Iron meteorites as remnants of planetesimals formed in the terrestrial planet region

Iron meteorites are core fragments from differentiated and subsequently disrupted planetesimals. The parent bodies are usually assumed to have formed in the main asteroid belt, which is the source of most meteorites. Observational evidence, however, does not indicate that differentiated bodies or their fragments were ever common there. This view is also difficult to reconcile with the fact that the parent bodies of iron meteorites were as small as 20 km in diameter and that they formed 1–2 Myr earlier than the parent bodies of the ordinary chondrites. Here we show that the iron-meteorite parent bodies most probably formed in the terrestrial planet region. Fast accretion times there allowed small planetesimals to melt early in Solar System history by the decay of short-lived radionuclides (such as 26Al, 60Fe). The protoplanets emerging from this population not only induced collisional evolution among the remaining planetesimals but also scattered some of the survivors into the main belt, where they stayed for billions of years before escaping via a combination of collisions, Yarkovsky thermal forces, and resonances. We predict that some asteroids are main-belt interlopers (such as (4) Vesta). A select few may even be remnants of the long-lost precursor material that formed the Earth.

[1]  Alain Doressoundiram,et al.  Spectroscopic Properties of Asteroid Families , 2002 .

[2]  Harold F. Levison,et al.  The Role of Giant Planets in Terrestrial Planet Formation , 2000 .

[3]  R. Binzel,et al.  Mantle material in the main belt: Battered to bits? , 1996 .

[4]  Robert Jedicke,et al.  Linking the collisional history of the main asteroid belt to its dynamical excitation and depletion , 2005 .

[5]  H. Haack,et al.  Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites , 2005, Nature.

[6]  O. Eugster.  Cosmic-ray Exposure Ages of Meteorites and Lunar Rocks and Their Significance , 2003 .

[7]  S. Weidenschilling.  The distribution of mass in the planetary system and solar nebula , 1977 .

[8]  R. Binzel,et al.  High‐calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites , 2004 .

[9]  A. Meibom,et al.  Evidence for the insignificance of ordinary chondritic material in the asteroid belt , 1999 .

[10]  Timothy J. McCoy,et al.  Non-chondritic meteorites from asteroidal bodies , 1998 .

[11]  G. Wetherill,et al.  Dynamical chemical and isotopic evidence regarding the formation locations of asteroids and meteorites. , 1979 .

[12]  J. Chambers,et al.  The Primordial Excitation and Clearing of the Asteroid Belt , 2001 .

[13]  J. E. Gunn,et al.  Color Confirmation of Asteroid Families , 2002 .

[14]  K. Keil,et al.  Meteoritic parent bodies: Their number and identification , 2002 .

[15]  Sho Sasaki,et al.  Production of iron nanoparticles by laser irradiation in a simulation of lunar-like space weathering , 2001, Nature.

[16]  E. Scott.  Meteorite Evidence for the Accretion and Collisional Evolution of Asteroids , 2002 .

[17]  H. Haack,et al.  Rapid Timescales for Accretion and Melting of Differentiated Planetesimals Inferred from 26Al-26Mg Chronometry , 2005 .

[18]  H. McSween,et al.  Heliocentric Zoning of the Asteroid Belt by Aluminum-26 Heating , 1993, Science.

[19]  G. Wasserburg,et al.  Evidence for Widespread 26Al in the Solar Nebula and Constraints for Nebula Time Scales , 1996, Science.

[20]  Robert Jedicke,et al.  The fossilized size distribution of the main asteroid belt , 2003 .

[21]  Andrew Scott Rivkin,et al.  Hydrated Minerals on Asteroids: The Astronomical Record , 2003 .

[22]  K. Keil,et al.  Consequences of explosive eruptions on small Solar System bodies: the case of the missing basalts on the aubrite parent body , 1991 .

[23]  Andrea Milani,et al.  The Determination of Asteroid Proper Elements , 2002 .

[24]  R. Jedicke,et al.  The origin and evolution of stony meteorites , 2004, Proceedings of the International Astronomical Union.

[25]  D. Vokrouhlický,et al.  The Effect of Yarkovsky Thermal Forces on the Dynamical Evolution of Asteroids and Meteoroids , 2002 .

[26]  K. Tsiganis,et al.  Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets , 2005, Nature.

[27]  Francesco Marzari,et al.  The Missing Psyche Family: Collisionally Eroded or Never Formed? , 1999 .

[28]  B. Hapke,et al.  Asteroid Space Weathering and Regolith Evolution , 2002 .

[29]  David J. Stevenson,et al.  Rapid formation of Jupiter by diffusive redistribution of water vapor in the solar nebula , 1988 .

[30]  Harold F. Levison,et al.  Dynamical Lifetimes of Objects Injected into Asteroid Belt Resonances , 1997 .

[31]  W. Hartmann,et al.  Meteorite Delivery via Yarkovsky Orbital Drift , 1998 .

[32]  William K. Hartmann,et al.  Planetesimals to planets: Numerical simulation of collisional evolution , 1978 .

[33]  M. Nolan,et al.  Velocity Distributions among Colliding Asteroids , 1994 .

[34]  Harry Y. McSween,et al.  Meteorites and the early solar system II , 2006 .

[35]  Richard P. Binzel,et al.  Phase II of the Small Main-Belt Asteroid Spectroscopic Survey: The Observations , 2002 .

[36]  Hideo Ohashi,et al.  Simulation of space weathering of planet-forming materials: Nanosecond pulse laser irradiation and proton implantation on olivine and pyroxene samples , 1999 .

[37]  Alessandro Morbidelli,et al.  Orbital and temporal distributions of meteorites originating in the asteroid belt , 1998 .

[38]  R. Jedicke,et al.  Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects , 2002 .