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Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Asteroids Comets Meteors.

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Presentation on theme: "Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Asteroids Comets Meteors."— Presentation transcript:

1 Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Clark R. Chapman Southwest Research Inst. Boulder, Colorado, USA Asteroids Comets Meteors 2005 Buzios, Rio de Janeiro, Brazil, 9 a.m., Monday, 8 August 2005 Asteroids Comets Meteors 2005 Buzios, Rio de Janeiro, Brazil, 9 a.m., Monday, 8 August 2005 Invited Review: Physical Properties of Small Bodies from Atens to TNOs Gary Emerson

2 Classes of “Small Bodies” Inner-Earth Objects (IEOs or Apoheles) NEAs (Atens, Apollos, Amors) Main-Belt Asteroids (incl. Hungarias, Cybeles, Hildas, etc.) Trojans (of Mars, Jupiter, Neptune…) Centaurs, Scattered-Disk Objects KBOs (Plutinos, Cubewanos) Oort Cloud (inner) Comets (JFCs, longer period comets) Planetary satellites (irregular, regular) IDPs, Meteoroids, Meteorites “Small bodies” ~10 m to 1000 km diam. Pluto, 2003 UB313, other large TNOs By Orbital Class By Size

3 Kinds of Physical Properties: Observables and “How Well?” Types of Observations spectral reflectance & emission (UV – radio) temporal variations (lightcurves, outbursts) satellite orbits, perturbations on other bodies imaging Earth-based (optical/IR AO, radar) Fly-by/orbital/lander spacecraft in situ measurements/sample return [future] Degrees of Knowledge of Properties rough size (no albedo), vis./IR colors spin period, albedo, spectral type, oblong/sph. detailed shape, major minerals/ices, spots detailed lab data on samples; parent unknown large-scale geology, spatial compos., mass Detailed obs./measurement by orbiter/lander What is Learned composition, regolith spin, shape, volatiles mass (density) structure, geology cosmochemistry, geophysics Minimal info/most objects Maximum info/few bodies

4 Colors of Centaurs, KBOs, SDOs Bi-modal colors especially Centaurs esp. not Cubewanos Weak correlations with orbital elements, dynamical groups Comets do not match colors of sources (implies processing) e i aa Doressoundiram et al 2005 Hainaut & Delsanti database Delsanti et al 2004 q B-R

5 Main-Belt Asteroid Colors: Then…and Now Asteroid data 35 years ago like TNO data today Disputed clusters partly OK Trends with a,e,i convincing only after debiasing (~1975) Matching colors/reflectance spectra to mineralogy only fair (space weathering, etc.) Today: abundant statistics, hi-res spectra, good compos. Colors for tens of thousands Reflectance spectra: 1000’s Good correspondence of taxonomy with meteorites Relationship of NEAs to main-belt asteroids clear Families as catastrophic collision products of (usually) homogeneous parent bodies Hapke (1971) Chapman (1971) Ivezic et al (2002) Data from Gehrels (1970) Burbine et al (2001) Lessons Learned

6 NEA Colors (Binzel et al. 2004) S/Q type colors Space-weathered (like M.B.) >5 km Range from ord. chond. – M.B. <2 km Spread of fresh to matured surfaces Implies there may be small M.B. Q’s NEA colors vs. M.B. Q’s are NEAs only More extremes D-types (upper-rt) 10-18% of NEOs could be extinct comets Diversity like M.B. Outer M.B. under- represented a bit (beyond low albedo bias)

7 Size Distributions NEAs less “wavy” than large Main Belt ast. TNOs have shallow slope at <20 km diam. Comets “truncated” km (Meech et al. 2004) Separate SDs for different families/groups Main Belt TNOs NEAs Bernstein et al Tedesco et al NASA SDT 2003

8 Detailed Earth-based Studies of Individual Objects (examples) The period of rotation, shape, density, and homogeneous surface color of the Centaur 5145 Pholus S.C. Tegler et al. (2005) Brown et al Cruikshank et al Pholus 4 Vesta 4179 Toutatis 5145 Pholus 4 Vesta 4179 Toutatis Bogard & Garrison 2003 Vernazza et al Hudson et al Mukai et al Kryszczynska et al HST Polarization

9 Shapes of Comet Nuclei & Asteroids Gaspra Mathilde Kleopatra Tempel 1 Wild 2

10 Geophysical Properties Spins, shapes, satellites, masses, densities, strengths, interior structures Most remote-sensing of surfaces reveals little about interior properties Rapid spins = monolithic structure; do slow spins imply rubble piles? Impact experiments, numerical modelling, scaling analysis NEAR laser altimetry probes interior of Eros Holsapple 2005 Neumann & Barnouin-Jha 2005 Korycansky & Asphaug 2005 NEAR Laser Altimeter: Eros

11 Spacecraft: Orbiters, Landers, and (soon) Sample Returns Many fly-bys of small bodies Significant reconnaissance Surprises: no 2 bodies same NEAR Shoemaker orbital mission to Eros (& landed!) Detailed remote-sensing Composition: ord. chondrite Impact, landers, sample ret. Deep Impact experiment Contact with Itokawa soon Awaiting sample returns by Stardust & Hayabusa Must extrapolate physical properties measured for few visited small bodies to vast, heterogeneous population Lim et al NEAR XRS data suggest Eros composition ~ ordinary chondrites

12 Unexpected Small- Scale Geology of Eros Flat ponds and “beaches” Small craters absent; dominant boulders

13 Itokawa (1) [Saito et al. 2006]

14 Itokawa (2) [Saito et al. 2006]

15 Surface Geology of Tempel 1 Flat, smooth areas; craters; ridges; bright spots… What processes are at work? Over what duration of time? Preliminary answers at 11 am today!

16 Dynamics: Relationships to Physical Properties Dynamical processes cause physical properties Spins and axis orientations due to Yarkovsky Effect Tidal interactions with planets/sun cause distortions and disruptions/disintegrations Collisions and catastrophic disruptions create families, rubble pile structures, satellites (initial spins, sizes) Physical properties elucidate dynamics Colors help identify dynamical families Yarkovsky/YORP effects depend on albedo, shape, thermal inertia, spin, density, etc. Dynamical analysis can determine physical properties Mass (hence density) Spins (very rapid spins indicate monolith, not rubble pile) Non-gravitational forces imply features of comet nucleus Dynamical analysis helps us study physical processes Specific ages for families specify rates for processes like space-weathering How perihelia evolve and facilitate volatilization

17 NEO Impact Hazard: Apophis (2004 MN4) In astronomy, only solar flares and impacts have major practical effects 1:8000 chance that 320m asteroid impacts 4/13/36 (~ South Asia tsunami) Physical properties affect: Whether it hits “keyhole” How Yarkovsky affects it How we could attach to it, couple energy to divert it How it responds to forces How it responds to tidal forces during 2029 fly-by Consequences of impact In the extremely unlikely event that it will hit, ground-zero will be somewhere on the red line

18 Themes and Issues How much are we astronomers fooled by the space-weathered, impacted optical surfaces? Can we really comprehend how processes work at near-zero gravity? Really what are the densities, porosities, granular structures, strengths? Are these splitting/vanishing comets “dust bunnies”? Are M-types metallic cores? (many evidently aren’t) Regolith-free bare rocks vs. “talcum powder” Biased view from what penetrates our atmosphere What are we missing? 2003 UB313: we weren’t looking for high-inclinations Hypotheticals: “vulcanoids”, Lou A. Frank “LAFOs” Interstellar small bodies? Asteroid belts/Oort clouds around other stars

19 Asteroids/ Comets: Evolving Perspectives… ASTEROIDS Rocky, metallic, no active geology, cratered, collisional fragments, some differentiated by heating COMETS Icy, under-dense, no active geology, pristine…until they come close to the Sun, become very active, disintegrate Traditional View ASTEROIDS Under-dense, rubble piles, many volatile-rich (except at surfaces), some non- impact geology, many satellites; NEAs tidally evolvedCOMETS Active, fluffy, evolved bodies with complex geology (impact & non- impact), easily split; precursor KBOs have satellites, interior “oceans” Emerging Continuum

20 Main-belt Comets (1)

21 Main-belt Comets (2)


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