Lecture 5: Canali and Canals (God of War)

• Introduction • Vital statistics • Interior • Surface • Water, water, anywhere? Schiaparelli (1879), • Atmosphere , … • Life Actual Imagined

Mars - vital statistics Interior of Mars – the models 1) Iron core contaminated by Orbital semi-major axis 1.524 AU sulphur so may always have Orbital period 686.98 days been liquid. But, fast rotating so why no convection Rotational period 24 hours 37 min 22 sec currents? No crystallisation? Eccentricity of orbit 0.093 2) MGS data suggest only Inclination of rotation axis 25.19º remnant magnetic field. If sulphur <15% of core, it may Diameter (at equator) 0.533 d (6788 km) Earth have mostly solidified.

Mass 0.107 M Earth Thermal+gravity models suggest some of core is molten. Mean density 3940 kg m -3 (0.71 Earth)

1 The surface of Mars (MGS) MGS: Mars gravity map

Elysium

Tharsis

Valles Marineris

Hellas

Tharsis Montes & Olympus Mons Shield volcanoes on edge of Tharsis

Olympus

Ascraeus

Pavonis

Arsia 700 km wide at base; 24 km above plain Caldera: 80 km wide; 2.5 km deep

2 Mars Express: Albor caldera Mars Global Surveyor Magnetic map

3-D view. Caldera 30 km wide, 3 km deep. Clear evidence for “magnetic stripes” similar to Entire volcano 160 km across, 4.5 km deep. those on Earth – more evidence for past tectonic activity.

Valles Marineris ? - Past

Tectonic origin but many features: Left - Copernicus (Moon) lava layering, weathering, (water?) Mars Express, high – erosion very important on Mars. res. image – 12m/pixel Right - (Mars) Fluidized ejecta?

3 Water on Mars? - Past Today? No surface liquid water. Water-ice can exist just below the surface down to few km. Depth upper limit depends on soil and latitude.

MGS images of gully flow inside a crater in Terra Sirenum. The “deposit” is several hundred meters Ravi Vallis long. Older ones can also Streamlined islands? Chaotic terrain + 300 km flows be seen.

The Atmosphere Present-day Atmosphere of Mars

CO 2 95.3 % Atmospheric surface pressure 1/150 of Earth. Thermosphere N2 2.7 % Ar 1.6 % No stratosphere (no O 3). Mesosphere Large surface temperature Mars O2 0.13 % range: ~273 K (day) ~150 K CO 0.27 % (night). Mean 218 K. H2O <0.003 % Greenhouse effect: ∆T +8 K Martian atmospheric composition similar to Venus but 4 with a CO 2 column 10 less massive (<1% Earth).

4 Atmospheric Circulation Martian CO 2 (+H 2O) polar caps • Mars rotates rapidly but has little atmosphere, no oceans and large polar regions. Circulation is complex. higher thus always • Seasonal, “ cell” at sub-solar point– condensation colder – North flows to/from the poles. Also day/night “thermal tides”. varies more. • Winds up to 10 m s -1 can drive massive dust storms.

North South

Mars Earth

Mars Express – Martian Moons Martian South Pole Phobos and Deimos – probably captured asteroids. Both exhibit synchronous rotation, i.e. they keep the same face towards Mars (like our own Moon).

Right: visible image Phobos (size ~20 km) Deimos (size ~15 km)

Centre: CO 2

Left: H2O

5 Curiosity: a 900kg habitability probe Postcards from Mars Viking (biological potential; geological and atmospheric evolution; surface radiation)

Spirit abrasion rasp drill Curiosity rover: landed 2012 August 6

Opportunity White veins: Calcium Sulphate?

Life on Mars? • Viking – null result? • Martian Meteorites – ALH84001 is 4 Gyr old; in space for 16 Myr; on Earth for 13000 yr. The End • Claim for fossil life based on carbonate globules: implies bacteria smaller than most on early Earth. • Methane recently discovered in atmosphere…

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