Mars
| A Near Miss for Life? | |
April 14, 2011, jeb
OUTLINE
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- Mars is the
4th Planet from the Sun
- semi-major axis ("radius") = 1.52 AU
-
1.38 AU at perihelion
-
1.67 AU at aphelion
-->(
large eccentricity)
- conjunction - Mars appears close to Sun in our sky
- opposition - Mars is on the opposite side of our sky to the Sun
- orbital period = 687 days (1.88 years)
- KEPLER'S LAW:
- (687/365)2 = (1.88)2 = 3.5 <-- square of the orbital period
- (1.52)3 = 3.5 <-- cube of the semi-major axis
- Fainter than Venus
- more than twice as far from Sun
- therefore, 1/4 as much light per square meter
- surface area = 30% of Venus
- reflectivity = 15% vs. 70%
- Radius = 3397 km = 0.53 Rearth
- Mass = 6.4 x 1023 kg = 0.11 Mearth
- => Density = 3900 kg/m3
- (more Moon-like than "terrestrial planet"-like, in this respect)
- Rotational Period = 24.6 hours
- Inclination of 24.0° (23.5° for Earth)
- note rotational period and inclination are Earth-like
- 1877 - Mars was unusually close to Earth
- Asaph Hall (US Naval Observatory) discovered two moons
- Italy: Giovanni Schiaparelli
- Observed network of linear markings (canali)
- translated into English as canals
- Thus began a long fascination with the Martian life
and fantasized "civilization"
-
Percival Lowell, in US
- Motivated by report of "canals", gives up successful Boston business
to build observatory in Flagstaff, Arizona
- devoted life to studying
"canals" and Martian intelligent society
- Mariner 4 (1965)
- First spacecraft to reach Mars
-
Viking 1 (1976)
- landed in Chryse Planitia
- in a windswept, gently rolling, rather desolate plane
- biological experiments to search for evidence of life
-
Viking 2 (1976)
- landed somewhat north of Viking 1 (Utopia)
- expect greater seasonal variations
- landing site
flat and featureless
- very rocky (more so than Viking 1 site)
- biological experiments to search for evidence of life
- Pathfinder (& Sojourner, landed July 4, 1997)
-
First Mars rover
-
landed at mouth of outflow channel
- rocks deposited by flood water
-
Mars Global Surveyer
- launched November, 1996
- start mapping, March, 1999
-
Mars Exploration Rover Mission
- Spirit landed on January 3, 2004, in a
rocky landscape
- Opportunity
landed halfway around Mars from Spirit
-
found rocks that had been very wet in the past,
after landing on January 23, 2004.
- The rovers were expected to last 3-6 months, but each continued to explore over a few kilometers and send data back for several years.
- Phoenix Mission
One discovery of these missions was that the surface of Mars contains much more
iron than the surface of the Earth. On Earth iron has gone toward the center of
the planet during differentiation, while this does not seem to have
occured as prominently on Mars
Another important result was that no evidence of life was found.
However, it is still possible that life resides within the
permafrost. Or that life existed in the past and has vanished from
the surface. Future missions will explore this issue more fully.
- Huge
shield volcanoes:
- Olympus Mons
- About 700 kilometers in diameter
- would cover all of Washington and half of Oregon
- Rises 25 kilometers above the surrounding plains
- largest volcano in the Solar System
- Deep canyons:
- North-south asymmetry:
- Northern Hemisphere:
lava plains
- Southern Hemisphere:
heavily cratered highlands
- THE MAJOR FEATURE:
-
Tharsis bulge
- size of North America
- near equator
- rises 10 km above rest of surface
- little cratering -> relatively new
(2-3 billion years)
- continent like - but not drifting
- => no sign of plate tectonics
- Impact cratering:
- wide spread cratering,
- eroded by the atmosphere
- appearance of craters (liquid splash)
suggest permafrost (water ice)
just below the surface
- Running water:
-
runnoff channels:
-
outflow channels:
- near equator
- from south to north
- catastrophic flood - enormous flow rates> 100xAmazon
- about 3 billion years ago
- Evidence for gullies formed relatively recently
- Ancient Ocean?
-
Polar Caps
- north and south
- residual cap
- seasonal variation
- dry ice (CO2)
- temperature remains below 150K
- Southern cap grows much bigger, due to
orbital
eccentricity and the
inclination of Mars
- 4000 km vs. 3000 km at maximium,
shrinking to 350-1000 km in summer
- Mars' has a weak magnetic field
- => about 1/800 of Earth
- (but rotation period is 24.6 hours)
- so -> core is non-magnetic
- or non-liquid
- or both
- planet probably never differentiated much
- - small size resulted in more
rapid cooling than Earth
- Mars has a very thin atmosphere
- (1/150 of Earth's atmosphere)
- 95.3% CO2 (by volume)
- 2.7 % Nitrogen
- 1.6% Argon
- 0.13% Oxygen
- 0.07% CO
- 0.03% Water (variable)
- surface temperature:
- noon, summertime 300K
- night-time - temp drops by 100K
- averge temperature about 50K lower than on Earth
- (Tearth=290K)
- low earth morning temperature often produce
water-ice "fog" in canyons
- little day-to-day variation
- except in southern summer
- => dust storms (occasionally
months-long)
- Composition of Mars' atmosphere similar
to Venus, yet
over 10,000 times thinner
- history must have been different
- would have acquired a secondary outgassed atmosphere early
in its history, as other terrestrial planets
- the runoff channels indicate that early (about 4 billion years
ago) Mars probably had a fairly dense atmosphere,
- complete with blue skies and rain
- over next billion years, atmosphere disappeared
- Reverse Greenhouse Effect
- CO2 dissolved in liquid water
- Mars cooled due to absence of
isolating atmosphere
- Mars has likely undergone the largest climate change in its
history of any of the inner planets
- Two very small moons:
- Phobos (fear) & Deimos (panic)
- named for the horses that drew the
Roman war god's (Mars') chariot
- Irregularly shaped
- Phobos: 28 km long & 20 km wide
- Deimos: 16 km long & 10 km wide
- Cratered
- Orbits at about 3 and 7 planetary radii
- (Earth's Moon orbits at about 60 radii)
- Both orbit synchronously
- tidally locked, like the Moon
- Both orbit prograde direction
- Phobos orbits in 7 hours 39 minutes
- Deimos orbits in 30 hours 18 minutes
- Large crater (called Stickney)
on Phobos
- Captured asteroids? Probably.
There has long been a fascination about life on Mars
-
Lowell's "charting of
canals on Earth and conviction that a civilization resides there
- Science Fiction writers have
written vociferously about life on Mars
Viking Experiments
- The Viking missions to Mars conducted three experiments to
detect life on Mars in 1976
- All three experiments are first produced positive results
- Careful study showed all results could be explained by inorganic (non-living) chemical reactions
- These experiments were only sensitive to life now living
Not sensitive to fossilized remains of past life
The Martian Asteroids:
- About a dozen meteorites from the surface of Mars have been found on
Earth
- (identified by gases trapped in rocks)
- 1984 - scientists discoverd a rock (
ALH84001) on Antarctic ice field
- 4.2 pounds (about the size of an Idaho patato)
- ALH84001 stored in cabinet for 8 years
- 1992 - detailed study of the rock - found (within a small region of the rock)
- organic molecules that might be associated with life
- iron sulfide and magnetite
- several minerals characteristic of biological activity
- tiny
tubular and
egg-shaped structures
resembling ancient
single-celled bacteria found on Earth
- These observations were announced August 7, 1996
- The history of ALH84001
- Age of rock: 4.5 billion years (oldest known rock)
- about 16,000,000 years ago meteorite struck Mars, ejecting this rock
into space
- this time is determined from the exposure to radioactive
nuclei in space
- 13,000 years ago, rock landed on Antarctic ice field
- 1984 - meteorite specialist drives up in snowmobile and finds the rock
- about ten years later
- geoligist identifies ALH84001 as coming from Mars
- and other scientists suggest it shows evidence of ancient life
- Evidence for life on Mars has not been accepted as FACT
- This evidence could all have been produced by chemical reactions
without any kind of life
- Could ALH84001 have been contaminated? (it sat on ice in Antarctica for 13,000 years
- More evidence is need to resolve this
- Some scientists have suggested that "if any rock is examined as closely as
ALH84001 has been, unusual properties will be found."
- Obvious related question:
- Did life emerge on Earth, or
- did it come from outer space (perhaps from Mars?)
- Many organic molecules are brought to Earth by comets, asteroids,
meteorites
- Every year
- tons of Martian material falls on Earth
- and material from Earth also falls on Mars
- It takes an average of about 10 million years to make the journey
Planet order from Sun
Orbital period
Semi-major axis
Mass
Radius
Density
Surface Gravity
Escape speed
Rotational Period
Inclination
Surface Magnetic Field
Surface Temperature
Number of Moons
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4
1.88 years (687 days)
1.52 AU
0.11 x Earth
0.53 x Earth
3930 kg/m3
0.38 x Earth
5.0 km/s
1.026 days
23.98°
1/800 x Earth
about 150-310 K
2 |
If You Went to Mars
Wear a space suit:
protects you from the sun's rays
-even though the sun is much
farther away from Mars than
from Earth,
- the planet's thin atmosphere does
not block harmful solar radiation.
Take an oxygen tank:
Mars does not have a breathable
atmosphere.
Your spacesuit would protect you from
lack of atmospheric pressure
It would insulate you against:
the cold: from 30° to -130°C
Bring water with you to drink,
although if you brought the proper
equipment you could probably get
some Martian water from the air
or the ground.
You would feel strange walking on
Mars because you would feel
much lighter than you do on Earth.
The ground would be dusty and red.
Huge sandstorms would occasionally
sweep over the red plains, darkening
the entire planet for days.
Instead of a blue sky, a dusty pink sky
would hang over you.
Mars is a close planetary neighbor
and is Earth-like in some ways.
It will probably be the first planet
visited by humans.
- Largest Volcano in the Solar System
- History of running water on the surface
- Largest historical climatic change of any of the inner planets
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