Nature Of Asteroids Research Articles

The reclassification of asteroids from planets to non-planets

It is often claimed that asteroids’ sharing of orbits is the reason they were re-classified from planets to non-planets. A critical review of the literature from the 19th Century to the present shows this is factually incorrect. The literature shows the term asteroid was broadly recognized as a subset of planet for 150 years. On-going discovery of asteroids resulted in a de facto stretching of the concept of planet to include the ever-smaller bodies. Scientists found utility in this taxonomic identification as it provided categories needed to argue for the leading hypothesis of planet formation, Laplace's nebular hypothesis. In the 1950s, developments in planet formation theory found it no longer useful to maintain taxonomic identification between asteroids and planets, Ceres being the primary exception. At approximately the same time, there was a flood of publications on the geophysical nature of asteroids showing them to be geophysically different than the large planets. This is when the terminology in asteroid publications calling them planets abruptly plunged from a high level of usage where it had hovered during the period 1801–1957 to a low level that held constant thereafter. This marks the point where the community effectively formed consensus that asteroids should be taxonomically distinct from planets. The evidence demonstrates this consensus formed on the basis of geophysical differences between asteroids and planets, not the sharing of orbits. We suggest attempts to build consensus around planetary taxonomy not rely on the non-scientific process of voting, but rather through precedent set in scientific literature and discourse, by which perspectives evolve with additional observations and information, just as they did in the case of asteroids.

Trajectory of asteroid 2017 SB20 within the CRTBP

Regular monitoring the trajectory of asteroids to a future time is a necessity, because the variety of known probably unsafe near-Earth asteroids are increasing. The analysis is perform to avoid any incident or whether they would have a further future threat to the Earth or not. Recently a new Near Earth Asteroid (2017 SB20) has been observed to cross the Earth orbit. In view of this we obtain the trajectory of Asteroid in the circular restricted three body problem with radiation pressure and oblateness. We examine nature of Asteroid’s orbit with Lyapunov Characteristic Exponents (LCEs) over a finite intervals of time. LCE of the system confirms that the motion of asteroid is chaotic in nature. With the effect of radiation pressure and oblateness the length of curve varies in both the planes. Oblateness factor is found to be more perturbative than radiation pressure. To see the precision of result obtain from numerical integration we show the error propagation and the numerical stability is assured around the singularity by applying regularized equations of motion for precise long-term study.

Asteroid Risk Assessment: A Probabilistic Approach.

Following the 2013 Chelyabinsk event, the risks posed by asteroids attracted renewed interest, from both the scientific and policy-making communities. It reminded the world that impacts from near-Earth objects (NEOs), while rare, have the potential to cause great damage to cities and populations. Point estimates of the risk (such as mean numbers of casualties) have been proposed, but because of the low-probability, high-consequence nature of asteroid impacts, these averages provide limited actionable information. While more work is needed to further refine its input distributions (e.g., NEO diameters), the probabilistic model presented in this article allows a more complete evaluation of the risk of NEO impacts because the results are distributions that cover the range of potential casualties. This model is based on a modularized simulation that uses probabilistic inputs to estimate probabilistic risk metrics, including those of rare asteroid impacts. Illustrative results of this analysis are presented for a period of 100 years. As part of this demonstration, we assess the effectiveness of civil defense measures in mitigating the risk of human casualties. We find that they are likely to be beneficial but not a panacea. We also compute the probability-but not the consequences-of an impact with global effects ("cataclysm"). We conclude that there is a continued need for NEO observation, and for analyses of the feasibility and risk-reduction effectiveness of space missions designed to deflect or destroy asteroids that threaten the Earth.

Tajikistan fireball network and results of photographic observations

The fireball network was created in Tajikistan with the aim of obtaining new data on the near-Earth meteoroid environment concerning large bodies, entering in the Earth’s atmosphere and producing fireballs, as well as new observational data on the activity of known meteor/fireball showers. The network consists of five observational stations equipped with the photographic fireball and digital all-sky cameras. Distances between the stations are from 53 to 184 km and the area covered by monitoring is around 11000 km2. For astrometric reduction of fireball photographs, a technique has been developed that allows positions of object details to be determined at an accuracy of about 1′, which is a sufficiently good result for negatives of this scale. In the method of photometric reduction, a dependence of measured widths of diurnal star trails on their magnitudes is used. As a result of processing of multi-station photographs of more than 200 fireballs, photographed by the fireball network for 2006–2013, the data on their atmospheric trajectories, coordinates of radiants, velocities, decelerations, orbits in the interplanetary space, light curves, photometric masses, and densities, as well as on the nature of origin of meteoroids which produced the fireballs are obtained; membership of the fireballs to the known fireball/meteor showers is determined. A brightness of the majority of fireballs is within the maximum absolute magnitude range from −5 to −8. It is shown that 62% of fireball-producing meteoroids have a cometary origin and the remaining 38% are of an asteroidal nature. The greater part of the photographed fireballs belongs to the known meteor/fireball showers, while the lesser part (almost 30%) relates to the sporadic background. The obtained results will noticeably replenish the world database with new information on fireballs and are required for solving contemporary astronomy problems associated with studying meteoroid environment in the near-Earth space and the asteroidal-cometary hazard as well as for discovering genetic links between small bodies of the Solar System.

Near-Earth objects: finding them before they find us

Illustrations vii Preface xi Acknowledgments xiii Chapter 1 Earth's Closest Neighbors 1 Chapter 2 The Solar System's Origin: The Classical View 15 Chapter 3 How and Where Do Near-Earth Objects Form? 29 Chapter 4 Near-Earth Objects as the Enablers and Destroyers of Life 47 Chapter 5 Discovering and Tracking Near-Earth Objects 57 Chapter 6 The Nature of Asteroids and Comets 79 Chapter 7 Nature's Natural Resources and the Human Exploration of Our Solar System 100 Chapter 8 Near-Earth Objects as Threats to Earth 109 Chapter 9 Predicting the Likelihood of an Earth Impact 125 Chapter 10 Deflecting an Earth-Threatening Near-Earth Object 140 References 155 Index of Asteroid and Cometary Objects 159 General Index 161

The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor

Near-infrared and mid-infrared observations of the site of the 2009 July 19 impact of an unknown object with Jupiter were obtained within days of the event. The observations were used to assess the properties of a particulate debris field, elevated temperatures, and the extent of ammonia gas redistributed from the troposphere into Jupiter’s stratosphere. The impact strongly influenced the atmosphere in a central region, as well as having weaker effects in a separate field to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites in 1994. Temperatures were elevated by as much as 6 K at pressures of about 50–70 mbar in Jupiter’s lower stratosphere near the center of the impact site, but no changes above the noise level (1 K) were observed in the upper stratosphere at atmospheric pressures less than ∼1 mbar. The impact transported at least ∼2 × 10 15 g of gas from the troposphere to the stratosphere, an amount less than derived for the SL9 C fragment impact. From thermal heating and mass-transport considerations, the diameter of the impactor was roughly in the range of 200–500 m, assuming a mean density of 2.5 g/cm 3. Models with temperature perturbations and ammonia redistribution alone are unable to fit the observed thermal emission; non-gray emission from particulate emission is needed. Mid-infrared spectroscopy of material delivered by the impacting body implies that, in addition to a silicate component, it contains a strong signature that is consistent with silica, distinguishing it from SL9, which contained no evidence for silica. Because no comet has a significant abundance of silica, this result is more consistent with a “rocky” or “asteroidal” origin for the impactor than an “icy” or “cometary” one. This is surprising because the only objects generally considered likely to collide with Jupiter and its satellites are Jupiter-Family Comets, whose populations appear to be orders of magnitude larger than the Jupiter-encountering asteroids. Nonetheless, our conclusion that there is good evidence for at least a major asteroidal component of the impactor composition is also consistent both with constraints on the geometry of the impactor and with results of contemporaneous Hubble Space Telescope observations. If the impact was not simply a statistical fluke, then our conclusion that the impactor contained more rocky material than was the case for the desiccated Comet SL9 implies a larger population of Jupiter-crossing asteroidal bodies than previously estimated, an asteroidal component within the Jupiter-Family Comet population, or compositional differentiation within these bodies.

SEARCHING FOR TROJAN ASTEROIDS IN THE HD 209458 SYSTEM: SPACE-BASEDMOSTPHOTOMETRY AND DYNAMICAL MODELING

We have searched Microvariability and Oscillations of STars (MOST) satellite photometry obtained in 2004, 2005, and 2007 of the solar-type star HD 209458 for Trojan asteroid swarms dynamically coupled with the system's transiting "hot Jupiter" HD 209458b. Observations of the presence and nature of asteroids around other stars would provide unique constraints on migration models of exoplanetary systems. Our results set an upper limit on the optical depth of Trojans in the HD 209458 system that can be used to guide current and future searches of similar systems by upcoming missions. Using cross-correlation methods with artificial signals implanted in the data, we find that our detection limit corresponds to a relative Trojan transit depth of 1\times10-4, equivalent to ~1 lunar mass of asteroids, assuming power-law Trojan size distributions similar to Jupiter's Trojans in our solar system. We confirm with dynamical interpretations that some asteroids could have migrated inward with the planet to its current orbit at 0.045 AU, and that the Yarkovsky effect is ineffective at eliminating objects of > 1 m in size. However, using numerical models of collisional evolution we find that, due to high relative speeds in this confined Trojan environment, collisions destroy the vast majority of the asteroids in <10 Myr. Our modeling indicates that the best candidates to search for exoTrojan swarms in 1:1 mean resonance orbits with "hot Jupiters" are young systems (ages of about 1 Myr or less). Years of Kepler satellite monitoring of such a system could detect an asteroid swarm with a predicted transit depth of 3\times10-7.

The significance of meteorite density and porosity

Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system.

The nature of comet-asteroid transition object (3200) Phaethon

Context. The study of asteroids that present sporadic cometary activity is of fundamental importance to address several astronomical problems including the end states of comet nuclei, the abundance of water in main belt asteroids, and its role as a possible source of terrestial water. Aims. We studied the composition of the surface of asteroid (3200) Phaethon, a paradigmatic case of asteroid-comet transition object, in order to determine its cometary or asteroidal nature. Methods. We report visible and near infrared spectra covering the 0.35–2.4 μ m spectral range, obtained with the 4.2 m William Herschel Telescope, the 2.5 m Nordic Optical Telescope, and the Italian 3.58 m Telescopio Nazionale Galileo at “El Roque de los Muchachos” Observatory (La Palma, Spain). Our spectrum is compared with those of meteorite samples and man-made mineral mixtures to determine possible components, modeled using multiple scattering formulations, and also compared with the spectra of comet nuclei and other comet-asteroid transitional objects. Results. Phaethon's spectrum does not show any sharp structure and has a negative slope at wavelengths >0.43 μ m, consistent with B-type asteroids. Below 0.43 μ m the reflectance decreases. The spectral shape is similar to that of aqueously altered CI/CM meteorites and of hydrated minerals. A surface composition with hydrated silicates is also suggested by the models. A possible spectral variability in the UV is suggested by the avaliable spectra, and is compatible with a slightly different abundance of hydrated silicates. Finally, Phaethon's spectrum shows important differences with the few comet nuclei properly observed at these wavelengths and is similar to the spectra of other peculiar comet-asteroid transition objects. Conclusions. The spectral properties and dynamical properties of (3200) Phaethon support an asteroidal nature rather than a cometary one. Phaethon is more likely an “activated” asteroid, similar to the population of activated asteroids in the Main Belt Comets, than an extinct comet.

Two-Body Optimization for Deflecting Earth-Crossing Asteroids

We present a formulation of a e nite-dimensional optimization problem associated with the dee ection of Earthcrossing asteroids. The performance measure is minimizing the delta-V requirement for achieving a minimum target separation distance. A number of astrodynamical constraints are identie ed and modeled. The constrained optimization problem is numerically solved using a sequential quadratic programming method. Our numerical analysis indicates that the minimum delta-V requirement is not a monotonically decreasing function of warning time; rather, there is a e ner structure associated with the orbital period of the colliding asteroid. The analysis tool presented here may be used for optimizing the interceptor mission for impact mitigation. HE crash of the comet Shoemaker-Levy 9 into Jupiter in July 1994 was a remarkable event. Watching the results 1;2 from the impact, we felt a chilling warning of the possibility of a similar eventhappeningtotheEarth. 3 Thereareatleast1000Earth-crossing asteroids capable of global environmental catastrophe upon Earthimpact, and e ve new ones are discovered every year. 4 Crude historical data suggest that we can expect an impact greater than the equivalent of 10 Mtons of TNTabout once per century on average. 3 About 50,000 years ago the Barringer crater (1.5 km in diameter ) in Arizona was formed by an explosion estimated to be equivalent to about20 Mtons of TNT. 5 Arecentlargeatmospheric explosion was the great Tunguska bolide (»20 Mtons ofTNT )of 1908, which was caused by about a 60-m-diam comet or asteroid and exploded with the force of 1000 Hiroshima bombs. (One Hiroshima bomb has an explosive yield equivalent to about 20 ktons of TNT. ) 6 Asa resultof thepossibility of an asteroidorcometimpacting the Earth, several workshops have been held to study the fundamentals of the impact and the impact mitigation problem. The concentration of the workshops has been related primarily on the detection problem, assessing the magnitude of the threat, and impact effects and hazards to Earth, as well as the political implications of developing an impact mitigation capability. Two spacecraft exploration missions, Near Earth Asteroid Rendezvous (NEAR)7 and Clementine, 8 have included intercepts of asteroids as a major part oftheirmission to study the nature of asteroids. Despite an increase in interest on the impact mitigation problem, 9i12 little astrodynamical analysis has been performed; in particular, the mathematical optimization problem has received scant attention. 13;14 A number of dynamics and control problems in hazard mitigation are dee ned in Ref. 14. Here, we further one of these problems in formulating and solving the astrodynamical optimization problem. The dynamics of the problem is based on a two-dimensional, two-body approximation. The analysis centers on how optimal impulses applied to an Earth-crossing asteroid (ECA)at various points on its orbit affect the outcome when there is a presumption of collisionotherwise.Theperformance measureisminimizingthe delta-V required for achieving a minimum target separation distance. The constrained optimization problem is numerically solved using the sequential quadratic programming (SQP) method that is available in the MATLAB TM optimization toolbox. 15 Our numerical analysis indicates that the minimum delta-V requirement is not a monotonically decreasing function of warning time; rather, there is a e ner structure associated with the orbital period of the colliding asteroid.

NEAR swings by Earth en route to Eros

The Near Earth Asteroid Rendezvous spacecraft (NEAR) conducted a swingby of Earth on January 23, 1998, en route to its final destination, the asteroid 433 Eros. The spacecraft, built and managed by the Applied Physics Laboratory of Johns Hopkins University in Laurel, Maryland, and launched February 17, 1996, aboard a Delta II‐7925‐8 rocket from Cape Canaveral, is on a mission to further our understanding of the nature of asteroids and their role in the formation of the solar system. The spacecraft is three‐axis stabilized, passively cooled, and uses four fixed solar panels to power five scientific instruments and transmit data to Earth through a 1.5 m, fixed, high‐gain antenna.As the first NASA Discovery‐class mission, NEAR was designed to return the maximum amount of information on a timely basis with minimal cost. Aside from the transponder that will be used to determine Eros' mass and gravity field, the science instruments are focused on understanding the geology, chemistry, and history of the target asteroid. The seven‐band Multi‐Spectral Imager (MSI), covering wavelengths of 0.5 to 1.1 microns, will image the entire surface of the 40 x 14 x 14 km (25 x 9 x 9 mi) asteroid, mapping its morphology and color [Hawkins et al., 1997]. The Near Infrared Spectrometer (NIS) will map out Eros' surface mineralogy using reflected sunlight in the 0.8 to 2.5 micron range [Warren et al., 1997], while the X ray/Gamma ray Spectrometers (XGRS) will determine surface elemental composition of key rock‐forming species such as Mg, Al, Si, S, Ca, Fe, Ti, and K [Goldsten et al., 1997]. The NEAR magnetometer will characterize the intensity and structure of any intrinsic magnetization of Eros [Lohr et al., 1997]. Finally, the NEAR Laser Rangefinder (NLR) altimeter will measure the asteroid's topography and shape to 1 m vertical resolution with its infrared 15 mJ pulsed beam [Cole et al., 1997].

Evidence for asteroidal origin of the Tunguska object

The progress in the understanding of the Tunguska object is reviewed in the light of evidence presented in numerous recent investigations, which appeared following the publication of my 1983 paper on the object's proposed asteroidal nature. The issues addressed extensively in the present review involve: (i) the fundamental characteristics of the event, such as the object's energy, altitude and velocity at the time of its terminal explosion and the dynamic pressure involved; (ii) the problem of atmospheric fragmentation of very massive impactors and the implications for their ablation and deceleration; (iii) new analysis of the orientation of the Tunguska object's heliocentric orbit based on the best data on the apparent radiant of the fireball's atmospheric trajectory; and (iv) comparison with the findings of other recent investigations, including compositional studies. Also employed in the arguments are the results now available on the impacts of comet Shoemaker-Levy 9's fragments into Jupier and the findings of a recent comparative study of two huge fireballs (one cometary, one stony, both involving impactors several meters across) observed with the cameras of the European Network of fireball monitoring. It is concluded that hypotheses based on presumed cometary origin of the Tunguska object encounter unsurmountable difficulties and that the interpretation of the event as a fall of a small stony or carbonaceous asteroid is not only plausible, but virtually certain.

Velocity distribution of meteoroids in the vicinity of planets and satellites

Collisions in the Solar System play an important role in its history. Impact processes depend essentially on the velocity distribution of meteoroids colliding with a chosen planet. According to Carleman’s theorem it is sufficient to find the set of Mk = mathematical expectation of v k , v being the collisional velocity. We suppose that M k for meteoroids of asteroidal nature differs slightly from that for asteroids themselves. So among all numbered minor planets we select those which may potentially collide with the chosen major planet. Then we calculatevat intersection points and count the average over all such points and all selected asteroids. The gravitation of a body-target may be taken into account or not. Numerical results are collected in four Tables.

A comparison between binary star light curves and those of possible binary asteroids

Since about ten years coordinated programs of photoelectric observations of asteroids are carried out to derive rotation rates and light curves. Quite a number of those asteroids exhibit features in their light curves, with similar characteristics as variable stars and especially eclipsing binaries. This would allow also an interpretation that there might be an evidence for the binary nature of some asteroids, based on observational hints. A few examples are given and a list of indications for the possible binary nature of asteroids, based on their light curve features, is presented.

A Comparison Between Binary Star Light Curves and Those of Possible Binary Asteroids

AbstractSince about ten years coordinated programs of photoelectric observations of asteroids are carried out to derive rotation rates and light curves. Quite a number of those asteroids exhibit features in their light curves, with similar characteristics as variable stars and especially eclipsing binaries. This would allow also an interpretation that there might be an evidence for the binary nature of some asteroids, based on observational hints. A few examples are given and a list of indications for the possible binary nature of asteroids, based on their light curve features, is presented.

8. Asteroid Versus Comet Discrimination from Orbital Data

The orbital comet-asteroid criteria, their premises, dynamical reasoning, and ranges of applicability are reviewed. Mapping of all known comets and asteroids in a plane of energy intergral in the two body problem (1/a) vs. that in the restricted three-body problem (Tisserand invariant) is presented. The potential evolutionary paths from different sources of active comets into short-period orbits are delineated and interfaced with the process of reducing the perihelion distances of the asteroids. The significance of resonances with Jupiter is emphasized. Statistics of observed close approaches of individual comets and asteroids to the Earth is analyzed to estimate their relative fluxes. Active cometary nuclei are found to represent about 1/8 of the flux of objects with radii exceeding 1 km in the vicinity of the Earth, and their contribution tends to diminish significantly for still smaller bodies. However, there is no evidence against comets leaving inactive asteroid-like nuclei with considerable lifetimes which may represent a significant, though secondary, source of meteors and even meteor streams. An overwhelming majority of the Apollo and Amor objects are suggested to be of asteroidal nature; the most probable exceptions are selected and recommended for detailed observation.

The Nature of Asteroids

The Nature of Asteroids

Angular momentum of Icarus

Inclusion of Icarus in an angular momentum density-mass diagram supports a 1967 prediction that asteroidal bodies smaller than about 1017 gm will depart from the planetary rotation law described earlier. Icarus' asteroidal nature and origin by fragmentation is thereby suggested.