11

The Nature of Mars

Goals• Mars attacks! The romance of Martian civilizations• What we know of Mars today• What we suspect of Mars past

22

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!

AntiquityThe 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.

1784William Herschel (UK) gave a talk on Mars, describing the conditions enjoyed by Martian “inhabitants.”

33

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.

44

Mars attacks!

1894-1895Percival Lowell (USA) built Lowell Observatory, and started mapping canals.

1898H.G. Wells (UK) wrote War of the Worlds.

1899Nikola Tesla (Austria/US) detects radio transmissions from Mars?

1905Vesto Slipher and Carl Lampland (Lowell observatory assistants) photographed the canals.

1920Seth Nicholson and Edison Pettit (Mt. Wilson Observatory) try to measure Mars’ surface temperature—they get 60-120ºF.

1930Eugène Antoniadi (Turkey), formerly a canal-proponent, concluded that the canals were optical allusions.

55

Mars attacks!

Perhaps…M̶Mars was a dry, semi-desert world;M̶During the spring, the polar ice would melt, watering the planet;M̶Martians had built a huge canal system to sustain agriculture;M̶Seasonal changes were due to the minimal water being used;M̶Martians might be desperate for water, and the Earth is water-rich.

66

Mars attacks!

1938Orson 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.

77

Mars attacks!

1950sAnti-communism fears recast as anxieties about invasions from Mars.

1976-1982Viking sees the “Face on Mars.”

2001-2007Mars Global Surveyor.

CurrentWill Mars ever leave us alone?

88

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– 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!

99

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)

1010

What we know of Mars today

Geological activityMars 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.

1111

What we know of Mars today

Polar capsPermanent 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.

1212

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.

1313

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?

1414

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.

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?

Big questions that remain