Planetary Geology

Principle of Equifinality

Different processes can produce similar landforms

Factors affecting impact crater morphologies

Intrinsic: projectile size, velocity and composition. Environmental: gravity, atmosphere, crust composition, volatile presence

Why is the spatial distribution of known terrestrial impact craters not homogenous?

Primarily due to different ages of the crust. Secondary factors are ease of identification in different environments etc.

How often do impacts of large bodies occur?

For a diameter of 1 km every 350 kyr or so. For diameters above 10 km every 150 Myr

What causes central peak formation in impact craters?

An abrupt transition from very high to low pressures at the sub-impact point

What kind of impactors are there?

Near Earth Objects, main belt asteroids, Kuiper belt and Oort cloud comets (difficult to predict)

Crater formation stages for simple craters

Schock wave at first contact => excavation and ejecta release => transient cavity (~1.5 times the final depth) => modification - partial filling with breccia lens including metal-rich material, ejecta drop down forming a blanket and an elevated crater rim

Types of impact craters in terms of size

Simple (on Earth up to 2km, on bodies with lower gravity the threshold is higher), complex (on Earth up to 100 km), multiring basins

What additional morphologies occur in complex craters and multiring basins, compared to simple craters?

Complex: terraced walls due to slumping and a central peak. Sometimes the central peak can be a ring. In multiring basins there are multiple concentric rings

How does the angle of impact α affect crater shape?

For α<45° there is no effect, for α>45° craters start becoming elongated and ejecta distribution loses symmetry

What's a rampart crater?

A crater with a low ridge and lobate appearance along the ejecta blanket edge, indicative of mudflow-like movement of ejecta. This would be caused by liquification due to the shock wave as the impact penetrates down to ice-rich underground layers

Has the flux of impactors hitting planetary bodies been constant in time?

No, there was a heavy bombardment 4 Gyr ago. Another late heavy bombardment 3.8 Gyr ago is also hypothesized.

What heat loss mechanisms are dominant on which planetary bodies?

Plate tectonics on Earth. Heat pipe volcanism on Io (also on early Earth). Conduction on the Moon, Mercury and Mars. Venus is uncertain, some mix of all three.

What's a plume?

A convective connection between the core-mantle boundary and the surface of a planet, leading to release of molten magma

What's the relationship between tectonics and volcanism?

The boundaries between tectonic plates are hot areas where plumes are likely to occur. Example: the "Ring of Fire" - a collection of volcanoes above the subduction zones of the Pacific Plate

What areas are suspected to be subject to active tectonism on Venus?

Beta Regio (a probable rift zone), Ishtar Terra (potential convergent mountain-building zone). Besides, coronae are hypothesized to be plume leftovers.

How do hypsometric distributions of Earth, Mars and Venus compare to each other?

Earth's is bimodal (continents+oceanic floor). Both Venus and Mars have unimodal distributions, but on Venus most points are in a +-2 km range, whereas on Mars it's +-8 km

Describe the composition of Moon's surface

Anorthositic highlands and basaltic mares. The latter is due to exposure through impacts after the magna ocean froze - indeed, in the magna ocean mafic minerals must have sunk deeper when they crystallized before the felsic ones.

Types of faults

Vertical displacement - normal fault due to extension and reverse fault due to compression. Horizontal displacement - strike-slip fault

What kind of a landscape is formed from a few parallel normal faults?

Either tilt blocks or horst& graben landscape (horst is the higher part)

Describe wrinkle ridges

They are long vein-like ridges formed by tectonic compression, consisting (in cross-section) of a backclimb, wrinkle (peak), a lobate front and extended frontlimb. They are common on the Moon, also appear on Mars and Mercury

Tectonism on Mars

Mostly in the past: an extensional phase around 3.8 and a contractional phase around 3.6 Gyr ago. (Mars shrinking and losing heat)

What are compressional and dilation shear bands? How to spot them on Mars?

Small (human sized) scale tectonic features caused by shear forces, compacting and extensional respectively. There is room for fluids to get in, so diagenesis can occur and make them more pronounced on color images of e g Mars

Why is crater transient depth bigger than the final depth?

Because ejecta partially fall back inside the crater and the walls may partially collapse too. Also the bottom material gets uplifted

What is a characteristic feature of impact crater rims which does not apply to volcanic craters?

Inverted stratigraphy (ejecta coming from a deeper layer but deposited on top).

Physical division of Earth's interior

Brittle lithosphere which forms tectonic plates (crust and uppermost mantle), ductile atenosphere on which the plates move (rest of the mantle)

Magma generation mechanisms

Residual heat from planet formation, decay of radioactive elements, tidal heating

Types of basaltic volcanism

Mid-oceanic ridges, hot spots related to plumes

Describe shield volcanoes

Low profile volcanoes formed by eruption of low viscosity basaltic lava

Describe cinder cones

Steep conical hills formed from loose pyroclastic material around a volcanic vent, usually related to basaltic volcanism

Describe flood basalts

Deposits resulting from giant basaltic volcanic eruptions, usually linked to plumes

Describe composite volcanoes

Also known as stratovolcanoes. Made of layers of high viscosity, felsic lava. Cone shaped. Examples include Mount Fiji and Iztaccihuatl

Describe calderas

Also known as supervolcanoes, they are large craters formed by collapsed surface rock into empty magma chambers

Describe rhyolitic domes

Dome shaped protrusions formed by slow extrusion of high viscosity lava

How are lava tubes formed?

When a low viscosity lava flow develops a continuous hard crust over a still following pahoehoe lava stream

What's a pyroclastic flow?

A fast moving (~100 km/h or even more) current of hot gas and volcanic rock, coming down from a volcano

What can be a source of water in a lahar?

Molten snow from the top of a volcano?

Describe maars and tuff rings

Both are low-standing volcanoes with bowl-shaped craters around pyroclastic cones. In maars, the crater would be below surrounding ground level and would therefore often host a lake. In tuff rings above

Describe tuyas

They are flat-topped, steep-sided mountains formed by volcanic eruptions occurring under glaciers / ice sheets

What is hyaloclastite?

Volcanoclastic accumulation of breccia with glass fragments formed by quenching of subglacial or submarine extrusion of lava

Volcanic landforms on the Moon, Mars and Venus

Moon - sinuous rilles, shield volcanoes. Mars - Olympus Mons with summit calderas, shield volcanoes, lahar deposits. Venus - pancake domes

What is cryovolcanism?

Eruption of volatiles (liquid water, ammonia, hydrocarbons) from under the ice on icy moons, driven by the same processes as magma formation on warmer bodies

Types of mass wasting

Landslides - rotational, translational and block slides. Rockfalls and topples. Debris/Earth flows and avalanches. Slumps and creeps

Mass wasting driving factors

Gravity, slope, material and presence of volatiles

Estimation formula and typical values of the angle of repose

arctan(f), where f is the friction coefficient, doesn't take into account cohesion etc. Values for fine sand are around 35°, for coarse sand around 40° and for pebbles 45°

What is a rock glacier?

A geomorphological landform moving and looking similarly to glaciers, but dominated by rocks with some buried interstitial ice

What do slopes of landslide area probability densities on planetary bodies tell us?

The slope on Earth is ~-2.3, on Mars ~-1, meaning that bigger landslides occur more preferentially on the latter (maybe due to rock fracture size, maybe because there's no rainfall to trigger smaller ones)

What is a typical trigger of terrestrial landslides?

Rainfall. Also earthquakes, human activity (disruptions from road construction), and others

What's the difference between subaerial and submarine landslides?

The latter can travel much larger distances for given fall heights (i e given initial potential energies)

Examples of mass wasting on Mars

Landslides, small gullies (might involve water flows), aureole deposits around Olympus Mons (uncertain origin, maybe former submarine landslides)

Examples of mass wasting on the Moon

Landslides, boulder tracks

How do landslides on Mercury and Moon compare to each other?

The ones on Mercury are a bit smaller, maybe due to stronger gravity

What determines the spatial distribution of deserts on Earth?

Global air circulation, leading to high pressure zones near tropics and poles. Also mountain ranges with the mountain shadow effect

What are draas?

Huge dunes with heights of over 100 m and wavelength of ~0.5-2.5 km

How fast do dunes move?

~1-100 m/yr on Earth, ~1 m / martian year (3.7 yr) on Mars

What types of dunes are usually highest?

Star dunes, as they accumulate sand from every direction instead of moving

What is a stokes surface and an associated erosional feature?

In an arid environment with some groundwater present deep down, the Stokes surface separates wet and dry sediment. It may become partially exposed by wind action with a preserved rock in the middle, called blowout feature

Where and how is a desert pavement formed?

In areas where many pebbles/cobbles/boulders exist within the sand, by blowing away of the sand and the rocks remaining on top of each other

Temperature ranges on Mars

[-123°C, 25°C]

When do annual dust storms occur on Mars?

During the northern hemisphere winter, which is when the planet is close to it's peryhelion

What are dome dunes?

Mounds of sand which may be degraded barchan dunes

How can grain sizes be inferred from remote sensing of planetary surfaces?

Based on thermal inertia calculated from infrared images

Mars exploration in the 20th century

1964 - Mariner 4, only pictured craters; 1972 - Mariner 9 and Viking 1 & 2 (orbiters and landers) show a variety of features including fluvial, 1996 - Pathfinder (Sojourner rover) and Mars Global Surveyor including MOLA and THEMIS

How is the martian datum defined?

An equipotential surface (based on topography) corresponding to the mean radius at the equator

Which part of Mars has more subsurface ice?

Southern highlands

Mars exploration in the year 2003

ESA Mars Express (radar measurements of water under the ice, mineral identification with OMEGA spectrometer). Mars Exploration Rovers from NASA (Opportunity and Spirit, able to clean the surface of rocks and study with a microscope)

Mars exploration in years 2006-2016

2006 - Mars Reconnaissance Orbiter with CTX, HiRISE, SHARAD radar (measuring layers in the northern polar ice cap). 2012 - Curiosity rover with nuclear power, precision landing, studying minerals in outcrops. 2016 - ESA EXO Mars, landing failed

Why are landing sites close to equator favored for martian rovers?

Solar power

Mars exploration in the year 2020

NASA - Perseverance rover with the Ingenuity helicopter, aimed to collect samples and bring them back to Earth. China - Tianwen-1 mission with a rover, UAE - Hope mission

Martian surface characteristics

Bright areas are dusty, with dust including paragonite, hematite, volcanic material. Dark areas are basaltic

When were valley networks on Mars formed?

In the noachian

Characterize small gullies on Mars

These gullies or troughs on slopes (preferentially poleward) may be due to melting ice or snow, but may also be due to dry flows of sand or CO_2 supported debris flows. Based on cross-cutting relationships they appear to be young - on the order of 10 Myr

Examples of glacial landforms on Mars

Eskers (sinuous sediment ridges) and kettles (depressions left by melting ice)

Where did the Opportunity rover land and what did it find?

It landed at Meridiani Planum and discovered hematite rich spherules known as blueberries

Describe the transient martian ocean theory

In the Hesperian oceans may have existed for ~100-1000 years, filled by outflow channel forming floods. Two possible shorelines have been identified but the outer one is far from equipotential line. May have been reworked by tsunamis and surface freezing

Characteristics of the Noachian, Hesperian and Amazonian periods

Noachian - heavy bombardment, valley network formation. Hesperian - volcanism, outflow channel formation, maybe oceans. Amazonian - late volcanism, low impact rates, late stage polar caps, cold and dry Mars

How are boundaries between Noachian, Hesperian and Amazonian periods set?

Based on crater counting. Absolute ages cannot be defined with certainty without direct sample analysis, but estimated around 3.7 Gyr for the Noachian/Hesperian and around 3.1 Gyr for the Hesperian/Amazonian boundary

Formation hypotheses for Phobos and Deimos

Either asteroid capture or an impact and coalescence of ejected debris

Principle of uniformitarianism

Natural laws do not change, but rates and intensities of processes can

Describe the proposed formation scenario for martian "blueberries" based on the Utah analog

They would be formed in a diagenetic concretion process in eolian/ playa environment. First hydrocarbon gas/fluid removes oxygen from oxides. Then water arrives and provides oxidizing conditions leading to precipitation of balls with hematite shells

How are sandstone chimneys formed and why are they interesting for astrobiology?

They form through groundwater sediment extrusion, fossilized fungi colonies have been found in Utah examples

Address the topic of methane on Mars

Trace amounts (on the order of ppb) have been found both through remote sensing and rover (Curiosity) measurements. Possible link with mud volcanoes. May have been formed biogenically,(bacteria) or diagenically (water -ock interactions)

If there were oceans on Mars, why are there so few carbonates found there?

SO_2 is more abundant on Mars, it's absorption in the water would make it acidic, inhibiting carbonate formation and forming sulfate rocks instead

Describe a hydraulic jump

Change of slope and depth shifts the Froude number above or below 1, making the flow super/sub critical and more or less erosive

Why are fluvial dunes better preserved than eolian?

They may contain larger grains, which cannot be moved by wind

Reynolds numbers of gravity flows

Low for debris flow, high for turbidity currents

Describe the alluvial fan formation process

The activity is happening only in some lobes, then dies out there and starts elsewhere (lobe switching). Channels incise in the upper part of the fan, deposit in the lower. A flow may be a debris flow, a sheet flow (more water & turbulence) or channelized

What are terminal fans?

Alluvial fans in arid areas, where the flow does out due to evaporation

What are fan deltas?

Alluvial fans directly transitioning to deltas due to the presence of a water body at the base of mountains. The Gilbert-type delta in the Jezero crater is considered an example

River morphologies vs discharge and gradient slope

Parallel downward lines separate straight/anastomosing, meandering and braided

Water movement in a meandering river

The flow is deeper and faster on the outer side of a meander

What happens in a crevasse splay after the flooding?

In arid environments water evaporates forming evaporite deposits. In humid areas standing water bodies can form and pedogenesis may be facilitated

What is the problem with Noachian formation of fluvial valley networks?

The atmosphere on Mars is not favorable for liquid water precipitation, and with the Sun having been 30% weaker back then should have been even less favorable

Characteristics of sapping valleys

Headward migration by collapsing walls, not well developed tributary system but mostly 1st order tributaries, similar depths of tributaries as the main valley, blunt amphitheater-shaped heads, structural control by fractures and tectonic levels.

How can a lake in a crater be sustained during a dry season?

By ground water flowing through the basaltic bedrock

Types of ice age catastrophic floods

Lake overbank spillage, ice impounding on a lake, sub-ice draining, subglacial water adding up to a lake, ice dam or sediment dam failure, subglacial volcanism (jökulhlaups)

How fast was the water in the Channelled Scabland flood and where was it coming from?

5-25 m/s, from the Glacial Lake Missoula and maybe also from under the northern ice sheet

What do dry falls in the Channelled Scabland correspond to?

Waterfalls in the waning stage of the flood

How was the erosion ongoing in the Channelled Scabland?

First loess was removed, then also some bedrock (differentially) by plucking and abrasion

What other sources of outflow channels occur on Mars besides chaotic regions?

Lakes in craters (e g Elaver Vallis), fracture zones (e g Athabasca Vallis from a fracture near Elysium, related to an active dyke that would have melted the ice, as supported by measurements from InSight)

What has been inferred from the study of the topography of Simud Vallis?

That it might have hosted a lake from which the water moved on to a potential northern ocean

Tsunami characteristics

Triggered by an earthquake or impact, a wave gets bigger as it approaches the shore, several hits with the first one being the highest, able to capture destroy everything up to ~50 m high above sea level. Water velocity comparable to catastrophic floods

Characteristic traces of tsunamis

Lobate deposits of marine sandy sediment traveling uphill inland, gullies deepened by erosion left by a subsiding wave

Arguments for shorelines on Mars

Similar elevations of different deltas and outflow channel mouths, lobate tsunami like deposits (including the Viking 1 landing site near a potentially submarine crater) and herringbone cross-stratification found by the Chinese rover

Where could liquid water exist in the martian surface today and why?

Bottom of Hellas basin (highest pressure), only in the summer(sufficiently high temperature

Why is there a lower bound on rampart crater sizes on Mars?

Necessity to excavate groundwater present at a certain depth

Difference between till and tillite

Tillite is lithified

Describe the snowball Earth model

Based on diamictites in paleoequatorial outcrops a suspicion that Earth was fully glaciated several times in Precambrian, likely last time before life emerged

Martian geomorphological features related to underground ice

Hourglass features, debris aprons, debris covered glaciers at mid-latitudes

Glacial landforms in the Tharsis rise

Deposits on the north-western sides of the four major volcanoes, particularly big for Arsia Mons

What are pingos?

Mounds formed by pushing out of the soil by an ice lens forming over unfrozen ground

Does Mars have Milankovitch cycles? How does it relate to the subsurface ice?

Not quite, the moons are too small to stabilize the obliquity which displays large chaotic variations. Consequently, ice may have been deposited in some equatorial regions (Arabia Terra) in periods of high obliquity.

What landform suggests former presence of ice in Valles Marineris?

Large scale deep-seated gravitational spreading at tops of internal ridges, which could have been formed when surrounding and covering ice melted

Polygonal feature dimensions in playa environments

Smaller polygons at topographically lower areas, likely due to halite (which is soluble so travels to lower elevations in the water) inhibiting development of large polygon networks. Higher, as minerals change through gypsum to carbonates, larger polygons

What do aligned spring mounds indicate?

Tectonic fractures

Define liquification

Transition of water-bearing sediment from a setting where clasts touch each other to the setting where they are separated by water

How do clastic pipes form?

1) Trigger from earthquake or impact leads to liquification of buried sediments 2) Liquified sediment squeezes out between non-liquified to form a sand volcano 3) Pipe cements, surroundings sink (removed base) 4) Erosion removes material around the pipe

Largest clastic pipes on Earth and proposed origin

~100 m in height and diameter, found in Utah. Maybe due to an impact, nearby Upheaval Dome might be a crater

Where are mud volcanoes commonly found on Earth?

Along orogenic belts, particularly in Azerbaijan, Pakistan, Japan

Conditions needed for mud volcanoes

Abundance of buoyant sediments, abnormally high rock porosity, high pressure gradient, a trigger such as an earthquake

How does a mud volcano eruption look like?

Release of mud, gas and oil. Resulting mudflow has a lot of gas bubbles inside and forms mud levees.

What did we learn from chamber simulations of a hypothetical martian mud volcano eruption?

In current martian conditions, mud would boil, erode a trench and freeze to a crust, creating structures similar to lava tubes

Where are candidates for mud volcanoes found on Mars?

A big cluster in the Chryse Planitia, also in other northern lowland areas such as Utopia Planitia (Chinese Zhurong rover came close), some in Valles Marineris

How are mud volcanoes reflected in the stratigraphic record?

Mud intrusion features

Characteristics of remote sensing observations of potential martian mud volcanoes

Low thermal inertia (contradicts magmatic alternative) and hematite spectral signatures along the rims (not occurring in terrestrial mud volcanoes)

If the methane on Mars has formed in ancient times and is slowly being released, what is trapping it?

Overlying ice or inclusion in CO_2 + CH_4 clathrate

Compare lunar basalts to terrestrial

Fe & Ti enriched, less viscous, higher melting temperature

What is lunar mare formation dated for?

4.12 - 3.16 Gyr ago

Moon formation hypotheses other than impact and why were they dismissed

Capture - unlikely for such a big body. Fission from Earth - would take too long. Accretion parallel with Earth - too different composition, particularly low iron content

Tectonic features in lunar maria

Grabens usually on the outer parts, wrinkle ridges closer to the central parts. Also influenced by gravity, including positive gravitational anomalies due to proximity to the mantle

How do we know that the Moon is moving away from the Earth?

Ancient tidal deposits indicate the tides used to be bigger. Nowadays we can also measure the subtle changes in the distance with lasers

What observational evidence is there for the multi-stage filing of lunar maria with basalt?

Ground penetrating radar measurements by the Japanese Kaguya mission showing layering with micrometeorite erosion caused regolith in between.

Volcanic features on the Moon

Suggested large and small shield volcanoes, sinuous rilles due to erosion by hot low viscosity lava, ring-moat dome structures clustered in maria due to extrusion of magmatic foam, skylights which may likely be lava tube openings

What do we know about water on the Moon?

May be brought by meteorites bearing ice. Likely preserved in deep craters in polar regions which are perpetually shaded, LCROSS mission intentionally crashed and detected a vapor plume. Remote sensing suggests OH in regolith, 1l of water from 1t regolith

Apollo program highlights before Apollo 13

Apollo 8 - first flight of humans around the Moon. Apollo 10 - testing all procedures without actually landing. Apollo 11 - first human landing, 20.07.1969, Mare Tranquillitatis. Apollo 12 - landing near Surveyor 3 lander and approaching it by astronauts

Apollo program highlights after Apollo 13

Apollo 15 - collecting samples from Hadley Rille, confirming lava flow origin. Apollo 16 - commander John Young flew to the Moon twice (before on Apollo 10). Apollo 17 - Harrison Schmidt as the only geologist who went to the Moon.

Artemis program plans

Artemis II - analogous to Apollo 8. Artemis III - landing humans near the lunar south pole. Artemis IV - Gateway, lunar vehicle from Toyota, In-situ resource utilization (ilmenite (FeTiO_3, known from Apollo samples and remote sensing) and hopefully ice)

Core volume fractions of inner Solar System planetary bodies

Mercury 42%, Venus 12%, Earth 16%, Moon 4%, Mars 9%

How many Mercurian days in a Mercurian year?

2/3

Mercury surface features

Caloris Basin (1550 km diameter) and antipodal chaos, impact craters, intercrater plains, smooth plains (likely volcanic)

Mercury volume change history

First expansion which formed intercrater plains. Later, as the planet was cooling, shrinking leading to a 1-2 km radius decrease, evidenced by extensive thrust faults

Evidence for volatiles on Mercury

Some rampart craters

Mercury exploration history

Mariner 10 -> 40 year hiatus -> Messenger -> BepiColombo (ESA/JAXA, arriving next year)

Does the Mercury have a strong magnetic field? Why?

Yes, likely because of the dynamo effect of the large core which is partially molten in the outer part

Where can we find water on Venus?

Only as vapor in the atmosphere, partial pressure 10 mbar

What is the atmosphere on Venus like?

Opaque in the optical because of sulfuric acid clouds. Lots of greenhouse gases: CO_2, SO_2, CO, HCl, water vapor (more in the past but it got subject to photodissociation: sunlight split it into escaping H and oxidizing O (affecting surface minerals)

How long is a year, rotation period and day on Venus?

Year - 225 days, rotation period - 243 days, retrograde, day - 117 days

What did Pioneer discover about hydrogen isotopes on Venus and what is the interpretation?

D/H ratio 100× as big as on Earth. Models suggest it could be explained by a presence of ocean in the first 2 Gyr which then quickly evaporated

Why does photodissociation of water vapor not occur on Earth?

Temperature gradient in the stratosphere leads to vapor condensation in it's lowest part (10-35 km high), preventing it from reaching ionosphere (> 50 km) where the sunlight would have such an effect

How did the runaway greenhouse effect happen on Venus and could it happen on Earth?

As the ocean was evaporating and the water vapor was subject to photodissociation, there was a positive feedback loop between temperature on Venus and capacity for vapor in the atmosphere. It will happen in ~2Gyr on Earth once the Sun shines 40% stronger

Main highland regions on Venus

Ishtar Terra (northern polar area), Lada Terra (southern polar area), Aphrodite Terra and Beta Regio (closer to equator)

Composition of venusian surface

Lowlands (80%) are basaltic, as we know from measurements made by Venera & Vega landers. Highlands (a k a tesserae) are likely more felsic (based on nighttime IR radiation, but no direct measurement yet)

Tectonism on Venus

There is no global plate tectonism similar to that on Earth, otherwise the hypsometric distribution wouldn't be unimodal. But there are some localized compressional (wrinkle ridges in the lowlands) and extensional (rifts, e g in Beta Regio) areas

What is the proposed formation scenario for venusian coronae?

Uplift from a plume, then collapse of the central part, flattening of the rim

What can be said about crater count dating of the venusian surface?

The distribution appears to be completely random, the entire planet's surface send to be similarly aged (estimated at ~0.5 Gyr)

What is a lower bound on impact crater dimensions on Venus?

Around 1 km, because of atmospheric screening (small impactors wouldn't make it to the surface)

Interpretation of pancake domes on Venus

Volcanic eruptions of high viscosity lava, flattened due to atmospheric pressure

Categories of channels on Venus

Lava channels (straight, with levees), sinuous rilles (tight meanders, low viscosity lava erosion), canali (fluvial like, with meanders and point bars, typically found in lowlands), outflow channel Kallistos Vallis, valley networks (maybe lava sapping)

Describe the largest known channel in the Solar System

Baltis Vallis, close to 7000 km, canali type channel on Venus, must be old as it's topographic profile indicates heavy tectonic deformation

Ideas about canali type channel formation on Venus

Basaltic, alkaline, or ultramafic lava; carbonatite lava (supported by high CO_2 fugacity); turbidity currents but under the atmosphere and not a sea)

What kind of lava is hypothesized to have carved venusian sinuous rilles?

Unpolymerized sulfuric or komatiite (high MgO content and erosional capacity), as they can have low viscosities comparable to water

Eolian features on Venus

Wind streaks, transverse dunes

Ideas about tesserae regions on Venus

They might be old, bearing traces of fluvial erosion, subsequent to which they were tectonically deformed and partially filled with lava

Astrobiology on Venus

From Earth-based observations we know there is PH_3 (phosphine) in the atmosphere, at the level of ~20 ppb, it could be a biomarker (produced biogenically on Earth), missions to further study atmosphere needed

Catastrophic model for the resurfacing of Venus

The viscous mantle losing water and building up heat until it becomes molten and global volcanism takes place, could occur in a cyclic manner

Equilibrium model for the resurfacing of Venus

Localized volcanism and resurfacing ongoing. This is supported by observations of high emissivity (emissivity drops quickly with oxidation time) volcanoes surrounded by young tectonic features, also by SO_2 fluctuations in the atmosphere

How was volcanism on Io first discovered?

A plume spotted on Voyager navigation images

Io density and composition

3.55 g/cm^3 (similar to lunar density of 3.34 g/cm^3), interpreted as iron core and light silicate mantle

Describe volcanism on Io

Large activity due to tidal heating, enhanced by eccentric orbit and 4-2-1 resonance with Europa and Ganymede. Primarily sulfuric volcanism which gives the moon its yellowish color. Also some silicate volcanism.

What do we expect about the ocean under the ice on Europa?

Based on density (3.01 g/cm^3) we expect ~15% water content and ice crust to be 10-30 km thick depending on the model (end member models are thin conductive and thick convective ice layer). NASA Europa Clipper should reach the ocean with radar

Landforms on Europa

Dilation bands, ridges, chaos regions (maybe linked to water plumes)

Which moons in the Solar System are larger than Mercury?

Ganymede and Titan

Densities of Ganymede and Callisto

1.93 & 1.83 g/cm^3, therefore 50-70 % water content, thick ice crusts

Summarize the theory about the expansion of Ganymede

Dark terrains appear to be cross-cut by younger (also based on crater counting,) bright terrains. An extensional event might have been due to tetragonal ice (which is denser than liquid water) having existed below the ocean and molten

Types of grooves on Ganymede

Tilt blocks (with listric faults, spreading center type) and horst&graben (crustal rifts)

What are palimpsests?

Ancient craters preserved as brighter spots on Ganymede's dark areas

Ideas about magma on Io

Either rising from the center, from the core-mantle boundary, forming a subsurface ocean or a sponge-like collection of pockets in the mantle

Titan atmosphere composition

95% N_2, 5% CH_4

What do we know about lakes on Titan?

They were hypothesized based on methane in the atmosphere and confirmed with Cassini radar images, found mostly in polar (particularly northern) areas. Liquid hydrocarbons, coming from haze particles dropping from atmosphere ("hydrological" cycle)

What is the temperature profile of Titan's atmosphere?

94 K at the surface, decreasing to 70 K up to 40 km high, then increasing again (similarly to Earth's atmosphere profile)

Why is the presence of methane in the Titan's atmosphere difficult to explain and what's the proposed explanation?

It should be unstable (~30 Myr). Therefore, it must be continuously replenished. A hydrocarbon ocean had been proposed, but lakes discovered by Cassini are too small. There must be more underground maybe trapped in clathrate and released by cryovolcanism

Was the hydro(carbon) sphere of Titan the same in the past?

Some lakes and rivers dried out but the landforms (and rounded cobbles transported by fluvial action) are preserved, particularly at equatorial and northern regions

Describe eolian process on Titan

Dunes, particularly fields of longitudinal dunes, have been found. They cover ~20% of the surface. The sediment is likely ice grains which have a different dynamic than sand on Earth

What's special about the planned landing site of the Dragonfly mission?

It will explore ejecta of a nearby crater, which can be excavated subsurface material

What can be said about Titan's interior?

Given the 1.88 g/cm^3 density, it should have some ice and inner ocean layers, similar to Europa or Ganymede

Describe the plumes on Enceladus

They are coming from a specific area - bluish Tiger Stripes on the southern hemisphere. They contain some liquid and gas, salt, hydrogen coming from deep within (core).

Theories about Enceladus's internal ocean based on heterogeneity of plume sources

Either the ocean is regional, as only a section of ice layer melted due to tidal heating, or maybe it is global but the thickness of ice crust is varied.

Orbital mechanics of Triton

It has retrograde rotation, it's tidally locked, it might have had a more elliptical orbit and Io like past

Characteristic landforms on Triton

Cantaloupe terrain, which may be due to cryovolcanism

Describe geysers on Triton

Plumes with nitrogen reaching 8 km high, maybe linked to a nitrogen atmosphere

Main categories of asteroids in terms of composition

S - silicate, C - carbonaceous, M - metallic

What is the difference between a dwarf planet and a planet?

A planet must clear it's orbital surroundings from other bodies

Characteristic features on the surface of Ceres

Cryovolcanism, mass wasting, bright salt deposits in craters

Other bodies besides Jovian and Saturn moons that are expected to have a lot of subsurface water

Triton, Ceres

What was the heat source for volcanism on Vesta?

Radiogenic decay of ^26 Al

Describe the concept of rubble pile asteroids

Bodies like Itokawa, Ryggu etc. have low density, comparable to icy moons, but it is not because of water but because of very high porosity. They are loosely held together and would fall apart if they spun too fast (e g Dimorphos detached from Didymos)

What determines the shape of asteroids such as Ryggu, Didymos, Bennu?

A net product of gravity and centrifugal force, which can be comparably big. Typically results in an equatorial bulge

What has been found in Ryggu samples?

Organic molecules, including aminoacids

What's a saxum?

Scientifically important boulder - larger than 1% of the size of the hosting asteroid

Describe the redder areas on Ryggu

They are near the equator due to solar exposure, likely the asteroid used to be closer to the Sun. Mid-latitude-level stripes were formed by mass wasting

What has already been discovered by the Lucey mission and what's coming?

It's a NASA mission launched in 2021 which will visit many Jupiter Trojan asteroids. It already visited Dinkinesh and Salem, which is a binary, and discovered that Salem is a contact binary by itself

What will the Psyche mission be looking for?

Evidence of ferrolcanism, the answer whether the composition of Psyche is pure metal or metal & silica mix, perspectives for space mining (rare elements like iridium)

Describe the atmosphere on Pluto

Tenuous (10 μbar), composed of nitrogen, methane, carbon monoxide

Upcoming missions to Venus

NASA: Veritas - new radar map at higher resolution, Da Vinci - atmosphere probing and landing on Tesserae to measure it's composition directly for the first time. ESA: EnVision - studying the climate and such to understand better the difference with Earth

Is Pluto always further from the Sun than Neptune?

No, the elliptical orbit is partially inside, e g 1979-1999

What are the dunes on Pluto composed of and how is the sediment transported?

200-300 μm methane ice particles. The winds at Pluto are strong enough to sustain their transport but not to initiate it, so maybe they form by sublimation in the atmosphere

Characteristic feature on Charon

A large graben-like trough

What other trans-Neptunian object was visited by New Horizons and what did we learn about it?

A contact binary Arrokoth, composed of two spherules: 19 km Ultima and 14 km Thule. It is similar to the 67P comet and in fact that comet came from the Kuiper Belt

What do we know about comet composition?

They are dirty snowballs, composed of volatiles (H_2O, CO_2, CO...), silicates and some organic compounds

Parent bodies for Orionid and Geminid meteor showers

Halley's comet and Phaeton, respectively