups, and another 111 irons for which there are insufficient analytical data for classification. Traditionally, a meteorite group or class is designated by n... | {
"Header 1": "Taxonomy and Composition of Irons",
"token_count": 917,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
There are a number of interesting isotopic anomalies associated with meteorites. The study of elemental and isotopic abundance variations of the noble gases in meteorites has become a major cottage industry, and large isotopic variations in the reactive volatile elements H, C, N, and O are well documented. Although the... | {
"Header 1": "Taxonomy and Composition of Irons",
"Header 2": "**Isotopic Composition of Meteorites**",
"token_count": 2030,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Little information is available on the isotopic composition of hydrogen in meteorites. Water is normally found in abundance only in the carbonaceous chondrites. CI chondrites contain about 20% water by weight, CMs have about half as much, and the CV and CO chondrites have only 0.3 to 3% water. The isotopic compositio... | {
"Header 1": "Taxonomy and Composition of Irons",
"Header 2": "**Isotopic Composition of Meteorites**",
"token_count": 2013,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
Beta decay of the long-lived radioisotope <sup>40</sup>K generates important amounts of <sup>40</sup>Ar, an isotope that is exceedingly rare in solar argon because of its instability during nuclear processing in stellar interiors (it is an odd–odd nuclide). Radiogenic argon atoms have extremely short ranges and are e... | {
"Header 1": "Taxonomy and Composition of Irons",
"Header 2": "**Isotopic Composition of Meteorites**",
"token_count": 2039,
"source_pdf": "datasets/websources/Astronomy_v1/Astronomy/Lewis_2004.pdf"
} |
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