Chapter 10: Mars A Near Miss for Life?

1. Chapter 10: Mars A Near Miss for Life? • Orbital Properties • Physical Properties • Seasons • Surface Features • Atmosphere • Satellites • Comparison to Earth and Venus

2. Objectives • After completing this chapter, you should be able to: • compare the general physical properties of Mars, Earth, Venus, Mercury, and the Moon. • compare the orbital and rotational properties of Mars, Earth, Venus Mercury, and the Moon. • describe the atmosphere, hydrosphere, lithosphere, magnetosphere, and biosphere of Mars and • compare to the terrestrial planets and explain their differences. • describe Mars' cycle of visibility as seen from the Earth. • describe the physical properties and origin of the Martian moons. • describe the "geologic" history of Mars and compare it to the other terrestrial planets.

3. Planetary Configurations • In their orbital cycles, planets assume various configurations relative to the Sun-Earth line. • For a planet farther from the Sun than Earth: • opposition - planet is closest to Earth and appears to be opposite the Sun (from Earth). • conjunction - planet is farthest from the Earth and the Sun lies between the planet and Earth. • quadrature - planet is 90o from the Sun-Earth line.

4. Earth-Sun line Conjunction Superior planet Earth Quadrature Opposition Superior Planet Configurations

5. Mars from Earth • Mars appears largest and brightest when it is at opposition. • If also at perihelion, Mars • is within 0.38 AU (56 million miles) of Earth, • has an angular size of 25”, • has surface features as small as 100 km across that can be resolved by Earth-based telescopes (about the same size as objects on the Moon resolved by unaided eye). • Will occur again in August 2003. • Mars appears less bright than Venus. • Twice as far from the Sun • surface area about 30% that of Venus • less reflective surface - only 15% of incident light reflected

6. Distance from Mars to Earth • Mars becomes easily visible about once every two years (780 days OR the period between oppositions), when it is • closest to the Earth, • visible all night long, and • highest in the sky at midnight. • At maximum brightness, it is the second brightest planet.

7. Earth-based Studies of Mars • First telescopic observations by Galileo. • Small angular size of Mars, Earth’s atmospheric turbulence limit observations • show daily changes in surface due to rotation • seasonal changes in colors of regions • length of day • tilt of rotation axis • 19th century observations by Schiaparelli interpreted surface as criss-crossed by straight lines, called canali. • U.S. astronomer Percival Lowell also observed the features in 1896; others did not. • Debate continued over half a century.

8. Mars in Two Views

9. Early Exploration from Space • In 1965, Mariner 4 passed near Mars and sent back 22 photographs of the surface. First picture of Mars from Mariner 4 First picture of craters on surface of Mars

10. Early Exploration from Space • In 1971, Mariner 9 was the first spacecraft to orbit another planet and sent back a series of photographs showing volcanoes (Olympus Mons), valleys (Valles Marineris), craters, and channels.

11. Early Exploration from Space • The Viking missions each had 2 spacecraft, orbiter and lander, to obtain high resolution images of the surface, examine the surface geology, and search for evidence of life.

12. Recent Missions to Mars • Pathfinder w/ Sojourner explored the Martian surface in 1997. • Mars Global Surveyor: arrived in Martian orbit Sept. 12, 1997. • Mars Polar Explorer: Lost contact December, 1999

13. Mars Global Surveyor Chasm in Valles Marineris Mars Global Surveyor: arrived in Martian orbit Sept. 12, 1997. Possible evidence of ponding in Martian crater Plateau in Valles Marineres

14. Current Mission: Mars Odysseyhttp://www.jpl.nasa.gov/odyssey/ • Mars Odyssey carries three scientific instruments designed to tell us what the Martian surface is made of and about its radiation environment: • a thermal-emission imaging system, • a gamma ray spectrometer and • a Martian radiation environment experiment. • Odyssey arrived at Mars on October 24, 2001, when it fired its main engine and was captured into Mars' orbit.

15. Odyssey

16. Current Mission: Mars Odyssey

17. Current Mission: Mars Odyssey http://www.jpl.nasa.gov/odyssey/ This thermal infrared image was the first acquired by Mars Odyssey's thermal emission imaging system on October 30, 2001. It is late spring in the Martian southern hemisphere. The extremely cold, circular feature shown in blue is the Martian south polar carbon dioxide ice cap at a temperature of about -120 °C (-184 ° F). Clouds of cooler air blowing off the cap can be seen in orange extending across the image to the left of the cap. The thin blue crescent along the upper limb of the planet is the Martian atmosphere. (NASA/JPL)

18. Mars Statistics • Satellites: 2 • Diameter: 6,785 km (0.52x Earth) • Mass: 0.11 x Earth • Density: 3.9 g/cm3 (Moon=3.3,Earth=5.5) • Surface Gravity: 0.38 x Earth • Escape Speed: 5.0 km/sec • Length of Solar Day: 24 hrs 37 min • Length of year: 687 Earth days • Orbital semi-major axis: 1.52 AU • Tilt of Axis: 23o59” • Orbital eccentricity: 0.093 • Minimum Distance from Sun: 205 million km (128 million miles) • Maximum Distance from Sun: 249 million km (155 million miles) • Temperature: 150K to 310K ( -116oF to 34oF), 218K average • Surface magnetic field: 1/800 X Earth

19. Seasons on Mars • Mars’ axial tilt only slightly greater than Earth’s. • expect seasons similar to Earth. • Mars’ orbital eccentricity greater than Earth’s. • S-hemisphere closest to Sun during summer, and farthest from the Sun during winter. • Summers warmer in S-hemisphere than N-hemisphere. • Winters colder in S-hemisphere than N-hemisphere. • Prediction for polar ice caps and variations with season?

20. Martian Sunset Picture taken by Mars Pathfinder mission. The color of the Sun is not correct since it is overexposed (should appear white or bluish-white).

21. Atmospheric Composition of Mars • Composition • 95.3% carbon dioxide • 2.7% nitrogen • 1.6 % argon • 0.13 % oxygen • 0.07% carbon monoxide • 0.03 % water vapor • Atmospheric pressure at the surface of Mars is ~ 1/100 x Earth’s. • may vary by 30% throughout Mars year because of variations in solar heating. • No recorded lightning or thunder.

22. Atmosphere of Mars • Troposphere where convection and "weather" occur. • Two types clouds: • water vapor w/ carbon dioxide; • white • appear in low-lying areas in morning • near poles in late summer/early fall • dust • yellowish • high speed surface winds (>100mph) • At noon in the summertime, surface temperatures may reach >300 K. • At night, • temperatures drop up to 100 K, • convection ceases, and • troposphere vanishes.

23. Atmosphere: Pressure and Temperature • Atmospheric pressure changes seasonally as carbon dioxide freezes and then evaporates from polar caps. • During southern hemisphere winters, the global air pressure drops by 30%. • Seasonal changes are also affected by Mars' distance from the Sun, and are also the cause of planet-wide dust storms that can obscure the planet's surface. • Diurnal temperature changes are quite extreme ranging from -225 F at night to 63 F during the day. • The greatest extremes occur in the southern hemisphere. • Occasionally carbon dioxide and water vapor clouds form because of the low temperature in the atmosphere. • Also frost can form on the ground.

24. Martian Dust Storms

25. Martian Dust Devil animation file:///H|/phys1050-fall2001/pictures/dustdevil.gif

26. Comparing Terrestrial Atmospheres

27. Goldilocks and the 3 Planets:A story about the Greenhouse Effect

28. Atmospheric History • Primary and secondary atmospheres similar to Earth and Venus. • Moderate greenhouse effect warms surface and allows liquid water to form. • Water dissolves carbon dioxide to form carbonate rocks. • Reduced carbon dioxide content diminishes greenhouse effect, so planet cools. • The surface atmospheric pressure decreases so that most of the liquid water is frozen. • Steps #4 & 5 propagate a runaway ice age effect.

29. Assuming no weathering, no life, and no gases escaping, atmospheres of the terrestrial planets would be:

30. Martian Hydrosphere • Liquid water is not expected on surface of Mars today. • The pressure and temperature combination is too low for liquid water to be stable, except possibly at the bottom of a deep canyon. • Only Earth in the inner Solar System has large amounts of liquid water. • Very little water vapor in the Martian atmosphere. • Less than Earth or Venus, but the relative humidity is 100%! • A comparison of atmospheric and ground water shows:

31. Evidence for Recent Water at Surface Images from Surveyor suggest geologically recent seeps of water to the Martian surface in gully landforms observed from latitudes of 300 - 700 in both hemispheres.

32. Martian Climate Changes • Mars is currently locked in a global ice age. It may not have always been that way in the past. • Changes in the tilt of its axis, orbital eccentricity, and/or precession of its rotation axis caused by the gravitational influence Jupiter could have greatly altered the Martian climate. • It may have been possible for liquid water to exist on the surface or Mars in the past.

33. Polar Regions of Mars • Polar ice caps composed of • water ice • carbon dioxide ice. • In summer, dry ice in N-cap sublimates and leaves water ice remnant. • S-cap retains some dry ice year round. • Layering observed in polar deposits implies periodic sedimentation from long-term, repetitive climate changes. N-pole cap Mariner 9 images S-pole cap

34. Evidence of Water on Mars? Runoff channels: resemble Earth’s river systems, ~4 billion years old

35. Water Erosion? Outflow channel: relic of catastrophic flooding ~3 billion years ago.

36. Run-off Channels Observations suggest that this water may have melted in the past causing huge floods. Other evidence points to runoff channels that might have formed under rainy conditions. (Photo from MOLA, Mars Global Surveyor)

37. Evidence of Water in the Past Sedimentary rock layers like these in Mars's Holden Crater suggest that the Red Planet was once home to ancient lakes. Martian gullies in Newton Crater. Scientists hypothesize that liquid water burst out from underground, eroded the gullies, and pooled at the bottom of this crater as it froze and evaporated.

38. New Information from Mars Global Surveyor • Wide-spread presence of olivine at surface suggests drier and colder throughout history than previously theorized. • green (yellow/green) - sulfates red - sulfate-free blue - olivine and pyroxenes (both volcanic) magenta - coarse-grained hematite

39. Seismic Activity on Mars • Each Viking lander carried a seismometer; only one worked. • Showed that Mars does have some seismic activity, but that the activity per unit area on Mars is less than on Earth. • Mars quakes that were recorded lasted about a minute. • Earthquakes last seconds • moonquakes last hours • Internal structure of Mars more similar to Earth than Moon.

40. The Surface of Mars • Mars Viking landers answered “why is Mars red?” • Viking soil analysis showed surface to consist of • mostly silicate rocks • large fraction (20%) as iron oxide • Soil is magnetic. • High surface abundance of iron combined with the overall density implies that Mars should not have much of an iron core. That is, Mars should show little differentiation.

41. Mars: Internal Structure • No direct measurements to constrain models of interior. • Average density and volcanic history imply some interior melting and differentiation. • thin crust (65-80 km) • rocky mantle more dense than Earth • small iron-rich core, possibly w/ sulfur • Lack of detectable magnetic field implies core is non-metallic and/or non-liquid. • No widespread geological activity in last ~2 billion years.

42. Martian Interior and Tectonics • There are no seismic data from Mars, because this equipment failed on one of the Viking landers. • Other indirect evidence suggests that Mars probably has no large iron core, and that the interior is not well differentiated. • The mantle must have been hot to cause volcanoes and rift valleys, but the crust may be too thick to allow plate tectonics to begin. • The planet probably froze solid before plate tectonics could begin.

43. Plate Tectonics • The mantle must have been hot to cause volcanoes and rift valleys, but the crust may be too thick to allow plate tectonics to begin. • The planet probably froze solid before plate tectonics could begin.

44. North Crustal Thickness Crustal thickness may be inferred from gravity observations made by Mars Global Surveyor. Red - thin Blue - thick

45. Martian Magnetosphere • No magnetic field has been detected, so the solar wind can interact directly with the Martian atmosphere. • No magnetic field suggests Mars has no or a very small liquid metallic core.

46. Martian Lithosphere Viking 1 view from surface of Mars

47. Surface Features:A view from HST

48. Terrains on Mars • Highlands - 60% • ancient • heavily cratered terrain • southern hemisphere • Northern Lowlands - 20% • younger, lightly cratered • resemble lunar maria • average elevation 4 km below highlands • dune fields, rift valleys, dry riverbeds, water flow patterns • Volcanic Highlands - 20% • Tharsis volcanic province • immense bulge the size of North America • volcanic plains, 10 km above surroundings • crowned by 4 volcanoes that rise another 15 km • few impact craters

49. The Surface of Mars • Mars Global Surveyor has been recording thermal emission spectra from the surface of Mars. • Analysis of the data suggests • low albedo regions composed of • volcanic basalts in the S-hemisphere • andesitic volcanics in N-hemisphere • high albedo regions show anomalous spectra consistent with atmospheric dust

50. Maps from Mars Global Surveyor: Hellas region