10/31/2010. Opposition and Conjunction. Opposition occurs every 2 years. Best opposition at perihelion. Percival Lowell

Transcription

1 Opposition and Conjunction Opposition occurs every 2 years Best opposition at perihelion Percival Lowell 1

2 Canals on Mars? Martians? Orson Welle s Broadcast (1938) The War of the Worlds H G Wells (1898) Science Fiction Mariner 4 Flyby (1965) Much of the surface of Mars is old and heavily cratered No sign of artificial canals! 2

3 Modern View of Mars The Earth s Axis Tilt The Day on Mars 1 mean terrestrial solar day = 24 hrs 1 mean Martian solar day = 24 hrs 39 mins = 1 sol Seasons on Earth Due to the axis tilt of not distance from the Sun! Seasons on Mars Seasons in the Northern and Southern hemispheres are inverted! Seasons last twice as long! Vary in duration and intensity due to elliptical orbit! 3

4 What season was it in the northern hemisphere of Mars when this image was taken? Topography of Mars No sign of plate tectonics planet is small and cooled quickly crust too thick The Geological History of Mars The northern plains of Mars which cover 40 % of the planet s surface are 4-5 km below the mean radius of the planet and may have been carved out by a giant impact The Southern Highlands of Mars Many craters are filled in and eroded with rounded rims Small craters are absent 4

5 10/31/2010 Hubble Space Telescope (2001) The Tharsis Region Massive uplift in Martian crust with huge shield volcanoes Olympus Mons: the solar system s largest volcano! Olympus Mons is huge! Formation of Tharsis The Mariner Valley 2500 miles long! 5

6 Liquid Water once flowed on Mars Layers of Sedimentary Rock on Mars? Recently, ancient lakes found on the Martian equator which existed during the Hesperian Era (3 bya) Most of the channels are located on the ancient highlands suggesting they were carved out billions of years ago during the Noachian Era Why no water on the surface of Mars today? Atmospheric Composition 95.3% CO 2 High temperatures due to runaway greenhouse like on Venus? 6

7 Average Surface Temperature 220 K = -63 ºF That s 60 K or 111 ºF colder! Why? Atmospheric Pressure at Surface P = atm 1/150 th the pressure on the Earth s surface So thin it cannot retain much heat! Where is the water today? Most is frozen out on beneath surface as permafrost! 7

8 Mars Odyssey Orbiter Water Map Fluidized Ejecta: Mud Flows around Craters Gullies in Santa Monica! Martian Gullies Zack West (Astro 5, Spring 07) Bluffs below Sunset Park overlooking PCH The Polar Caps have two layers Some is locked up in the Martian polar caps! 8

9 Seasonal Variations in the Martian Polar Caps Residual North Polar Cap of Water Ice Martian Clouds A small amount remains in the atmosphere forming clouds! To explain the water erosion features, Mars must have had a much thicker carbon dioxide atmosphere in the past! Where did this carbon dioxide go? 9

10 Viking Orbiter Viking Landers searched for Life in Martian soil Martian Surface from Viking 1 Landing Site CO 2 Frost at the Viking 2 Landing Site Earth: blue skies, red sunsets Mars: red skies, blue sunsets! 10

11 Taking soil samples Carbon Assimilation Experiment A sample of Martian soil was exposed to carbon dioxide labeled with radioactive carbon-14 ( 14 CO 2 ) to see if any of the radioactive carbon was incorporated into the soil by living organisms Result: radioactive carbon was indeed incorporated! However, this still occurred even after the sample was heated to 175 ºC for 3 hours suggesting some sort of chemical process rather than a biological one! Gas Exchange Experiment A sample of martian soil was mixed with a broth containing organic nutrients brought from Earth to see if any gases might be released by the metabolism of martian microbes in the soil Result: as soon as the nutrients were added oxygen gas was given off. However, this still occurred even when the experiment was performed in the absence of light (required to produce oxygen by photosynthesis) or if the sample was preheated to high temperatures! Labeled Release Experiment A broth of nutrients labeled with radioactive carbon-14 was added to a sample of martian soil to see if gases containing the radioactive isotope were given off from metabolic processes in the soil Result: radioactive gases were given off indicating metabolic activity! Also, when the sample was preheated to 50 ºC the amount of gas given off was reduced and eliminated altogether when the sample was preheated to 160 ºC. This suggested that heat was gradually killing organisms in the soil! Gas Chromatograph/Mass Spectrometer This experiment looked for organic molecules in the soil by first heating a sample of martian soil to 500 ºC which would cause any organic molecules into the soil to be broken up an vaporized. These vapors were then passed into a gas chromatograph which chemically separates out the gases into its different components followed by a mass spectrometer which determines the masses of the molecules passing through it. If organic Life were present this experiment should have found significant amounts of organic molecules Result: no organic molecules were found in the martian soil to a level of a few parts per billion (10 million times lower than that found in terrestrial soils) indicating organic Life was not present! Overall Conclusions The Martian soil appears to be very reactive chemically but not biologically! 11

12 Mars Pathfinder (1997) Pathfinder landed on surface using airbags! Sojourner micro-rover on Mars Mars Exploration Rovers Sojourner and Opportunity Scientific Goal Search for direct evidence of sedimentary rocks exposed to water on Mars! 12

13 Mer-A (Spirit) Landing Site: Gusev Crater latitude 14.6º S, longitude 175 º E Mer-B (Opportunity) Landing Site: Meridani Planum latitude 2º S, longitude 354º E An impact crater which was once believed to have been filled with water A flat plain where remote sensing orbiting satellites indicate there are abundant quantities of the mineral, gray hematite which most commonly forms in the presence of water Grey Hematite Launch on Delta II Rocket from Cape Canaveral, FL Spirit: June 10 th 2003 Opportunity: July 7 th 2003 An mineral of iron and oxygen which most commonly forms in water First Image from Spirit Jan 4 th 2004 (Sol 1) First Color Image from Spirit 13

14 Spirit s Landing Site Close-up First Images from Opportunity Jan 25 th 2004 (Sol 1) First Color Image from Opportunity Opportunity's Landing Site from Orbit Lander rolls into a small, 65ft diameter impact crater! Analyzing Rocks on the Martian Surface Mars Reconnaissance Orbiter Image of Victoria Crater 14

15 Opportunity seen from orbit! Phoenix Lander (2008) Powered Landing Scientific Goals 1. Study the history of water in the Martian arctic 2. Search for evidence of a habitability and assess the biological potential of the icesoil boundary Phoenix Instruments Launch Aug 4 th

16 Mars Landers Martian Landing Sites Corresponding Landing Site on Earth Polygon Patterned Terrain Phoenix Landing Ellipse Mars Reconnaissance Orbiter (MRO) Image of Phoenix Descent 16

17 Solar Power Grid First image of surface under lander First Color Image of Landing Site May 25 th 2008 Close-up of Polygonal Pattern on Mars MRO Image of Phoenix Landing Site 17

18 Landing Site Panorama Ice uncovered beneath lander? Soil Sample inside robotic arm scoop Sample Trenches Soil sample about to be placed in TEGA cell Disappearing ice? 18

19 Wet chemistry lab animation Sample being deposited into the wet chemistry lab Microscope image of soil sample A Martian Dust Devil Results Soil is very alkaline (ph = 8-9) and contains salts suggesting it has been in contact with water in the past. Composition is similar to samples found in the Antarctic Dry Valleys Snow detected falling from sky although vaporized before reaching ground Calcium carbonate (CaCO 3 ) a sedimentary mineral formed in water found in soil samples Nila Fossae Carbonate rocks seen which are similar to those formed by the earliest life on Earth 19

20 ALH The Martian Meteorite Meteorites Rocks from space which fall to Earth How do we know it came from Mars? Where was it found? they have unusual oxygen isotope ratios that are not found in rocks on Earth they are all volcanic rocks indicating they originated from a planet large enough to have volcanism most of the rocks are less than a billion years old suggesting they came from a world with recent volcanism possibilities: Venus or Mars! However, unlikely to be Venus due to its high gravity! final proof: rocks contain trapped gases with compositions identical to the Martian atmosphere! Antarctic Meteorites How did it get here? 20

21 Where did it come from? Recent observations by orbiters suggest it could have been blasted from a 20 km diameter impact crater in a branch of the Mariner Valley! May be a good location for a future sample return mission! Eos Chasma Fossilized Bacteria? Could Life have been transplanted from Mars to Earth? Evidence: 1 in 10,000 meteorites may travel from Mars to earth in a decade or less terrestrial bacteria have been shown to survive at least 6 years in space Deinococcus radiodurans Viking 1 Orbiter (1976) Cydonia Region Can withstand very high levels of radiation Transported from Mars in meteorites? 21

22 Old Man of the Mountain, NH Mars Global Surveyor Orbiter (2001) Mars Global Surveyor Orbiter Happy Face Crater! 22