Exploring and Understanding the Primitive Bodies of the Solar System: Progress Report from the Primitive Bodies Panel of the Decadal Survey

J. VEVERKA, H. MCSWEEN AND THE PRIMITIVE BODIES PANEL

AGU MEETING SAN FRANCISCO, CA DECEMBER 18, 2009 Primitive Bodies Panel: Decadal Study

Erik Asphaug UC Santa Cruz Mike Brown Caltech Don Brownlee University of Washington Marc Buie Southwest Research Institute Marc Rayman Jet Propulsion Laboratory Ed Reynolds Applied Physics Laboratory Mark Sephton Imperial College, UK Jessica Sunshine University of Maryland Faith Vilas MMT Observatory

J. Veverka, Chair Cornell University H. McSween, Vice Chair University of Tennessee Primitive Bodies Panel: Meetings

Washington, DC September 9 – 11, 2009 Irvine, CA October 28 – 30, 2009 Knoxville, TE April 26 – 28, 2010 What is “Primitive”?

NEO’s Comets Man Belt Asteroids Centaurs Trojan Asteroids TNO/KBO’s

Small Satellites (e.g. Phobos & Deimos) Primitive Bodies: Importance of Ground-based Observation

! Numbers of known NEO’s, MBA’s, Trojans, Centaurs, TNO/KBO’s increasing rapidly ! Telescopes/surveys essential to physical and spectral characterizations of these objects ! Radar observations provide additional characterizations of closer objects AND extremely accurate orbital determinations Primitive Bodies: Importance of Ground-based Observation Arecibo Radar

Arecibo radar image • More than 50% of NEO binary of 2006 VV2 systems discovered at Arecibo 7.5-m resolution – Unambiguous detection in a single night – Geometry not important for detection – Size ratio not important for detection • Both known NEO triple systems discovered by radar 2001 SN263 • Size and semi major axis 75-m resolution determinations yield masses and m densities directly 7494.81145

10.31765 m/s Primitive Bodies: Importance of Ground-Based Observations Sloan Digital Sky Survey

! Multi-color survey of the sky yielded correlation between color and orbital elements of 30,000 MBA’s ! Can study color differences within individual families ! Can identify unusual objects which merit further study ! Can estimate albedo using approximate color/albedo correlation Primitive Bodies: Importance of Ground-based Observation Large Synoptic Survey Telescope (LSST)

! Planned 8.4 meter sky survey telescope in Chile ! In ten years of operation will detect ! 100,000 NEO’s ( >0.1 km) ! 5.5 million MBA’s (>0.3 km) ! 300,000 Trojans ( >1 km) ! 40,000 KBO’s ( >100 km) Missions to Primitive Bodies The Past Decade

Asteroids Comets KBO’s NEAR Deep Space 1 New Horizons Hyabusa Stardust Rosetta Deep Impact Dawn DIXI Stardust-NExT Rosetta Asteroids What Have We Learned About Asteroids?

Examples ! Resolution of S-asteroid/ordinary chondrite dilemma ! Rubble-piles exist (Hyabusa) ! Binary asteroids are common ! Yarkowsky and YORP effects are important Multiple Asteroids

! 1/6 of near-Earth asteroids larger than 200 m have satellites! ! Can determine densities and estimate porosities Asteroids

! Spacecraft study of first “rubble pile” asteroid, 25143 Itokawa:

25143 Itokawa, studied by the JAXA Hayabusa spacecraft Close-up of 25143 Itokawa Rubble Pile Asteroids: Circa 1950 Asteroid Detection Programs Have Identified 474,894 Asteroids (JPL Horizons 12/07/09)

Capabilities now exist to detect and study NEOs prior to impact: ! Ground-based telescopes able to observe photometry, reflectance spectra, light curve on approach ! Can determine trajectory and impact point accurately

2008 TC3

Jenniskens et al., 2009 Recovery of 2008 TC3 Asteroids Retain Some Mysteries Comets What Have We Learned About Comets?

Examples ! Pre-solar grains are rare in comets (Stardust) ! High T and Low T materials are mixed in comets (Stardust) ! Comet Nuclei are underdense (DI) ! Some comet nuclei are layered (DI; hints also in DS- 1 and Stardust) ! Smooth flows erupted to surface (?) (DI) Sample Analysis results from the Stardust Mission

Capture track of a strong >10!m particle Most tracks of 1-10!m particles are of this type

Capture track of a weak >10!m particle Many tracks of ~100!m Particles are of of this type Comets in the Microscope

diopsid fassaite e

spinel

gehlenite

melt anorthite

Ti+V nitride & FeNi anorthi te Impact melt Comet Wild 2

! Comet Wild 2 is not predominately made of stardust ! The isotopically anomalous presolar grain content < meteorites ! Most > micron rocky materials were made in the inner SS ! And transported to the Kuiper Belt ! A major fraction of >micron rocky components formed >1400K ! (includes chondrule & CAI fragments) ! Comet Wild 2 contains glycine Key Issues in Cometary Science

! What are the elemental, isotopic, molecular compositions and physical interrelationships of cometary volatiles, organics, and minerals? ! How do comets work? What are the evolutionary processes active on comets and what drives them? Does (primordial?) heterogeneity drive evolution or is the heterogeneity the result of differential evolution? Wild 2

! The surface of 4.5 km Wild 2 is unlike the surfaces of other imaged comets, asteroids or small satellites What Have We Learned About TNO/KBO’s

Examples

! Vast numbers exit (more than 1000 known)

! Population contains “large” (i.e. Pluto-sized objects)

! Binaries are common

! Surfaces properties differ (why?) Largest Known Trans-Neptunian Objects (TNOs) TNO’s: Differences in Surface Composition New Horizons

! Arrives at Pluto on July 14, 2015

! Will Pluto look anything like Triton?

! What about Chiron, Nix and Hydra? Rosetta

! On its way to Comet C-G ! Arrives in 2014 ! Rendezvous and deploys lander to the surface Dawn’s Mission to Vesta

September 2011 – May 2012

Then on to Ceres Dawn at Ceres: August 2014

HST Image What Does a Very Active Comet Look Like?

! For most JF comets less than 10 – 20% of Hartley 2 Encounter 4 November 2010 surface is active (perihelion + 7 days) undergoing sublimation Sun ! DIXI – the former Deep 1.064 AU Earth* Impact spacecraft is on 0.156 AU its way to Hartley 2 Approach phase ! Hartley 2 is unusual: angle = 86.1º

nearly 100% of surface V = 12.319 km/s must be active to

explain observe H2O production rates Nucleus * Earth 30.3º below Sun - V-inf plane Comet declination 6.6º from Earth How Much Does a Comet’s Surface Change Between Perihelion Passes?

! Deep Impact imaged Tempel 1 near perihelion in 2005

! Stardust-NExT will return to Tempel 1 at the next perihelion in 2011 Some Suggestions from the Community (no priority order)

! Primitive Body Sample Return (Comet or Asteroid) ! Main-belt Asteroid Lander/Rover ! Trojan or Centaur Orbiter ! Kuiper Belt Explorer (as a new Horizons follow-on) ! Etc., etc. Primitive Bodies Goals Mission Types

! Discovery-class essential but not sufficient ! Challenges ! Affordable Launch Vehicles ! Power Sources ! ITAR Bureaucracy ! Most urgent need: * Predictable AO Release Schedule at 18 month intervals Primitive Bodies Goals Mission Types

! New Frontiers-class mission can address most but not all Primitive Bodies goals ! Challenges ! Current cost cap too low: should be at least $1B ! Power sources for distant missions no longer available Primitive Bodies Goals Mission Types

! Flagship-class mission necessary to address some key goals (e.g. Cryogenic Comet Sample Return) ! Challenges ! Currently there is only one class of Flagship Mission: HUGE ! Need to define a class of “modest Flagship Missions” in $2B range ! Need to facilitate international cooperation on such missions