Lecture 28 - Mercury and Venus

ASTR 1210 (Exam 3)

Where did the water on Mars go?

• Light was able to destroy water molecules in the Martian atmosphere - IMPORTANT

  • Light and particles that passed into the Martian atmosphere - energy snacked into those particles to vibrate and rotate and destroy it - photo ionization or photo disassociation

  • Earth is surviving because we have a strong magnetic field that protects water from harmful chemicals and reacts entering Earth’s atmosphere

• Some of it became trapped beneath the surface

• Now frozen in the polar regions

• See evidence of seasonal melt (stratification of rocks)

  • See some water erosion (beneath the surface)

  • Ice caps spectroscopically show a lot of ice water — there is water ice beneath the dry ice

Mercury

• Densest of terrestrial worlds - denser than Earth!

• Much smaller than Earth

• Rotates incredibly slow 

• Distance from Sun 0.39 AU

• Period 87.97 days

• Can affect surface of Mercury and its characteristics

• No source resupplying heat - geologically dead 

• Orbital inclination 7.0 degrees

• Orbital eccentricity 0.206

• Mass 0.055 M_Earth

• Density 5.43 gm/cm³

• Rotation period 58.6 days

What do we know about Mercury?

• Two spacecrafts sent to Mercury — images require you to go to planets

• Images we have 10s of years old

• We have to observe from the Earth

  • Takes a lot of money to send spacecrafts to each planet

• We see phases from Earth

  • Closer to us: crescent

  • Further from us: full

• Always near the Sun - hard to see with own naked eye - only seen from greatest elongation from Sun (couple of degrees)

  • Need clear horizon to see Mercury

• Transit of Mercury - passes in front of Sun

  • See it for a couple of times

• Highlands and craters

What are some similarities and differences between the Moon and Mercury? 

• Maria on Moon - lava planes

  • Created flat dark regions

• Mercury has less of those - less flat planes/less lava planes

  • Lava can’t seep out as easily

  • Mercury didn’t have thin side to make more lava planes

• Moon forming near Earth made near side thinner, and far side thicker

  • Near side has more lava planes

• Mercury didn’t have tectonic activity

  • No volcanoes, mountain ranges

Topography of Mercury’s Northern Hemisphere

• Lowest crater to highest peak - height difference is 6 miles/10 km

  • Mount Everest is 5 miles

• 10 Km difference on MercuryMerc is less than height difference between lowest and highest place of Earth

  • Mt Everest reaches about 9 km off surface and Mariana Trench is about 11 km beneath surface for 20 km difference

• Because less tectonically activity than Earth (Mercury)

Mercury

• Has a very large iron core (about 65% of mass of the planet)

  • Besides Earth, it is the second most dense

• Small magnetic field - smaller than Earth but not 0

• Although Mercury has large iron core, geologically dead and the planet is small - should’ve cooled off

• Because Mercury in inner solar system, it got chipped away or smacked against

  • Maybe planetesimals near Sun are made of Iron and Nickel?

Cratering of Mercury 

• Has heavily cratered and smooth regions like Moon

• Smooth regions are likely ancient lava flows 

• Pretty big craters - entire crater is bigger than Cville 

• Large cliffs on Mercury 

Tectonics on Mercury

• Cliffs suggest tectonic activities

• Mercury might’ve shrank to create steep cliffs

  • A little like tectonic activity

• Should see stretch marks

Mercury 

• Closest planet to the Sun - Sun tries to tidally lock Mercury (one face always towards it)

  • Significantly slowed Mercury’s rotation

• Takes 2 Mercury years for it to fully turn once with respect to Sun

• Impacts temp on day side of Mercury vs night side

• Spend Mercury year in darkness, Mercury year in day

  • Night: super cold

  • Day: super hot

• No atmosphere - can’t bring energy from one side to other (like Earth with wind)

MESSENGER

• 10 years since we had spacecraft orbiting Mercury (MESSENGER)

• Mariner 10 orbited Mercury 50 years ago 

• Closest to sun - hard to get stable orbit from Earth to interior of solar system

  • Easier to go to the farther side

  • Flow by Venus until it zipped by Mercury, creating some of the images

Venus

• Next most traveled to planet behind Mars (not counting Earth and Moon)

• Traveled to about 40 times

• Distance from Sun 0,72 AU

• Can only see atmosphere of Venus

• Period 224.7 days

• Orbital inclination 3.4 degrees

• Close to density of Earth

• Less massive

• Orbital eccentricity 0.007

• Year on Venus is shorter than day on Venus

• Rotates wrong direction

• Super slow rotation

• Diameter 12,104 km =7,521.0769 mi 0.95 diameter of Earth

• Mass 0.82 Mass of Earth

• Density 5.24 gm/cm³

• Rotation period = 243.0 days

What geological processes have shaped Venus?

• Shadow volcanos

• Volcanically active Earth

• Stratovolcanoes

• Has atmosphere

• How can we study the surface features of Venus?

  • Cannot see thru atmosphere (thick) - much thicker than Earth

  • Send some light

  • Bounce radar off its surface to spacecraft

  • Create radio waves

  • Limited with resolution you see on Venus

• Shoot infrared light and back - sees how long it takes to smack into different parts of planet and back

• Topographic map of Venus - see a bunch of radio light or infrared light

Radar Map of Venus

• Colors indicate elevation (blue means low, white/brown means high) 

• Depressions and elevations — higher density than continental plates

Continents on Venus

• Two major continents

• No liquid ocean

• Aphrodite content (equatorial region and about size of Africa) and Ishtar (northern highland and about size of Australia)

• No water

• Lead to intense CO2-filled atmosphere

Cratering on Venus

• Impact craters - fewer than Moon, Mercury, or Mars

• As many volcanoes as Earth - shield and strato-

• Not sure if they’re active

Tectonics on Venus 

• Seems to be tectonic activity on Venus - fractured and contorted surface indicates tectonic activity 

Erosion on Venus

• Photos of rocks taken by landers show little erosion (from the land) - only lasted a couple of hours

• Can get to 900 degrees Fahrenheit - relying on small bits of energy to send signals back

Erosion

• Wind erosion creates sand dunes on Earth - Venus doesn’t seem to have that

• More flaky rocks

• Limited in spacecrafts going to Venus, like Mercury

• Two missions planned to launch to Venus to explore its atmosphere

Does Venus Have Plate Tectonics?

• Has long been thought Venus doesn’t have plate tectonics

• Not sure if volcanically active

• Venus has evidence of lava flows and entire surface seems to have been repaved 750 million years - older than oceanic plates, younger than continental plates