phys 214. planets and life - engineering physicsphys214/lecture26.pdfphys 214. planets and life dr....
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Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Lecture 25. Searching for life in our Solar system.
Mars I
March 17th, 2008
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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.
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Contents
• Textbook pages 261-290
• Biological tour of our Solar system - Mars
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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.
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Mars
Liquid water cannot exist for very long on the surface of Mars today
because its atmosphere is too thin (pressure too low).
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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.
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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.
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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.
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Mars dunesField of spotted polar dunes spanning about 3
km near the Martian North Pole.
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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.
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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.
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Mars - Dust devils
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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.
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Mars – major geological features
Why volcanism affected the northern plains so much compared to southern
highlands and why they differ so much in elevation?
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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.
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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
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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.
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Evidence of volcanism
Mount Olympus – probably the largest
volcano in the solar system – base
600km, 26 km above average
surface, 80 km wide caldera.
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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.
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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
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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
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Craters
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Mars exploration
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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
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Mars and Earth dust storms
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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.
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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.
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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.
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Evidence of Water on Mars
Unusual Silica Rich Soil = such soil on Earth is usually created by either volcanic steam or a hot spring.
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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.
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Evidence of water on Mars
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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.
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Evidence of water on Mars
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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.
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Evidence of water on Mars
Frozen seas of ice just beneath the surface
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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.
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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.
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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
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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.
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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.
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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
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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!
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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.
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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.
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The Face on Mars
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The Face on Mars?
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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.
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Next lecture
Movie on Mars exploration on Wednesday!