17 Mercury&Venus

7/23/2019 17 Mercury&Venus

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Terrestrial Worlds 1

Mercury, Venus,



Mercury basics

• Closest to Sun (0.4 AU), 10th largest world

• Orbit -88 Earth days

• Surface gravity -3.7 m/s2

(38% of Earth)• 10-14 bars of pressure (negligible)

• Temperatures- 800 oF in day (second hottest)

- -300 oF at night• Weak magnetic field

• Spacecraft- Mariner 10



Mercury’s Surface



Mercury’s Surface

• A mixture of heavily cratered and smoothregions like the Moon

• Smoother regions are likely ancient lava flows



Caloris basin

Multi-ring impact basin

(Only half visiblefrom Mariner 10)



Caloris basin MESSENGER 2009 -1550km



Volcanism on Mercury

• ancient lava flows, no large floods



Mercury-Discovery

Rupes

A fault scarp

caused by cooling

and shrinking of

Mercury



Mercury- Lobate Scarps fault scarps mostly run N-S, can be up to 2000 ft high



Tectonics on Mercury

Mapping the location and size of the scarps tells how muchMercury has shrunk.

Current numbers suggest Mercury's radius has lost 1.5 km



Mercury Atmosphere

• Sensitive measurements show Moon andMercury have extremely thin atmospheres

• Gas comes from impacts that eject surface atoms

MoonMoon MercuryMercury



VENUS



Venus basics

• 2nd planet from Sun (0.7 AU), 6th largest world.• Orbit -224 Earth days

• Sidereal rotation -243 Earth days (solar day-117 Eds)

• Surface gravity-8.8 m/s2 (90 of Earth)

• 90 bars of pressure (90 x Earth)

• 96% CO2 3.5% N2 < 1% others

• Venus is the hottest planet. 870 oF

• Intense cloud cover - highly reflective in visible light,surface unseen except by radar

• Spacecraft- Pioneer, Magellan (USA)

Venera 9-16 (Russia)



Venus As

Seen in

Radar

light



Highlands on Venus- Aphrodite Terra



Venus - Chasma

Vast mountain and canyon systems.

-3km high and 3km deep running

for thousands of miles



Venus-Regios

RegionsWhere

canyon

systems

join at a

high volcano



Tectonics• Downwelling

-Highlands and faultedregions called tessera

• Upwelling

-Extension rifts at hot spots= chasmas and regios

Crust too strong to

break all the way

through. No plate

tectonics



Volcanism on Venus

• 80% of Venus is resurfaced by volcanism

• Volcanic shapes controlled by height and

location.

• Hot spots -large shield volcanoes.

• Lowlands - volcanic floods.

• Middling heights- fields of cinder cones.

• High areas - lava too hard to rise - coronae



Venus Regios - Volcanic hotspots

C F il d l



Coronae -Failed volcanoeslava tries & fails to break the surface in the mountains,

-leaves a circular depression (unique to Venus)



Surface of Venus



Venus Surface Processes - WindWind streak showing wind direction



Venus Cratering

• Lots of small to middle-sized craters, fewlarge ones

• Even distribution -Most of Venus’ surfacehas a similar age

• Most of Venus resurfaced by catastrophiclava flooding < 1 billion yrs ago.

• Current activity??



Venus Atmosphere

• 90 bars of pressure (90 x Earth)

• 96% CO2

• Massive greenhouse warming.

• Clouds- sulfuric acid!

• Slow rotation - almost no coriolis effect.



• Venus closer to the Sun than Earth, plusrotation is too slow for a magnetic field.

! Initial water would vaporize.

• Runaway greenhouse effect made Venus

too hot for liquid oceans

• All carbon dioxide remains in atmospheremaintaining a huge greenhouse effect

Why No Oceans?

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17 Mercury&Venus