Exoplanets and Astrobiology - InSight Cruises · 2017-12-20 · • The basic molecular chemistry...

Exoplanets and Astrobiology: Abiogenesis: The Greatest Unknown in the Story of Our Origins

Edwin L. Turner Department of Astrophysical Sciences, Princeton University

The Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo

Program in Interdisciplinary Studies, Institute for Advanced Study ++++++++++++++

Bright Horizons 27, m/s Noordam, 31 October 2015

Lectures

!  Exoplanets: Strange New Worlds by the Thousands October 26

!  The Quest for Nova Terra, An Earth Twin October 28

!  Life as We Don’t Know It Among the Stars October 30

!  Abiogenesis: The Greatest Unknown in the Story of Our Origins October 31

TheMolecularBiologyofTerrestrialLife

•  Extraordinarilycomplex&inter-connectedchemicalprocesses,vastlyricherandmoreintricatethananyotherknownchemicalsystems

•  Basicbiochemistrysharedbyallknownterrestrialorganismsplusmanyofitsdetails

•  Carbonbasedandwaterdependent•  Hierarchicallystructured(usingmuchsimplersubcomponents),polymerizedmacromolecules

•  Few(4)generalclassesofcompoundsbutmanyindividualoneswithhighlyspecializedandspecificbiologicalfuncIons

OriginofLifeProblem

•  RequiresnoexoIccondiIonsorconsItuents•  Appearstohavehappenedonlyonce,butquitequickly,onEarth

•  Intricatecomplexity->originproblem– VastcomplexityjumpwrtotherabioIcchemistry– Noobviousrouteforgradualdevelopment– Nosurvivingremnantsor“fossils”ofit– LiVleornofirst-principletheoreIcalinsights

•  EvoluIonaryadaptaIonanddevelopmentoncenaturalselecIonstarted

Oparin-Haldane(1920s)Scenario

StandardModernRNA-WorldScenario

ADevilishDetail:TheRibosome

NaturalSelecIonRequirements

•  FlexibleinformaIonstorage•  FuncIonalexpressionofstoredinformaIon

•  ReplicaIonofstoredinformaIon– Copiesmustbegoodbutnotperfect(“errors”crucial)– ReplicaIonmustberobustdespite“errors”– “Errors”mustbestochasIc

•  Self-sustaining/self-powered

AddiIonalDownstream“Jumps”

•  RNAWorldtoDNAWorld•  NucleicAcidstoProteins•  ProkaryotestoEukaryotes•  Animal-plantdivision

•  Metazoa

•  Nervoussystems

•  …

Why We Think the Universe to be ∞ Why We Think the Multiverse Exists

•  Universe’s large scale properties are very simple (odd!?) •  Simplest possible space-time metric astonishingly

accurate •  Confirmed by ~90 years of increasingly accurate and

diverse data •  Inflationary Big Bang model explains all available data

and makes detailed & successful quantitative predictions •  Nature is extravagant in scale and scope •  ∞ is a VERY round and natural “number” •  But ∞ universe has many paradoxical/weird implications •  Not empirically verifiable even in principle (science?)

UnaVracIveButPlausibleScenario:ImprobableLife

LifeonEartharoseviaanextraordinarilyimprobableeventorseriesofevents,inotherwordsbyanextremestaIsIcalanomaly,inaninfiniteuniverse/mulIverse.LetustakethistomeanthatPabiogenesis<<<1perHubblevolumeperHubbleIme,i.e.,thatitisextremelyunlikelythatthereisanyextraterrestriallifeintheobservableuniverse.ItalsoimpliesthatweareunlikelytoeverunderstandtheOoLontheEarth.

AnUnappealingTheory

•  Whyitisunappealing(tomost)•  IrraIonalconsequencesofitsunappealingcharacter

•  Usualresponse=thereareotherpossibiliIes•  Ourgoaltoday=afairexaminaIon

•  Fair=evidencethatsupportsit,whatitexplains,whatdisfavorsit&itsrelaIvemeritcomparedtoknownalternaIves

SUPPORTING/SUGGESTIVEEVIDENCEI:Combinatoricimprobabilityofbiopolymers

•  “LeVers"ofbio-alphabetproducednaturallyinfairconcentraIons

•  Enormousflexibility–“Legolife”•  Vast"space"ofpossibiliIes->anyspecificbio-polymervanishinglyimprobable

•  MonkeysandtypewriterswriIngsonnetsandnovelsetc

•  Minimalcomplexity(fornaturalselecIontobegin)appearstobesubstanIal

•  ThebasicmolecularchemistryofallterrestriallifeisessenIallyidenIcalandverycomplex.

•  Twoclassesofmacro-molecules,proteinsandnucleicacids,playcentralrolescurrently,butitisoienthoughtthatRNAalonemighthavesufficedforanearlierformoflife(the“RNAworld”).

•  Thebuildingblocksofbothproteins(aminoacids)andnucleicacids(nucleoIdes)areasetofsmallmoleculeswhichformbondsinanarbitraryordertocreatethelongpolymerswhicharethesemacro-molecules.

•  BothaminoacidsandnucleoIdesareproducedinreasonableabundancebyphysical(abioIc)chemicalreacIonsthatcaneasilyoccurinnature.

•  However,thepolymersinquesIonarehuge,typically100sto100sofmillionsof“buildingblocks”long,withevenminimallyfuncIonalonesrequiring~100nucleoIdesoraminoacids

•  Smallestgenomes=1821&112,091basepairs(humangenomeabout3x109basepairs)

•  Theprobabilityofanyspecificonearisingrandomlyisthencombinatoriallysmall,easily≈10-1000sormuchless.

•  Aribosomecontains~4x107basepairs+~30-50proteins(nucleicacidinfo"proteins).Ribosomerequiredtomakeanewribosome,“chicken&egg”!

Abiogenesis:StochasIcLegoConstrucIon?

SUPPORTING/SUGGESTIVEEVIDENCEII:BennerObjecIons

•  TheDevoluIonProblem:tar•  TheWaterProblem:corrosion

•  TheLowConcentraIonProblem:isolaIon

•  TheTwoBirdswithOneStoneProblem:bothself-catalysisandcontrolledreplicaIon,butthesearequitedisInctinknownRNA

•  TheSelf-DestrucIonProblem:mostprobableRNA-enzymesdestroy/cutRNAstrands

SUPPORTING/SUGGESTIVEEVIDENCEIII:"RareEarth"TypeArguments

•  Inthe“GalacIchabitablezone”•  Asuitablecentralstarandplanetarysystem•  Inthecircumstellarhabitablezone•  Asuitablesizedterrestrialplanet•  Agasgiant“guardian”,giantimpactinhibitor•  Alargesatellite•  Amagnetosphere•  Platetectonics•  Rightamountofwater•  Afavorablechemistryofthelithosphere•  Atmosphereandoceans•  …

NATURALLYEXPLAINEDI:Biological/Physical

•  Huge"missinglink"ofintermediatecomplexitylifeandproto-life,noabiogenesis"fossils”

•  Failuretosynthesizelifeinthelabtodate•  NohighprofilelifeelsewhereintheSolarSystem

NATURALLYEXPLAINEDII:Astronomical

•  Fermi-HartParadox:nolocalaliens->noGalacIccolonizaIon->notravelingaliens

•  Universeappearstobeawilderness->nohyper-advanceddistantaliens

•  FailureofSETItodate->nochaVyaliens

NoaliensatallisaparsimoniousexplanaIon.

CHALLENGESTOTHEIMPROBABLELIFESCENARIO

•  Life arose (on Earth) despite infinitesimal probability, but just a selection effect in an infinite universe or multiverse

•  Life appeared on Earth very quickly, but this datum provides no meaningful lower limit on the abiogenesis probability (Spiegel & ELT)

•  Progress in understanding self-organizing systems and the emergence of complexity: Is decreasing min entropy/complexity analogous to thermodynamics…an inherent physical “direction” of change? (Maybe, but LAWKI is a set of small measure in the space of all possible complexity.)

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MERITRELATIVETOOTHERAVAILABLEOoLTHEORIES

•  AsgoodasanyotherOoLscenario/theoryandbeVerthanmanyonpurelyempiricalgrounds

•  AnypossiblealternaIveseemstoentailsomethingakinto“intelligentdesign”,i.e.,theemergenceoflifesomehowinherentinthebasiclawsofnature,auniverse“madefor”life

•  Eminentlyfalsifiable

“Thefirstprincipleisthatyoumustnotfoolyourselfandyouaretheeasiestpersontofool.”―RichardP.Feynmanonscience

CONCLUSIONTheimprobablelifescenarioshouldberegardedasarealisIcpossibilitybyastrobiologistsandOoLresearchers(eventhoughtheyhateit!).

ThesoluIontotheOoLproblemmaybeinImatelyconnectedtothelargestscalenatureoftheCosmos.

“Ithinkit'smuchmoreinteresIngtolivenotknowingthantohaveanswerswhichmightbewrong.”―RichardP.Feynman

DarkEnergyvsOoLMysteries

•  MuchFirstPrinciplesPhysicsvsLiVle/NoFirstPrinciplesBiology

•  WellDefinedDEExperiments/Measurements&TheoreIcalIssuesvsNoClear/ConsensusPathForwardOfAnySort

•  ASingleHardProblemvsMulIpleOnes•  QuanItaIvevsQualitaIveChallenge•  BothInviteAnthropicPrincipleExplanaIons

"OoLisabigger/deepermysterythanDE