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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records

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NASA NTRS1977

On the orbital dependence of the asteroidal collision process

Collision of asteroids with the main-belt asteroid population is considered with the effect of the impact kinetic energy taken into account. It is found that objects in eccentric orbits have a larger probability of destructive collision as compared to objects in orbits with mean values of eccentricity (equal to 0.15) and inclination (equal to 10 deg); also orbits with small semimajor axes (about 2.3 AU) are found to have peak values of the probability of destructive collision.

Ip, W.-H.↗

NASA NTRS1993

Asteroid collisions: Target size effects and resultant velocity distributions

To study the dynamic fragmentation of rock to simulate asteroid collisions, we use a 2-D, continuum damage numerical hydrocode which models two-body impacts. This hydrocode monitors stress wave propagation and interaction within the target body, and includes a physical model for the formation and growth of cracks in rock. With this algorithm we have successfully reproduced fragment size distributions and mean ejecta speeds from laboratory impact experiments using basalt, and weak and strong mortar as target materials. Using the hydrocode, we have determined that the energy needed to fracture a body has a much stronger dependence on target size than predicted from most scaling theories. In addition, velocity distributions obtained indicate that mean ejecta speeds resulting from large-body collisions do not exceed escape velocities.

Ryan, Eileen V.↗

NASA NTRS1986

Scaling laws for the catastrophic collisions of asteroids

Collisions of asteroids have traditionally been studied through laboratory experiments involving targets with masses some 15 to 20 orders of magnitude less than the bodies they are intended to simulate. Here the problem of extrapolation of experimental results up to the size regimes of interest is considered. Scaling relations are developed for the shattering threshold and the size and velocity distributions of collisional fragments. A methodology which has often been used assumes that collisional outcomes (e.g., the size of the largest remaining fragment) are completely characterized by Q, the kinetic energy of the impactor normalized by the mass of the target body. This scaling is shown to be an unlikely special case of a more general scaling theory which indicates that collisional outcomes should depend on target size and encounter velocity, even when Q is held constant. In particular, as target size increases, the critical value of Q required to shatter a body, and the characteristic fragment velocities should initially decrease (in qualitative agreement with the recent model of Farinella et al., 1982) up to an asteroid size of perhaps 40 to 50 km; then, as the gravitational forces start to dominate, the value of Q will again increase (in qualitative agreement with the recent model of Davis et al., 1983 and 1985).

Holsapple, K. A.↗

NASA NTRS1990

Antimatter applied for Earth protection from asteroid collision

An Earth protection system against asteroids and meteorites in colliding orbit is proposed. The system consists of detection and deorbiting systems. Analyses are given for the resolution of microwave optics, the detectability of radar, the orbital plan of intercepting operation, and the antimatter mass require for totally or partially blasting the asteroid. Antimatter of 1 kg is required for deorbiting an asteroid 200 m in diameter. An experimental simulation of antimatter cooling and storage is planned. The facility under construction is discussed.

Satori, Shin↗

NASA NTRS1979

Chronology of asteroid collisions as recorded in meteorites

Because meteorites are derived from asteroidal objects, the chronology of meteorites give age information on the histories of the asteroidal parents. With a few possible exceptions, the radiometric chronology of less than 4.4 Gyr determined in meteorites can be attributable to collisions among meteorite parent bodies. Three types of collisional chronologies which have been determined are: (1) cosmic ray exposure ages, which generally date the time of the last fragmentation of the parent object when the meteorite is reduced to meter size, and which generally fall over the wide range of 1-1000 Myr; (2) the collisional shock ages shown by many meteorites, which are believed to date the times of major collisions among parent bodies in the asteroid belt in the time interval of 30-700 Myr; and (3) the brecciation ages of several meteorites which are believed to date the times of their collisional formation from regoliths of larger parent bodies over the period of 1.4-4.4 Gyr.

Bogard, D. D.↗

NASA NTRS1978

Asteroid collisions, craters, regoliths, and lifetimes

Laboratory experiments and computer modeling are used to predict the development of regoliths on all asteroids more than a few tens of kilometers in diameter, allowing for a wide range in the intrinsic strength of asteroidal surface materials. The high frequency of interasteroid collisions requires nearly all asteroids to be fragments of precursors.

Chapman, C. R.↗

NASA NTRS1993

Asteroidal collision probabilities

Several past calculations of collision probabilities between pairs of bodies on independent orbits have yielded inconsistent results. We review the methodologies and identify their various problems. Greenberg's (1982) collision probability formalism (now with a corrected symmetry assumption) is equivalent to Wetherill's (1967) approach, except that it includes a way to avoid singularities near apsides. That method shows that the procedure by Namiki and Binzel (1991) was accurate for those cases where singularities did not arise.

Bottke, William F., Jr.↗

NASA NTRS1986

The formation and origin of the IRAS zodiacal dust bands as a consequence of single collisions between asteroids

Debris fom the single collisions between asteroids that are presently suggested as an explanation for zodiacal dust bands discovered by IRAS is distributed about the plane of the ecliptic, as particles undergo differential precession of their ascending nodes because of their semimajor axes' dispersion. On time scales of 100,000 to 1,000,000 yr, two bands are formed on each side of the ecliptic for each collision; the IRAS band pairs are probably due to collisions of aproximately 15-km diameter asteroids which occurred within the last several million yr. The model presented suggests that asteroid collisions suffice as a basis for most of the observed zodiacal emission.

Sykes, M. V.↗

NASA NTRS1992

Deflection and Fragmentation of Near-Earth Asteroids

Collisions by near-earth asteroids or the nuclei of comets pose varying levels of threat to man. A relatively small object, approximately 100 m diameter, which might be found on an impact trajectory with a populated region of the Earth, could potentially be diverted with a velocity of approximately1 cm/sec from an Earth impacting trajectory by impact (at 12 km/sec) by a rocket launched, 10^2 to 10^3 Kg impactor. For larger bodies, the use of kinetic energy impactors appear impractical because of the larger mass requirement. For any size object, nuclear explosions appear to be more efficient, using either the prompt blow-off from neutron radiation, the impulse from ejecta of a near-surface explosion for deflection, or, least efficiently, as a fragmenting charge.

Harris, Alan W.↗

NASA NTRS1992

On the origin of interplanetary dust within recorded history

The possibility of an abrupt origin of interplanetary dust as a result of a collision between asteroids or an extraordinary comet is considered. If all interplanetary dust were produced in one event within recorded history, it would have been visible from the Earth with the unaided eye. The rate, surface area, and brightness of asteroid collision remnants are derived. Ancient Chinese records are searched for extraordinary comets aand bright pointlike objects with small angular motion and concentration to the ecliptic.

Reach, William T.↗

NASA NTRS2001

Continued Investigations of the Accretion History of Extraterrestrial Matter over Geologic Time

This grant supported our ongoing project to characterize the accretion rate of interplanetary dust particles (IDPs) to Earth over geologic time using He-3 as a tracer. IDPs are derived from collisions in the asteroid belt and from disaggregation of active comets. Owing to their small size (few to few hundred micrometers diameter) these particles spiral into the sun under Poynting-Robertson drag typically in less than a few tens of kyrs. Thus IDPs must be continually resupplied to the zodiacal cloud, and because the processes of IDP production are likely to be sporadic, time variation in the IDP accretion rate to Earth is likely to be time-varying. For example, major asteroidal collisions and comet showers should greatly enhance the IDP accretion rate. Our ultimate objective (still ongoing) is to document this time variance so as to better understand the history of the solar system, the source of IDPs accreting to Earth, and the details of the mechanism by which particles are captured by Earth. To document variations in IDP accretion rate through time we use He-3 as a tracer. This isotope is in extremely low abundance in terrestrial matter, but IDPs have very high concentrations of He-3 from implantation of solar wind ions. By measuring He-3 in seafloor sediments, we can estimate the IDP accretion rate for at least the last few hundred Myrs. Under an earlier NASA grant we identified the existence of a large increase in He-3 flux in the Late Eocene (35 Myr ago), coincident with the two largest impact craters of the Cenozoic Era. The simplest interpretation of this observation is the occurrence of a shower of long period comets at that time, simultaneously increasing the impact cratering probability and accretion rate of IDPs to Earth (Farley et al., 1998). Comet showers produced by stellar perturbation of the Oort cloud should be fairly common in the geologic record, so this is not an unreasonable interpretation of our observations.

Farley, Kenneth↗

NASA NTRS1979

Earth-crossing asteroids - Orbital classes, collision rates with earth, and origin

Asteroids that can intersect the orbit of the earth are discussed, which include Aten asteroids (semimajor axis (a) less than 1 AU, aphelion greater than 0.983 AU), Apollo asteroids (a greater than 1 AU, perihelion less than 1.017 AU), and Amor asteroids (perihelion distance between 1.017 and 1.3 AU). The principal sources of earth-crossing asteroids appear to be extinct comet nuclei and collision fragments from regions in the main asteroid belt. The total population of earth-crossers is estimated at 13,000, of which approximately 8% are Atens, 50% are Apollos, and 40% are Amors,and the present collision rate of such asteroids with the earth is estimated at about 3.5 objects, to absolute magnitude 18, per million years.

Shoemaker, E. M.↗

NASA NTRS1999

Scale Effects in Strength-Dominated Collisions of Rocky Asteroids

The application of laboratory collision experimental results to the larger scales of asteroid impacts is complicated by the fact that the dynamic strength of rock typically decreases as the loading duration increases. Because loading times increase with the size scale of a collision, large bodies are effectively weaker than small ones. While this effect has been postulated for over a decade, it has never been verified in actual collision experiments. This paper summarizes collision tests performed under the conditions required to examine scale effects, i.e., increasing the size scale of the experiment while holding the impact velocity and impact kinetic energy per target mass constant. Granite targets are used, with a diameter variation of a factor of 18. The larger targets experienced significantly more collisional damage than small ones, confirming a decrease in dynamic strength with increasing size scale. The results are compared to a scaling model based on the concept that fragmentation is accomplished through the growth and coalescence of preexisting flaws. Measurements of the actual flaw-size distribution are used to validate the model. Field observations of flaw and fault sizes at scales to 10 km are used to construct a scaling model that is believed to apply to the shattering of a wide range of rock types. The results show that kilometer-sized rocky bodies may be significantly weaker than indicated by previous estimates.

Housen, Kevin R.↗

NASA NTRS1975

On the alleged collisional origin of the Kirkwood Gaps

This paper examines two proposed mechanisms whereby asteroidal collisions and close approaches may have given rise to the Kirkwood Gaps. The first hypothesis is that asteroids in near-resonant orbits have markedly increased collision probabilities and so are preferentially destroyed, or suffer decay in population density, within the resonance zones. A simple order-of-magnitude analysis shows that this hypothesis is untenable since it leads to conclusions which are either unrealistic or not in accord with present understanding of asteroidal physics. The second hypothesis is the Brouwer-Jefferys theory that collisions would smooth an asteroidal distribution function, as a function of Jacobi constant, thus forming resonance gaps. This hypothesis is examined by direct numerical integration of 50 asteroid orbits near the 2:1 resonance, with collisions simulated by random variables. No tendency to form a gap was observed.

Heppenheimer, T. A.↗

NASA NTRS2000

The Impact Threat and Public Perception

Recent popular movies have raised public consciousness of the very real possibility of a comet or asteroid collision with the Earth, and a news report last year implying that asteroid 1997 XF11 had a distinct chance of hitting the Earth in the year 2028 further caught the public's eye. The report of possible impact was withdrawn the very next day, and the public perceived either that astronomers had made mistaken calculations, or that the pre-discovery observations found that day had been responsible for the revised prediction. But in fact, the original report of the possibility of impact in 2028 was simply a premature assessment. The XF11 affair has demonstrated the need for clarity and precision in public communications dealing with the possibility of Earth impact, as well as the importance of peer review before results are released to the press. This year, another potentially hazardous asteroid, 1999 AN10, has made the news, and this time there is indeed a remote chance of collision. Although impact is not possible during the asteroid's primary close approach in 2027, the uncertainties allow for a remarkably close passage, and embedded within the encounter's uncertainty region are many narrow "keyholes" which could bring the asteroid back for a close approach in a later year. Three keyholes have been identified which could perturb the asteroid onto trajectories that collide with the Earth in the years 2044, 2046, or 2039. At the time of this writing, the estimated impact probability for 1999 AN10 is on the order of 1 in 500,000, larger than for any other known object, but still significantly less than the probability of an undiscovered asteroid of equivalent size striking the Earth before 2044. Additional astrometric measurements of 1999 AN10 will likely drive its impact probability down to near-zero, but this may not happen for years, testing the public's reaction to a lingering remote possibility of impact. A side effect of the increasing discovery rate for Near Earth objects will be a growing number of cases like 1999 ANIO.

Chodas, Paul W.↗

NASA NTRS1985

Asteroid Collisional Evolution Studies

Understanding asteroid collisional evolution is important for characterizing the physical state of asteroids today and for learning about the processes that acted in this region of the solar system early in its history. The collisional outcome algorithm in the numerical simulation of asteroid evolution was revised to reflect pressure-strengthening. Asteroid collisions are now treated as a distribution of oblique impacts rather than as only head-on collisions. The initial and evolved size distribution of a plausible asteroid population is compared with the observed size distribution. Asteroid accretion times and reconstruction of the primordial solar nebula suggest that there was significantly more mass in this part of the solar system when the asteroids were accreting.

Davis, D. R.↗

NASA NTRS1999

Asteroids and Comets Outreach Compilation

Contents include various different animations in the area of Asteroids and Comets. Titles of the short animated clips are: STARDUST Mission; Asteroid Castallia Impact Simulation; Castallia, Toutatis and the Earth; Simulation Asteroid Encounter with Earth; Nanorover Technology Task; Near Earth Asteroid Tracking; Champollian Anchor Tests; Early Views of Comets; Exploration of Small Bodies; Ulysses Resource Material from ESA; Ulysses Cometary Plasma Tail Animation; and various discussions on the Hale-Bopp Comet. Animation of the following are seen: the Stardust aerogel collector grid collecting cometary dust particles, comet and interstellar dust analyzer, Wiper-shield and dust flux monitor, a navigation camera, and the return of the sample to Earth; a comparison of the rotation of the Earth to the Castallia and Tautatis Asteroids; an animated land on Tautatis and the view of the motion of the sky from its surface; an Asteroid collision with the Earth; the USAF Station in Hawaii; close-up views of asteroids; automatic drilling of the Moon; exploding Cosmic Particles; and the dropping off of the plasma tail of a comet as it travels near the sun.

Source record↗

NASA NTRS1966

The Martian surface.

Martian surface markings, brightness along optical equator, crater erosion, asteroid collision and yellow dust clouds

MARS SURFACE↗