# Asteroids IV

P. Michel
F. E. DeMeo
W. F. Bottke
With the assistance of Renée Dotson
https://www.jstor.org/stable/j.ctt18gzdvc

1. Front Matter
(pp. i-viii)
(pp. ix-xii)
3. List of Contributing Authors
(pp. xiii-xiii)
4. Scientific Organizing Committee and Acknowledgment of Reviewers
(pp. xiv-xiv)
5. Foreword
(pp. xv-xvi)
Richard P. Binzel

In the founding volume of what would become the Space Science Series, Tom Gehrels (1925–2011) wrote, “We are now on the threshold of a new era of asteroid studies” (Gehrels, 1971). These words once again trumpet the state of the field four decades later with the release ofAsteroids IV. Yet why do asteroids captivate our curiosity in a way that so greatly exceeds their small total mass relative to the rest of our solar system? It is because asteroids matter. Now more than ever before, we realize how much asteroids matter to scientists, to explorers, and to the...

6. Preface
(pp. xvii-xviii)
Patrick Michel, Francesca DeMeo and William F. Bottke
7. ### PART 1: INTRODUCTION

• Asteroids: Recent Advances and New Perspectives
(pp. 3-10)
Patrick Michel, Francesca E. DeMeo and William F. Bottke

Asteroids are thought to be leftover planetesimals that are closely related to the precursor bodies that formed both the terrestrial planets and the cores of the giant planets. The most primitive ones contain a record of the original composition of the solar nebula in which the planets formed. The organic matter and properties of water that some contain provide us with critical clues about how life started on Earth. Moreover, some of them cross the trajectory of our planet and therefore pose a risk to humanity.

The sizes, shapes, and rotational, internal, and surface properties of asteroids are the outcome...

• ### 2.1. Asteroid Composition and Physical Properties

• The Compositional Structure of the Asteroid Belt
(pp. 13-42)
F. E. DeMeo, C. M. O’D. Alexander, K. J. Walsh, C. R. Chapman and R. P. Binzel

By the early 1990s, in the era ofAsteroids II, roughly 10,000 asteroids had been discovered, only a fraction of the total number of asteroids that are now known to exist. At that time, asteroids were discovered by visually inspecting photographic plates for light trails. In the 1990s, many of the major automated discovery surveys came online. By the year 2000, around the time ofAsteroids III, ~20,000 asteroids were known (see Fig. 1). Today (in 2015,Asteroids IV) there are roughly 700,000 asteroids with known orbits, revealing much new information about the asteroid belt’s dynamic past. About 100,000 asteroids...

• Mineralogy and Surface Composition of Asteroids
(pp. 43-64)
Vishnu Reddy, Tasha L. Dunn, Cristina A. Thomas, Nicholas A. Moskovitz and Thomas H. Burbine

Physical characterization of small bodies through the use of reflectance spectroscopy provides insight into the diversity of chemical compositions in the solar system and enables meteorites in our terrestrial collections to be linked to specific parent bodies in space. Since the publication ofAsteroids III, there have been numerous advances in the mineralogical characterization of asteroid surfaces using visible/near-infrared (VIS/NIR) and mid-IR spectra. One of the most significant developments in groundbased characterization of small bodies over the last decade is the commissioning of the SpeX instrument in the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai‘i. The ideal spectral...

• Astronomical Observations of Volatiles on Asteroids
(pp. 65-88)
Andrew S. Rivkin, Humberto Campins, Joshua P. Emery, Ellen S. Howell, Javier Licandro, Driss Takir and Faith Vilas

The concept of the “snow line” (also known as the “waterfrost line”) is often used in discussing the water inventory of small bodies in our solar system. The snow line is the heliocentric distance at which water ice is stable enough to be accreted into planetesimals. The placement of the snow line has varied in different models. A location just inside Jupiter helps explain the greater mass of the giant planets as they accrete a larger fraction of the mass in the solar nebula. Although the location of the snow line before and during planet formation is uncertain, some studies...

• Space-Based Thermal Infrared Studies of Asteroids
(pp. 89-106)
Amy Mainzer, Fumihiko Usui and David E. Trilling

A variety of remote-sensing techniques have given rise to much of our understanding of the small-body populations in our solar system. Groundbased surveys operating at visible wavelengths have discovered most of the minor planets that are known today. At present, roughly 700,000 asteroids have been discovered in the main belt between Mars and Jupiter, ~13,000 near-Earth objects (NEOs) are known at all sizes, and some 5000 jovian Trojans have been found. While these numbers are thought to represent only a tiny fraction of the small bodies believed to exist in our solar system, much can be learned about these populations...

• Asteroid Thermophysical Modeling
(pp. 107-128)
Marco Delbo, Michael Mueller, Joshua P. Emery, Ben Rozitis and Maria Teresa Capria

Asteroid thermophysical modeling is about calculating the temperature of asteroids’ surface and immediate subsurface, which depend on absorption of sunlight, multiple scattering of reflected and thermally emitted photons, and heat conduction. Physical parameters such as albedo (or reflectivity), thermal conductivity, heat capacity, emissivity, density and roughness, along with the shape (e.g., elevation model) of the body, its orientation in space, and its previous thermal history are taken into account. From the synthetic surface temperatures, thermally emitted fluxes (typically in the infrared) can be calculated. Physical properties are constrained by fitting model fluxes to observational data.

It is important to differentiate...

• Asteroid Photometry
(pp. 129-150)
Jian-Yang Li, Paul Helfenstein, Bonnie J. Buratti, Driss Takir and Beth Ellen Clark

Planetary photometry concerns how the brightness of a planetary surface depends on the illumination and observing geometry. Figure 1 shows the scattering geometry and definition of terms that will be important for the rest of this chapter. The angle between the light source and local surface normal is incidence angle, i; the angle between the observer and the local surface normal is emission angle, e; and the angle between light source and observer, as seen from the object, is phase angle, α. The dependence of the brightness of the surface on (i,e,α) is determined by the optical and mechanical properties...

• Asteroid Polarimetry
(pp. 151-164)
Irina Belskaya, Alberto Cellino, Ricardo Gil-Hutton, Karri Muinonen and Yuriy Shkuratov

Polarimetry is a powerful tool to study surface properties, putting constraints on albedo and surface texture. The state of partial linear polarization of the sunlight scattered by planetary surfaces in different illumination conditions is diagnostic of refractive index, particle size, packing density, optical heterogeneity, etc.

The application of the polarimetric technique to asteroid studies has a long history beginning in 1934, when the first polarization measurements of bright asteroids were obtained by B. Lyot using a photographic polarimeter. Since 1954, photoelectric polarimeters have been used to measure asteroid polarization with better accuracy. Results of polarimetric observations of six asteroids were...

• Radar Observations of Near-Earth and Main-Belt Asteroids
(pp. 165-182)
Lance A. M. Benner, Michael W. Busch, Jon D. Giorgini, Patrick A. Taylor and Jean-Luc Margot

Planetary radar astronomy is an active form of observation in which the observer illuminates the target with radio waves having known properties and measures the reflected signal in order to investigate the physical properties of the target and to improve its orbit. Radar observations can occur during the day, in cloudy weather, during rain, and in a real sense represent a laboratory experiment on objects at distances of up to hundreds of millions of kilometers.

The world’s most sensitive facilities for radar observations of asteroids are the Arecibo Observatory and the Goldstone Solar System Radar. Arecibo has a diameter of...

• Asteroid Models from Multiple Data Sources
(pp. 183-202)
Josef Ďurech, Benoît Carry, Marco Delbo, Mikko Kaasalainen and Matti Viikinkoski

The determination of asteroid physical properties is an essential part of the complex process of revealing the nature of the asteroid population. In many cases, this process starts with obtaining observational data, continues with creating a model of the asteroid (i.e., its size, three-dimensional shape, and spin state, in the first approximation), and ends with interpreting new facts based on the model or a set of these. In this sense, modeling is a crucial mid-step between observations and theory. Results based on individual well-studied asteroids can be generalized to other members of the population. On the other hand, a statistically...

• ### 2.2. Populations

• The Complex History of Trojan Asteroids
(pp. 203-220)
Joshua P. Emery, Francesco Marzari, Alessandro Morbidelli, Linda M. French and Tommy Grav

Originally considered as simply an extension of the main belt, Trojan asteroids have become recognized as a large and important population of small bodies. Trojans share Jupiter’s orbit around the Sun, residing in the L4and L5stable Lagrange regions. Leading and trailing Jupiter by 60°, these are regions of stable equilibrium in the Sun-Jupiter-asteroid three-body gravitational system. The moniker “Trojan” is an artifact of history — the first three objects discovered in Jupiter’s Lagrange regions were named after heroes from theIliad. The naming convention stuck for Jupiter’s swarms, and the term Trojan eventually came to be used for...

• The Active Asteroids
(pp. 221-242)
David Jewitt, Henry Hsieh and Jessica Agarwal

Small solar system bodies are conventionally labeled as either asteroids or comets, based on three distinct properties: (1) Observationally, small bodies with unbound atmospheres (“comae”) are known as comets, while objects lacking such atmospheres are called asteroids. (2) Dynamically, comets and asteroids are broadly distinguished by the use of a dynamical parameter, most commonly the Tisserand parameter measured with respect to Jupiter (Kresak, 1982;Kosai, 1992). It is defined by

${{\text{T}}_{\text{J}}}\text{=}\frac{{{\text{a}}_{\text{J}}}}{\text{a}}\text{+2}{{\left[ \left( \text{1-}{{\text{e}}^{\text{2}}} \right)\frac{\text{a}}{{{\text{a}}_{\text{J}}}} \right]}^{\text{1/2}}}\text{cos(i)}$(1)

where a, e, and i are the semimajor axis, eccentricity, and inclination of the orbit (relative to Jupiter’s orbit), while aJ= 5.2 AU is the semimajor axis...

• The Near-Earth Object Population: Connections to Comets, Main-Belt Asteroids, and Meteorites
(pp. 243-256)
Richard P. Binzel, Vishnu Reddy and Tasha Dunn

Few topics within the field of asteroid studies garner more widespread attention than the near-Earth population. Many reasons motivate this attention, including: (1) These are the objects that (by definition) are capable of impacting Earth, thereby delivering meteorites (many times annually) and civilization-threatening impacts (centuries to geologic timescales). (2) These are the most accessible spaceflight destinations for both robotic and human missions, including foreseeable in-space resource utilization. (3) The population is dynamic in terms of its ongoing resupply from both main-belt asteroid and comet sources, where such resupply must occur because planetary encounters have long ago depleted the initial population....

• Small Near-Earth Asteroids as a Source of Meteorites
(pp. 257-280)
Jiří Borovička, Pavel Spurný and Peter Brown

Well before the first asteroid was discovered, people unknowingly had asteroid samples in their hands. Could stones fall from the sky? For many centuries, the official answer was no. Only at the end of the eighteenth century and the beginning of the nineteenth century did the evidence that rocks did fall from the sky become so overwhelming that this fact was accepted by the scientific community. It was the German scientist Ernst Chladni who first recognized their extraterrestrial origin in 1794. Nevertheless, it took some time before his idea became accepted (see, e.g.,Lauretta and McSween, 2006).

The stones that...

• Meteoroid Streams and Zodiacal Cloud
(pp. 281-296)
Peter Jenniskens

All asteroids and comets in our solar system are gradually falling apart into meteoroids. These meteoroids move at a high relative speed to other objects in the solar system and are therefore an impact hazard to satellites, a cause of asteroid surface weathering, and create meteors when impacting a planetary atmosphere. Streams of meteoroids provide a history of parent body activity and can warn us about the presence of potentially hazardous objects.

Interplanetary matter falls to Earth at a rate of 10,000–40,000 tons per year, mostly in the form of ~150-μm (10 μm–1 mm)-sized meteoroids (Love and Brownlee,...

• ### 2.3. Families

• Identification and Dynamical Properties of Asteroid Families
(pp. 297-322)
David Nesvorný, Miroslav Brož and Valerio Carruba

As witnessed by the heavily cratered surfaces imaged by spacecrafts, the chief geophysical process affecting asteroids is impacts. On rare occasions, the impact of a large projectile can be so energetic that the target asteroid is violently torn apart, and the pieces are thrown into space. The sites of such cosmic accidents are filled with debris that gravitationally accumulate into larger conglomerates, and drift away at speeds that are roughly commensurate with the escape speed from the original target body (Vesc). Initially, all orbits are similar, because Vesc≪ Vorb, where Vorb= 15–20 km s–1is the...

• Asteroid Family Physical Properties
(pp. 323-340)
Joseph R. Masiero, Francesca E. DeMeo, Toshihiro Kasuga and Alex H. Parker

Asteroid families provide waypoints along the path of dynamical evolution of the solar system, as well as laboratories for studying the massive impacts that were common during terrestrial planet formation. Catastrophic disruptions shattered these asteroids, leaving swarms of bodies behind that evolved dynamically under gravitational perturbations and the Yarkovsky effect to their present-day locations, both in the main belt and beyond. The forces of the family-forming impact and the gravitational reaccumulation of the collisional products also left imprints on the shapes, sizes, spins, and densities of the resultant family members (see the chapter by Michel et al. in this volume)....

• Collisional Formation and Modeling of Asteroid Families
(pp. 341-354)
Patrick Michel, Derek C. Richardson, Daniel D. Durda, Martin Jutzi and Erik Asphaug

Observed asteroid families in the main asteroid belt are each composed of bodies that are thought to originate from the catastrophic disruption of larger parent bodies (e.g.,Farinella et al., 1996). Cratering collisions can also lead to families, such as the one associated with asteroid Vesta, but we do not address this origin scenario here as few families have been linked to cratering events and their modeling requires a different approach (for more details, see the chapter by Jutzi et al. in this volume). A few tens of asteroid families have been identified, corresponding to groups of small bodies well-concentrated...

• ### 2.4. Multiple Systems

• Asteroid Systems: Binaries, Triples, and Pairs
(pp. 355-374)
Jean-Luc Margot, Petr Pravec, Patrick Taylor, Benoît Carry and Seth Jacobson

Multiple-asteroid systems are important because they represent a sizable fraction of the asteroid population and because they enable investigations of a number of properties and processes that are often difficult to probe by other means. The binaries, triples, and pairs inform us about a great variety of asteroid attributes, including physical, mechanical, and thermal properties, composition, interior structure, formation processes, and evolutionary processes.

Observations of binaries and triples provide the most powerful way of deriving reliable masses and densities for a large number of objects. The density measurements help us understand the composition and internal structure of minor planets. Binary...

• Formation and Evolution of Binary Asteroids
(pp. 375-394)
Kevin J. Walsh and Seth A. Jacobson

There have been considerable advances in the understanding of the formation and evolution of binary systems since theAsteroids IIIreview byMerline et al.(2002) and a subsequent comprehensive review byRichardson and Walsh(2006). The current properties of this population are detailed in the chapter in this volume by Margot et al., and this review will rely on their analysis in many places as we review work on the formation and dynamics of these systems. While the inventory of known binary systems in all populations has increased, for some populations the understanding of dynamics and formation have advanced...

9. ### PART 3: SPACE MISSIONS

• Hayabusa Sample Return Mission
(pp. 397-418)
Makato Yoshikawa, Junichiro Kawaguchi, Akira Fujiwara and Akira Tsuchiyama

Hayabusa, the world’s first asteroid sample return mission, was built and launched by the Institute of Space and Astronautical Science (ISAS), which was later merged with the Japan Aerospace Exploration Agency (JAXA). The project code name was MUSES-C, and after launch in May 2003 was given the name “Hayabusa,” which literally translates to “falcon.” Hayabusa arrived at its target asteroid in September 2005, and returned to Earth in June 2010. The main purpose of the mission was to demonstrate the key technologies required for future planetary missions. Hayabusa made a roundtrip flight to a celestial object outside of Earth’s gravity...

• The Dawn Mission to Vesta and Ceres
(pp. 419-432)
C. T. Russell, H. Y. McSween, R. Jaumann and C. A. Raymond

Geochemical investigations of meteorites pinpoint the beginning of the solar system to be 4.567 Ga, when the calcium-aluminum-rich inclusions (CAIs) were formed. At that time, the solar system was seeded with short-lived radioactive elements such as26Al and bodies that accreted then trapped these radionuclides and their heat. If sufficiently large, the earliest-formed bodies melted and differentiated. The differentiation led to metallic cores, ultramafic mantles, and mafic crusts. Bodies that accreted later did not incorporate as much radiogenic heat of short-lived nuclides, and hence did not differentiate, so they did not devolatilize as completely as those formed earlier. The period...

• The Flybys of Asteroids (2867) Šteins, (21) Lutetia, and (4179) Toutatis
(pp. 433-450)
M. Antonietta Barucci, Marcello Fulchignoni, Jianghui Ji, Simone Marchi and Nicolas Thomas

In the last few years three successful asteroid flybys have been completed by two spacecraft. Two main-belt asteroids, (2867) Šteins and (21) Lutetia, were visited in September 2008 and July 2010 respectively by the European Space Agency’s (ESA) Rosetta spacecraft on its journey toward Comet 67P/Churyumov-Gerasimenko (Schulz et al., 2009). The near-Earth asteroid (4179) Toutatis was flown by on December 2012 by the China National Space Administration (CNSA) lunar exploration probe, Chang’e-2.

Rosetta is an ESA cornerstone mission and is expected to make a major contribution to the study of the small bodies of the solar system. The mission, named...

• Phobos and Deimos
(pp. 451-468)
Scott L. Murchie, Peter C. Thomas, Andrew S. Rivkin and Nancy L. Chabot

Once the Galilean satellites of Jupiter were discovered and the Copernican model of the solar system became widely accepted, Mars’ apparent lack of a moon was notable. By the end of the seventeenth century, Saturn was known to have at least five satellites, a number that swelled to seven by the end of the eighteenth century. By 1800 a new planet, Uranus, was discovered and found to have at least two satellites. By 1870, two more uranian satellites and another saturnian satellite were detected, along with another new planet (Neptune) with its own satellite. Yet Mars remained moonless. Based on...

• ### 4.1. Dynamical Evolution

• New Paradigms for Asteroid Formation
(pp. 471-492)
Anders Johansen, Emmanuel Jacquet, Jeffrey N. Cuzzi, Alessandro Morbidelli and Matthieu Gounelle

The solar system contains large populations of pristine planetesimals that have remained relatively unchanged since their formation. Our proximity to the asteroid belt provides astronomers, planetary scientists, and cosmochemists access to extremely detailed data about asteroid compositions, sizes, and dynamics. Planetesimals are the building blocks of both terrestrial planets and the cores of the giant planets, as well as the super-Earths (with various degrees of gaseous envelopes) that are now known to orbit around a high fraction of solar-type stars (Fressin et al., 2013). The formation of planetesimals is thus a key step toward the assembly of planetary systems, but...

• The Dynamical Evolution of the Asteroid Belt
(pp. 493-508)
Alessandro Morbidelli, Kevin J. Walsh, David P. O’Brien, David A. Minton and William F. Bottke

The asteroid belt helps us in reconstructing the origin and the evolution of the solar system, probably better than the planets themselves. This is because the asteroid belt provides several key constraints that can be used to effectively guide the development, calibration, and validation of evolutionary models. Compared to other small-body populations, such as the Kuiper belt or Oort cloud, the constraints provided by the asteroid belt are probably more stringent, due to the fact that the number and the properties of the asteroids are better known, thanks to groundbased observations, space missions, and meteorite analysis.

The structure of this...

• The Yarkovsky and YORP Effects
(pp. 509-532)
David Vokrouhlický, William F. Bottke, Steven R. Chesley, Daniel J. Scheeres and Thomas S. Statler

Interesting problems in science usually have a long and complex history. It is rare, though, that they have a prehistory or perhaps even mythology. Yet, until recently this was the case for the Yarkovsky effect. Ivan O. Yarkovsky, a Russian civil engineer born in a family of Polish descent, noted in a privately published pamphlet (Yarkovsky, 1901;Beekman, 2006) that heating a prograde-rotating planet should produce a transverse acceleration in its motion and thus help to counterbalance the assumed drag from the then-popular ether hypothesis. While this context of Yarkovsky’s work was mistaken and he was only roughly able to...

• ### 4.2. Differentiation

• Asteroid Differentiation: Melting and Large-Scale Structure
(pp. 533-552)
A. Scheinberg, R. R. Fu, L. T. Elkins-Tanton and B. P. Weiss

Chondrites consist of material that never heated sufficiently to melt, while primitive achondrites only underwent partial melting. Such samples can be explained as fragments of relatively homogeneous small bodies without invoking differentiation processes. However, iron meteorites analogous to planetary cores and stony achondrites analogous to differentiated planetary crusts demonstrate that metal-silicate differentiation occurred in planetesimals during the first few million years after the formation of calcium-aluminum-rich inclusions (CAIs) (e.g.,Kleine et al., 2012;Markowski et al., 2006;Baker et al., 2005).

Differentiation requires heating above the melting temperature of iron-nickel alloys and may require melting beyond the silicate solidus as...

• Hydrothermal and Magmatic Fluid Flow in Asteroids
(pp. 553-572)
Lionel Wilson, Phil A. Bland, Debra Buczkowski, Klaus Keil and Alexander N. Krot

Largely due to the recovery of huge numbers of meteorites from cold and hot deserts, the number of asteroidal meteorites in captivity has increased tremendously in recent years to about 50,000 (Meteoritical Bulletin Database, 2014). Study of these meteorites indicates that all asteroids have experienced some degree of parent-body thermal alteration due to internally produced heat.Keil(2000) estimated that the world’s meteorite collections sample at least ~27 primitive, chondritic and ~108 partially and totally melted asteroids, andBurbine et al. (2002) similarly estimate this number to be ~100–150 distinct asteroids. The thermal alteration effects range from aqueous and...

• Early Impact History and Dynamical Origin of Differentiated Meteorites and Asteroids
(pp. 573-596)
Edward R. D. Scott, Klaus Keil, Joseph I. Goldstein, Erik Asphaug, William F. Bottke and Nicholas A. Moskovitz

Laboratory studies of igneously formed meteorites suggest that numerous meteorite parent bodies were melted to form metallic cores and silicate mantles. Studies by the Dawn spacecraft confirm that (4) Vesta melted in this way (McSween et al., 2013; see the chapter by Russell et al. in this volume). In principle, one would think the origin of iron and stony-iron meteorites and achondrites would be straightforward to investigate, but this is not the case. If disrupted Vesta-like differentiated bodies were once common in the main belt and they were the ultimate source of the differentiated meteorites, one might expect collisions to...

• ### 4.3. Physical Evolution

• Asteroid Surface Alteration by Space Weathering Processes
(pp. 597-616)
Rosario Brunetto, Mark J. Loeffler, David Nesvorný, Sho Sasaki and Giovanni Strazzulla

Space weathering (SW) processes affect airless bodies in the solar system. These processes include irradiation by solar ion populations (solar wind, flares, solar-energetic-particle events), galactic cosmic rays, electrons, UV and X-rays, and bombardment by micrometeorites. The surface alteration varies not only as a function of the surface composition, but also location in the solar system. Generally, SW processes have been widely studied for the Moon and S- and V-type asteroids, and they are currently being investigated for other asteroid types. Fundamental reviews on SW have been published, and the reader is invited to refer toHapke(2001),Clark et al....

• The Formation and Evolution of Ordinary Chondrite Parent Bodies
(pp. 617-634)
Pierre Vernazza, Brigitte Zanda, Tomoki Nakamura, Edward Scott and Sara Russell

Observations of main-belt asteroids (MBAs) performed between the early 1970s and the late 1990s, along with meteorite measurements, led to the determination of a preliminary version of the compositional distribution in the asteroid belt (see the chapter by DeMeo et al. in this volume;Gradie and Tedesco, 1982;Mothé-Diniz et al., 2003;DeMeo and Carry, 2013, 2014):

1. Two main asteroid populations were identified: the so-called S-types [comprising mostly but not only ordinary chondrite (OC)-like asteroids] and C-types [comprising mostly but not only carbonaceous chondrite (CC)-like asteroids], accounting for more than 50% of all MBAs, and several minor populations (comprising the...

• Sources of Water and Aqueous Activity on the Chondrite Parent Asteroids
(pp. 635-660)
Alexander N. Krot, Kazuhide Nagashima, Conel M. O’D. Alexander, Fred J. Ciesla, Wataru Fujiya and Lydie Bonal

In this paper, we address the nature of aqueous activity in and the sources of water ice accreted by the chondrite parent bodies. We also discuss how these observations could be used for testing some of the predictions of the recently proposed Nice (Gomes et al., 2005;Morbidelli et al., 2005;Tsiganis et al., 2005;Levison et al., 2009) and Grand Tack (Walsh et al., 2011) dynamical models of the evolution of the solar system. This chapter is organized as follows: In section 2, we describe the modern classification of chondritic meteorites, emphasizing the large chemical and isotopic diversity among...

• ### 4.4. Collisions

• Global-Scale Impacts
(pp. 661-678)
Erik Asphaug, Gareth Collins and Martin Jutzi

The most important parameter governing the global extent of an impact is the mass ratio of the projectile to the target, γ = M2/M1. In the case of a cratering event this ratio is small, and there is a well-defined geometric locus. Crater scaling then becomes a powerful tool (e.g.,Housen et al., 1983) that allows simple analytical approaches to be applied to determine whether an impact “goes global” — for instance, whether the surface is shaken everywhere to the escape velocity, or whether the target is shattered or melted.

At the other extreme, as M2→ M1, there is...

• Color Section
(pp. None)
• Modeling Asteroid Collisions and Impact Processes
(pp. 679-700)
Martin Jutzi, Keith Holsapple, Kai Wünneman and Patrick Michel

The modeling of impact processes can be based upon mathematical synthesis of experimental results, on direct theoretical application of the principles of physics, or on the use of those principles in numerical codes.

The direct application of experimental results is not usually possible, because the experiments cannot be performed at the actual conditions of interest. To bridge the gap, scaling theories are developed using physical principles to extrapolate experimental results to the actual conditions of interest. For some time, principal scaling theories have been based upon the physical concept of a “point source,” wherein the genesis of an impact process...

• The Collisional Evolution of the Main Asteroid Belt
(pp. 701-724)
William F. Bottke, Miroslav Brož, David P. O’Brien, Adriano Campo Bagatin, Alessandro Morbidelli and Simone Marchi

The main asteroid belt is a living relic. It contains a record of what happened to the solar system in terms of bombardment since the planet-formation epoch. Ongoing collisional and dynamical evolution processes, however, are slowly obscuring the traces left behind. The goal of modeling efforts is to use all possible observational data to discern the initial conditions and evolution processes that occurred during and after the planet-formation epoch. For example, the questions one can probe with main-belt constraints include the nature and mass of planetesimals inside Jupiter’s orbit, the timing of Jupiter’s formation, the distribution of volatiles in the...

• ### 4.5. Surface Geology and Geophysics

• Cratering on Asteroids
(pp. 725-744)
Simone Marchi, Clark R. Chapman, Olivier S. Barnouin, James E. Richardson and Jean-Baptiste Vincent

Until the space age, craters had only been observed on a single astronomical body, the Moon. It was only with the analysis of the first lunar samples, however, that it finally became clear that the vast majority of lunar craters (and a recognizable minority of terrestrial craters) were caused by cosmic impacts and were not generally of volcanic or other endogenic origin (e.g.,Wilhelms, 1993). Three decades later, when the Galileo spacecraft flew past (951) Gaspra, then a few years later past (243) Ida, craters were found on asteroids. During the subsequent two decades, spacecraft flybys and dedicated orbital missions...

• Asteroid Interiors and Morphology
(pp. 745-766)
D. J. Scheeres, D. Britt, B. Carry and K. A. Holsapple

The past decade has seen an astonishing array of advances across a wide spectrum of important inputs to the problem and mystery of asteroid interiors. These include the development of a large database concerning asteroid component strengths, as evidenced by meteors and meteorites (section 2); the compilation of extensive densities and inferred porosities for asteroids based on groundbased observations (section 3); the development of new computational techniques for the simulation of how asteroid rubble piles deform and fission or shed mass when subject to extreme rotation rates (section 4); and the development of crucial insights into the unique geophysics of...

• Asteroid Surface Geophysics
(pp. 767-792)
Naomi Murdoch, Paul Sánchez, Stephen R. Schwartz and Hideaki Miyamoto

Before the first spacecraft encounters with asteroids, many scientists assumed that the smallest asteroids were all monolithic rocks with a bare surface, although there had been a few articles suggesting possible alternative surface properties and internal structures (e.g.,Dollfus et al., 1977;Housen et al., 1979;Michel et al., 2001;Harris, 2006). Given the low gravitational acceleration on the surface of an asteroid, it was thought that regolith formation would not be possible; even if small fragments of rock were created during the impact process, nothing would be retained on the surface (e.g.,Chapman, 1976). However, the NASA Galileo, Near...

11. ### PART 5: GROUNDBASED SURVEYS, HAZARDS, AND FUTURE EXPLORATION

• Surveys, Astrometric Follow-Up, and Population Statistics
(pp. 795-814)
Robert Jedicke, Mikael Granvik, Marco Micheli, Eileen Ryan, Timothy Spahr and Donald K. Yeomans

Without asteroid surveys there would be no asteroid science. The cumulative efforts of more than 200 years of asteroid surveying has resulted in the discovery of over half a million asteroids in the inner solar system that range from just a tenth of an astronomical unit from the Sun to beyond Jupiter’s orbit. The surveys have identified asteroids that are the targets of spacecraft missions, that are the remnants of larger asteroids that were catastrophically disrupted long ago, and that allow us to untangle the complicated processes that formed our solar system billions of years ago. The surveys’ capabilities have...

• Orbits, Long-Term Predictions, and Impact Monitoring
(pp. 815-834)
Davide Farnocchia, Steven R. Chesley, Andrea Milani, Giovanni F. Gronchi and Paul W. Chodas

Determining asteroid orbits is a challenging problem that the scientific community has faced since 1801, when Piazzi discovered (1) Ceres, the first main-belt object. Shortly after discovery Ceres was heading for conjunction, thus making it impossible to keep collecting observations. To prevent Ceres from being lost, Gauss computed its orbit using the observations collected by Piazzi and successfully predicted where Ceres would be observable after emerging from the Sun. Interestingly, the orbit determination of Ceres represents the first remarkable application of the famous method of least squares, which since then has been one of the most used mathematical tools with...

• Asteroid Impacts and Modern Civilization: Can We Prevent a Catastrophe?
(pp. 835-854)
Alan W. Harris, Mark Boslough, Clark R. Chapman, Line Drube, Patrick Michel and Alan W. Harris

The planets of the solar system started out as clumps of material, so-called planetesimals, with diameters of around 1–100 km, which grew by accreting particles and small bodies from the cloud of gas and dust that surrounded the newly formed Sun. Some planetesimals enjoyed rapid growth and quickly developed significant gravitational fields, thereby attracting and absorbing more and more small bodies to become fully fledged planets. Others were destroyed in violent collisions that produced clouds of fragments. A large fraction of the asteroids present in the solar system today are collisional fragments, orbiting the Sun in the main asteroid...

• Human Exploration of Near-Earth Asteroids
(pp. 855-880)
P. A. Abell, B. W. Barbee, P. W. Chodas, J. Kawaguchi, R. R. Landis, D. D. Mazanek and P. Michel

Asteroids have generated significant worldwide interest in recent years as a result of flyby, rendezvous, and sample return missions. Robotic missions to near-Earth asteroids (NEAs) have already been completed by several space agencies, and subsequent robotic missions to these bodies are under development or consideration. In addition, human-led exploration missions to these destinations are now also being seriously considered. In 2009, the Review of the United States Human Spaceflight Plans Committee, also known as the Augustine Commission, identified NEAs as high-profile destinations for human exploration missions beyond the Earth-Moon system as part of the “Flexible Path” approach (http://www.nasa.gov/pdf/384767main_SUMMARY%20REPORT%20-%20FINAL.pdf, accessed July...

12. Index
(pp. 881-895)