Sources of cosmic dust in the Earth's atmosphere Carrillo‐Sánchez, J. D.; Nesvorný, D.; Pokorný, P. ...
Geophysical research letters,
16 December 2016, Letnik:
43, Številka:
23
Journal Article
Recenzirano
Odprti dostop
There are four known sources of dust in the inner solar system: Jupiter Family comets, asteroids, Halley Type comets, and Oort Cloud comets. Here we combine the mass, velocity, and radiant ...distributions of these cosmic dust populations from an astronomical model with a chemical ablation model to estimate the injection rates of Na and Fe into the Earth's upper atmosphere, as well as the flux of cosmic spherules to the surface. Comparing these parameters to lidar observations of the vertical Na and Fe fluxes above 87.5 km, and the measured cosmic spherule accretion rate at South Pole, shows that Jupiter Family Comets contribute (80 ± 17)% of the total input mass (43 ± 14 t d−1), in good accord with Cosmic Background Explorer and Planck observations of the zodiacal cloud.
Plain Language Summary
The solar system contains a significant quantity of cosmic dust. This is generated from comets when they orbit close to the sun and evaporate, and also from collisions between asteroids in the region between Mars and Jupiter. The amount of cosmic dust which enters the Earth's atmosphere every day is highly uncertain, ranging from 5 to 270 tonnes. This study combines an astronomical model of dust in the solar system with a model describing the fate of dust particles when they enter the atmosphere at high speed. The dust input is then constrained with three observations: the rate of injection of sodium atoms into the upper atmosphere where some of this dust evaporates; the rate of injection of iron atoms; and the rate of accumulation of cosmic spherules (meteorites that melted during atmospheric entry) at the South Pole. The conclusion is that about 80% of the dust comes from comets with short orbital periods (less than 20 years), and the daily input is between 29 and 57 tonnes.
Key Points
Solar system dust sources are fitted to the cosmic spherule accretion rate and the Na and Fe fluxes in the mesosphere
Jupiter Family Comets provide ~80% of the cosmic dust entering the atmosphere, with 12% from long‐period comets and 8% from asteroids
The resulting differential ablation of Ca and Fe relative to Na explains the relative abundances of these metal layers in the mesosphere
Doppler and transit observations of exoplanets show a pile-up of Jupiter-size planets in orbits with a 3 day period. To explain these observations we performed a series of numerical integrations of ...planet scattering followed by the tidal circularization and migration of planets that evolved into highly eccentric orbits. We considered planetary systems having three and four planets initially placed in successive mean-motion resonances, although the angles were taken randomly to ensure orbital instability in short timescales. The simulations included the tidal and relativistic effects, and precession due to stellar oblateness. Our results show the formation of two distinct populations of hot Jupiters. The inner population (Population I) is characterized by semimajor axis a < 0.03 AU and mainly formed in the systems where no planetary ejections occurred. Our follow-up integrations showed that this population was transient, with most planets falling inside the Roche radius of the star in <1 Gyr.
We infer the crater chronologies of Ceres and Vesta from a self-consistent dynamical model of asteroid impactors. The model accounts for planetary migration/instability early in the history of our ...solar system and tracks asteroid orbits over 4.56 Gyr. It is calibrated on the current population of the asteroid belt. The model provides the number of asteroid impacts on different worlds at any time throughout the solar system's history. We combine the results with an impactor-crater scaling relationship to determine the crater distribution of Ceres and Vesta and compare these theoretical predictions with observations. We find that: (i) The Ceres and Vesta chronologies are similar, whereas they significantly differ from the lunar chronology. Therefore, using the lunar chronology for main belt asteroids, as often done in previous publications, is incorrect. (ii) The model results match the number and size distribution of large (diameter >90 km) craters observed on Vesta, but overestimate the number of large craters on Ceres. This implies that large crater erasure is required for Ceres. (iii) In a model where planetary migration/instability happens early, the probability to form the Rheasilvia basin on Vesta during the last 1 Gyr is 10%, a factor of ∼1.5 higher than for the late instability case and ∼2.5 times higher than found in previous studies. Thus, while the formation of the Rheasilvia at ∼1 Gyr ago (Ga) would be somewhat unusual, it cannot be ruled out at more than 1.5 . In broader context, our work provides a self-consistent framework for modeling asteroid crater records.
Evidence in the Solar system suggests that the giant planets underwent an epoch of radial migration that was very rapid, with an e-folding time-scale shorter than 1 Myr. It is probable that the cause ...of this migration was that the giant planets experienced an orbital instability that caused them to encounter each other, resulting in radial migration. A promising and heavily studied way to accomplish such a fast migration is for Jupiter to have scattered one of the ice giants outwards; this event has been called the 'jumping Jupiter' scenario. Several works suggest that this dynamical instability occurred 'late', long after all the planets had formed and the solar nebula had dissipated. Assuming that the terrestrial planets had already formed, then their orbits would have been affected by the migration of the giant planets as many powerful resonances would sweep through the terrestrial planet region. This raises two questions. First, what is the expected increase in dynamical excitement of the terrestrial planet orbits caused by late and very fast giant planet migration? And secondly, assuming that the migration occurred late, can we use this migration of the giant planets to obtain information on the primordial orbits of the terrestrial planets? In this work, we attempt to answer both of these questions using numerical simulations. We directly model a large number of terrestrial planet systems and their response to the smooth migration of Jupiter and Saturn, and also two jumping Jupiter simulations. We study the total dynamical excitement of the terrestrial planet system with the angular momentum deficit (AMD) value, including the way it is shared among the planets. We conclude that to reproduce the current AMD with a reasonable probability (∼20 per cent) after late rapid giant planet migration and a favourable jumping Jupiter evolution, the primordial AMD should have been lower than ∼70 per cent of the current value, but higher than 10 per cent. We find that a late giant planet migration scenario that initially had five giant planets rather than four had a higher probability of satisfying the orbital constraints of the terrestrial planets. Assuming late migration, we predict that Mars was initially on an eccentric and inclined orbit while the orbits of Mercury, Venus and Earth were more circular and coplanar. The lower primordial dynamical excitement and the peculiar partitioning between planets impose new constraints for terrestrial planet formation simulations.
The size and velocity distribution of cosmic dust particles entering the Earth's atmosphere is uncertain. Here we show that the relative concentrations of metal atoms in the upper mesosphere, and the ...surface accretion rate of cosmic spherules, provide sensitive probes of this distribution. Three cosmic dust models are selected as case studies: two are astronomical models, the first constrained by infrared observations of the Zodiacal Dust Cloud and the second by radar observations of meteor head echoes; the third model is based on measurements made with a spaceborne dust detector. For each model, a Monte Carlo sampling method combined with a chemical ablation model is used to predict the ablation rates of Na, K, Fe, Mg, and Ca above 60 km and cosmic spherule production rate. It appears that a significant fraction of the cosmic dust consists of small (<5 µg) and slow (<15 km s−1) particles.
Key Points
The atmospheric impacts of three cosmic dust models are compared
Slow cometary particles produce the measured cosmic spherule accretion rate
These particles also produce significant differential ablation in the mesosphere
Abstract
We present a new crater chronology for Jupiter’s Trojan asteroids. This tool can be used to interpret the collisional history of the bodies observed by NASA’s Lucy mission. The Lucy mission ...will visit a total of six Trojan asteroids: Eurybates, Polymele, Orus, Leucus, and the near-equal-mass binary Patroclus–Menoetius. In addition, Eurybates and Polymele each have a small satellite. Here we present a prediction of Trojan cratering based on current models of how the solar system and the objects themselves evolved. We give particular emphasis to the time lapsed since their implantation into stable regions near Jupiter’s Lagrangian L
4
and L
5
points. We find that cratering on Trojans is generally dominated by mutual collisions, with the exception of a short period of time (∼10 Myr) after implantation, in which cometary impacts may have been significant. For adopted crater scaling laws, we find that the overall spatial density of craters on Trojans is significantly lower than that of Main Belt asteroids on surfaces with similar formation ages. We also discuss specific predictions for similar-sized Eurybates and Orus, and the binary system Patroclus–Menoetius.
•The lunar mantle started to record highly siderophile elements only since the complete crystallization of the lunar magma ocean and mantle overturn.•The imbalance in highly siderophile elements ...abundances in the terrestrial and lunar mantles is explained by the elate crystallization of the lunar magma ocean.•The cratering record of the Moon 3–4 Gy ago is consistent with a monotonic decline of the bombardment.
The timeline of the lunar bombardment in the first Gy of Solar System history remains unclear. Basin-forming impacts (e.g. Imbrium, Orientale), occurred 3.9–3.7 Gy ago, i.e. 600–800 My after the formation of the Moon itself. Many other basins formed before Imbrium, but their exact ages are not precisely known. There is an intense debate between two possible interpretations of the data: in the cataclysm scenario there was a surge in the impact rate approximately at the time of Imbrium formation, while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail-end. Here, we revisit the work of Morbidelli et al. (2012) that examined which scenario could be compatible with both the lunar crater record in the 3–4 Gy period and the abundance of highly siderophile elements (HSE) in the lunar mantle. We use updated numerical simulations of the fluxes of asteroids, comets and planetesimals leftover from the planet-formation process. Under the traditional assumption that the HSEs track the total amount of material accreted by the Moon since its formation, we conclude that only the cataclysm scenario can explain the data. The cataclysm should have started ∼ 3.95 Gy ago. However we also consider the possibility that HSEs are sequestered from the mantle of a planet during magma ocean crystallization, due to iron sulfide exsolution (O’Neil, 1991; Rubie et al., 2016). We show that this is likely true also for the Moon, if mantle overturn is taken into account. Based on the hypothesis that the lunar magma ocean crystallized about 100–150 My after Moon formation (Elkins-Tanton et al., 2011), and therefore that HSEs accumulated in the lunar mantle only after this timespan, we show that the bombardment in the 3–4 Gy period can be explained in the accretion tail scenario. This hypothesis would also explain why the Moon appears so depleted in HSEs relative to the Earth. We also extend our analysis of the cataclysm and accretion tail scenarios to the case of Mars. The accretion tail scenario requires a global resurfacing event on Mars ∼ 4.4 Gy ago, possibly associated with the formation of the Borealis basin, and it is consistent with the HSE budget of the planet. Moreover it implies that the Noachian and pre-Noachian terrains are ∼ 200 My older than usually considered.
Context.
Very young asteroid families may record processes that accompanied their formation in the most pristine way. This makes analysis of this special class particularly interesting.
Aims.
We ...studied the very young Adelaide family in the inner part of the main belt. This cluster is extremely close to the previously known Datura family in the space of proper orbital elements and their ages overlap. As a result, we investigated the possibility of a causal relationship between the two families.
Methods.
We identified Adelaide family members in the up-to-date catalogue of asteroids. By computing their proper orbital elements we inferred the family structure. Backward orbital integration of selected members allowed us to determine the age of the family.
Results.
The largest fragment (525) Adelaide, an S-type asteroid about 10 km in size, is accompanied by 50 sub-kilometre fragments. This family is a typical example of a cratering event. The very tiny extent in the semi-major axis minimises chances that some significant mean motion resonances influence the dynamics of its members, though we recognise that part of the Adelaide family is affected by weak, three-body resonances. Weak chaos is also produced by distant encounters with Mars. Simultaneous convergence of longitude of node for the orbits of six selected members to that of (525) Adelaide constrains the Adelaide family age to 536 ± 12 kyr (formal solution). While suspiciously overlapping with the age of the Datura family, we find it unlikely that the formation events of the two families are causally linked. In all likelihood, the similarity of their ages is just a coincidence.
Aims. We investigate the process of Neptune trojan capture and permanence in resonance up to the present time based on a planetary instability migration model. Methods. We do a numerical simulation ...of the migration of the giant planets in a planetesimal disk. Several planetesimals became trapped in coorbital resonance with Neptune, but no trojan survived to the end of the integration at 4.5 Gy. We increased the statistics by running synthetic integrations with cloned particles from the original integration and keeping the same migration rates of the planets. Results. For the synthetic integrations, Neptune trojans survived to the end of the simulations. The total mass that corresponds to these surviving trojans is about 1.6 × 10-4 Earth mass and the distributions of eccentricities, inclinations, and libration amplitudes are respectively 0.007−0.173, 4.9°−32.9°, and 6.9°−64.3°. In a specific run where Neptune to Uranus mean motion ratio reached 1.963 and decreased to its present value (1.961), many more trojans escaped the coorbital resonance with Neptune and in the end there was an equivalent mass of 5 × 10-5 Earth mass of Neptune trojans. Conclusions. The simulations yielded Neptune trojans that match the orbital distribution of real Neptune trojans quite well. Since planetary migration in an instability model shows the possibility that in the past Neptune was a little farther from the Sun than it is today, it is reasonable to consider this possibility to explain the relatively low mass of Neptune trojans.
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