Lesson4c

Other processes on Mars

Dendritic (tree-like) drainage valleys

Earth Mars

Stream-lined islands

Fluting – Longitudinal lines caused by fluid flow

Fluting – Longitudinal lines caused by fluid flow

Summary

• We have seen that, today, liquid water can not exist on the surface of Mars. The atmospheric pressure is too low.

• We have seen that there are ancient features on the surface of Mars that look like water flow features, including meander, ox-bow lakes, dendritic drainage systems, streamlined islands and fluting.

• Given these observations what can you conclude about the these features and the planet Mars?

.

1. The feature were made by wind. Liquid water can’t exist on surface.

2. The features were made by lava. Liquid water can’t exist on surface

3. The features were made by liquid water in the past when Mars must have had a thicker atmosphere.

4. The features were made by water ice, or maybe liquid water under ice.

Answer #1

• Mars does have a wind that over enormous periods of time can cause erosion of the surface.

• This produces wind-blown (aeolian) features.

Martian Yardangs

Aeolian features tend to be linear

Wind erosion shows underlying rock strata

More wind-

sculpted, rock strata

on Mars

Dust braids on crater wall

North Pole – spiral structure from wind

Wind-blown Sand Dunes

Difficult for wind to make…

• Aeolian features tend to be more linear, although sometimes wind can be channeled and cause certain features that look similar to fluid flow.

• Aeolian processes usually can not account for characteristics such as meander and dendritic systems.

What about lava flows?

• It is clear that lava has flowed from volcanoes and in various regions on the surface of Mars in the distant past.

• Can lava make the flow features that are observed on Mars?

• There is some evidence from the Moon and Venus that it is possible.

Neither Moon nor Venus have water.

Lunar Rille Lava flow on Venus

Venus – Oxbow and streamlined

Oxbow Lava feature

Streamlined Island

Moon – Meandering channels

Moon – Dendritic

lava channelsin Mare Imbrium

Did lava cause the channels?

• It is very likely that graben and collapsed lava tubes cause many large channels on Mars.

• But the large outflows and intricate dendritic channels on Mars appear more likely to be caused by water than the features seen on the Moon and Venus.

If Water is the cause, how? Liquid water can’t exist on the surface of Mars.

• For liquid water to exist long ago, the pressure had to be higher than it is today.

• Mars might have had a thicker atmosphere in the distant past which also would have increased the temperature on Mars

• Water could have come out of sapping springs, then the water would have frozen on top and allowed liquid water to flow under the ice causing erosion.

• How can liquid water exist under ice on Mars?

Water trapped under ice can exist because the local pressure is much higher than the atmospheric pressure. If water starts to evaporate, it will increase the pressure under the ice, keeping it in a liquid state. Also, the ice would insulate the water allowing it to stay warm longer.

ICE

Soil

Water

• Another possibility is that glaciers cut the channels. This only requires lots of frozen water.

Active glacier on Mars – Spectroscopic observations confirm this is water ice.

Glacier markings – Apparent uphill flow

Uphill

• Glaciers move along the surface because of gravity. How can it possibly flow uphill?

• Portions of glaciers can flow uphill, if the pressure behind the glacier is great enough.

• The weight of glaciers do compress the ground, which does rebound when the ice is gone. (Example: Lake Erie and Niagara Falls)

• If any of the water/ice possibilities are the cause, where is all the water on Mars today?

Clues of water… North Pole on MarsIn summer mostly water ice is all that

remains

CO2 frostRemnant H2O ice cap

Temperatures at the poles in summer are high enough to allow CO2 to sublime. The

result is dust storms.

Water ice at bottom of crater

Splosh craters – Many of the craters on Mars have strange debris aprons.

Splosh from water hitting the floor

Splosh crater

on Mars

• If there are large quantities of frozen ice under the surface of Mars, then when a meteorite impacts the surface the heat of the impact can melt the ice. This causes a slurry of soil and liquid water to flow out away from the impact and then refreeze.

• This is thought to be the reason for “splosh” craters.

Evidence from new craters on Mars

• This is a new crater on Mars. It was not seen in previous images taken by the Mars Orbiter camera.

• This could be water ice that has been exposed because of the impact.

• What would you try to do in order to tell if this is likely to be water ice?

.1. Watch to see if puddles of water

form when the temperature is hotter.

2. Watch to see if substance sublimes away.

3. Go to Mars and see if you can build a snowman.

Watch to see if the white substance sublimes away. Below is a brand new, 20 foot wide crater

on Mars.

October 18, 2008 January 14, 2009

The Phoenix Lander at North Pole

Four Martian

days go by and

substance is

subliming

Four Martian

days go by and

substance is

subliming

Hydrogen detection

under surfaceof Mars

Mars Reconnaissance OrbiterHigh Energy Neutron Detector

• Cosmic Rays are fast moving charged particles that come from many astrophysical sources. (one source is the Sun).

• When these particles violently collide with atomic nuclei on the surface of Mars, neutrons are released from the nucleus of the atom.

• The High Energy Neutron Detector measures the amount of neutrons coming from the surface of Mars.

• What would happen when the cosmic ray hits a hydrogen nucleus?

.1. No neutrons will be released.2. A larger signal will occur than normal

since hydrogen has the smallest nucleus.

3. The hydrogen will explode due to nuclear fusion.

4. The hydrogen will bond to the cosmic ray and make water.

Neutrons are not released. Hydrogen has no neutrons. The neutron signal is

suppressed

• Most hydrogen atoms on Earth are not free. They are locked up in molecules of water.

• H2O

• Places where the neutron signal is very low on the surface of Mars, is an indication of soil that has a high percentage of water.

• Cosmic rays only penetrate about 1 meter deep on the surface.

• This map shows where there is water under the surface, at a depth of 1 meter.

How should we interpret this data?

.1. All the underground water on Mars is

located near the poles.2. Places where lots of underground water

is today, is likely where oceans on Mars use to be.

3. Near the equator on Mars there is little water at a depth of one meter.

• 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.