AST 248, Lecture 19

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

April 20, 2020

The Search for Intelligent Life in the Universejames.lattimer@stonybrook.edu

James Lattimer AST 248, Lecture 19

Mars in History

James Lattimer AST 248, Lecture 19

Mars in History

James Lattimer AST 248, Lecture 19

James Lattimer AST 248, Lecture 19

Mars

I Mass (1/10), radius (1/2) andatmosphere (.7–.9%) smallerthan Earth’s.

I Rotation rate is nearly that of Earth’s.

I Reddish color due to iron oxide.I Noachian epoch: before 3.5 Gyr; oldest

surface features (Tharsis bulge) andlate, extensive water flooding

I Hesperian epoch: between1.8 and 3.5 Gyr; formationof extensive lava plains

I Amazonian epoch; after 1.8Gyr; formation of OlympusMons and other lava flows

James Lattimer AST 248, Lecture 19

Mars Geology

I Has craters and high volcanos (higherthan on Earth due to lower gravity).

I No active volcanos or geologic activity forlast 1–2 Byrs, due to low mass andtherefore less radioactivity.

I Valles Marineres is a large canyon(7 km deep, 100 km wide, stretches 1/4across planet), formed by cracking ofcrust as Mars cooled.

James Lattimer AST 248, Lecture 19

Mars Topography

James Lattimer AST 248, Lecture 19

Mars Atmosphere

I Polar caps (mostly H2O with surface CO2)which grow and shrink with seasons.

I Atmosphere only 0.7% of Earth’s, belowthe triple point of water, so no liquidwater possible at any temperature.

I 95.7% CO2, 2.7% N2, 1.6% Ar, 0.2% O2,0.07% CO, 0.01% H2O, 0.01% NO2

James Lattimer AST 248, Lecture 19

Phases of Matter

James Lattimer AST 248, Lecture 19

Phases and Heating/Cooling

heat of fusion

heat of vaporization

James Lattimer AST 248, Lecture 19

Phase Diagrams of Water and Carbon Dioxide

Mars

Earth

.006 MarsEarth

.006

-125◦C

James Lattimer AST 248, Lecture 19

Phases on Other Objects

Mars

Titan

bVenus

James Lattimer AST 248, Lecture 19

Mars Dust StormsI High velocity winds and giant dust

storms on occasion. Winds causedby large temperature differences(day/night and pole/equator)and CO2 condensation/evaporation.Dust loading catastrophicallydevelops into storms like a superDust Bowl (no vegetation toblock it).

James Lattimer AST 248, Lecture 19

Mars and Water

I Evidence for water in past:runoff and outflowchannels. Near-saturation ofatmosphere with waterindicates presence ofsubsurface ice (permafrost).

James Lattimer AST 248, Lecture 19

Mars and Water

Right: Spirit and Opportunity Mars Rovers con-firmed past existence of liquid water by discov-ering ’blueberries’ (nodules from leaching ofminerals to rock surfaces) that formed in rockswhich had been eroded and layered by water.

Below: New deposits in gullies suggestwater carried sediment through themsometime between 1999 and 2005.

James Lattimer AST 248, Lecture 19

Sub-Glacial Water Lake

Found by Mars Express

High salinity acts as an antifreeze.

Lake could absorb oxygen, making it more hospitable for life.

James Lattimer AST 248, Lecture 19

Some Previous Evidence of Water is Suspect

Analysis shows that the flows all end at approximately the same slope,

which is similar to the angle of repose for sand.

James Lattimer AST 248, Lecture 19

NASAJames Lattimer AST 248, Lecture 19

Summary Of Evidence For Water

I Polar caps and other locations are underlain by water ice.I Basalt weathers upon exposure to water into goethite

(iron hydroxide), gypsum, opaline silica and clays, all ofwhich exist on Mars.

I Martian meteorites were exposed to water.I Many former river valleys and lake basins (some with

deltas) have been discovered.I The InSight lander uncovered magnetic pulses and

oscillations consistent with a planet-wide reservoir of deepunderground liquid water.

I The Mars Odyssey orbiter discovered surface H thought tooriginate from underground water.

I The Mars Express orbiter radar detected a 1.5 km-thicksubglacial lake below the southern polar cap, whichpossibly remains liquid due to the anti-freeze effect of Mg-and Ca-perchlorates.

James Lattimer AST 248, Lecture 19

Methane and Organic Molecules on Mars

“Tough” organic molecules discovered in martian sedimentary rocks.

Concentrations of organic carbon are 10 parts per million, the same as

exists in martian meteorites, and a thousand times greater than

previously detected on martian surface.

Seasonal variations in methane discovered, which peak in summer; likely due

to water-rock chemistry and not life.

James Lattimer AST 248, Lecture 19

Evolution of MarsI Original atmosphere of Mars was 600

times as dense, similar to presentthickness of Earth’s atmosphere, andmostly CO2. Where did this gas go?

I Water on Mars’ surface dissolvedsome CO2, some froze into polar caps,some lost to catastrophic impacts.

I Lack of ozone layer led to UVdissociation of N2 and H2O andtheir loss from atmosphere.

I Cooling and solidification of iron coreled to loss of magnetic field and solar-wind stripping of atmosphere.

I Net result: Runaway Refrigerator effect.I Mars is not necessarily too far from Sun to

be Earth-like, but it is too small (not enoughgravity, too rapid cooling) to retain atmosphere and liquid water.

Mars from Pathfinder

Victoria Crater from OpportunityJames Lattimer AST 248, Lecture 19

Viking ExperimentsI Gas exchange (GEX) — Soil sample placed in contact with a

nutrient (“chicken soup”), Gas chromatograph analyzes theatmosphere for changes.

I Labeled release (LR) — Soil sample placed in contact withradioactive C14 nutrient.Radiation detectors monitorsthe atmosphere for changes.

I Pyrolitic release (PR) — Soilsample incubated with radioactiveCO and CO2, then heated to1023 K . Organic gases trapped,checked for radioactivity.

PR experiment designed withoutH2O/nutrient:

I Liquid water cannot exist on Marstoday, so it could trigger a varietyof reactions that mask biologicalactivity.

I The “chicken soup” might end upbeing poisonous to organisms.

James Lattimer AST 248, Lecture 19

Results of Viking Experiments

I GEX — Large amounts of O released, later attributed to inorganicreactions of soil and H2O.

I LR — Wetting produced rise in radioactivity, greater than observedon Earth. Second wetting produced no further response, suggestingthat organic molecules in nutrient reacted with O-rich soil andproduced CO2.

I PR — Radioactive C became part of the compounds in the soilsample. However, when soil sample pre-heated at high temperatures,same effect observed, although microorganisms should already havebeen killed.

However, it’s been suggested that there were so few metabolisingorganisms in the martian soil to be detected by the equipment.Also, organics could have been destroyed upon heating by perchlorates,producing chloromehtane and dichloromethane found by Vikingexperiments.So absence of organics might be a false interpretation.This is not evidence for life, but rather shows the need for more cleverexperiments.

James Lattimer AST 248, Lecture 19

Other Missions up to the PresentI Phobos 1 and 2 – 7 and 12 July 1988; orbited but failed to landI Mars Observer – 25 September 1992; failed orbiterI Mars Global Surveyor – 7 November 1996; orbiterI Mars 96 – 16 November 1996; failed orbiter/landerI Nozomi (Planet-B) – 3 July 1998; orbiterI Mars Climate Orbiter – 11 December 1998; failed orbiterI Mars Polar Lander 00 – 3 January 1999; failed landerI Deep Space 2 – 3 January 1999; failed penetratorI Mars Odyssey – 7 April 2001; orbiter (active)I Mars Express – 2 June 2003; orbiter (active), lander Beagle 2 failedI Spirit – 10 June 2003; roverI Opportunity – 8 July 2003; rover (active)I Mars Reconnaisance Orbiter – 12 August 2005; orbiter (active)I Phoenix – 4 August 2007; Mars Scout landerI Phobos-Grunt – 8 November 2011; failed landerI Yinghuo-1 – 8 November 2011; failed orbiterI Curiosity – 26 November 2011; rover (active)I Mangalyaan – 5 November 2013; ISRO (India) orbiter (active)I Maven – 18 November 2013; Mars Scout orbiter (active)I ExoMars 2016 – 14 March 2016; ESA orbiter/lander (active)

James Lattimer AST 248, Lecture 19

Disadvantages of manned missions:

I Tremendously increased costs of transporting astronauts’ weightincluding food and life-support, including radiation shielding andwater extraction and recycling

I Risks astronaut’s lives; history shows that a large fraction ofmissions to Mars fail.

I Danger of contamination both ways

I History shows they will be based on political, not scientific,considerations

James Lattimer AST 248, Lecture 19

Some Recent Mars MissionsI Mars Global Surveyor

I Thermal emission spectrometers

I Mars Pathfinder, Sojourner roverI Mars was in its past warm and wet,

with water existing in its liquidstate and a thicker atmosphere.

I Mars Odyssey, Mars Surveyor OrbiterI Mars weather and climateI radiation hazards (martian radiation

environment experiment)I gamma-ray spectrometer subsurface

chemistry and waterI thermal emission imaging system for

detecting past water (hematite)

I Spirit and Opportunity, Mars roversI Exploration for evidence of water

I RosettaI Mars and asteroid flyby

I Mars Express

James Lattimer AST 248, Lecture 19

James Lattimer AST 248, Lecture 19

Planned Missions

I InSight - 5 May 2018; lander to arrive January 2019

I ExoMars 2020 (2018 launch) ESA rover and Russian surfaceplatform to arrive 2019

I Mars 2020 (July/August 2020) Curiosity-style rover to arrive March2021

James Lattimer AST 248, Lecture 19

Did Life Once Exist on Mars?

SNC meteorites: unusually young ages, formed on aplanet, blasted into space and exposed to cosmicrays after formation. Hard to blast matter offMercury, Venus or Earth into Earth-crossing orbit,implying Mars or Moon origin. Trapped gases nearlyidentical to atmospheric composition of Mars.Three groups of SNC meteorites:

1. formation age 4.5 Gyr, impact (transit) age 15 Myr

2. formation age 1.3 Gyr, impact (transit) age 12 Myr

3. formation age 170 Myr, impact (transit) age 3 Myr

James Lattimer AST 248, Lecture 19

Did Life Once Exist on Mars?Recently, a NASA team announced possibly detecting evidence of formerlife in ALH 84001, which landed in Antarctica 13,000 yrs ago. Evidenceassociated with carbonate globules, spherical crystals formed as carbonateprecipitates from liquid water permeating the rock 3.6 Gyr ago:

I Carbonate grains with layered structure, indicating biological activity.I Carbonate grains with shapes resembling Earth bacteria, 1/100

thickness of human hair, the same as smallest known Earth bacteria.I Carbonate grains contain biominerals, possibly formed as a result of

biological activity (magnetite, pyrrhotite, and greigite).I Carbonate grains contain complex polyaromatic hydrocarbons (PAH)

whose concentration increases with depth, implying terrestrialcontamination unlikely. These PAHs differ from those observed inother meteorites or cosmic dust.

I Coincidence of 3.6 Gyr globule age with liquid water on Mars.BUT:

I There are nonbiological ways to produce layered carbonates.I Extremely small size of nanobacteria-like shapes disturbs

biochemists, as there is no evidence of cell walls, reproduction,growth, or cell colonies.

I 32S/34S higher than in Earth life.I Discovery of terrestrial microorganisms in meteorite shows that some

contamination has occurred, and could explain the PAH evidence.I Previous claims of “life” in meteorites have always proved false.

James Lattimer AST 248, Lecture 19