Apollo Objects Research Articles

The Santa Filomena meteorite shower: Trajectory, classification, and opaque phases as indicators of metamorphic conditions

AbstractOn August 19, 2020, at 13:18—UTC, a meteor event ended as a meteorite shower in Santa Filomena, a city in the Pernambuco State, northeast Brazil. The heliocentric orbital parameters resulting from images by cameras of the weather broadcasting system were semimajor axis a = 2.1 ± 0.1 au, eccentricity e = 0.55 ± 0.03, and inclination i = 0.15o ± 0.05. The data identified the body as an Apollo object, an Earth‐crossing object with a pericenter interior to the Earth's orbit. The chemical, mineralogical, and petrological evaluations, as well as the physical analysis, followed several traditional techniques. The meteorite was identified as a H5‐6 S4 W0 ordinary chondrite genomict breccia. The large amount of metal in the meteorite made a metallographic evaluation based on the opaque phases possible. The monocrystalline kamacite crystals suggest a higher petrological type and the distorted Neumann lines imply at least two different shock events. The absence of the plessite phase shows that the meteorite did not reach the highest shock levels S5 and S6. The well‐defined polycrystalline taenite is indicative of petrologic types 4 and 5 due to the conserved internal tetrataenite rim at the boundaries. The presence of polycrystalline taenites and the characteristics of the Agrell Effect suggest that the Santa Filomena meteorite did not reheat above 700°C. The absence of martensite confirms reheating temperatures <800°C and a slow cooling rate. The Ni contents and sizes of the zoned taenite particles indicate a slow cooling rate ranging from 1 to 10 K Myr−1.

Evaluación de la probabilidad de impacto de la Tierra con el Asteroide 2011 AG5

El objeto NEA 2011AG5 es un asteroide de unos 140 metros de diámetro, descubierto el 8 de enero de 2011 desde el Monte Lemmon en Estados Unidos. Tiene una órbita que lo convierte en un asteroide potencialmente peligroso, o sea un objeto cuya órbita tiene una distancia menor a 0.05UA respecto a la órbita de la Tierra en su punto más cercano. Por sus características orbitales, se trata de un objeto tipo Apolo, o sea asteroides que cruzan la órbita de la Tierra con un perihelio menor a 1.0167UA. En este trabajo se modeló el movimiento orbital del objeto NEA 2011AG5 para un período aproximado de 28 años, que abarca desde el año 2012 hasta el año 2040 utilizando el integrador numérico EVORB, un programa basado en arquitectura FORTRAN para modelar la dinámica de los objetos en un sistema estelar. Se realizaron 100 corridas del programa con base en los parámetros orbitales estimados al 18 de abril de 2013. Después de asegurar que los parámetros orbitales de entrada, obtenidos aleatoriamente, cumplen con una distribución normal dado su Jarque Bera menor a 5.991 para un α=0.05, se estimó que el máximo acercamiento ocurrirá el 4 de febrero de 2040. Para este acercamiento se estima una distancia media de 1,087,412 Km con una desviación estándar de 46,637 Km, en un acercamiento probable calculado para el 4 de febrero de 2040 a las 8h37m hora universal, con una desviación estándar de 48m04s. La probabilidad de impacto se concluye nula.

Near-Infrared Spectroscopy of Low-Albedo Surfaces of the Solar System: Search for the Spectral Signature of Dark Material

We obtained I–J–H–K band spectroscopy of 18 low-albedo objects of the Solar System using the University of Hawaii 88-in. telescope equipped with the near-infrared spectrograph KSPEC. Most of our targets were selected from among the population of the Cybele, Hilda, and Trojan groups of asteroids, based on their low albedos and the relatively steep slopes of their reflection spectra at visible wavelengths. The outer jovian satellite Himalia and the Apollo object 3200 Phaethon were also observed. None of the spectra show absorptions similar to those found in the spectrum of 5145 Pholus, which remains the only asteroid-like object whose H–K band reflection spectrum contains a few broad absorptions due to organics. The near-infrared slope and the (1.0- to 2.2-μm) infrared color-index have been derived for each surface. This sample of primitive objects of the Solar System can be interpreted in terms of cometary-like objects that have undergone different degrees of aging.

Meteorites from Comets? Recent Observational Developments

AbstractAlthough most meteorites come from asteroids, some could originate from short-period comets. The identification of comet-asteroid transition object 4015 Wilson-Harrington as the first Apollo object known to have a cometary origin, confirms that short-period comets leave behind nonvolatile residues, from which meteoroids with low Earth-encounter velocities can originate. Studies of cometary fireballs suggest that some cometary meteoroids have high enough strengths to have survived atmospheric entry as cometary meteorites, which have either not been found or recognized. The presence of unequilibrated anhydrous silicates in cometary dust represents a significant difference between cometary material and CI and CM meteorites.

The computation of orbits in indeterminate and uncertain cases

view Abstract Citations (21) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The computation of orbits in indeterminate and uncertain cases Marsden, B. G. Abstract Physically meaningful results are obtained in mathematically indeterminate cases via a modification of the Gauss-Enke-Merton (GEM) form of the Gaussian method of three-observation orbit determination. The modified procedure allows situations to be isolated where at least one observation is erroneous. A logical extension of the procedure provides a mechanism for using only two observations of a minor planet to identify additional data. Though analogous to the 'modified' Vaisala method, the new procedure is found to be more convenient for application in practice and to have distinct advantages in the case of Apollo objects, which in the Vaisala method must unrealistically be presumed at aphelion. It is also shown that the three-observation procedure can readily be extended to incorporate additional observations. The relative performance of the GEM method and traditional orbit-determination methods in cases of discrete nontrivial multiple solutions is discussed. Publication: The Astronomical Journal Pub Date: October 1991 DOI: 10.1086/115979 Bibcode: 1991AJ....102.1539M Keywords: Asteroids; Orbit Calculation; Planetary Orbits; Celestial Mechanics; Gauss Equation; Astrophysics full text sources ADS |

Multiple impacts in the Earth's cratering history

Post-bombardment periods of increased impact flux on Earth are probably due to the decay of captured Apollo object group orbits. The origin of the Messier binary impact structure on the Moon implies the breakup of a single impactor as the origin of a Cretaceous/Tertiary multiple impact.

Cratering of the terrestrial planets by Apollo objects

Abstract— Absolute and relative cratering rates on the terrestrial planets have been calculated using the same asteroidal collision model and Monte Carlo program used for previous studies of the terrestrial meteorite flux, the steady‐state number of Apollo‐Amor objects, and the orbital distribution of both meteorites and Apollo‐Amor objects. The most straightforward result is that projectiles from the asteroid belt appear to provide about one‐third the observed present‐day production of terrestrial craters larger than 10 km in diameter. When uncertainties in the calculations and observations are included, it cannot be excluded that the entire terrestrial cratering flux is asteroidal. On the other hand, assumption of an additional Apollo‐Amor source of extinct comets, in the same quantity permitted by Apollo‐Amor observations, provides better agreement with the observed cratering rate. In addition, a significant (e.g., ∼30%) terrestrial contribution from active long and short period comets is acceptable within the uncertainties of the assumptions required.The ratios of the cratering rates on the different terrestrial planets are somewhat sensitive to the assumed source. A purely asteroidal source predicts a martian cratering rate per unit area about four times that on Earth, whereas the difference is reduced to about a factor of two for the mixed asteroid‐extinct comet source. The opposite effect is found for Mercury. As discussed by previous authors, the predicted lunar cratering rate is significantly higher than that observed. It is not clear whether this is a result of scaling to impacts on a body considerably smaller than Earth, or if it indicates an increase in the cratering flux during the Phanerozoic.

End Products of Cometary Evolution: Cometary Origin of Earth-Crossing Bodies of Asteroidal Appearance

AbstractBecause there is no necessary connection between the time required to remove the volatile component of a cometary nucleus by solar heating (physical lifetime) and the dynamical lifetime of a comet, it is possible that a comet may evolve into an observable object of asteroidal appearance. Almost all comets have dynamical lifetimes much shorter than their physical lifetimes and in these cases complete loss of volatiles will not occur. Mechanisms do exist, however, whereby a small but significant fraction of comets will have longer dynamical lifetimes, permitting them to evolve first into Jupiter-family short period comets and then into comets with relatively safe decoupled orbits interior to Jupiter’s orbit. Observed Jupiter-family objects of asteroidal appearance (e.g., 1983SA) are much more likely to be of cometary rather than asteroidal origin. “Decoupling” is facilitated by several mechanisms: perturbations by the terrestrial planets, perturbations by Jupiter and the other giant planets (including resonant perturbations) and non-gravitational orbital changes caused by the loss of gas and dust from the comet. The dynamical time scale for decoupling is probably 105–106 years and almost all decoupled comets are likely to be of asteroidal appearance. Once decoupled, the orbits of the resulting Apollo-Amor objects will evolve on a longer (107–108 year) time scale, and the orbital evidence for these objects having originally been comets rather than asteroids will nearly disappear. Statistically, however, a large fraction of the bodies in deep Earth-crossing orbits with semi-major axes ≳ 2.2 AU are likely to be cometary objects in orbits that have not yet diffused into the steady state distribution. For plausible values of the relevant parameters, estimates can be made of the number of cometary Apollo-Amor “asteroids,” the observed number of Earthcrossing active and inactive short period comets, and the production rate of short period comets. These estimates are compatible with other theoretical and observational inferences that suggest the presence of a significant population of Apollo objects that formerly were active comets.

Where do the Apollo objects come from?

Monte Carlo calculations have been carried out to trace the orbital evolution of ∼1- to 45-km-diameter bodies produced by collisions in the asteroid belt interior to 2.6 AU. It is found that about 3% of the asteroidal fragments ejected at 100 m/sec in this size range are perturbed into Earth-crossing orbits as a consequence of the 3:1 Jovian commensurability resonance at 2.5 AU and the ν dot 6 secular resonance in the innermost asteroid belt. For ejection velocities of 100 m/sec the calculated steady-state number of Apollo objects (454) and Amor objects (1600) brighter than absolute V magnitude 18 is in the general range of the estimated number based on observations. Considering the uncertainties in both the theoretical results and the observational data, this should be considered to be good agreement. Even though the initial Earth-crossing orbits of these bodies are concentrated near 1 AU, their steady-state orbital distribution is widely dispersed. There is strongly suggestive, but not yet compelling, evidence for an additional component of Apollo-Amor objects that are inactive comets. It is found that a modest production rate (∼1 in 6 × 10 4 years) of extinct comets with V(1,0) < 18 in Encke-like orbits is required to maintain a steady-state population of cometary Apollos equal in number to the asteroidal Apollos.

Dynamical relations between asteroids, meteorites and Apollo-Amor objects

A Monte-Carlo technique has been used to investigate the orbital evolution of asteroidal collision debris produced interior to 2.6 AU. It is found that there are two regions primarily responsible for production of Earth-crossing meteoritic material and Apollo objects. The region adjacent to the 3:1 jovian commensurability resonance (2.5 AU) is unique in providing material in the required quantity and orbital distribution of the ordinary chondrites. This region should also supply a comparable preatmospheric flux of carbonaceous meteorites. The innermost asteroid belt (2.17-2.25 AU), via the v6secular resonance, provides a fluxca.9% that of the ordinary chondrites, and appears to be the strongest candidate for the basaltic achondrite source region. It is unlikely that a significant number of meteorites originate beyond 2.6 AU. It is speculated that enstatite achondrites are derived from the Hungaria region, interior to the main belt, and that iron and stony-iron meteorites originate from many main-belt sources interior to 2.6 AU.

Paleoceanography of the Cretaceous/Tertiary Boundary Event: Inferences from stable isotopic and other data

We report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction, whole rock, and benthic foraminifers, CaCO3 and coarse fraction percentage determinations, and trace element (Sr) analyses on carbonate constituents across the Cretaceous/Tertiary (K/T) boundary in Deep Sea Drilling Project (DSDP) sites 47.2, 356, 384, and 577 and compare them with published results from K/T boundary sections in other DSDP sites. We used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study. The ∂18O data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late Maestrichtian followed by somewhat fluctuating temperatures in the early Paleocene. However, there is no indication of either a significant warming or cooling at or following the K/T boundary. Several sites do exhibit somewhat heavier ∂18O values by about 0.5‰ across the boundary, which might suggest a 2‐3°C cooling at most. However, we interpret these somewhat heavier ∂18O values as reflecting slightly better preservation of ∂18O of carbonate constitutents in relatively clay‐rich intervals (e.g., lower diagentic potential) characteristic of the K/T boundary. The ∂13C values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary. The surface water and deepwater ∂13C values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest Paleocene are consistent with a major decrease in productivity across the K/T boundary. The decrease in CaCO3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters. The low‐productivity episode lasted at least 1 m.y. beyond the K/T boundary crisis, suggesting that hypothesized catastrophic events alone, such as impact of an apollo object, are not the only explanation for the observed long‐term decrease in productivity. There is also an indication in the ∂13C curves from several sites that the surface water ∂13C decrease began in the latest Maestrichtian, suggesting that the decrease in productivity may have been independent of a hypothesized impact event.

ASTEROIDAL SOURCE OF ORDINARY CHONDRITES*

The orbital evolution of asteroidal fragments with diameters ranging from 10 cm to 20 km, injected into the 3:1 Kirkwood gap at 2.50 A.U., has been investigated using Monte Carlo techniques. It is assumed that this material can become Earth‐crossing on a time scale of 106 years, as a result of a chaotic zone discovered by Wisdom, associated with the 3:1 resonance. This phenomenon, as well as close encounter planetary perturbations, the v6 secular resonance, and the ablative effects of the Earth's atmosphere are included in the determination of the orbital characteristics of meteorites impacting the Earth derived by fragmentation of this asteroidal material. It is found that the predicted meteorite orbits closely match those found for observed ordinary chondrites, and the total flux is in approximate agreement with the observed fall rate of ordinary chondrites. About 10% of the predicted impacting bodies are meteorite‐size bodies originating directly from the asteroid belt. The remainder are obtained by subsequent fragmentation of larger (∼1 m to 20 km diameter) Earth‐crossing asteroidal fragments. The largest of these fragments are observable as Apollo‐Amor objects. Thus the apparent paradox between the orbital characteristics of observed ordinary chondrites and those predicted from Apollo object sources is reconciled. Both appear to be complementary aspects of the same phenomena. No other asteroidal resonance is found to be satisfactory as a source of ordinary chondrites. These meteorites are therefore most likely to be derived from S asteroids in this limited region of the asteroidal belt, the largest of which are 11 Parthenope, 17 Thetis, and 29 Amphitrite.

The discovery of 1982 DB, the most accessible asteroid known

A small Apollo object was found while photographing the split comet DuToit 2-Hartley on February 27/28, 1982. Designated 1982 DB, this Earth-crossing asteroid passed the Earth at a distance of 4.08 million km about 1 month prior to its discovery. Asteroid 1982 DB has been determined to be the most accessible near-Earth minor planet known. It provides many excellent opportunities for rendezvous and sample return missions, and a rare dual rendezvous mission with 1980 AA as the second target. For a mission to be realized, opportunities to observe 1982 DB during future apparitions must be taken.

Steady state populations of Apollo-Amor objects

The steady-state distribution of orbits of Apollo-Amor objects is calculated for a variety of possible sources. These include asteroids near the inner edge of the belt, cometary orbits similar to Encke, and hypothetical extinct cometary orbits with perihelia larger than that of Encke. In all but one case, the steady-state distributions are similar for all these sources, and predict Amor/Apollo ratios of 1.5 to 3. These ratios are lower than those predicted by work in which the effects of the ν 6 secular resonance were not considered. These results are in general agreement with observation, although the higher (∼3) Amor/Apollo ratios found for many of the sources may turn out to be unacceptably high. The absolute number of Apollo-Amors observed is found to require an injection rate of ∼15 objects/(10 6 years). This rate is easily achieved if the present existence of Encke is assumed to be a reasonably probable event, and if Encke becomes a ∼1-km-diameter Apollo object following exhaustion of its volatile material; best estimates of the injection rate from the asteroid belt [∼1.5/(10 6 years)] are too low. Hence a dominant cometary component is suggested. The predicted number of Apollo objects in small ( q < 1.0 AU, a < 1.4 AU orbits is in agreement with observation. Predicted lunar and terrestrial cratering rates agree approximately with observation. An unexplained difference between the lunar and terrestrial results is probably caused by uncertainties in the scaling laws or crater counts used. This discrepancy precludes an exact test of these calculations using cratering data.

5. Populations of Planet-Crossing Asteroids and the Relation of Apollo Objects to Main-Belt Asteroids and Comets

From discoveries made in several independent surveys of the sky, the number of Apollo asteroids to absolute visual magnitude 18 is estimated to be of the order of 103; the ratio of Mars-crossing asteroids to Apcllos is estimated to lie between 10 and 60. The loss of Apollos to magnitude 18 over the last 3 billion years, by collision with the planets and ejection from the solar system, is estimated to have been several times 104 objects. Mars-crossing asteroids appear to be an inadequate source for all of these objects. Most Apollos probably are dead short-period comets.

Where do the meteorites come from? A re-evaluation of the earth-crossing apollo objects as sources of chondritic meteorites

The total number of Earth-crossing Apollo objects larger than 500 m in radius is estimated to be 600, based on failure of chance rediscovery, lunar crater frequency and completeness-of-search results of Shoemaker, Helin and Gillett. The number of Amor objects (perihelion between 1.0 and 1.3 A.U.) is estimated to be about 500. These estimates are about an order of magnitude higher than those given by previous workers, and these objects appear sufficiently numerous to dominate post-mare lunar and terrestrial cratering ( d ≥ 10 km). The terrestrial meteorite and meteorite yield of 100-10 6 g bodies derived from fragmentation of Apollo objects is re-evaluated using this estimate, together with more recent data on asteroid albedos and on hypervelocity impact. Terrestrial rate of impacts of these fragments at sufficiently low velocities to penetrate the atmosphere is estimated to be ~2 × 10 8g/yr. This is in the middle of the range of the actual extraterrestrial impact rate based on photographic fireball surveys (Prairie Network), lunar seismometry, and recovery of meteorites. It is likely that most ordinary chondrites are fragments of Apollo objects, provided that these fragments are sufficiently strong to survive atmospheric entry. Possible asteroidal and cometary sources of Apollo objects are reviewed. Several mechanisms for the removal of asteroids into Earth-crossing orbit are qualitatively acceptable, but appear inadequate by at least an order of magnitude to supply the required number. Most Apollo objects are probably the cores of comets which have lost their volatile material by repeated solar evaporation, as proposed by Öpik. The distribution of the component of the Apollo objects' angular momentum perpendicular to the plane of the solar system is tabulated. It is found that considerable non-random clustering of these values exists, for which no adequate explanation is known.

On following up newly-discovered earth-approaching minor planets

AbstractRecent experience suggests that it is not necessary to introduce a 24-hour information service for following up discoveries of fast-moving objects. Success can be achieved by intelligent action and only a moderate degree of urgency. There is some interest in making deliberate searches for new Apollo objects and hence a great need for follow-up observations.

On the Relationship between Comets and Minor Planets

Previous work suggested that P/Neujmin I and P/Arend-Rigaux may represent a transition phase between comet and minor planet. Earlier results on the librations of minor planets are confirmed here by means of numerical integrations in which allowance is also made for the perturbations by planets other than Jupiter. With the exception of Hidalgo, all known minor planets are able to avoid encounters with Jupiter. Since the short-period comets characteristically have frequent encounters with Jupiter, it follows hat although cometary remnants may look like minor planets, they have subsequent lifetimes that are several orders of magnitude shorter than those of conventional minor planets. A new orbital analysis of Hidalgo sug- gests that nongravitational forces may be acting and that it is an object like P/Neujmin 1 and P/Arend- Rigaux. There is thus little real evidence that comets turn into truly planetary objects, and it is still question- able whether the Apollo objects, for example, can be ex-comets. Long-term analysis shows that short-period comets are sometimes affected by librations similar to those involving minor planets, although the librations are of a temporary nature, existing for a millennium or so, and still often involve close approaches to Jupiter. However, P/Arend-Rigaux and P/Neujmin 1 have apparently been more successful than all other short- period comets in avoiding Jupiter. P/Neujmin 1 is found to librate about the 2 :3 resonance with Jupiter (i.e., in an 18-yr period) in spite of the strong gravitational influence of Saturn. Because its perihelion distance must have remained relatively constant for centuries (or even millennia), it is reasonable that a comet that avoids Jupiter or temporarily librates could indeed be approaching the end of its cometary life.

25. Orbits of photographic meteors

New photographic observations of meteors in the brightness range −5 &gt; Mp &gt; −18 (?) and with a median value of M = −8·5 have yielded orbits with a precision of better than 1° in the angular elements and of about 0·05 in e and 1/a. A comparison of 100 of these fireball orbits with Super-Schmidt orbits shows: (1)A class of orbits, comprising about 25% of the faint meteors, of long period, is almost completely absent among the fireballs.(2)Small perihelion distances (q &lt; 0·2 AU) are not found. A maximum at q ~ 0·7 AU, which also appears in the Super-Schmidt orbits of short period, corresponds to the perihelion distances of all but two of the Apollo objects.(3)The distribution of aphelia shows a marked decrease at Jupiter when compared to a similar distribution of small, faint meteor orbits. With the existing material, we cannot determine whether this represents an important evolutionary distinction between meteoroids of different mass or is simply the result of an inappropriate choice of the division between ‘large’ and ‘small’ orbits in the faint meteor data.Provisional values of the bulk density of 28 of the fireballs as determined from the photometric mass and the observed mass-area ratio indicate that these meteoroids do not differ significantly from those observed with the Super-Schmidt cameras. Evidence of gross fragmentation of these large objects at high elevation and evidence of small or negligible terminal masses suggest that the material is friable. There is no certain evidence that any appreciable fraction of fireballs is produced by high-density, cohesive material.If the above analysis is correct, we should expect an occasional (1 year−1 106 km−2?) meteorite fall of discoverable size originating from a low-density meteoroid.