sign in sign up
<<
Home , Chasma, Martian meteorite

The Solar System as we know it and the Story of ALH84001 30 km 30 km belt 2-4 AU Karen J. Meech, Astronomer Trish Doyle, Geo- / Cosmochemist Institute for Astronomy

Amended Freedman et al. (2008)

Searching for on Mars: Overview

Criteria for life & Meteorites What tools are needed • History & formation • Falls of note • The US Meteorite program What would you consider Searching for Mars Life • • The Mars Viking Experiment as convincing evidence • History ALH84001 • Findings for life on a planet? • Description • Pieces of evidence

Summarize Findings

What would you consider as What Tools Would you Need? convincing evidence for life on a planet? In situ / Physical specimen Physical evidence e.g. In situ / Physical specimen Physical evidence e.g. Fossils

Crinoid stems Tubes made by a worm-like organism Collection team Scanning electron microscope Realistic setting – time / space Biological indicators e.g. Realistic setting – time / space Biological indicators e.g. isotopes !13C (‰) 0- DIC marine CO atm -10- 2 C4 plants phytoplancton -20- C3 plants -30- exposure dating -50- Biogenic -110- Methane CO2 Primary producers Consumers Adapted from Boschker & Middelburg (2003) Atmospheric measurements dating Gary Huss (2007) Scanning Electron Microscope What May Cause Concern?

In situ / Physical specimen Physical evidence e.g. Fossils ! Accessible technology ! Focused e- interact with sample Contamination Sample surface Storage & preparation ! Magnetic fields move the beam over sample Biogenic vs. inorganic ! So good: see new features! signatures Realistic setting – time / space Biological indicators e.g. isotopes ! Works best if sample is coated ! Vapor coating of carbon, , palladium 2-20 nm - Not derived from analogues a habitable zone

- Funding for Good background research

James Lovelock & Mars NASA Searching for : Viking (1961) ! Asked to provide advice on life detection – how to recognize it ! A planet will exhibit an atmosphere which is far from chemical equilibrium if there is life ! if there is life, it must be pervasive (i.e. there can’t be a little bit of life) ! life uses liquids and atmosphere to "communicate" or interact by sharing nutrients, wastes & evolution, Viking experiments ! Thus the chemistry of the environment should be constantly changing in the presence of life ! Prediction: ! Life will not be found on Mars – because it exhibits Atmospheric equilibrium chemistry

N2 < 2% N2 ~ 77% N2 < 3% CO2 ~ 95% CO2 ~ 0.03% CO2 ~ 95% No O2 O2 ~ 21% No O2 Chemical eqm Disequilibrium Chemical eqm

Viking Mars Mission Viking Orbiter Images

! 1968 James Martin asked to lead mission science ! Launch Viking 1 8/20/75; Viking 2 a mo later ! Viking 1 lands - 20 July 1976 ! Viking 2 lands - 3 September 1976 ! 2 program – search for life

Viking 1 orbiter image Candor () 1978 Mars Environment

! Viking temperatures – similar at both landing sites Viking 1 panorama after landing (300o FOV); dunefield; rocks & silt – no obvious life ! Effect of large dust storm is seen in the Temperature profile

Sunset 20 Aug 1976

Mars Viking Life Experiments Viking Life Experiments Press Conference

! Gas Exchange Experiment (GEX) ! changes in the makeup of gases (related to biological activity) in a test chamber “Viking not only found no life on Mars, it showed why there is no life there.... the extreme dryness, the pervasive short- ! Labeled Release Experiment (LR) wavelength UV radiation... ! Detect the uptake of a radioactively-tagged liquid nutrient by microbes ! Gases emitted by microbes would show tagging. Viking found that Mars is even dryer than had previously been thought... ! Pyrolytic Release Experiment (PR)

! "cooking" regolith samples exposed to radioactively-tagged CO2 to see if the chemical had been used by organisms to make organic compounds. The dryness alone would suffice to guarantee a lifeless Mars; combined with the planet's radiation flux, Mars becomes ! Gas Chromatograph – Mass Spectrometer Experiment (GCMS) almost moon-like in its hostility to life." ! Heated a regolith sample ! Revealed an unexpected amount of water ! Failed to detect organic compounds. This absence was so absolute that it seemed there must be some mechanism actually destroying carbon compounds on the surface.

Viking Life Searching for Life on Mars:

! Lead scientist, H. P. Klein said the experiments didn’t rule out life, either ! Levin (Mars team) said LR experiment showed life Meteorite background ! Most scientists believe chemicals created a false positive

! Data is available to the public ! The debate continues

! NAI – important to understand the biomarkers – what would be the sign of life. Meteorite History Origin of Meteors / Meteorites

• Earth passes through dust in orbit • Burns in Earth atmosphere • Larger chunks resulting in meteorite finds come from • Moon • Mars ! Most famous European fall – 17 Nov 1492 • Asteroid collisions ! Witnessed (boy) – m-deep hole ! Attracts attention of Emperor Maximilian ! Considered good omen – preserved

Fireballs / Debris The 15 Feb 2013 Fireball

• Chelyabinsk Russia • Largest since 1908 • Size ~ 17 m (larger than early est) • ~ 104 tons, v = 18 km/s • Energy ~ 500 kilotons TNT • Fall found – ordinary • < 10% metallic iron • Largest piece likely in lake

Tagish Lake Meteorite US Antarctic Meteorite Program • Canadian fall 18 Jan 2000 ! NSF – Funds collection near transantarctic mountains ! Desert-like conditions • 56 ton ! Contrast between low albedo meteorites & snow • 4m diam (500 fragments found) ! NASA – Examines at JSC in Houston • Primitive CC () ! Smithsonian – Curates • 2 diff types mixed (CI, CM) ! 15,000 specimens, 13,000 from 6 – some with carbonates ! Oldest – Earth residence 10 yrs ! 1981 – first recognized from Moon • Full of nanodiamonds

• Low density ! 2006 Mt. expedition (UHNAI postdoc) • Form farther out in SS • D-type parent: 773 Irmintraud Meteorites Meteorites Undifferentiated Differentiated Undifferentiated Differentiated (Non-chondritic meteorites) (Non-chondritic meteorites) Chondritic Meteorites 3 types - Ordinary - Carbonaceous - Enstatite

5 main components ALH 77005 (Mars) ALH 77005 (Mars) (including the oldest dated material in the Solar System)

Allende (CC) Allende (CC) Adapted from http://www.mnh.si.edu/earth/text/5_1_4_0.html Adapted from http://www.mnh.si.edu/earth/text/5_1_4_0.html

Meteorites Meteorites Differentiated Differentiated (Non-chondritic meteorites) (Non-chondritic meteorites) Stony (including ) Ni-Fe meteorites Stony Stony • 95% of all meteorites • Widmanstatten pattern

• size is related to cooling times for • From differentiation Stony- • Melt near surface • 1% of total finds Stony-Iron Stony-Iron

Iron • 4% (most often found) • Pure metal – Ni/Fe alloy Iron Iron • Form by differentiation then breakup of parent

Meteorites Differentiated Mars Meteorites (Non-chondritic meteorites) • Stony • • • • HED (3 types) ! Mars Origins

• Lunar Stony-Iron ! Large volatile composition " • (4 types; SNC) has atm • Shergottites • Typical of terrestrial ! Isotopic Fractionation " • pattern unique: Mars • Larger Fe-rich / • Form with aqueous alteration ! Find Locations Iron • ! 50% in Antarctica • 90% olivine, 10% pyroxene ! • (ALH84001) 1 from Nigeria Krot et al. (2003)

D Meteorite Allende (CC) Which of the following meteorites is least likely to be a ?

C Peekskill stony A Stony-Iron

B Stony

Searching for Life on Mars History – ALH 84001 Case Study: ALH 84001 ! Discovered in Antarctica (‘84) Physical specimen Physical evidence e.g. Fossils ! Known from Mars because of

Human history Fossils? atm gases Description Remnants of Fe3O4 from ! Notable

! Oldest from any planet

Realistic setting – time / space Biological indicators e.g. isotopes ! Orthopyroxenite (not SNC)

Carbonates ! Notoriety (‘96) Meteorite history Presence of organics & Fe3S4 ! NASA: evidence for life on Mars

Description of the Meteorite Life Story of ALH84001 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Gy Possible wet era Possible formation of carbonates

Mars Ejection ! Or ejection from parent ! Cosmic ray exposure age Impact ! 95% orthopyroxene ! 16-17 x 106 yrs ago ! Brings ALH84001 to the surface ! Crystal structure has many cracks ! Cracks have glasses (melted rock) from 30 GPa shock pressure ! Shock deformed impact glasses 10 (3x10 atm) ! Pressures exceed 30 Gpa ! Cracks have 0.1mm carbonate (CO3) globules " flattened Crystallization Fall to Earth (grew in cracks) ! Large % of orthopyroxene (Mg,Fe)SiO3 ! 13,000 ago ! Polycyclic Aromatic Hydrocarbons (PAHs) near carbonates ! Large " slow cooling ! 14C dating ! Crystals settle in magma " lg reservoir ! Dissolved carbonates " and iron sulfide (Fe3S4) Life Story of ALH84001 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Gy The Fossils Possible wet era

Possible formation of carbonates ! Tube-shaped " similar to filamentous cyanobacteria ! 20 nm in size Mars Ejection

Apex Chert 3.5Gy " Impact

Crystallization Fall to Earth

Magnetite & Fe3S4

Compelling evidence for life Physical specimen Physical evidence e.g. Fossils ! Bacteria use magnetite as a compass to aid in navigation

Realistic setting – time / space Biological indicators e.g. isotopes

ALH84001 – Mars Life Morphology alone Essential Findings cannot be used unambiguously for ! 6 Aug 1996 Press Conference primitive life detection ! NASA Administrator W. Huntress & David McKay Physical specimen Physical evidence e.g. Fossils “ . . .in examining the Martian meteorite ALH84001 we have found that the following evidence is compatible with the existence of life on Mars . . . “

! penetrated with fluid " mineral formation & biogenic Realistic setting – time / space Biological indicators e.g. isotopes activity ! SEM images of carbonates " structures similar to microfossils ! Fe sulfide & magnetite " life process signature ! Concentrated PAH’s

Extraordinary claims require extraordinary evidence – C. The Fossils Sample Preparation?

Very controversial ! Too small for life " 100x smaller than terrestrial ! Life requires cellular structure ! Too small to test composition ! Ruled out contamination

! Thick coatings can “crack” " “segmented” features ! Coatings can smooth out features ! Surfaces can be examined w/o coating " lower resolution

Carbonates Magnetotactic Bacteria?

! Inorganic precipitation ! Neutral pH ! Cannot explain Fe S ! Low T formation ! High T formation 3 4 ! Simultaneous precipitation ! Aqueous 30-80o C ! Petrographic analysis suggests ! ! O isotopic ratios this method Requires high pH (alkaline) ! Carbonates # " life process ! Elemental abundances ! Dissolved CO3 " low pH (acid) on Earth (low T) ! Requires assumptions about ! Acid should affect other ! Supported by O isotopic chemical equilibrium (unverified) minerals (not seen) abundances ! Biogenic disequilibrium ! If formed in liquid " should see ! Life process (?) as on Earth other hydrated minerals (missing) ! Other processes?

Crystal Structure Presence of Organics

Movie ! Inorganic minerals align when one solid forms on surface of another ! No organics from Viking ! Mass spectrum totally flat at zero ! Movie @ left " (Fe,Mg,Ca)CO 3 ! Should have Mars organics formed on inclined fracture ! Near C-rich ! Non-circular craters ! in voids " oriented ! Only form from oblique impacts with respect to CO3 ! Implies a close source – in orbit ! and are CM type material (organic rich) ! Magnetite crystals forms inside CO by diffusion of atoms 3 ! UV destruction in upper regolith layers

Alternate Ideas – Contamination? Presence of Organics

Compound/Atomic Mass ALH84001 EET79001 Ice Napthalene (128) Not detected Not detected Present Fluorene (166) Not detected Not detected Not detected ! PAH ! Groups of benzene rings Phenanthrene (178) Present Present Present ! Present on Earth in decayed organic Chrysene (228) Present Present present material (e.g. coal) ! PAH found in ALH84001 Perylene (252) Present Present Present ! Not caused by lab contamination Anthanthrene (276) Not detected Present Not detected ! Not caused by Antarctic contamination ! Mass spectrum Anthanthracene (278) Present Present Present ! Simpler than any on Earth Coronene (300) Not detected Not detected Present ! Different from meteorite mass spectra ! Possible early life? ! EET79001 – only L-amino acids found (contaminates) Don’t know character of ancient DNA ! Carbonates absorb PAHs from water (L. Becker expt) ! ALH84001 was sitting on Antarctic ice for 13,000 yr

Carbonates Fe S / Magn. Organics Fossils 3 4 Consequences of ALH 84001

High Mag Both Other CCs IDPs ISM corrode Samp Contam ! Oldest rock from any planet T form neutral high pH ? dust Prep. ! Shows ancient Mars crust very well preserved

CO 3 Low mass absent ! Stimulated an era of bioastronomy low pH Distn high m diff ! Sequence of Mars Missions Low T ! Renewed vigor for life searches H2O Bio non (e.g. President’s 2004 initiative) Earth fossils Similarities eqlbm Too complex Date uncertain, ! Stimulated new research H2O era possible Resid mag from Early life " When • Where • Form • Amount 10-100x too small! Earth bacteria same simple PAH?

Closing Thoughts

“Science is self correcting. ! The goal is to know. ‘Possibly! perhaps! maybe’ are not firm answers, and feel-good solutions do not count.” - The Hunt for Life on Mars .

“The absence of evidence is not evidence for absence” - Sagan .