Phys 214. Planets and Life

Dr. Cristina Buzea

Department of Physics

Room 259

E-mail: cristi@physics.queensu.ca

(Please use PHYS214 in e-mail subject)

Lecture 25. Searching for life in our Solar system.

Mars I

March 17th, 2008

Calendar update and assignment no 3!

Assignment no 3.

This is an assignment related to Lecture 4 - Methods of Modern Science! You have to show you

can be objective with your peers, that you understand the methods of moderns science in order

to evaluate the debates going on in science.

Every student will be a member of the Committee of the Pretend Conference on Astrobiology.

Her/His job is to read and rank the abstracts submitted to the Conference.

Your mark for this assignment will reflect how well you were able to judge your peers, based on

comparison to my ranking and with the rankings made by your colleagues. There are no low

marks for this assignment.

All the abstracts will be posted Wednesday on the Phys 214 website. You have to give mark based

on the scientific content and not on the literary merit. Maximum mark - 10, minimum - up to

you. I will e-mail to each of you an Excel sheet you have to fill in with the marks.

Contents

• Textbook pages 261-290

• Biological tour of our Solar system - Mars

Biological tour - Mars

Mars Earth

Mass (MEarth) 0.107 1

Escape velocity (km/s) 5 11.2

Orbital semimajor

axis (AU) 1.52 1

Orbital inclination (o) 1.9 0

Orbital period (days) 686 365

Axial rotation (days) 1.03 0.997

Axial inclination (o) 25.2 23.5

Radius (km) 3390 6371

Density (x103kg m-3) 3.93 5.51

Surface gravity (m s-2) 3.7 9.8

Mean surface T (K) 223K (-50C) 288K (15C)

Max surface T(K) 293K (20C) 310K (37C)

Min surface T(K) 133K (-140C) 260K (-13C)

Atmospheric surface

pressure (bar) 6x10-3 1

Atmosphere 95% CO2, 2.7% N2 N2, O2

Satellites 2 1

Largest known

surface feature Mount Olympus Mt. Everest

Vales Marineris (8 km above

sea-level)

Mars moonsprobably capturedasteroids; toosmall to stabilizeMars’ axis tilt

The lack of oxygen implies Mars lacks an

ozone layer – unprotected from UV radiation.

Mars

Liquid water cannot exist for very long on the surface of Mars today

because its atmosphere is too thin (pressure too low).

Seasons and polar caps on Mars

Seasons on Mars are similar to those on the Earth but twice as long.

Seasonal variations on Mars are due both to its axis tilt and its changing distance from the Sun.

Mars is closer to the Sun on average during summer in the Southern Hemisphere -> Southern

Summer on Mars will be short & hot.

Mars is closer to the Sun on average during winter in the Northern Hemisphere -> Northern

Winter on Mars will be short & mild.

Seasons and polar caps on Mars

Summer Northern Hemisphere =

small Northern polar cap (water

ice) &

large Southern Polar cap (CO2 ice

overlaying water ice).

The residual polar caps on Mars

are made of water ice.

The seasonal polar caps on Mars

are made of carbon dioxide

ice.

Mars dunes

Defrosting sand dunes.

As spring dawns on the Northern Hemisphere of Mars, dunes of sand near the pole are

beginning to thaw. The carbon dioxide and water ice actually sublime in the thin

atmosphere directly to gas. Thinner regions of ice typically defrost first revealing sand

whose darkness soaks in sunlight and accelerates the thaw. The process might even

involve sandy jets exploding through the thinning ice. By summer, spots will expand to

encompass the entire dunes.

Mars dunesField of spotted polar dunes spanning about 3

km near the Martian North Pole.

Mars - Global dust storms

During summer in the Southern hemisphere of Mars, winds travel from the South Pole to the North

Pole. Pole-to-pole winds on Mars cause: local and global dust storms, and dust devils.

Polar temperatures at the

winter pole are very low

(minus –130oC) that CO2

condenses into dry ice,

forming a polar cap of

CO2 – a meter thick

extending as far south as

latitude 40o.

Frozen CO2 at the

summer pole sublimates

into CO2 gas, leaving

only a residual polar cap

of water ice.

Atmospheric pressure

increases at the summer

pole compared to the

winter pole, driving

strong pole-to-pole winds.

Mars – Global dust storms

Opportunity rover photographed the edge of Victoria Crater as dust made the Martian airincreasingly opaque.

Windy dust storms are blocking much needed sunlight from reaching the solar panels of boththe Spirit and Opportunity rovers exploring Mars.

Mars - Dust devils

The surface of Mars appear

to have been shaped by

liquid water – Mars must

once have had a much

hospitable climate.

The Southern hemisphere has a higher elevation and is covered with

impact craters.

The Northern hemisphere has a lower elevation and is relatively

smooth,with fewer craters.

Southern highlands are much older surface than the northern plains.

Mars – major geological features

Why volcanism affected the northern plains so much compared to southern

highlands and why they differ so much in elevation?

Tharsis region = bulge most likely formed by a plume of molten mantle material rising to the surface.

In the Tharsis region of Mars we find huge volcanoes like Olympus Mons.

The most likely origin of the Valles Marineris on Mars - a tectonic fracture associated with theformation of the adjacent Tharsis bulge.

Northern plains show features characteristics of lava flows – eruptions covered up older impact

craters.

Volcanism = the most

important geological

process that removed

craters from the Martian

surface in the past

(tectonics and erosion

played some roles as well).

Wind erosion = the most

important geological

process occurring on Mars

today.

Ancient water erosion

features on the surface of

Mars suggest that the

planet must have had a

much warmer, thicker

atmosphere in the past.

Mars – evidence of volcanism, water, wind erosion

Geological Eras on mars from crater counts

Frequency of volcanic eruption decreased

steadily since 3.5 billion years ago – because

Mars is a small planet and it lost fast its

internal heat.

Counting craters on the slope of Tharsisvolcanoes indicated that they have beeninactive for at least tens of millions of years.

Radiometric dating of martian meteorites shoesome of them are made of volcanic rocks thatsolidified 180 million years ago – quite recent.

Mars probably still retains some of its internalheat, enough to melt some underground iceinto water.

The best place to find life on Mars todaywould be in geologically active areas likeTharsis where subsurface water may exist.

Evidence of volcanism

Mount Olympus – probably the largest

volcano in the solar system – base

600km, 26 km above average

surface, 80 km wide caldera.

Valles Marineris

Valles marineris –

4,000 km long, 200

km wide, 7 km deep.

Tectonic stresses led

to cracking of the

surface accompanying

the uplift of adjacent

Tharsis bulge.

Some features of the

valley – layering –

probably caused by

lava or by deposits of

sediments.

Some places are very

deep, probably the

walls were several km

underground, exposed

to subsurface liquid

water.

Valles Matineris may be among the best places to look for fossil evidence of past martian life.

Mars atmosphere

The color of the martian sky depends on how much dust is in the atmosphere.

The air on Mars scatters visible sun light like the air on Earth –more blue than red. But

because there is less air on mars – it scatters less the light.

The dust in the atmosphere has an opposite effect – absorbs blue light – final color of the shy

= brownish-pink.

The thinning of the Martian atmosphere occurred due to:

- the photodissociation of water molecules by ultraviolet light in the atmosphere;

- the stripping of the atmosphere by solar wind particles from the Sun;

- atmospheric gases being blasted into space by large impacts.

Photograph of Martian Sunset taken from the Gusev crater. NASA's Mars Exploration Rover: Spirit

Exploration of Mars – evidence of water

The most probable places for water evidence were chosen as landing sites.

Mars Pathfinder landing site - the surrounding rocks are scattered and stacked against each

other. This suggests that the spacecraft landed in an ancient floodplain

Gusev Crater was chosen at the landing site for the Mars Exploration Rover Spirit because

was probably once filled with water.

Meridani Planum was chosen at the landing site for the Mars Exploration Rover Opportunity

because remote sensing measurements from the Mars Odyssey orbiter indicate that

deposits of the mineral hematite (which commonly forms in water) are present.

The red color of the

rocks is caused by an

abundance of iron in

the soil. The Martian

surface is covered by

rocks, huge craters,

fantastic canyons, and

gigantic volcanoes that

dwarf any on Earth

Craters

Mars exploration

Mars exploration

Mars Exploration Rover "Spirit“

Results from the Mars

Exploration Rovers Spirit

and Opportunity suggest

that liquid water was once

plentiful on the surface of

Mars.

Recent observations by the Mars

Odyssey orbiter show that

most of the water on Mars

today is frozen beneath the

surface

Mars and Earth dust storms

Evidence of water on Mars

The branching nature suggests they were carved gradually, so liquid water was stable at or just

below the surface.

Because the low temperature and low atmospheric pressure make liquid water unstable on the

surface of mars today, we conclude that mars must have had a much warmer and thicker

atmosphere some time ago.

Features looking like dry riverbeds

– almost certainly carved by

running water (runoff after the

rainfall, erosion by water rich

debris flow, or from an

underground source).

Crater counts in the channels ->

the water has not flowed through

them since 2-3 billions years ago.

Evidence of water on Mars

Surface evidence – from Mars rovers

Spirit and Opportunity indicate water

was abundant once on Mars.

Tiny spheres – nicknamed

“blueberries” – formed in standing

water – contain iron-rich mineral

hematite and other minerals that form

in water.

Chemical analysis suggest formation

in an acidic, salty environment – sea

or ocean.

The layering of the sedimentary rocks

suggest a changing environment of

waves or wind.

Evidence of water on Mars

The wall of Endurance crater

shows bedrock layers altered

by water. Close-up shows

hematite “blueberries” eroding

out of the rocks.

Evidence of Water on Mars

Unusual Silica Rich Soil = such soil on Earth is usually created by either volcanic steam or a hot spring.

Evidence of water on Mars

Crater counts suggest that little or no rain has fallen during the last 2-3 billion years.

Many surface features show evidence of more recent water flows.

Despite the fact that liquid water is unstable on mars surface, a large quantity of water that suddenly

erupts onto the landscape may take a short time to freeze or to evaporate.

Catastrophic floodwater – from beneath the surface – could survive long enough to carve channels

and other surface features.

Evidence of water on Mars

Evidence of water on Mars

The presence of channels carved out on the

slopes of large Martian volcanoes is

consistent with the existence of past

underground pockets of water.

Evidence of water on Mars

Evidence of recent water flow on Mars

Evidence for very recent water erosion on Mars comes from the observations of gullies in the rims of

craters. Subsurface ice melts and gushes out from crater walls before freezing or evaporating.

Evidence of water on Mars

Frozen seas of ice just beneath the surface

Evidence of water on Mars

Hydrogen content of martian surface with neutron

detectors, indicating possible water ice within

a meter of the surface.

Map showing Mars color-coded by

elevation. Blue are below average

surface level, red and brown are the

highest.

Mars climate history

Once Mars was warmer – because the greenhouse effect – volcanic outgassing of CO2 and water.

Mars today could have liquid water if it has a 400 times a denser CO2 atmosphere than now

(surface pressure of about 3 bar and temperatures above freezing).

Mars lost its much denser atmosphere after loosing its magnetic field (as the planet cooled, the

core solidified and lost its magnetic field).

Much of the water was lost as well because Mars lacks an UV absorbing atmosphere. Atmospheric

water is easily broken apart by UV radiation in H2 and O2. H2 is lost by thermal escape

because is very light! Part of the oxygen was stripped by solar wind and the rest reacted

chemically with the rocks – rusted red rocks.

Mars climate changebecause of itsrelatively small size.

Mars climate change

The Earth’s axis tilt has changed little over its history due to the stabilizing effects of the Moon’s

gravity

Compared to the Earth, Mars has experienced wild swings in its axis tilt over relatively short time

periods. This is because of its proximity to Jupiter and its lack of a large moon.

The extent to which Mars has been habitable essentially is related to the length of time liquid water

has been present at or below its surface.

Mars still undergoes significant climate change over

geologically short period of time – hundreds of

thousands of years – from changes in axis tilt!

Models suggest that martian axis tilt varies

over time from 0o to 80o.

Thinner atmosphere

Weaker greenhouse effect

Warmer Mars

Stronger greenhouse effect

Is Mars habitable?

Is Mars habitable? It has energy sources,

however we need to have liquid

water.

Mars has abundant liquid water – was

habitable before 2-3 billion years

ago. But for how long was habitable?

Long enough for indigenous life to

arise, or only for short intermittent

periods?

We have evidence that pockets of liquid

water might exists today

underground, kept warm by

remaining volcanism.

Mars might be habitable when its axis tilt

is large.

1976 Viking landers experiments - Life on Mars?

Carbon Assimilation Experiment – assumption -> living organisms in the soil should

incorporate carbon from atmospheric gases.

Gas Exchange Experiment - living organisms in the soil should give off gases when they

metabolize nutrients.

Gas Chromatograph/Mass Spectrometer Experiment - soil with living organisms in it should

contain organic molecules.

Labeled Release Experiment - radioactive gases should be produced when radioactive

nutrients are added to a soil sample - the only biology experiment on the Viking

landers which gave a positive result!

• Overall summary of the findings from the Viking biology experiments = the Martian

soil is chemically reactive but shows no signs of biological activity.

Before Viking left the

launch pad the same type of

Gas Chromatography failed

to detect organic matter on

a tested Antarctic soil,

despite the fact that a wet

chemistry analysis

confirmed the presence of

organic matter.

Life on Mars - Martian meteorite ALH84001

Evidence the Martian meteorite ALH84001 may have once contained life:

1) is highly magnified images of carbonate grains found inside reveal rod-shaped structures that look

much like terrestrial nanobacteria.

2) contains crystals of magnetite, with size, shapes matching those on Earth when made by

magnetotactic bacteria.

The claim of fossilized life in the Martian meteorite ALH84001 is controversial because there are many

possible nonbiological explanations for the observed evidence.

Martian meteorite

ALH84001 was

singled out for intense

study because it is a

very old rock, dating

back from the time

when Mars probably

had liquid water on its

surface.

It probably came from

Mars because contains

trapped gases with a

similar composition to

Martian atmosphere.

1) 2)Magnetite made by Earth bacteria

Mars magnetite

Life on Mars? – Methane on Mars

In 2004 ESA mission Mars Express detected methane gas on Mars.

Methane gas cannot last more than a few centuries in Mars atmosphere before chemical

reactions transform it into other gases.

This means Mars has an ongoing source of methane on or beneath the surface

Causes: comet impact, volcanic activity, and life!

Microscopic life on Earth produces methane.

Volcanic activity means that subsurface liquid water might exist to sustain life!

Life on Mars?

Dark pits, about 150 meters across and at least 78 meters deep, on the north slope of ancient

martian volcano Arsia Mons - thought to be related to collapse pits in the lava flow,

similar to Hawaiian volcano pit craters Black spots have been discovered on Mars that

are so dark that nothing inside can be seen.

Quite possibly, the spots are entrances to deep underground caves capable of protecting

Martian life, were it to exist.

Such holes and underground caves might be prime targets for future spacecraft, robots, and

even the next generation of human interplanetary explorers.

Life on Mars?

Mars: Left image was taken in visible-wavelength light. The other two were taken in thermal

infrared wavelengths, indicating the relative temperatures of features in the image. The center

image is from mid-afternoon. The hole is warmer than the shadows of nearby pits to the north

and south, while cooler than sunlit surfaces. The thermal image at right was taken in the pre-

dawn morning, about 4 a.m. local time. At that hour, the hole is warmer than all nearby

surfaces.

Earth: views of Devil's Throat pit crater on the upper east rift zone of Kilauea Volcano,

Hawaii. The crater is about 40 m in diameter.

The Face on Mars

The Face on Mars?

The Face on Mars?

In the mid-1970s, the Viking 1 orbiter discovered a

feature in the Cydonia region of Mars which

resembled a human face. The currently accepted

scientific explanation for this feature is that it is a

natural hill-like feature that simply looked like a

face using the low-resolution cameras installed on

Viking.

Next lecture

Movie on Mars exploration on Wednesday!