Future Life Search Missions: Primitive Bodies Future Life Search Missions: Primitive Bodies Don Brownlee University of Washington Don Brownlee University of Washington Comet Wild 2 from Stardust Asteroid Itokawa from Hayabusa

Bodies that retain abundant solids that were made in the solar nebula or in pre-solar environments Primitive bodies a working definition: With this definition: Most meteorites are not from highly primitive bodies (really primitive materials do not survive atmospheric entry to become meteorites!) With this definition: Most meteorites are not from highly primitive bodies (really primitive materials do not survive atmospheric entry to become meteorites!)

Most solar system primitive bodies formed beyond the “snow line” Most solar system primitive bodies formed beyond the “snow line” Long-lived solar system reservoirs of primitive bodies Kuiper belt Oort cloud Main belt asteroids Trojans- Jupiter & Neptune Some captured Moons Long-lived solar system reservoirs of primitive bodies Kuiper belt Oort cloud Main belt asteroids Trojans- Jupiter & Neptune Some captured Moons high abundance of water, carbon and nitrogen relative to Earth & Mars high abundance of water, carbon and nitrogen relative to Earth & Mars All planetary systems probably have Kuiper belts & Oort clouds

Primitiveness & Heliocentric Distance 80% of ~135 asteroids sampled by meteorites are igneous! Remaining 20% are metamorphic or altered by water (Keil 2000) 80% of ~135 asteroids sampled by meteorites are igneous! Remaining 20% are metamorphic or altered by water (Keil 2000) “main belt” comets Asteroid spectral reflectance classes Asteroid spectral reflectance classes

Transformation of Primitive to Non-primitive Degradation of primitive materials inside small bodies is largely driven by heat 1) Temperature 400 ºC to 1600 ºC for rocks 50K to >150K for ices 2) Aqueous alteration of silicates (T > -15 ºC) Degradation of primitive materials inside small bodies is largely driven by heat 1) Temperature 400 ºC to 1600 ºC for rocks 50K to >150K for ices 2) Aqueous alteration of silicates (T > -15 ºC)

The major heat source for small bodies extinct 26 Al (T 1/2 = 720,000 yrs) The major heat source for small bodies extinct 26 Al (T 1/2 = 720,000 yrs) Al/Mg ratio excess 26 Mg 26 Al/ 27 Al = 50ppm Melted rocks in bodies >150km that accreted <3my Melted ice in very small bodies that accreted <3my Melted rocks in bodies >150km that accreted <3my Melted ice in very small bodies that accreted <3my

Ghosh et al 2006 Primitive! Metamorphism ranges from mild to severe All meteorites are metamorphosed to some degree Metamorphism ranges from mild to severe All meteorites are metamorphosed to some degree Main-belt comets Main-belt comets Heliocentric effects of 26 Al heating = f(accretion rate) Temp (ºC)

Do primitive bodies play a role in the origin of life? 1.Perhaps 2.Perhaps not 1.Perhaps 2.Perhaps not They might play different roles for life formation on HZ planets VS “differently challenged” bodies like Europa & Enceladus They might play different roles for life formation on HZ planets VS “differently challenged” bodies like Europa & Enceladus

Have primitive bodies made or harbored life? BUT: primitive bodies appear to be lifeless & not congenial to life BUT: primitive bodies appear to be lifeless & not congenial to life Primitive bodies are the most organic-rich & water-rich bodies in the solar system! & Many had warm wet interiors for millions of years! Primitive bodies are the most organic-rich & water-rich bodies in the solar system! & Many had warm wet interiors for millions of years! No consensus evidence for life in meteorite parent-bodies Morphological evidence of microfossils - widely dismissed Claus & Nagy 1961 Hoover et al 1998 No consensus evidence for life in meteorite parent-bodies Morphological evidence of microfossils - widely dismissed Claus & Nagy 1961 Hoover et al 1998

Are primitive bodies truly lifeless or are they a planetary protection hazard? Are primitive bodies truly lifeless or are they a planetary protection hazard? P & D type asteroid samples were listed as category II Strict Containment & Handling Warranted  P & D type asteroid samples were listed as category II Strict Containment & Handling Warranted  Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies  Lifelessness is not 100% accepted! In the 1998 NRC Space Studies Board report:

Mixing Effects in the Solar Nebula & possible magic bullets needed for life Mixing Effects in the Solar Nebula & possible magic bullets needed for life Were there magic bullets made in the nebula that were only carried by specific bodies? Were there magic bullets made in the nebula that were only carried by specific bodies? Probably not - at least for >µm materials made at moderate or higher temperature Probably not - at least for >µm materials made at moderate or higher temperature The Stardust comet sample return mission showed that nebular solids were transported over the full spatial range of the solar nebula disk The Stardust comet sample return mission showed that nebular solids were transported over the full spatial range of the solar nebula disk Anything made anywhere was transported everywhere! Anything made anywhere was transported everywhere!

1) Are needed “bio-elements” sufficiently delivered in Moon/Mars-sized embryos or other non-primitive bodies? 2) Are all needed pre-biotic molecules made in-situ on HZ planets? 1) Are needed “bio-elements” sufficiently delivered in Moon/Mars-sized embryos or other non-primitive bodies? 2) Are all needed pre-biotic molecules made in-situ on HZ planets? Are materials from primitive bodies needed to make life on HZ planets? ….. Or not? Perhaps

Predictable roles of primitive bodies for Habitable Zone planets 1.Extinctions caused by major impacts 2.Delivery of H,C & N 3.Delivery of H 2 O & complex organics 1.Extinctions caused by major impacts 2.Delivery of H,C & N 3.Delivery of H 2 O & complex organics

If life needs critical et compounds Are they delivered from primitive bodies? Or from altered ones like meteorite parent-bodies? “cooking” and aqueous alteration inside less primitive bodies may provide critically needed compounds such as amino acids and nucleobases as well as the seeds for homochirality Are they delivered from primitive bodies? Or from altered ones like meteorite parent-bodies? “cooking” and aqueous alteration inside less primitive bodies may provide critically needed compounds such as amino acids and nucleobases as well as the seeds for homochirality

Did Amino acids form inside asteroids? From only trace quantities Tagish Lake (the most C-rich meteorite!) To 250 ppm!! The CR chondrite GRA95229 (Martins et al 2008) From only trace quantities Tagish Lake (the most C-rich meteorite!) To 250 ppm!! The CR chondrite GRA95229 (Martins et al 2008) variations are likely due to internal parent-body processes not nebular processes (nebular materials reasonably mixed) variations are likely due to internal parent-body processes not nebular processes (nebular materials reasonably mixed) The amino acid content of C-rich meteorites varies by orders of magnitude The amino acid content of C-rich meteorites varies by orders of magnitude

L excesses up to 18.5% seen in isovalene Excesses correlate with degree of aqueous alteration Glavin and Dworkin 2009 Suggests formation inside warm-wet parents L excesses up to 18.5% seen in isovalene Excesses correlate with degree of aqueous alteration Glavin and Dworkin 2009 Suggests formation inside warm-wet parents L-amino acid excesses in meteorites

GiottoComet Halley VegaComet Halley GallieoGaspara, Ida, Dactyl Near-ShoemakerMathilde, Eros Deep Space 1Comet Borrelly Deep ImpactComet Tempel 1 StardustComet Wild 2, Anne Frank HayabusaItokawa DawnVesta, Ceres RosettaComet Churyumov-Gerasimenko, Steins Missions to asteroids & comets No comet or asteroid mission has had a strong AB focus

Future Mission Goals Determine organic contents of both primitive & non-primitive bodies at “sample return” level of sensitivity, precision & flexibility Determine organic contents of both primitive & non-primitive bodies at “sample return” level of sensitivity, precision & flexibility 1)Provide pro or con evidence that et bodies provide HZ planets with critically needed pre-biotic compounds 2) Determine the relative importance of “cooked” VS primitive bodies 1)Provide pro or con evidence that et bodies provide HZ planets with critically needed pre-biotic compounds 2) Determine the relative importance of “cooked” VS primitive bodies

An important question for new missions What is the origin of et organics carried to HZ planets 1.Pre-solar? 2.Formed by nebular processes? 3.Formed inside bodies? 1.Pre-solar? 2.Formed by nebular processes? 3.Formed inside bodies? The pre-solar silicate content of primitive meteorites is <300 ppm The pre-solar grain in comet Wild 2 is even less! The survival of pre-solar organics is presumably less (<10 -4 ) The pre-solar silicate content of primitive meteorites is <300 ppm The pre-solar grain in comet Wild 2 is even less! The survival of pre-solar organics is presumably less (<10 -4 )

What might small solar system bodies tell us about the evolution of life around other stars? What might small solar system bodies tell us about the evolution of life around other stars? If “ 26 Al cooked asteroids” are needed chemical factories to make critical pre-biotic compounds If “ 26 Al cooked asteroids” are needed chemical factories to make critical pre-biotic compounds They will not occur around all stars

1)Some planetary systems will either: a) not have long-lived asteroids b) not form them before 26 Al decays 2) Many stars form without 26 Al If the solar system 26 Al came from Wolf Rayet stars Only ~6% of stars will form with solar-like 26 Al abundance Gaidos et al )Some planetary systems will either: a) not have long-lived asteroids b) not form them before 26 Al decays 2) Many stars form without 26 Al If the solar system 26 Al came from Wolf Rayet stars Only ~6% of stars will form with solar-like 26 Al abundance Gaidos et al Cooked Asteroids Elsewhere Most will be 26 Al poor Et Life loves radioactivity??

Asteroids and comets retain the only direct evidence that we have the Early solar system Asteroids and comets retain the only direct evidence that we have the Early solar system Future missions are needed to both primitive and “cooked” bodies to understand their possible roles in the origin of life around stars

“Stimulus Package” Mission List Primitive bodies active comets- different types cryogenic return of sub-surface samples Cooked bodies asteroids various types (meteorites are a biased sample) Haumea - a 1500 km KBO (big cooked comet!) dense rock with bits of preserved frozen ocean a collisionally broken-up Pluto-like planet Primitive bodies active comets- different types cryogenic return of sub-surface samples Cooked bodies asteroids various types (meteorites are a biased sample) Haumea - a 1500 km KBO (big cooked comet!) dense rock with bits of preserved frozen ocean a collisionally broken-up Pluto-like planet