10-Mercury

When was the late heavy bombardment?

3.9-3.8 billion years ago.

• enhanced impact bombardment on the moon

• evidence from age dates of Apollo samples and lunar meteorites

• Nice model, suggests that changes in the orbits of gas giant planets disrupted the asteroid belt, causing large amounts of asteroids to be thrown into the inner Solar System impacting the moon and other bodies

What is the order of planetary volcanism in the order of explosivity?

• Hawaiian (least explosive)

• Strombolian

• Vulcanian

• Plinian (most explosive)

Rampart craters and pit craters?

Of craters are above 3km in diameter, about 40% have layered ejecta blankets, often called rampart craters

• these lobate ejecta blankets are thought to have formed as the target rock was rich in water ice or other volatiles

Over 200 craters that are in the 1-150km diameter size range have been observed to have pits in their centre, indicating that volatiles might have been uplifted from lower stratigraphic horizons.

• these sites are interesting for their astrobiological interest, as they could have preserved long-term hydrothermal systems, that might have been ideal habitats for life to develop and thrive, protected at depth from surface radiation.

Why is Mercury hard to observed from Earth?

It stays close to the Sun in the sky; only visible at sunrise or sunset

Mercury’s orbit and rotation?

3:” spin orbit resonances → rotates 3 times for every 2 orbits

Length of a Mercury day?

One solar day = 2 mercury years

Surface temp on Mercury?

-170 to 430 huge day night variation

What makes Mercury unusual compared to other terrestrial planets?

It has an extremely large metallic core.

How large is Mercury’s core?

83% of the planet’s diameter

Why is Mercury so dense?

High proportion of metallic iron

Two main hypothesis for Mercury’s large core?

1. Giant impact (hit and run) stripped mantle

2. Formation close to the Sun → iron rich building blocks

Does Mercury have a magnetic field?

Yes - weak (1% of Earth’s Strength)

Why is this important?

Indicates an active or partially molten core

Does Mercury have an atmosphere?

No - only a thin exosphere

What is Mercury’s exosphere made of?

Mostly helium, sodium, and other volatiles from solar wind & micrometeorites

What is the first mission to Mercury?

Mariner 10 (NASA 1974 - 75)

What did Marine 10 do?

• 3 flybys

• imaged only one hemisphere

• discovered magnetic field

• detected exosphere

What is the most important mercury mission so far?

Messenger

Launched 2004

Orbited Mercury 2011-2015

What did the Messenger discover?

• global surface mapping

• surface chemistry (x-ray, gamma ray, neutron spectroscopy)

• volcanism, tectonics, hollows

• evidence for polar water ice

Upcoming current Mercury mission?

BepiColombo (ESA + JAXA)

Launched 2018

Enters orbit 2026/2027

Two orbiters:

• ESA: surface chemistry

• JAXA - magnetosphere

How old is Mercury’s surface?

Mostly >3-4 billion years old

Date Mercury’s surface through crater counting (no samples available)

What is the number of large impact basins on Mercury?

46

What is the Caloris basin?

The largest basin on mercury is the Caloris Basin.

Diameter - 1550km

Age 3.8-3.9 Ga

Why is Caloris hard to see?

Flooded by younger volcanic smooth plains

What is the main type of volcanism on Mercury?

Effusive flood volcanism (very runny lava)

Thickness of smooth plains lava is up to 1km thick

When did major volcanism stop?

3.5 - 3.6 Ga

What is the evidence for explosive volcanism on Mercury?

• pyroclastic deposits

• vent structures

• bright halos

Youngest possible volcanic activity age as recent as 1Ga

What are the key surface chemistry techniques used on Mercury?

X ray spectroscopy (uses sun as x ray source)

Why does this x ray spectroscopy only work on airless bodies?

Atmosphere absorbs X rays

What unusual chemistry does Mercury show?

• high magnesium regions

• high sulfur content

What Earth rock is Mercury’s high Mg terrain compared to?

Komatiites (ultramafic, high temp lavas)

What are hollows?

Small, shallow, bright pits on Mercury’s surface

composition - sulfur rich, volatile rich

Hollows form from volatile loss (sublimation) and possibly explosive volcanism.

Does Mercury have plate tectonics?

No - single plate planet

What is the main tectonic feature on Mercury?

Lobate scarps (thrust faults)

Causes by global contraction as the planet cools.

Scale 1-2km planetary radius shrinkage.

Does Mercury have water ice?What evidence?

Likely yes, at both poles in permanently shadowed craters.

Evidence for ice:

• radar bright deposits

• neutron spectroscopy

• optical reflectance

What are the possible sources of ice?

• comets

• hydrous meteorites

• solar wind hydrogen

What would a Mercury meteorite look like?

• young (3.6-4.3 Ga)

• differentiated (basaltic / kamatiitic)

• sufur rich minerals

Non-confirmed if we have any Mercury meteorites.