Lesson4d

Working out the global history of Mars

• There is much less water at a deep of one meter, near the equator of Mars, compared to the polar regions.

• At lower latitudes (near equator) the temperature is higher than at the poles.

• This can cause ice near the surface, at low latitudes, to melt and then evaporate away.

• The measurement doesn’t show that there is no underground water at low latitudes on Mars.

• It only shows that there is little water at a depth of one meter, at low latitudes.

Geologic history of Mars

• If you consider that a surface that has not been destroyed for billions of years will have a large impact crater density it is possible to tell where most of the geologic history of Mars has taken place.

Which hemisphere is younger

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1. Northern2. Southern

Is there evidence of plate tectonics?

Earth

• http://www.google.com/mars/

Is there evidence of plate tectonics?

Evidence of Plate tectonics on Mars?

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1. Yes2. No

Evidence of Plate tectonics

• Mountain ranges along plate boundaries• Strato-volcanoes over subduction zones.

• Although there are ridges that might be construed as some type of mountain range, there are no strato-volcanoes on Mars.

• All volcanoes are shield volcanoes with gently sloping sides due to the low viscosity of the lava.

Tectonics vs. Plate Tectonics

• Remember tectonics is changes due to motions in the crust. This includes graben, fissures, stress fractures, volcanism.

• Plate tectonics is the whole sale motion of large portions of crustal materials. Like the motion of North and South America.

• Although it is very clear that the Tharsis bulge area has had lots of tectonism, there is little evidence of plate tectonics on Mars.

Why is Olympus Mons so big?

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1. Lack of thick atmosphere allows volcanoes to grow large on Mars

2. No strato-volcanoes means lava has to come out of shield volcanoes making them large

3. No plate tectonics so same lithosphere stays over the magma plume

Plate tectonics makes new volcanoes as crust moves over magma plume

Let’s use what we have learned• Mars is much smaller than the Earth. This

means that is also cooled much more rapidly, causing a thick crust to form rapidly.

When Earth’s crust was still molten, Mars already had a well established surface.

Let’s use what we have learned• Mars is much smaller than the Earth. This means

that is also cooled much more rapidly, causing a thick crust to form rapidly.

• (Surface Area/Volume)earth = 3/6371 = 0.00047

• (Surface Area/Volume)mars = 3/3397 = 0.00088

• Mars cooled faster than Earth by a factor of 2.• This set up a thick crust with little time for plate

tectonics.

• Mars was still hot on the inside but was not able to release this heat through plate tectonics.

• Instead a single, enormous magma plume developed in one region of Mars. The Tharsis Bulge.

• Mars was still hot on the inside but was not able to release this heat through plate tectonics.

• Instead a single, enormous magma plume developed in one region of Mars. The Tharsis Bulge.

• Mantle plume caused uplift of crust in the Tharsis region. Pressure from uplift allowed shield volcanoes to form, which contributed to layers of lava on top of the Tharsis region.

• This created great overlying weight in region.

• Eventually the magma plume subsided and the weight of the Tharsis region caused portions of the bulge to sink down.

• http://www.google.com/mars/

• Eventually the magma plume subsided and the weight of the Tharsis region caused portions of the bulge to sink down.

• http://www.google.com/mars/

• The result of portions sinking is an enormous graben feature that formed Valles Marineris.

• Uplift and retreat of Tharsis region likely happens multiple times.

• This activity pumped energy into the Tharsis region in the form of stress heat and underground magma chambers.

• There are signs of lava flow away from the Tharsis region. There is also evidence of water flow that originated from heated underground ice deposits.

• http://www.google.com/mars/

What about the North?

• There is a strange dichotomy between the northern and southern hemispheres on Mars.

• The crust in the Southern hemisphere is very thick and old. The Northern hemisphere is very low.

• What about relative age of the regions?

Possibilities

1) Giant collision with asteroid that removed the crust in the Northern Hemisphere.

This is similar to the theory that Earth had two moons which gently collided and spread a thicker crust onto the farside of the Moon.

Possibilities

1) Giant collision with asteroid that removed the crust in the Northern Hemisphere.

2) Entire global lithosphere of Mars rotated. This could happen if magma plume builds up crust from underneath very early on in Mars history.

Possibilities

1) Giant collision with asteroid that removed the crust in the Northern Hemisphere.

2) Entire global lithosphere of Mars rotated. This could happen if magma plume builds up crust from underneath very early on in Mars history.

3) Could the Northern hemisphere be an ancient ocean bed?

• What would be required for the Northern Hemisphere to be the floor of an ancient ocean?

What would be required for Mars to have an ocean?

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1. Lots of water2. Thick atmosphere3. No polar ice caps4. Living creatures

Did Mars ever have a thicker atmosphere?

Evidence would be if there was ever standing water on Mars.

Spirit and Opportunity think so.

Both landed on Mars in January 2004.Opportunity is still actively researching Mars.

Spirit/Opportunity rovers

Hematite signal from orbitHematite is an iron compound which typically

forms in the presence of water

The Opportunity landing site

on Meridiani Planum

Eagle Crater

Inside Eagle Crater

Blue Berries – Hematite spheres

Abrasion tool collects samples

Spectral analysis confirms Hematite

Analysis of rock shows Sulfur, Chlorine and Bromine: All of which are soluble in water

High sulfur suggests basalt rocks (Jarosite) that have been dissolved in water

Triple combination

• The triple combination of sulfur, chlorine and bromine make the evidence clear that water was present in the rocks.

• These three chemicals are deposited when water evaporates and leaves them behind.

• Combining this with the Hematite which formed within the sedimentary rock layers is conclusive that water was on the surface at Meridiani Planum.

Standing water about 3.7 billion years ago.

• If there was standing water in the distant past on the surface of Mars, then what happened to the atmosphere?

Mars Science LaboratoryLanded on Aug 5, 2012

Determine whether life ever arose on Mars

Characterize the climate

Characterize the geology

Landing site for MSL – Gale Crater

• Landing site

Smectite clay on earth from 100 million years ago.

Model for the formation of Gale crater.

Running water on Mars

So it appears that there was standing water and running water on Mars in the distant past.

Why is the Martian atmosphere so very thin Today?

• What does having an atmosphere depend on?

• Venus has a very thick atmosphere. The Earth has a substantial atmosphere and Mars has a very thin, low density atmosphere.

• Mercury and the Moon have no atmosphere.

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1. The planet must be massive

2. The planet must have water

3. The planet must have plate tectonics

• The Earth has an atmosphere but the Moon does not.

• The mass of the planet dictates the force of gravity present to hold the gasses from escaping into outer space.

• The Earth is not massive enough to hold Helium in the atmosphere. It escapes into space.

• Mercury has no atmosphere but Saturn’s largest moon, Titan, which is virtually the same size as Mercury, has a thick atmosphere.

Titan has 1.45 times the Earth’s atmospheric pressure

• Mercury has no atmosphere but Saturn’s largest moon, Titan, which is virtually the same size as Mercury, has a thick atmosphere.

• Given this evidence, what else must having an atmosphere also depend on?

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1. Must also depend on having water

2. Must also depend on having geologic activity

3. Must also depend on the temperature

• It depends on the temperature of the planet.• Near the Sun, where temperatures are high it

is easier for atmospheric gasses to escape into outer space because the gasses are heated and therefore moving rapidly.

• Far from the Sun, where temperatures are very low, the atmospheric gas motions are very slow and easy for a smaller planet to hang onto.

• Mars is massive enough and far enough from the Sun that it should have held on to much of its atmosphere.

• There is evidence that Mars use to have a thicker atmosphere, especially if there was once liquid water on the surface.

• Also, volcanism releases gasses such as CO2, H2O and methane (CH4). This would add to the atmosphere.

• Something else must have happened.

Magnetic Field of the Earth

• Magnetic fields arise from the motion of charges.

• When free electrons flow through a wire, the wire produces a magnetic field.

Compasses positioned around current carrying wire.

The right hand rule.

Inside this current loop, which way does the magnetic field point?

Current

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1. To the left2. To the right3. Up4. Down5. Out of the screen6. Into the screen

The Earth has a liquid core with free electrons circulating around.

• When the molten material cools and sinks back toward the inner core, the rapid rotation of the Earth causes the flow to follow a helical path.

No, or slow, rotationRapid rotation

Field is actually very complex

• So to have a magnetic field for a planet, you need a molten core and you need the planet to rotate quickly in order to set up the currents.

• Venus has no measureable magnetic field.• It rotates on its axis, once every 243 Earth

days.

• Does Venus have a liquid core?

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1. No2. Yes3. Maybe

Impossible to say for sure.

• Venus does show signs of geologic activity and it is the same size as the Earth.

• It likely has a liquid core like the Earth does.• But the rotation is so slow that it can not set

up helical currents that would produce a net magnetic field.

• Mars has a rotation period of 24 hours and 37 minutes. (Virtually the same as Earth).

• It’s magnetic field is 800 times weaker than the Earth’s magnetic field.

• What can you conclude from this?

• Mars probably no longer has a liquid core.• It is likely that it cooled to the point of being a

solid.

• How will this effect things on Mars?

The Earth gives us clues – The Aurora Borealis

Fast moving, charged particles from the sun (solar wind) are defected by the Earth’s magnetic field. Some particles are redirected to the Earth’s poles.

• When these charged particles hit the molecules in the Earth’s atmosphere the air molecules become ionized (lose an electron).

• The electrons recombine with the ions and this produces light (electromagnetic radiation).

• This is why the Aurora Borealis is typically seen over the poles of the Earth.

The magnetic shield

• The magnetic field of the Earth prevents most of the solar wind from reaching the Earth’s atmosphere. They are generally blocked at a distance which is over 10 times the height of the atmosphere.

• This prevents the top of the atmosphere from being completely ionized.

What about Mars?

• Mars has only an extremely weak magnetic field.

• As a result there is almost nothing to prevent the top of the atmosphere from becoming ionized.

• Now consider what will happen next.

What happens to these positively charged particles?

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They repel each other and spread out

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• With the repulsion and the energy added by the impact of the solar wind, molecules gain enough speed to escape the planet.

• Over very long periods of time, (hundreds of millions of years) the atmosphere of Mars is lost to outer space.

• With the repulsion and the energy added by the impact of the solar wind, molecules gain enough speed to escape the planet.

• Over very long periods of time, the atmosphere of Mars is lost to outer space.

• But there is a problem with this model.

Venus has90 times the Earth’s atmosphere

Mars has0.006 times the Earth’s atmosphere

Define the Problem

1. Venus is hotter than Mars, so why does it have a thick atmosphere?

2. Mars has had volcanic activity like Venus, it should have a thick atmosphere

3. Venus has no magnetic field, why does it have a thick atmosphere?

• When a planet has a thick atmosphere, like Venus does, some molecules are ionized and lost, but those that are not lost build an ionosphere around the planet.

• Since these ions are moving charges they create a magnetic field that acts as a shield against the incoming solar wind.

• Some atmosphere is lost, but at a very slow rate.

• Mars with a thin atmosphere has less of an ionosphere to protect it.

Mars does have weak, local magnetic fields in the rock

The magnetic field is locked in the rocks in the southern hemisphere, but not really seen in the Northern hemisphere.

Why is this?

• Over time Mars has lost most of its original atmosphere through these types of processes.

A Possible History of Mars

• Mars is small relative to the Earth and therefore cooled more quickly.

• It formed a thick crust which locked in the internal heat and prevented plate tectonics from occurring.

• This early crust is still seen in the Southern Hemisphere where the surface has a large crater density

• In the first billion years, one extremely large magma plume forms and begins to uplift the Tharsis bulge area.

• Volcanoes begin to form and release gasses which build up the atmosphere.

• The atmosphere becomes thick enough for liquid water to exist on the surface.

• At the same time, tectonic activity and magma reservoirs heat water ice in the crust allowing it to flow and accumulate in the Northern Hemisphere lowlands.

• As time goes by Mars interior cools some more and the major geologic activity begins to shut down.

• As this is happening Mars core solidifies and it loses its protective magnetic field.

• As the atmosphere thins Mars becomes cold and there is less opportunity for liquid water.

• Volcanism begins to wane and there is less out-gassing to replenish the atmosphere.

• About 2-3 billion years ago, Mars becomes a cold, dry planet with only smaller localized volcanism.

What about life?

Best possibilityH2O + CO2 – CH4 +O2

Geologic or Biologic?

• Heat of summer is affecting the surface of Mars in some way.

• If methane is from a geologic process, it must be in the presence of liquid water.

• It could also arise from microbes in underground water reservoirs that become active in the summer.

• The Martians may still be around.