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Terrestrial Planets – Begin With Mercury

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Guiding Questions

1. What makes Mercury such a difficult planet to see? 2. What is unique about Mercury’s rotation? 3. How do the surface features on Mercury differ from those on the Moon? 4. Is Mercury’s internal structure more like that of the Earth or the Moon? 88 days

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Solar Transit Earth-based optical observations of Mercury are difficult Transits occur • At its greatest eastern and western elongation, about Mercury is never more than 28° from the Sun twelve • It can be seen for only brief periods just after times a sunset or before sunrise century when the sun, Earth and Mercury are There was a aligned transit on

5 November 8, 6 2006

1 Earth-based Views of Mercury Mercury rotates slowly and has an unusual Difficulties observing Mercury from Earth led early spin-orbiting coupling astronomers to incorrectly decide that Mercury always kept the same face towards the sun in synchronous orbit

Note phases like the moon

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Radio telescope observations from sites such as Arecibo gave evidence of a non-synchronous orbit

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•Mercury • Strong tidal spins 1 ½ effects, Mercury’s times on slightly its axis elongated for every shape and its complete very orbit eccentric •Mercury orbit cause spins this strange 3-to-2 orbit three times •A “day”of solar light on during Mercury every two would be 88 orbits11 earth days 12

2 MESSENGER Images from revealed Mercury’s heavily cratered surface

• Most of our detailed information about Mercury’s surface is from the Mariner 10 Image from Flyby #3 - 2009 flyby mission in 1974/1975. • Mariner only saw one side of the planet. • The MESSENGER mission spacecraft is now at Mercury. – It is adjusting its flight path for an ultimate orbit of Mercury – 3 flybys to date – Will achieve orbit in 2011

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•Heavily cratered surface Note • Less how dense much cratering more than moon densely •Gently the rolling craters plains occur on •Scarps the •No Moon’s evidence of surface. tectonics

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Scarps are cliffs

This one is more than a km high

They probably formed as the planet cooled and shrank

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3 The seismic waves from •The the impact Caloris that caused the Caloris Basin is Basin caused evidence this of a large deformation on the impact opposite side of Mercury

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Mercury has an core and a surprising magnetic field • Most iron-rich planet in the solar system with a core that is 75% of the diameter • The earth’s core is 55% of its diameter and the moon’s core is 20% of its diameter • Highest density for the planets • Weak magnetic field indicating part of the core is liquid • Magnetic field causes a magnetosphere similar to Earth’s but weaker

This may be evidence of ice at 21 22 Mercury’s North Pole.

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4 The magnetosphere blocks the solar wind from reaching the surface of the planet

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Cloud-Covered Venus

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• At its greatest Guiding Questions eastern and western elongations, Venus 1. What makes Venus such a brilliant “morning star” or “evening star”? is about 47° from 2. What is strange about the rotation of Venus? the Sun 3. In what ways does Venus’s atmosphere differ • It can be seen for radically from our own? several hours after 4. Why do astronomers suspect that there are active sunset or before volcanoes on Venus? sunrise 5. Why is there almost no water on Venus today? Why do astronomers think that water was once very common on Venus? 6. Does Venus have the same kind of active surface as the Earth?

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5 The surface of Venus is hidden beneath a thick, In 1962 the unmanned U.S. spacecraft highly reflective cloud cover made the first close flyby of Venus •Venus is similar to the Earth in its size, mass, average density, and surface gravity •It is covered by unbroken, highly reflective clouds that conceal its other features from Earth-based observers 31 32

Venus’s rotation is slow and “retrograde” Venus has a hot, dense atmosphere and corrosive cloud layers

• Spacecraft measurements reveal that 96.5% of the Venusian atmosphere is carbon dioxide • Most of the balance of the atmosphere is nitrogen. • Venus’s clouds consist of droplets of concentrated sulfuric acid. • The surface pressure on Venus is 90 atm, and the surface temperature is 460°C • Venus rotates slowly in a retrograde direction with a solar day of 117 • Both temperature and Earth days and a rotation period of 243 Earth days pressure decrease as altitude increases • There are approximately two Venusian solar days in a Venusian year. 33 34

The upper cloud layers of the Venusian atmosphere move rapidly around the planet in a retrograde direction, with a period of only about The circulation of the Venusian atmosphere is dominated by two huge 4 Earth days convection currents in the cloud layers, one in the northern hemisphere 35 and one in the southern hemisphere 36

6 Volcanic eruptions are probably responsible for Venus’s clouds •Venus’s clouds consist of droplets of concentrated sulfuric acid •Active volcanoes on Venus may be a continual source of this sulfurous material

The density of craters suggests that the entire surface of Venus is no more than a few hundred million years old.

According to the equilibrium resurfacing hypothesis, this happens because old craters are erased by 37 38 ongoing volcanic eruptions

The climate on Venus followed a different evolutionary path from that on Earth

• Venus’s high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight. • The early contained substantial amounts of water vapor • This caused a runaway greenhouse effect that evaporated Venus’s oceans and drove carbon dioxide out of the rocks and into the atmosphere • Almost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere. • The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earth’s oceans 39 and chemically bound into its rocks 40

The surface of Venus shows no evidence of plate tectonics • The surface of Venus is surprisingly flat, mostly covered with gently rolling hills • There are a few major highlands and several large volcanoes • The surface of Venus shows no evidence of the motion of large crustal plates, which plays a major role in shaping the Earth’s surface 41 42

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Venusian Surfaces

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What I’ll Talk About • Some history – a view at the start of the 20th century • Mariners to Mars • Viking Mission – in search of life of Mars •A meteorite – in search of life in a rock • Some latest views from Mars •Conclusions – keeping it simple 47 48

8 The High Hopes

• “The planet Mars, on the other hand, exhibits in the clearest manner the traces of adaptation to the wants of living beings such as we are acquainted with. Processes are at work out yonder in space which appear utterly useless, a real waste of Nature’s energies, unless, like their correlatives on earth, they subserve the wants of 49 organized beings.” [Richard Proctor, 1902] 50

From Schiaparelli… To Percival Lowell

• As seen by telescopes from Earth • Percival Lowell – An orange-red orb, with (1855-1916) some darker patches and bright polar caps sometimes – appointed MIT visible astronomy professor • Giovanni Virginio in 1902 Schiaparelli (1835-1910) – published books – 1876 announced discovery • Mars (1895) of “canali” (channels) on • Mars and its Canals Mars (1906) – misreported as canals • Mars as the Abode (artificial) by the press 51 of Life (1908) 52

More Historical Background Lowell’s Observations and Explanation

• At the turn of the 20th century: •No canals – publication offered a reward for anyone • human brain tendencies coming forth with proof of life on another • connect unrelated planet or anywhere in space EXCEPTING points together by lines Mars • Recent theory – just about every major observatory had • Lowell’s telescope acted as released hand paintings of Mars and some an ophthalmoscope were even releasing photographs as • caused Lowell to see astrophotography was in its infancy the reflection of the • no two drawings could agree on the radial pattern of his own formations on the planet's surface retinal blood vessels •they showed a Mars with a varied surface possessing darker and lighter areas, as well as the polar caps 53 54

9 , 6 and 7 Mariner 4 Photographs

•Mariner 4 – mission – closest approach came on July 15, 1965 – pictures from this mission showed no canals and a surface that was disappointingly looking like that of the moon, quite LIFELESS • In 1969 the United States launched Mariner 6 (February) and Mariner 7 (March) • At closest approach (July for Mariner 6 and August for Mariner 7) both craft were at a distance of approximately 3400 kilometers 55 56

Mariners 6 and 7 A Time to Fail and Succeed

• The Mariners (6 & 7) contained: • In 1969 – narrow and wide angle cameras – two unsuccessful attempts by the Russians – infra-red radiometer • In 1971 – both Americans and Russians had unsuccessful – infra-red spectrometer missions to Mars – ultra-violet spectrometer – Russian and • Temperature, pressure and atmospheric • both equipped with modules but neither lander was successful constituents were analyzed – Americans • Pictures were still anything but • reached Mars during a global dust storm – the storm did eventually subside and the mission was spectacular enough of a success so as to provide pictures for the 57 choosing of a site for landing the upcoming Viking missions 58

Mariner’s Atmosphere Mariner 9 Photographs

• First look provided by Mariner spacecraft – Mariner 9 specifically • faced presence of a global dust storm • illustrated the progress of a feature that looked very much like a terrestrial cold front, visible as a bright band extending across many of the images • saw evidence of dust storm associated with strong winds • saw large crater rim produce wave clouds, believed to be composed of water ice (resembling "sonic boom shock wave”) produced by strong low level winds passing over the crater • saw day-to-day variations indicative of day-to-day weather changes and frontal systems 59 60

10 A Prelude to Viking Viking Liftoff

• First approved in December of 1968 for a • launched August 20, 1975 1973 launch • Launch date postponed due to Congressional • Viking 2 launched September 9, 1975 funding cutbacks • Each Viking orbiter consisted of: • Idea was to launch the craft in 1975 for a – television camera system landing to take place on Independence Day in – an atmospheric water detector 1976 • Viking 1 was to be launched on August 11, 1975 – an infra-red thermal mapper but was postponed due to a malfunction • While fashioning repairs for the spacecraft, the twin unit was substituted and so Viking 2 became Viking 1 and vice versa 61 62

Viking Instruments Arrival at Mars

• Each Viking lander contained: • Viking 1 arrived at Mars on June – television camera system 19,1976 – gas chromatograph mass spectrometer – took pictures to aid in the choice of a – x-ray fluorescence spectrometer landing site for the lander – seismometer • caused a delay in the landing beyond its – biology lab Independence Day rendezvous – weather station • Using the latest pictures, the western – sampler arm slopes of were selected • Each contained: for the landing of Viking Lander 1 – a retarding potential analyzer – upper-atmosphere mass spectrometer 63 64

Another Giant Leap for Mankind The Viking Look

• On July 20, 1976 (seven years after a •The Viking cameras man had taken his first steps on the – not cameras in the conventional sense moon) –each consisted of: – Viking Lander I successfully descended • a nodding mirror upon the soil of Mars • a rotating turret which caused the images to • immediately after successful touchdown, the be reflected down to the photodiode, which lander had instructions for taking pictures with built up a picture as a series of pixels from its camera (there was actually a concern that each scan of the mirror and rotation of the the lander might sink into the soil, and so at turret least a picture was desired before it – criticized for its inability to detect any conceivably had sunken) 65 moving objects (some still felt it possible that 66 there might be macroscopic creatures on the planet)

11 Viking Orbiter Photograph The Face on Mars

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The Face on Mars - Caption The Changing Face

• The picture shows eroded mesa-like landforms. The huge rock formation in the center, which resembles a human head, is formed by shadows giving the illusion of eyes, nose and mouth. The feature is 1.5 kilometers (one mile) across, with the sun angle at approximately 20 degrees. The speckled appearance of the image is due to bit errors, emphasized by enlargement of the photo. The picture was taken on July 25 from a range of 1873 kilometers (1162 miles). Viking 2 will arrive in Mars orbit next Saturday () with a landing scheduled for early September.

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Viking Lander Photograph Reach Out and Touch

• On July 22, 1976 the sampler arm was to be deployed – however, there were difficulties • overcome by ingenious engineers • The sampler arm was finally deployed on July 28

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12 First Results from Soil Sample A Mass Disappointment

• X-ray fluorescence spectrometer (to determine the inorganic composition of • Gas chromatograph mass the soil sample) spectrometer results – 15-30 percent – indication of carbon dioxide –12-16 percent iron – little water – 3-8 percent – NO organic compounds – 2-7 percent aluminum • The beginning of a controversy – this negative result conflicted with results from the biology experiments

73 • indicative of the existence of microbial life 74

Looking for Life Pyrolytic Release Experiment

• The biology laboratory • PI was Norman Horowitz – approximately a single cubic foot of volume •Basis of experiment – consisted of: – ability of an organism to metabolize carbon • pyrolytic release experiment dioxide and produce some product (reverse process of Levin's experiment) • labeled release experiment – soil sample placed in test chamber for five days • gas exchange experiment and incubated with/without light – if soil had fixed or metabolized the carbon dioxide (carbon-14 tagged) then pyrolysis of the sample would allow detection of labeled carbon in the chamber’s gas

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Gas Exchange Experiment Labeled Release Experiment

•PI was Vance Oyama •PI was Gilbert Levin •Basis of experiment • Basis for experiment – evidence of metabolism by noting – property of microorganisms to changes in the gaseous environment of metabolize organic compounds in a the sample nutrient broth – sample would be introduced into the – organics in broth tagged with carbon 14 chamber and the chamber's atmosphere – If organisms in the sample were analyzed metabolizing the nutrient, the carbon-14 • after a period of incubation, the gas would be would appear in the chamber's gas by re-examined and a comparison is made the appearance of tagged carbon between this analysis and the initial analysis 77 monoxide or carbon dioxide 78

13 Biology Experiment Results Explaining Biology Away

• All three biology experiments registered results which were indicative • Theories dealing with superoxides, of some very active samples, and if peroxides and superperoxides to explain these results were obtained on earth apparent positive results away the there would be no doubt that organisms results of were responsible • Only hold-out for the possibility that • Doubt of the biological results once the the biology experiments still might GCMS had failed to detect any organics indicate the existence of within the soil sample was Gilbert Levin [only science team member that still maintains belief that evidence of life was 79 found] 80

Levin’s View 25 Years Later Viking’s View of Atmosphere

• Viking Lander meteorological • “After 25 years, the Mars LR data still excite attempts at a chemical explanation, three within the instruments last year. This indicates that none of the 30 non- – at end of boom that deployed after landing biological explanations offered to date has been • contained thermocouple units to measure the completely convincing. New findings concerning the atmospheric temperature and wind speed existence of liquid water on the surface of Mars, and extremophile microorganisms on Earth, are consistent – an atmospheric pressure sensor which was with my conclusion that the LR detected living not on the boom so as to be shielded from microorganisms in the soil of Mars (Levin 1997), which winds may explain the difficulties with the non-biological theories.”

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First Mars Weather Report Viking Looks at Climate

•Seymour Hess stated: • Long term data available – "Light winds from the east in the late afternoon, changing to light winds from the –from Viking Lander 1 through southwest after midnight. Maximum winds Novermber 5, 1982 were 15 miles per hour. Temperature ranged from minus 122 degrees Fahrenheit –from Viking Lander 2 through just after to minus 22 degrees April 11, 1980 Fahrenheit. Pressure steady at 7.7 millibars."

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14 Viking Climate Conclusions More on Atmospheric Findings

• discovered nature of surface pressure • Other characteristics of Martian variations over the seasons and the cycling atmosphere of the atmosphere between the polar caps – difference in pressures between the two – minimum in the pressure cycle occurs during the southern winter when the carbon dioxide mass landers condensing onto the south polar cap is a • attributed to the difference in elevations maximum between the two sites – as the seasonal carbon dioxide sublimes out of – there was also much noise on the pressure curves, the south polar cap, the pressure rises until the which, in the end, was determined NOT to be noise, but associated with traveling cyclones of the kind north polar cap starts to form that had been speculated upon based on images from – process reverses seasonally and carbon dioxide Mariner of the dust storms reforms at the south polar cap 85 » these cyclones occurred only during the winter 86

A Little Pressure Meridional Circulation [Say What?]

• Pressure variations detected • Landers helped produce charts of meridional – linked to optical depth computations and circulation demonstrated the presence of what – on Earth we have the familiar pattern of rising meteorologists call atmospheric tides motion in the tropics and a descending motion in the • atmospheric tides should not to be confused subtropics with a connecting meridional flow pattern with gravitational tides – on Mars, there is a strong seasonal varying circulation – wind and pressure variations that are produced by rather than one centered about the equator the daily cycle of heating over the whole atmosphere – in summer the air rises near the subsolar point in the • what results from the daily loading cycle, southern hemisphere subtropics and crosses the among other things, are traveling waves that equator to a point where it can descend [more like a follow the sun and have both diurnal and one-cell circulation with a strong descending motion in semidiurnal periods 87 88 the winter hemisphere]

A Little Mars Geology More Beautiful Pictures

• Viking Orbiter images – largest volcano in solar system, Olympus Mons • High resolution images from Viking Orbiters – contributed to better understanding the surface – large canyon, Valles Marineris – indication that the darker areas are where the silicates – a global appearance roughly organized latitudinally are somewhat more reduced and richer in ferrous rather • equatorial belt is somewhat darker than the mean albedo than ferric silicates and very changeable over time – areas that were originally considered for landing were • northern and southern mid- regions are brighter, found to be too hilly due probably to the deposits of very fine, bright material – surprised to find that the Lander was actually in a field • a dark collar around the north polar region strewn with rocks (e.g. Little Joe) large enough so that if • polar regions with the very bright polar caps the Lander had landed on one of them the mission would have failed

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15 Summary of Sites Pathfinder at Ares Vallis

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Map: UCAR Image credit: NASA/JPL

Sojourner

• weighed 10 kg and spent 3 months roaming on the surface • Orbiting Mars from 1996 to the present –evidence of “recent” subsurface water

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Odyssey 2001

Mars Global Surveyor

Image credit: NASA/JPL/MSSS 95 96

16 Rover

Opportunity Rover

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Mars Interior Mars Interior •The core is solid, not liquid • do not expect a strong magnetic field • on MGS have •Mars core discovered a weak magnetic field • FeS (iron sulfide), over certain regions of the planet • FeS has a lower • Mars once had a liquid core and density compared to magnetic dynamo in the past, and the Earth’s Fe and Ni this has permanently magnetized • diameter 40% of some rocks. Mars • These magnetic rocks are very old, • similar proportion suggesting the field was only ‘on’ for to the Earth’s the first few hundred million years core/diameter of Mars’ history. • Mars is differentiated • Mantle and Crust 99 100 Figure credit: Albert T Hsui, Univ. Ill

Olympus Mons Valles Marineris • Largest of the four great Tharsis volcanoes first seen by Mariner 9

• Largest volcano in the entire solar system

• About 27 km high and 700 km wide at the base •A giant canyon system discovered by Mariner 9 • named after the spacecraft! •Stretches more than 4000 km in length, 500 km wide, and up to 8 km deep

101 102 Figure credit: NASA Figure credit: NASA/USGS

17 • Largest impact basin on Mars; rim of mountains showing much erosion Valles Marineris • Approximately 2000 km across; 5 km below mean Martian surface level • Clouds sometimes found in interior region • Tectonic in origin • Impact occurred during Late Heavy Bombardment stage of solar system • Huge cracks in the crust widened and shaped by erosion formation, approximately 3.9 Gyr ago

Hellas Basin

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Figure credit: NASA/JPL. Viking mosiac of Western Candor Chasma Figure credits: (left) NASA/JPL (right) MGS/MOLA

Terrain Comparison The Tharsis Bulge

A massive uplifted region • Compare Olympus Mons with Everest (fold mountain) and Mauna Loa (shield volcano) on Earth. • 10 km above its surroundings • Mountains on Earth and Venus can only rise 10-15 km before the rock • one of the least cratered terrains on Mars begins to deform under its own weight • Area equal to North America

•Why can mountains on Mars get so big?

• Hint: Martian gravity is about 40% that of the Earth 105 106

Figure credit: Universiity of North Dakota Figure credit: NGDC/USGS

Canyon Widening Evidence Impact Craters

• Evidence of “mass wasting”

• Ejecta patterns differ from the lunar impact craters • Craters on Mars display a more fluid ejecta pattern •Consider what may have caused differences Figure credit: NASA/JPL. Vikingimage of Western Candor Chasma 107 108

Figure credit: NASA ARC/CMEX

18 Channels Real Dunes • Three major types of channels 1. Runoff channels 2. Outflow channels 3. Gullies • This image is of • Runoff channels ‘cemented’ sand • similar to terrestrial dry river beds dunes in the • often seen on the steep Herschel crater of sides of crater walls the Terra Cimmeria • as old as the cratered taken by Mars Global highlands Surveyor •Evidence for a thicker, warmer atmosphere in the • Image credit to past MSSS/NASA/JPL

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Outflow Channels Meteorite from Mars

• ALH84001 • Larger and less – possible common than runoff evidence of channels fossil microbes • Caused by flooding from Mars • Evidenced by teardrop islands, terraced walls, and sandbars • carved by flood waters rushing over original terrain 111 112

Image credit: NASA/JPL

Statement from Daniel S. Goldin, NASA Goldin Statement (August 6, 1996) Administrator

• "NASA has made a startling discovery that points to the possibility that a primitive form of microscopic • “I want everyone to understand that we are not life may have existed on Mars more than three billion talking about 'little green men.' These are extremely years ago. The research is based on a sophisticated small, single- cell structures that somewhat resemble examination of an ancient Martian meteorite that bacteria on Earth. There is no evidence or suggestion landed on Earth some 13,000 years ago. that any higher life form ever existed on Mars. • “The evidence is exciting, even compelling, but not • “The NASA scientists and researchers who made this conclusive. It is a discovery that demands further discovery will be available at a news conference scientific investigation. NASA is ready to assist the tomorrow to discuss their findings. They will outline process of rigorous scientific investigation and lively the step-by-step 'detective story' that explains how scientific debate that will follow this discovery. the meteorite arrived here from Mars, and how they set about looking for evidence of long-ago life in this ancient rock. They will also release some fascinating 113 114 images documenting their research."

19 Science Paper by McKay et al. Paper by Scott et al. • “In examining the Martian meteorite ALH84001 we have found that the following evidence is compatible with the existence of past life on • “In an electrifying paper published in August, 1996 in the journal Mars: (i) an igneous Mars rock (of unknown geologic context) that was penetrated by a fluid along fractures and pore spaces, which then Science, David McKay (NASA ) and his became the sites of secondary mineral formation and possible biogenic colleagues suggested there were fossils of martian organisms activity; (ii) a formation age for the carbonate globules younger than associated with carbonate minerals in martian meteorite the age of the ; (iii) SEM and TEM images of carbonate ALH84001. How these carbonate minerals formed (biologic globules and features resembling terrestrial microorganisms, origin or not) and the temperature at which they formed (low or terrestrial biogenic carbonate structures, or microfossils; (iv) high) are hotly debated questions. We have proposed an entirely and Fe-sulfide particles that could have resulted from different origin: the carbonates in ALH84001 formed in seconds oxidation and reduction reactions known to be important in terrestrial at high temperatures (>1000oC) from melts produced during a microbial systems; and (v) the presence of PAHs associated with large impact on .0 billion years ago (Scott and others, surfaces rich in carbonate globules. None of these observations is in itself conclusive for the existence of past life. Although there are 1997). We infer that it is unlikely that the carbonates or any alternative explanations for each of these phenomena taken individually, minerals in them contain mineralogical evidence for ancient when they are considered collectively, particularly in view of their martian life.” spatial association, we conclude that they are evidence for primitive life on early Mars.” 115 116

Paper by Scott and Barber A Quick Review of Mars

• “Magnetic minerals in Martian meteorite ALH 84001 formed as a result of impact • Has been of interest for a century heating and decomposition of carbonate; – originally felt to show evidence of life they were never used as compasses by • Has been targeted for study Martian microorganisms.” – numerous missions - some fail, some succeed • Has been suggested as source of microbes • Will be studied in future 117 • Future life may well be human 118

Simplified Conclusions re Mars

• Did Viking find life on Mars? – Nope, but it’s considered uncertain and controversial • Did Viking find ruins of an ancient civilization? –Nope • Does ALH84001 contain microfossils? –Nope • Do we know that there is no life on Mars?

–Nope 119

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