The Nature of Mars
Goals
Mars attacks! The romance of Martian civilizations
• What we know of Mars today
• What we suspect of Mars past
•
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Mars attacks!
Mars, perhaps more than any other astronomical object, has been
associated with extraterrestrial civilizations.
Making observations of this small, subtly colored planet is
exasperating!
Antiquity
The Roman name “Mars” connects the blood-red planet to war.
1610-1720 (post Galileo)
Astronomers note that Mars is about the same size as the Earth, has a
rotation period about 24 hours long, has polar caps, and dark
markings that change with the Martian seasons—all very similar to
gentle Earth.
1784
William Herschel (UK) gave a talk on Mars, describing the
conditions enjoyed by Martian “inhabitants.”
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Mars attacks!
1869
The 192km-long Suez Canal was built, linking the Red Sea to
the Mediterranean Sea in Egypt. This was a huge engineering
feat, and in this era, canals were identified as the peak of
human engineering abilities.
1877
Asaph Hall (US) discovered two moons of Mars, and named
them Phobos and Deimos (Fear & Terror).
1877
Giovanni Schiaparelli (Italy) published maps showing 79
linear, streaky canali. Schiaparelli presumably meant canali
to indicate “channels”, but this was frequently translated as
“canals.”
1894
Edward Barnard (US) observed Mars but could not detect the
elusive channels.
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Mars attacks!
1894-1895
Percival Lowell (USA) built Lowell Observatory, and started mapping
canals.
1898
H.G. Wells (UK) wrote War of the Worlds.
1899
Nikola Tesla (Austria/US) detects radio transmissions from Mars?
1905
Vesto Slipher and Carl Lampland (Lowell observatory assistants)
photographed the canals.
1920
Seth Nicholson and Edison Pettit (Mt. Wilson Observatory) try to
measure Mars’ surface temperature—they get 60-120ºF.
1930
Eugène Antoniadi (Turkey), formerly a canal-proponent, concluded
that the canals were optical allusions.
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Mars attacks!
Perhaps…
̶ Mars was a dry, semi-desert world;
̶ During the spring, the polar ice would melt, watering the planet;
̶ Martians had built a huge canal system to sustain agriculture;
̶ Seasonal changes were due to the minimal water being used;
̶ Martians might be desperate for water, and the Earth is water-rich.
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Mars attacks!
1938
Orson Welles broadcasted a radio
dramatization of War of the Worlds;
• Commercial-free broadcast—no
commercial interruptions.
• The format was of a series of news
broadcasts interrupting a concert.
• Many viewers tuned in late and
missed the introduction.
• Widespread panic, concern,
flooded phone lines.
• 100,000-1.7 million were duped.
• Poor Cement, Washington!
• Reports of UFOs rise.
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Mars attacks!
1950s
Anti-communism fears recast as anxieties about invasions
from Mars.
1976-1982
Viking sees the “Face on Mars.”
2001-2007
Mars Global Surveyor.
Current
Will Mars ever leave us alone?
We now know that Mars is full of joy and love!
Landers
– Viking 1, 2 (USA; 1975)
– Mars Pathfinder wi/Sojourner rover (USA; 1996)
(now called the Carl Sagan Memorial Station)
– MER-A/B (Spirit & Opportunity*) (USA; 2003)
– Phoenix (USA; 2007-2008)
Orbiters/Flyby missions
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Mariner 4, 6, 7, 9 (USA; 1964-1971)
Mars 2, 3, 4, 5, 6, 7 (USSR; 1971-1973)
Phobos 2 (USSR; 1988)
Mars Global Surveyor (USA; 1996)
2001 Mars Odyssey (USA; 2001)*
Mars Express (ESA; 2003)*
Rosetta (ESA; 2004)*
Mars Reconnaissance Orbiter (USA; 2005)*
More missions are planned, including one-way
missions of death!
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What we know of Mars today
What have we learned?
Atmosphere & surface conditions
– 96% CO2
– 0.007 atm
– -50ºC (but up to freezing)
– 0.38 Earth gravity
– Water in a glass would freeze, or evaporate.
– Large dust storms as CO2 cycles pole to pole
Any hopes for water would require some kind of special
conditions, such as local volcanism.
Otherwise, all the water on Mars is locked in the polar ice caps
(and possibly extensive permafrost)
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What we know of Mars today
Geological activity
Mars has enormous volcanoes—the largest in the solar
system! Olympus Mons is 600 km across, 26 km tall
(3×Everest!).
Mars has huge cracks; Valles Marineris—4000 km long,
200 km wide, 7 km deep.
These are indications of primitive tectonics.
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What we know of Mars today
Polar caps
Permanent polar caps of H2O possibly 1 km thick. The
southern polar cap also has several meters of CO2 dusting
the top of the cap. During the winter, an additional 1
meter or so of CO2 accumulates, over a broad area.
While the polar caps are always mostly water (by mass)
the winter polar ice caps are much larger in extent.
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What we know of Mars today
Evidence of liquid water
– Water-weathered craters, channels;
– Hematite/jarosite nodules (blueberries);
– Recurring slope lineae (RSL) have been
observed on equatorial-facing crater walls,
during the height of summer. Brine-water
flows have been suggested.
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What we suspect of Mars past
Water was stable on Mars 2-3 b.y.a.
How could water be stable on Mars? You would need a much thicker
atmosphere. An atmosphere of CO2 about 400 × thicker than the
current atmosphere (3 atm) would give rise to an adequate
greenhouse effect to warm Mars to provide stable water.
– Such an atmosphere could have been produced by extensive
volcanism.
– Even so, this would require astronomers to modify their accurate
solar brightening models.
– Perhaps the warm periods were intermittent? Without a large
moon, axial tilt changes could cause climate changes.
Where did this putative CO2 and H2O go?
– Solar stripping?
– UV disassociation of the H2O?
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Take-home messages
In the past, Mars was habitable, for at least tens of millions of years, and
perhaps much longer.
This was at the same time that life evolved on the Earth.
Big questions that remain
Was water available (A) for long continuous stretches, or was it available (B)
only during short intervals?
If “A”, the only thing that might stop, or allow, life from developing is luck.
If “B”, could it have developed over episodes?
Were there energy-rich locations, protected from UV radiation?
If life evolved, did it develop methods to cope with Mars’ changing climate?
Is life still on Mars, perhaps underground or near volcanic thermal sites?
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