PTYS 214 – Spring 2011

Homework #8 available for download from the class websiteDue Tuesday, Apr. 5

Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/

Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Mars http://mars.jpl.nasa.gov/

Announcements

Why is Mars important for Astrobiology?

Relative proximity – first planet where we can realistically test for biological potential and life

Similarity to Earth – It is a rocky, terrestrial planet in the inner part of the Solar system with an atmosphere - yet it is also very different

If life would be found on Mars it may provide a strong argument in favor of life being a common phenomenon in the galaxy, unless…

it may simply prove panspermia…

Telescopes brought beliefs of “canals” and the Martians who could have built them

History of “Martian civilization”“Canals” mapped by Schiaparelli, 1877

Canals mapped by Lowell, 1894

Viking Orbiter, July 1976

Mars Global Surveyor, April 2001

HiRise Camera, April 2007

Let’s not forget about the famous “Face on Mars”

Which is just one of thousands erosional landforms!

It is about half the size of Earth(6787 km)

It has about 1/3 the gravity of

Earth (3.63 m/s2)

Mars has the same amount of land as the Earth… but no oceans

Earth-Mars Similarities Position in the Solar system – Martian orbit is 1.52 A.U.; Earth’s

is 1 AU (Jupiter: 5.2 AU; Neptune: 30 AU)

Bulk chemical composition – Both have a Si-rich crust and mantle, and a Fe-rich core

Size – Mars is about one-half the Earth’s size by radius

Atmosphere – Like Earth, Mars has CO2 and some amount of N2, but NO oxygen (or ozone)

Similar rotation rate – 24.6 hours

Similar axis tilt – 25.2° for Mars versus 23.5° on Earth

Geology is similar on both planets

Plenty of water (on Mars it is mostly frozen)

Earth-Mars Differences

Global-scale plate tectonics − present on Earth, not on Mars

Liquid water − Earth has global oceans on its surface, Mars does not

Atmosphere − Martian atmosphere (0.006 bar) is much thinner than Earth’s ( 1 bar)

Magnetic Field − Earth has one, Mars does not

Mars today…

…is a sterile, alien desert, hostile to life

Problems for life on the Martian surface

Cold (average temperature ~210K) - Why? – not many organisms can grow under these temperatures

Thin atmosphere – open liquid water is unstable

Very little oxygen – no terrestrial-like animal life

Very little ozone – no UV protection

No magnetic field – poor protection from cosmic rays (charged particles)

Could Mars once have had a warm, wet environment for life?

Mars and Earth formed about 4.5 Gyr ago and experienced a similar evolution

What about Mars?

Over 3 Gyr ago Earth had simple life

Follow the water!

Given that the bulk chemical composition of Mars is very similar to the Earth’s we can expect that nutrients and carbon are available on Mars

Even though Mars is further away from the Sun than the Earth, it still receives significant amount of the solar energy – photosynthesis is possible

Therefore, the critical factor for the potential martian biosphere is the presence of liquid water on the surface of Mars

Temperature

triple point

boiling

Earth

gas

liquid

solid

plasma

sublimation

melting

Mars

273 K 10,000K

Pre

ssur

e

1 bar

WaterWater373 K

Problem: Liquid water is unstable under current Martian conditions

Liquid water may have been present on the Martian surface in the past!

Geo-morphological evidence:

1) Features that are similar in appearance to terrestrial water-formed features

2) Degradation (weathering) of ancient impact craters

Mineralogical evidence

1) Minerals deposited in water

2) Water presence

Valley Networks on Mars Ancient

Terrains

Valleys converge downstream

Individual valleys are over 1 km

across

Martian Outflow Channels on Younger Surfaces

Well-defined margins of the channel indicate confined flow

Tear-drop-shaped islands are erosional remnants left behind obstacles

Youngest geologic features

Gullies have been identified on the walls of canyons, channels and impact craters

Water seepage?

New Gullies!

Evidence of water ice near the surface (<1 m)

Mars Odyssey (2001) Gamma Ray Spectrometer

Gamma Rays and Surface Composition

Energy of gamma rays is

indicative of the element that emits

them

The history of Mars and its water is recorded in the rocks!

“EYES”Remote Sensing Package

Pancam Mini-TES

“HANDS”Microscopic Imager

Alpha Particle X-Ray Spectrometer Mössbauer Spectrometer

Rock Abrasion Tool

Mars Exploration Rovers (MER):The robot “geologists”

High Gain Antenna

Low Gain Antenna

UHF Antenna

“FEET”It is mobile (and pretty stable!

Viking, Pathfinder, MER, and Phoenix

Landing Sites

Cryse Basin Elysium Mons

Hellas

Meridiani Gusev

Olympus Mons

Vallis Marineris

Spirit Rover - Gusev Crater Site

THEMIS infrareddaytime images

Basalt rock

Gusev

Drilled .15 in in the rock with the abrasion tool

Patch of nearly pure silica indication of hot springs?

Opportunity Rover - Meridiani Site

Few mm up to a cm in size

Water-formed Water-formed hematite?hematite?

Plains strewn with hematite spherules (blueberries)

Hematite spherules within bedrock

Bedrock is a sulfate

Deposited in water!

Cross-bedding ScallopsSurface water!

Liquid water may have been present on the Martian surface in the past!

Geo-morphological evidence:1) Features that are similar in appearance to terrestrial

water-formed features2) Degradation (weathering) of ancient impact craters

Mineralogical evidence

1) Minerals deposited in water2) Water presence

Mineralogical Evidence:

Martian Meteorites

Pieces of rocks ejected from Mars after impact events and reaching Earth’s surface

Of over 30,000 meteorites found on Earth, only 34 have been identified as Martian meteorites

They are also known as SNC, from the names of the most representative types (Shergotty, Nakhla, Chassigny)

Nakhla(1911)

Chassigny(1815)

How do we know that some meteorites are from Mars?

Age separates them from other meteorites - Almost all Martian meteorites are much younger (180-1300 Myr) than most meteorites, and have a composition similar to terrestrial basalts

Oxygen isotopes separates them from Earth’s rocks - values of 16O, 17O, and 18O are distinct from terrestrial rocks and group all 34 Martian meteorites together

The isotopic composition of gases trapped in the meteorites is almost identical to the Martian atmosphere (comparison with Viking measurements)

Comparison of Mars atmosphere measured from Viking to trapped gases in EETA79001 (Shergottite):

Values are the same!

The impact that ejected the meteorites causes some melting of the rock

The melt cooled very rapidly and formed a glass that trapped atmospheric gases

Atmospheric gases

Evidence of Water inMartian Meteorites

Carbonate minerals - Liquid water flows through fractures in rocks and dissolved CO2 can be precipitated

Hydrated minerals have martian D/H (deuterium to hydrogen ratio)

Electron Microscope image of clay and carbonate (siderite) vein in meteorite Lafayette

ol: olivine

Evidence of Water in Martian Meteorites

• “Rusty” minerals that require liquid water to form

• Some several hundred million years old

they formed on Mars

View of the Lafayette meteorite, 1mm across

Beyond Water: Evidence of life? ALH84001 is a Martian meteorite that became famous

because it appeared to contain structures that were considered to be fossilized remains of bacteria-like lifeforms

More in the next lecture…

Quiz Time !