Final Exam Flashcards Preview

EASC206 - History of the Solar System > Final Exam > Flashcards

Flashcards in Final Exam Deck (68)
Loading flashcards...
1
Q

Explain how asteroids are classified

A

They can be classified by

  1. physical type - solid (single body, can have any fractures, can have regolith. can have impact craters) -rubble piles (numerous pieces of rock and dust held together by gravity and electrostatic forces, lower than expected densities, no visible impact craters)
  2. grouped by orbit type
  3. grouped by spectra and albedo
2
Q

Describe the different spectral types of asteroids

A
  • 14 classes (A, B, C, D, E, F, G, M, P, Q, R, S, T and V)
  • based on infrared or radar spectroscopy from ground-based telescopes
  • Three main designations: C-type, S-type and M-type
  • Synthesis of available reflectance spectra from the 1980s suggests that the proportions of different asteroids classes vary systematically with heliocentric distance
  • S-type concentrated in the inner belt
  • C-type and related (B, G and F) asteroids occur in the middle
  • Very dark D and P asteroids occur mainly in the outer belt
3
Q

What was the DAWN mission?

A
  • DAWN is a spaceprobe launched by NASA in 2007 with the mission of studying two of the three known protoplanets of the main asteroid belt
  • Orbited Vesta 2010 – 2012 and is currently in orbit around Ceres
  • Mission goal: Learn more about make-up and formation of the Early Solar System
  • Instruments: dual Framing Cameras (geologic imagery and navigation), a Visible and Infrared Spectrometer (VIR) for mineral identification and mapping, and a Gamma Ray and Neutron Detector (GRaND) for geochemical analysis and mapping
4
Q

Describe the different types of meteorities

A

Major division = differentiated versus undifferentiated (primitive)

5
Q

Explain how we know martian meteorities came from Mars and HED meteorites came from Vesta

A
  • the differences in composition tell us which came from Mars and which are HED from Vesta HED meteorites are (another slides describes martian meteorites)
  • Vesta samples; represent 5% of all meteorites in earth’s collection (Howardite Eucrite Diogenite HEDs)
  • Eucrites composed of plagioclase and pyroxene and subdivided based on texture
  • Fine-grained volcanic (basaltic) and coarse-grained plutonic (gabbroic)
  • Diogenites are ultramafic rocks formed by accumulation of orthopyroxene ± olivine
  • The majority are breccias (monomict versus polymict)
  • If both eucrite and diogenite clasts are represented in the breccia it is called a howardite
  • crystallization ages can be determined from radiogenic isotopes
  • oxygen isoptope composition lie on the same 18O-17O-18O mass fractionation line that is parallel to but offset from the TMFL
  • Global distribution maps from VIR and GRaND have been developed that measures terrains dominated by eucrite, diogenite and howardite on Vesta
  • Rheasilvia excavated deeply enough to expose mantle rocks (Howardite) on basin floor
6
Q

Explain how asteroid types and meteorite types are linked together

A
  • Can compare the reflectivity of various types of powdered meteorites to asteroid spectra
7
Q

What is eccentricity

A

the amount an orbit varies from circular

  • most orbits are slightly eccentric

Mercury = 0.206

Venus = 0.007

Earth = 0.0167

Mars = 0.093

Jupiter = 0.048

Saturn = 0.054

Uranus = 0.046

Neptune = 0.01

8
Q

What is orbital resonance

A

When two orbiting bodies exert a regular, periodic gravitational influence on each other

  • Usually because of orbital periods (e.g. 1:2)
  • Greatly enhances the mutual gravitational influence which usually results in an unstable system (i.e. Saturn’s inner moons)
  • Sometimes results in a stable system - when the two bodies never closely approach (i.e. 1:2:4 resonance of Ganymede, Europa, and Io, 2:3 resonance of Pluto and Neptune)
9
Q

What are the different asteroid orbital types

A
  1. Aten group: inside orbit of Earth, but steeply inclined to the ecliptic
  2. Apollo group: cross orbits of Earth and Mars, but steeply inclined to the ecliptic
  3. Amor group: cross orbit of Mars, but inclined 8-36°
  4. Main Belt group:

a. Inner main belt: low eccentricities, close to plane of ecliptic (1-15°)
b. Middle main belt: eccentricities 0.07-0.34, inclinations 3-35°
c. Outer main belt: eccentricities 0.03-0.22, inclinations 1-26°

  1. Hilda group In a 2:3 resonance with Jupiter Located opposite Jupiter or at L4 or L5 Lagrange points
  2. Trojan group: L4 and L5 Lagrange points of Jupiter, in clusters In a 1:1 resonance with Jupiter
10
Q

Describe the characteristics of the C-Type spectral Asteroids

A

C-type or carbonaceous asteroids are very dark with albedos of 0.03 to 0.09

  • thought to be compositionally similar to the sun but depleted in H, He and other volatile elements with hydrated mineral present
  • Most abundant asteroid type (75%)
  • Inhabit the main belt’s outer regions
  • Reflect ~5% of sunlight
  • Examples of asteroids belonging to this class include 253 Mathilde, 2 Pallas, and 1 Ceres (dwarf planet) - Spectrally similar to C-chondrites
11
Q

Describe the characteristics of the S-Type spectral Asteroids

A

S-type or siliceous asteroids are a mixture of ferromagnesian silicates (olivine and pyroxene) and FeNi-metal

  • 2nd most abundant type of asteroid in the main belt
  • ~17% of all asteroids are S-type - Reflect 15% to 20% of the sunlight hitting them
  • Albedos vary from 0.10 to 0.22
  • Dominate the inner portion of the main asteroid belt
  • Asteroids belonging to this class include Itokawa, 6 Hebe, 951 Gaspra and 243 Ida
12
Q

Describe the characteristics of the M-Type spectral Asteroids

A

M-type or metal asteroids are composed of FeNi-metal (either pure or mixed with “stony” material; these rare type of asteroids are brighter than S or C asteroids)

  • Moderately bright; albedos of 0.1 to 0.2
  • Remains of the core of differentiated asteroids fragmented by impacts
  • 16 Psyche is the largest M-type asteroid it is >200-diameter asteroid located in the outer main belt

Two theories for formation

1 – Psyche accreted with the rest of the belt and was large enough to differentiate; over millions of years collisions stripped away the mantle 2 – result of collision between two differentiated protoplanets

13
Q

Describe the characteristics of the D- and P-Type spectral Asteroids

A
  • D-and P-type asteroids are among the darkest objects known with generally featureless spectra
  • “reddened” appearance at longer wavelengths
  • Low albedo + reddened spectra = composed of organic-rich silicates, carbon and anhydrous silicates
  • Do not contain the 3-μm λ absorption feature characteristic of hydrated minerals
  • No known meteorites have spectra or mineralogy that resembles D- or P-type asteroids

– possibly Tagish Lake?

  • Some Interplanetary Dust Particles (IDPs) may be samples
  • Martian moon Phobos
  • Nice Model suggests they may have originated in the Kuiper Belt
14
Q

Describe some of the results of the DAWN Mission to Vesta

A

DAWN mission to Vesta found:

  1. Vesta to be the 2nd largest object in the main belt
  2. Diameter ≅ 525 km (510 km avg)
  3. Official name = 4 Vesta
  4. Rotates once every 5h18min
  5. Temperature range -3 °C to -188 °C
  6. Mean Density 3.456 g/cm3
  7. Irregular shape
  8. Iron core D = 220 km
  9. Differentiated planetesimal – parent body of the Howardite Eucrite Diogenite (HED) meteorites
  10. Covered with regolith (impact-comminuted rocks)
  11. No lava flows or volcanic constructs
  12. Two impact basins Rhea Silvia (D = 467 km) and Veneneia (D = 400 km)
  13. Rheasilvia central mountain ~23 km high - ~1.0 Ga (crater counting)
  14. Also launched many km-size bodies that are still orbitally-linked (Vestoids) - Other rocks nudged into nearby resonances (Kirkwood Gaps) to become meteorites (HEDs)
15
Q

Describe some of the results of the DAWN Mission to Ceres

A

Ceres is a qwarf planet first discovered in 1801

  1. Largest object in main belt
  2. Orbit 2.8 AU
  3. Diameter ≅ 950 km
  4. Rounded body (oblate spheroid)
  5. Density = 2.08 g/cm3 - Atmosphere and Internal ocean unknown - ¼ mass from water ice; ¾ mass from rock
  6. More akin to Mars & Earth than most asteroids
  7. In 2014, ESA’s Herschel Space Observatory found evidence for water vapor on Ceres - Cryovolcanoes or near surface sublimating ice?
  8. Highly reflective material in Occator Crater followed by discovery of at least 10 other bright spots in this crater alone;
  • 130 confirmed in other places on Ceres’ surface
  • Bright spots first identified by Keck II telescope in 2002 and HST in 2005
  • Origin: water-ice, Fe-depleted clay minerals or salt deposits
  • Spectral signatures suggest hydrated magnesium sulphate minerals deposited by sublimation of water vapor from a briny liquid
  1. Crater model age = 78 Ma
  2. A tall mountain named Ahuna Mons (dome, with smooth steep walls), ~6 km high with reflective material along slopes
16
Q

Explain why Chrondrites are important

A
  1. “Primitive” no melting since initial accretion and thought to represent samples of the pre-planetary Solar Nebula - Asteroid parent bodies
  2. Provide the best estimates for mean abundances of condensable elements in the solar system
  • Crucial for stellar nucleosynthesis theories
  • Presolar grains
  1. Offer insights into the processes that occurred during formation of the Sun and planets from a collapsing cloud of interstellar dust and gas
  2. Impact history of our solar system 5. Physical and mineralogical structure of asteroids; assessment of Near Earth Objects
17
Q

What are the components of chrondrite?

A
  1. Chondrules - Spheres of pyroxene and olivine crystals in a glassy mesostatis
  • 0.25 – 2 mm size
  • Comprise up to 80% chondrites, less abundant in carbonaceous chondrites
  • Textural types (barred, granular, porphyritic, radial, metal)
  • Some contain relict grains (CAIs)
  1. Calcium-aluminium inclusions (CAIs) - Refractory inclusions
  2. Amoeboidal Olivine Aggregates - Aggregates of anhedral forsteritic olivine
  3. Opaques - Primary opaques are Ni-Fe metal & sulphides
  • Abundance varies depending on chondrite type
  • terrestrial weathering results in oxidation
  1. Matrix - Describes the material interstitial to macroscopic components made of low temperature phases (dust)
  • broken chondrule fragments - made from low temperature fraction
  • Silicates, oxides, sulphides, metal and (in carbonaceous chondrites only) organics
  • Interstellar (presolar) grains (Diamond / silicon carbide / graphite)
  • Matrix is most abundant in carbonaceous chondrites
18
Q

What is a meteorite?

A

Meteorites are extraterrestrial rocks captured by the gravitational field of a planetary body that reach the surface as a solid object

OR

A natural, solid object larger than 10 microns in size, derived from a celestial body, that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself (even it if was the same body from which it was launched).” Rubin and Grossman (2010) Meteoritics & Planetary Science, v. 45:114-122.

19
Q

What are the different types of chondrites based upon composition

A
  1. H-type ordinary chondrites = High total iron and high metallic iron (15-20% FeNi metal by mass)
  2. L-type ordinary chondrites = Low total iron content (7-11% FeNi metal by mass)
  3. LL-type ordinary chondrites = Low total iron and Low metal contents (3-5% FeNi metal by mass
20
Q

What is thermal metamorphism?

A
  • Occurred in asteroid parent bodies, within a few 10s of million years after accretion
  • Heat source = Short-lived radionuclides (e.g., 26Al)
  • Increasing thermal metamorphism causes textural changes from recrystallization of matrix and devitrification of glasses in chondrules
  • when compositional equilibration is reached silicate compositions become more uniform
  • Peak metamorphic temperatures 950 °C
  • No change in pressure (asteroids are small)
21
Q

What are the characteristics of differentiated iron meteorites?

A
  • Ni-Fe metals (kamacite + taenite)
  • Widmanstättan pattern
  • Classified primarily based on texture and composition into ~15 groups
  • From the core of large differentiated asteroids (20-300 km across)
22
Q

What are the characteristics of differentiated stony-irons meteorites?

A
  • ~Equal parts silicate (olivine and/or pyroxene) / Ni-Fe metal
23
Q

What are the characteristics of differentiated achondrites?

A
  • No chondrules as the chondrules have been destroyed by heating and / or alteration
  • Some are volcanic lavas of the Moon and Mars (basaltic achondrites)
  • Include Howardite Eucrite Diogenite (HED) meteorites
24
Q

Describe the composition of martian meteorites

A
  • Currently 101 unpaired martian meteorites in the world’s collection
  • All are igneous rocks (SNCs) or ancient impact breccias) composed of various igneous lithologies fused together
  • “SNCs” Shergottites = basalts Nakhlites = clinopyroxenites Chassignites = dunites
25
Q

How can you determine if a meteorite is martian?

A
  • They contain iron-rich oxide minerals (magnetite, chromite, ilmenite) but no metallic iron
  • Trace element ratios such as Fe/Mn are distinctive
  • They have a narrow range of oxygen isotopic composition which are different from all other achondrites
  • Many are quite young (154-474 Ma)
  • The composition of gasses trapped in shock melts match that of the martian atmosphere
  • All are shoked and possess evidence of transit through atmosphere
26
Q

Describe Jupiter’s internal structure

A
  • suspect a rocky core that may be the size of earth
  • Estimated core Temperature = 22,000 K
  • Estimated core pressure = 70 million atm
  • Note: temperature for H-fusion = 12 x 10^6 K - Pressure in interior so high hydrogen is compressed to an electrically conductive liquid (~7000 km depth)
27
Q

Describe Jupiter’s magnetic field characteristics

A
  • Rapid rotation + metallic hydrogen convection = strong magnetic field
  • Shape of Jupiter’s magnetsophere is the same as Earth but 1200 times larger
28
Q

Describe Jupiter’s atmospheric composition and structure

A
  • 90% hydrogen, 10% helium, 0.07 % CH4, traces (0.93%) of H2S, H2O, NH3, Ar, Kr, Ne etc.
  • Escape velocity of Jupiter = 60.2 km/s;
  • Jupiter retained its original primordial atmosphere because it is difficult for even light gases to escape
  • Atmosphere ~5000 km “thick”
  • Lacks a clear lower boundary
  • Transitions gradually to metallic H layer
29
Q

Explain how Laplace resonance and tidal heating result in Io’s intense volcanism

A
  • *Laplace Resonance**
  • Periods of Io:Europa:Ganymede are in ratio 1:2:4
  • Eccentricities get pumped up to much higher values than if the satellites were not in a resonance
  • High eccentricities mean higher dissipation in the satellites and a tendency for the orbits to contract
  • This tendency is counteracted by dissipation in Jupiter, which tends to cause the orbits to expand (like the Moon)
  • The system is currently (roughly) in equilibrium
  • *Tidal Heating** -
  • The moons’ orbital geometry results in tidal stressing of the satellites and generation of internal heat
  • Maximum deformation occurs at perijove when the satellite is closest to Jupiter and the least amount of deformation occurs at aphelion when it is furthest away
  • The magnitude of this effect decreases with increasing distance from Jupiter (1/r3): Io is most affected and Callisto is virtually unaffected Volcanism
  • Geophysicists calculated the amount of heat generated from Io’s tidal flexing and predicted active volcanism
  • Predicted volcanism even though surface temperatures range from -148 °C to -138 °C Io has more than 100 active volcanoes.
  • Most volcanically active body in the Solar System
  • No impact craters
  • Lava flows ~1750 °C: molten silicates (basalt / komatiite) and not sulfur
  • High albedo (63%) due to the presence of light-colored sulfur and sulfur compounds that cover underlying dark rocks
  • Lava flows on Io have the same characteristics as low-viscosity basaltic and komatiitic lavas on earth
  • Rate of lava production covers the entire surface at a rate of 1 m / 100 years
30
Q

Describe the volcanic, tectonic and crater characteristics of Io

A
  • Most volcanically active body in the Solar System
  • No impact craters
  • Lava flows ~1750 °C: molten silicates (basalt / komatiite) and not sulfur
  • High albedo (63%) due to the presence of light-colored sulfur and sulfur compounds that cover underlying dark rocks
  • Lava flows on Io have the same characteristics as low-viscosity basaltic and komatiitic lavas on earth
  • Rate of lava production covers the entire surface at a rate of 1 m / 100 years
31
Q

Describe the characteristics of Jupiter

A
  • Mean diameter = 139,822 km (~11 Earths) - Mass = 1.89 x 10^27 kg (317 Earths)
  • Orbital Period = 11.86 Earth years - Day = 9.925 hours
  • Rapid spin causes equator to bulge and contributes to atmospheric circulation patterns
32
Q

List the major Galilean moons of Jupiter

A

Jupiter has at least 63 moons
Four “Galilean” satellites

a. Io
b. Europa
c. Ganymede
d. Callisto

  • All are in synchronous rotation with Jupiter (tidally locked like the Moon)
  • Jovian (Jupiter-facing) and anti-Jovian (side opposite Jupiter) hemispheres
33
Q

Describe the volcanic, tectonic and crater characteristics of Europa

A
  • Ice-covered satellite (albedo = 64%)
  • Water ice crisscrossed by curved dark fractures
  • Reddish discoloration from salts, meteorite debris, interplanetary dust particles and organic matter
  • Surface of Europa covered by a complex sets of intersecting ridges separated by narrow valleys formed by tidal deformation of crust
  • Internal structure from gravitational and magnetic field observations
  • Density = 3.04 g/cm3 (rock and metal with a water ice surface)
  • Strongest evidence for subsurface ocean: magnetic field observations Induced by electrical currents as a result of convecting saline water
  • Some models predict the outer ice layer is 1-2 km thick underlain by a 10 km thick ocean while other models favor a thick crust
  • Scarcity of craters means Europa’s surface is <50 Ma
  • Most of the impact craters that did form have been erased by burial of ice “lava” flows, destroyed by breakthrough of water to surface, creep and sublimation of ice exposed at the surface
34
Q

Describe Europa’s Chaos Terrains

A
  • Angular blocks of ridged ice imbedded in hummocky ice
  • Several large blocks (icebergs) have been rotated while others are displaced from the surrounding crustal ice by widening fractures0
  • Several hypothesis
  1. . Upwelling of ice diapirs
  2. Extrusion of water-ice slurries through the crust to form dome-shape lobate deposits
  3. Local melting of thin crust by rising plumes of warmer water
35
Q

Describe the volcanic, tectonic and crater characteristics of Ganymede

A
  • Properties intermediate between Io and Europa Largest moon in the solar system
  • Diameter = 5,280 km
  • Density = 1.93 g/cm3
  • Albedo = 43% - Structure = icy crust with convecting (ice / water) upper mantle, silicate lower mantle and Fe-rich core
  • Icy crust divided into two major terrains
  1. Dark, heavily cratered ice (older than 4 Ga) Largest = Galileo Regio (3200 km across) Dark ice = remnants of original crust that was broken up
  2. Bands of light-colored grooved ice (younger than dark areas)
  • *Impact Craters**
  • Range in diameter from <5 km to >100 km
  • Small craters (5-20 km) have raised rims, central uplifts and ejecta blankets
  • Larger craters (20-100 km) have a central pit
  • Crater >60 km contain a dome within the central pit
  • Largest craters >100 km have relaxed shapes due to ice creep palimpsests
  • Rayed craters indicated that dark regions are underlain by bright ice
36
Q

Describe the volcanic, tectonic and crater characteristics of Ganymede

A
  • Properties intermediate between Io and Europa Largest moon in the solar system
  • Diameter = 5,280 km |- Density = 1.93 g/cm3 |
  • Albedo = 43%
  • Structure = icy crust with convecting (ice / water) upper mantle, silicate lower mantle and Fe-rich core
  • Icy crust divided into two major terrains
  1. Dark, heavily cratered ice (older than 4 Ga)
    Largest = Galileo Regio (3200 km across)
    Dark ice = remnants of original crust that was broken up
  2. Bands of light-colored grooved ice (younger than dark areas)
  • *Impact Craters**
  • Range in diameter from <5 km to >100 km
  • Small craters (5-20 km) have raised rims, central uplifts and ejecta blankets
  • Larger craters (20-100 km) have a central pit
  • Crater >60 km contain a dome within the central pit
  • Largest craters >100 km have relaxed shapes due to ice creep palimpsests
  • Rayed craters indicated that dark regions are underlain by bright ice
  • *Ganymede’s Ocean**
  • Low average density (1.93 g/cm3) suggests a composition composed of roughly equal party rock : ice, mostly water ice with some ammonia ices
  • Layered ocean separated by different phases of ice?
  • Intrinsic magnetic field Convection in liquid Fe-rich core
  • Ganymede is older and darker (lower albedo) compared to Europa attributed to a longer exposure age (space weathering, accumulation of dust / meteoritic debris)
  • Thicker ice crust on Ganymede
  • tides of Jupiter are less efficient at generating heat on Ganymede versus Europa (no active or inactive cryovolcanoes, plumes of gas or geysers)
37
Q

Describe the volcanic, tectonic and crater characteristics of Callisto

A
  • Darkest of Galilean satellites (albedo = 17%)
  • Least dense (1.79 g/cm3)
  • ~60% ice; 40% rock - Not appreciably affected by Jupiter’s tidal influence
  • Largest non-differentiated body in solar system (D = 4840 km)
  • Spectral identification of surface materials include water ice, CO2 ice, silicates and organic compounds
  • *Impact Craters**
  • Surface has reached saturation (equilibrium density)
  • Surface exposure age ~4.6 Ga
  • Largest crater = Valhalla (D = 1500 km) multi-ring basin
  • Light (white) ejecta blankets surrounding craters indicates and underlying icy layer
  • Same turnover in plot of Crater diameter vs. depth as observed on Europa and Ganymede
38
Q

Describe the general characteristics of Saturn

A
  • diameter =120,660 km
  • mass = 5.69 x10^28kg - Bulk density =0.690
  • Albedo = 46% - Orbit around sun = 29.46 yrs
  • rotation = 0.426 day axial tilt - 26.7 degrees
  • Rapid rate of rotation = 9.8% oblateness
  • Internal structure derived from oblateness + physical chemistry of molecular hydrogen at increasing temperature and pressure
  • Rocky core (~13 g/cm3) surrounded by ices, followed upward by a layer of electrically-conducting “metallic” liquid hydrogen
39
Q

Describe Saturn’s atmospheric structure and features

A

At ~26,000 km below the cloud tops liquid hydrogen loses its metallic character and gradually transforms to a gas with decreasing pressure

  • Fastest winds in the solar system: up to 1 800 km/hr
  • Great White Spot
  • Short-lived storm once per Saturn year (next in 2020)
  • North Pole hexagonal cloud, each side is ~13 800 km long. possibly due to differential wind speeds
40
Q

Explain why Saturn’s rings are different brightnesses and why there are gaps/divisions between rings

A
  • The rings of Saturn are divided into three main parts (A, B and C) with two apparent gaps (Cassini Division and Encke Gap) the Encke gap = 270 km wide
  • G and E rings are located outside the F ring
  • *SLIDE does not answer why different brightness and why there are division gaps you will need to look this up**
41
Q

Explain how the plumes at Enceladus’ south pole were identified and how they may be generated

A
  • To date, 53 moons of Saturn have been officially named they vary drastically in shape, size, surface age, and origin
  • Composite infrared spectrometer map of Enceladus shows a dramatic warm spot centered on the south pole
  • Cannot be explained with sunlight as the only source of heat, therefore heat is escaping from interior
  • icy plumes erupting off the surface of Enceladus was captured by Cassinni in 2005
  • In 2005, Cassini detected water vapour spewing from the south polar region
  • Later confirmed there is a plume emerging from the tiger stripes or long fissures
  • Composed of H2O vapour and ice, CH4, CO2, N2
  • Alternative: clathrate hydrates, CO2, CH4, N2
  • Amount of material suggests the plume is generated from a near-surface body of water
  • Detected using the signal from occultations
  • Compared spectra from occultation for Scorpii and Orionis and mapped it to water vapour
42
Q

Explain why most surface data from Titan is either RADAR or from the Huygens Probe

A
  • Huygen space probe was an atmospheric Eetry probe that landed successfully on Titan in 2005
  • Sent data through descent and 90 minutes after landing on the surface
  • Most distant landing of any human-made craft
  • Built and operated by ESA
  • *NO MENTION OF RADAR in slides will need to look up**
43
Q

Explain how we know there are liquid hydrocarbons on Titan’s surface

A
  • Believed to be liquid ethane, methane, and dissolved N2 on Titan’s surface
  • Hypothesised after Voyager 1 and 2
  • Suggested in Hubble observations in 1995
  • Possibly confirmed by Cassini in 2004 by enigmatic dark feature near south pole “Ontario Lacus” this was confirmed to contain liquid methane in 2008 by VIMS (Visual and Infrared Mapping Spectrometer)
  • Confirmed by Cassini in 2006
  • Large number of smooth-to-radar features near north pole
44
Q

Describe the volcanic, aeolian, and impact features on Titan

A
  • *Cyrovolcanism**
  • Predicted because of low temperatures and 40Ar in atmosphere
  • Volcanoes produced “lava” composed of water and ammonia; also eject methane
  • No definite detections Sand Dunes
  • Radar images of sand dunes on Titan from the Cassini orbiter composed of solid hydrocarbons rather than silica grains as on Earth
  • the dunes can be 1-2 km wide and 100 meters tall extending for hundreds of kilometers Impact Craters
  • ~60 impact craters have been resolved on Titan
  • Very few impact craters found on the surface of Titan which are most likely being filled by the shifting hydrocarbon sands and eroded by methane streams-
45
Q

Describe the main characteristics of Uranus

A

■first observed between 1690 and 1781, but thought to be a distant star because of slow apparent motion, identified as seventh planet by William Herschel in 1781

■obliquity is 97.86° and satellites are closely aligned to equatorial plane, not orbital one

■ magnetic field, generated by induction resulting from electrical currents caused by flow of plasma in its interior (50 times greater that Earth’s)

■axis makes an angle of 58.6° with rotational axis and is offset from planetary centre

■north mag pole located in northern hemisphere

■21 satellites

■Approaching 2:1 resonance with Neptune

■Lost most of heat of formation

■diameter 51 118 km

■mass 8.68E25 kg

■density 1.29 g/cm3

–rocky core surrounded by layers of liquid and gas H, He, CH4

–no metallic H because Temperature and Pressure not high enough

■Temperature at 1 bar = -195°C

■P = 84 yrs

■a = 19.18 AU

■period of rotation is 18 hrs

■because of axial tilt, appears to rotate retrograde

■oblateness = 2.29% (lower than Jupiter and Saturn)

■e = 0.047

46
Q

Describe the interior structure of Uranus

A
  • core is silicate/ Fe-Ni rock
  • mantle is ammonia, water and methane ices
  • atmosphere - hydrogen, helium and methane gases
    *
47
Q

Describe Uranus’ atmosphere

A

■Atmosphere: 83% H2, 15% He, 2% CH4 (percent by number)

–Noble gasses and volatile compounds make up less than 1%

–In general, similar to composition of sun at -200 C

■Ratio of C/H 30-40 times higher in Uranus’ atm

■Structure is similar to other gas giants, despite obliquity

–E.g. latitudinal banding

–However, no cyclones observed and heat comes from solar radiation

48
Q

Describe Uranus’ rings

A

■Eleven rings: 6, 5, 4, α, β, η, γ, δ, λ, ε (inside out)

–λ discovered by voyager 2 very faint and almost invisible

–Two newer rings discovered by Voyager 2 and Hubble: R1 and U2

■ε is main ring

–60 km wide, located 51149 km from centre of Uranus and within Roche limit

–Confined by satellites Cordelia (inside) and Ophelia (outside) which may also constrain the edges of the delta, gamma, and lambda rings

■Composed of particles 0.1-10 m diameter

■albedo only 1.5% (Saturn’s are 20-80%)

■Composed of methane and ammonia ice coated with carbon dust and organic molecules

■Gaps contain powdered ice

■Thickness varies 10-100 m

49
Q

What are the theories on how Uranus’s rings were formed

A

■Three (four) main theories:

  1. Remnants of original protoplanetary disc that failed to accrete because within Roche limit
  2. One or more icy satellites were disrupted when orbital decay brought them within the Roche limit (or were broken up by impacts and couldn’t reassemble)
  3. Ice planetessimals were captured by Uranus and broken up, similar to Shoemaker-Levy 9
50
Q

Explain the main hypothesis for Uranus’ high obliquity

A

■Initially, all planets formed obliquity zero

■Therefore, some large force had to change it

■Likely tipped by collision with another body while still forming in protoplanetary disc

■Disc of gas and particles that orbited Uranus prior to collision realigned itself with equatorial plane after impact and rings and satellites formed in new orientation

■Satellites may have formed from impactor

–Densities higher than Saturnian satellites (except Titan)

51
Q

List five classical satellites of Uranus and what may have formed the visible features

A

■Uranus has 27 satellites, eleven of which have D < 150 km

–Named after characters in Shakespeare’s plays (except Belinda and Umbriel named after characters in a play of Alexander Pope)

5 classic satellites are :

  1. Miranda
  2. Arial
  3. Umbriel
  4. Titania
  5. Oberon
52
Q

Describe the properties of the five classical satellites of Uranus and what may have formed the visible features

A

■Miranda, Ariel, Umbriel, Titania, and Oberon

■Diameters are 470-1580 km

■Interior structures not well-known.

–bulk densities 1.3-1.7 g/cm3, therefore likely mix of ice and rock

–may be differentiated if tidal forces were enough to heat them and cause differentiation

■rocky cores surrounded by thick layers of ice

53
Q

Describe the properties of Miranda

A
  • One of the classic satellites of Uranus
  • Discovered by Gerard Kuiper in 1948
  • Smallest of classical satellites
  • Three large, rectangular coronas: Arden, Inverness, Elsinor (places mentioned in Shakespeare’s plays)
    • Straight sides 200-300 km on a side with rounded corners
    • Contain grooves and ridges that follow the straight sides and form concentric patterns
    • Surrounding ice heavily cratered, whereas coronas contain only a few craters (~ 1 Ga)
    • Suggest that Miranda was fragmented by high-energy impacts and subsequently reassembled
    • Alternative is “warm” ice plumes
  • Heat for internal differentiation from tidal friction
  • Orbit currently too circular and spin-orbit coupled to result in much tidal heating, therefore may have been different in the past
    • May have had more eccentric orbit or no spin-orbit coupling in past
    • May have been in resonance with Umbriel (increases eccentricity)
  • Heat may have caused “warm” ice to rise in plumes and initiated cryovolcanism
54
Q

Describe the properties of Ariel

A

■One of the classic satellites of Uranus

■Closest neighbour to Miranda

■Discovered by William Lassell in 1851

■Heavily cratered surface

■Dark surface covered by sediment of organic matter and amorphous carbon derived from methane embedded in the water ice

■Several large, recent craters expose white ice

■Intersecting sets of grooves and ridges

■Several graben (rift valleys) with steep sides and flat floors

–Indicates Ariel was tectonically active in youth

■“lava” flows made of water-ammonia and water-methane mixtures

–Heat from tidal friction, therefore orbit once more eccentric than current

55
Q

Describe the properties of Umbriel

A

■One of the classic satellites of Uranus

■One of the darkest satellites in the solar system (19%; Ariel is 40% and Miranda 34%)

■Discovered by William Lassell in 1851 at same time as Ariel

■Heavily-cratered surface not resurfaced by cryovolcanism

■Dark colour from sediment of organic matter and amorphous carbon

■Sediment covers light-coloured ice, exposed in a few places

■Do not know whether differentiated or not

56
Q

Describe the properties of Titania

A

■Largest Uranian satellite

■Discovered by William Herschel in 1787

■Heavily cratered surface

■Steep-sided rift valleys similar to those on Ariel

■Albedo 28% – organic-rich sediment not as thick (or dark?) as on Umbriel

■Once tectonically active, surface rejuvenated by “lava” flows of water containing ammonia and methane

57
Q

Describe the properties of Oberon

A

■One of the classic satellites of Uranus

■“Twin” of Titania (similar in size and appearance)

■Discovered by William Hershel in 1787

■Extensional rift valleys and “lava” flows of water-ammonia mixtures

■Mountain lower left limb

58
Q

Describe the basic characteristics of Neptune

A
  • Diameter - 49,528Km
  • Mass - 1.02 x 1026kg
  • Bulk Density - 1.64 g/cm3
  • Albedo % - 51
  • Temperature measured at 1 bar = -204 oC
  • Atmosphere - H2 + He (trace CH4)
  • Semi-major Axis AU- 30.06
  • Period of revolutions (yrs)164.86
  • Period of rotation (days) - 0.80
  • Obliquity - 29.6o
  • Magnetic field

–Tilted from rotational axis 47°

–Offset from planetary centre, but less than Uranus

–25 times stronger than Earth’s

59
Q

Describe Neptune’s interior structure

A
  • core - rock and ice
  • mantle - water, ammonia and methane ices
  • atmosphere - hydrogren, helium and methane gases
60
Q

Describe Neptune’s atmosphere

A

■80% H2, 19% He, trace amount methane

■High altitude cloud bands

■Troposphere T anomalously high

–Too far from sun to be from radiation

–May be heated by ions interacting with the magnetic field or gravity waves dissipating in the atmosphere

61
Q

Explain how Neptune was found

A

■Discovered 1846

■First planet to be found by mathematical prediction rather than empirical observation

■In 1821, Alexis Bouvard published tables of Uranus’ orbit, but subsequent observations revealed substantial deviations from these tables

–Bouvard predicted another body that was perturbing the orbit through gravitational forces

■In 1843-46, John Couch Adams began calculating Uranus’ orbit

■1845-46, Urbain Le Verrier independently did the same

–worked with an astronomer from the Berlin Observatory, Johann Gottfried Galle, who observed Neptune within one degree of where Le Verrier predicted

■Visited by Voyager 2 in 1989

62
Q

Describe what we know of Neptune’s moons (excluding Triton)

A

■13 known satellites

■Named for minor water deities

■Triton, Nereid, and Larissa discovered prior to Voyager 2

■Six inner moons: Naiad, Thalassa, Despina, Galatea, Larissa, and Proteus

  • Proteus resembles irregular polyhedron

■Larger than Mimas which is spherical, so irregular shape may be due to past collisions

■In 2002-03 ground-based telescopic surveys discovered five additional outer moons: Halimede, Sao, Psamathe, Laomedeia, and Neso.

■Larissa was first observed during occultation study looking for rings

  • Occultation lasted only several seconds, making it more likely that it was a moon
  • Re-discovered by Voyager 2 along with five inner moons
63
Q

Describe Neptune’s rings

A

■Not definitely discovered until Voyager 2 flyby

■Five principle rings orbiting 41 000-63 000 km from planet

■Very faint, dusty, more closely resembling the rings of Jupiter than Saturn

■Made of extremely dark material, likely organic, similar to Uranus

■Named after astronomers who contributed important work on the planet: Galle, Le Verrier, Lassell, Arago (sometimes considered a bright edge to the Lassell ring), and Adams

■Also unnamed ring coincident with orbit of Galatea

Adam’s ring

■Consists of five bright “arcs” (regions of clumping) embedded in a fainter continuous ring

–Liberté, Egalité 1 and 2, Fraternité, Courage

–Fraternité is longest and brightest, Courage the dimmest

–No satisfying model to explain stability of the rings

■Arcs are in lagrangian points of moon orbiting inside rings, but Voyager 2’s observations place strict constraints on size and mass of undiscovered moons and makes this theory unlikely

■Co-rotational Eccentricity Resonance (CER): identifies stable points in orbit based on the perturbing potential of the ring

64
Q

Explain why it is thought that Triton is a captured satellite and the effects of that capture on the Neptunian system

A

■Captured satellite

■Evidence:

–Retrograde orbit

–Icy composition

–Much more massive than any other moons

–Paucity of other moons orbiting Neptune

■In order to be captured, a passing body must lose sufficient energy that it cannot escape

–Triton may have been slowed by collision with another object

–Triton may have had a massive companion (similar to Charon), making it a binary system

■When approached Neptune, interaction transferred orbital energy to other body, which was expelled and Triton captured

■After capture, orbit would be highly eccentric

–Create chaotic perturbations in original inner satellites, causing them to collide and break up

–After Triton’s orbit re-circularised, inner moons could accrete again

–Would have resulted in tidal heating and differentiated the moon

■May explain extremely eccentric orbit of Nereid and the scarcity of moons compared to other gas giants.

65
Q

Describe the surface features of Triton and how they may have formed

A

■Largest satellite

■Discovered by William Lassel shortly after Neptune itself

■Orbits retrograde and inclined (127-173°, currently 130°) relative to Neptune’s equator

■P = 5.875 days, average distance 330 000 km above cloud tops

■D= 2705 km

■Mean density = 2.066 g/cm3

■Surface T ~ 38 K

■Second known satellite in Solar System to have a significant atmosphere

■40% of surface imaged by Voyager 2

■Surface appears young and was probably modified by internally driven processes (cryovolcanism) within the last few million years

■Most geologic structure likely formed of water ice

■Thin, uneven veneer of nitrogen and methane ice (sublimates at <100 K)

■Very bright, reflects 60-95% of light (Earth’s moon reflects 11%)

■Impact craters are rare

  • Only ~180 unquestionably impacts (Miranda has >800)
  • Almost all concentrated in leading hemisphere, however, no complete imaging of trailing surface

■Cantaloupe terrains are a series of fissures and depressions (30-40 km in diameter) that resembles cantaloupe skin

■Mostly dirty water ice

■Depressions possibly due to diapirism, but alternate hypotheses include collapses or flooding by cryovolcanism

66
Q

Explain how the Pluto-Charon system may have formed

A
  • Pluto is dwarf planet with one large satellite (Charon) and four very small satellites (Nix, Hydra, P4 (discovered 2011), P5 (discovered 2012) D <56 km)
  • Pluto-Charon–forming impact yielding a planet-moon system
  • The impacting objects have uniform serpentine compositions. After an initially very oblique impact with a 73° impact angle (A), the two objects separate (B and C) and during this period the smaller impactor receives a net torque from the distorted figure of the target.
  • After a second, even more grazing encounter (D), an additional portion of the impactor is accreted onto the planet, while the rest self-contracts into an intact moon containing 12% of the central planet’s mass that is again torqued by the ellipsoidal figure of the target (D and E) onto a stable orbit with a semimajor axis of 6.5 Rp and an eccentricity of e = 0.5. The final moon in (F) is described by 2232 SPH particles.
67
Q

Explain why Pluto is a dwarf planet

A

To be a planet (defined by IAU) a celestial body:

  • is in orbit around the Sun,
  • has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
  • has “cleared the neighbourhood” around its orbit

To be a dwarf planet:

  • The first two only
  • Five confirmed dwarf planets:
  • Ceres, Pluto, Eris, Haumea, and Makemake
  • Many other probable dwarf planets in Kuiper Belt

So Pluto is a dwarf planet because it has not cleared its neighbourhood around its orbit, but is in orbit around the Sun and has sufficient mass to assume hydrostatic equilibrium (a nearly round shape.

68
Q

Describe the surface features and composition of Pluto

A
  • Diameter = 2300km
  • Density = 2.03 g/cm3
  • Albedo ~ 60%
  • escape velocity 1.10km/s
  • semi major axis - 39.53 AU
  • rotational days - 6.39 days
  • period of revolution - 247.7 years
  • Tombaugh Regio , nicknamed “The Heart”
    • Largest bright surface feature on Pluto = possible impact basin
  • Surface has ices of N2, CO, CH4, and H2O
  • numerous impact craters on surface as well as cryovolcanos