This review presents our understanding of cometary dust at the end of 2017. For decades, insight about the dust ejected by nuclei of comets had stemmed from remote observations from Earth or Earth’s ...orbit, and from flybys, including the samples of dust returned to Earth for laboratory studies by the Stardust return capsule. The long-duration Rosetta mission has recently provided a huge and unique amount of data, obtained using numerous instruments, including innovative dust instruments, over a wide range of distances from the Sun and from the nucleus. The diverse approaches available to study dust in comets, together with the related theoretical and experimental studies, provide evidence of the composition and physical properties of dust particles, e.g., the presence of a large fraction of carbon in macromolecules, and of aggregates on a wide range of scales. The results have opened vivid discussions on the variety of dust-release processes and on the diversity of dust properties in comets, as well as on the formation of cometary dust, and on its presence in the near-Earth interplanetary medium. These discussions stress the significance of future explorations as a way to decipher the formation and evolution of our Solar System.
Abstract Mercury is notoriously difficult to form in Solar System simulations, due to its small mass and iron-rich composition. Smooth particle hydrodynamics simulations of collisions have found that ...a Mercury-like body could be formed by one or multiple giant impacts, but due to the chaotic nature of collisions, it is difficult to create a scenario where such impacts will take place. Recent work has found more success forming Mercury analogues by adding additional embryos near Mercury’s orbit. In this work, we aim to form Mercury by simulating the formation of the Solar System in the presence of the giant planets Jupiter and Saturn. We test out the effect of an inner disk of embryos added on to the commonly used narrow annulus of initial material. We form Mercury analogues with core-mass fractions (CMFs) > 0.4 in ∼10% of our simulations, and twice that number of Mercury analogues form during the formation process but are unstable and do not last to the end of the simulations. Mercury analogues form at similar rates for both disks with and without an inner component, and most of our Mercury analogues have lower CMFs than that of Mercury, ∼0.7, due to significant accretion of debris material. We suggest that a more in-depth understanding of the fraction of debris mass that is lost to collisional grinding is necessary to understand Mercury’s formation, or some additional mechanism is required to stop this debris from accreting.
The Rosetta mission orbiter science overview: the comet phase Taylor, M. G. G. T.; Altobelli, N.; Buratti, B. J. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
07/2017, Letnik:
375, Številka:
2097
Journal Article
Recenzirano
Odprti dostop
The international Rosetta mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P/Churyumov-Gerasimenko by ...remote sensing, and to examine its environment in situ and its evolution in the inner Solar System. Rosetta was the first spacecraft to rendezvous with and orbit a comet, accompanying it as it passes through the inner Solar System, and to deploy a lander, Philae, and perform in situ science on the comet's surface. The primary goals of the mission were to: characterize the comet's nucleus; examine the chemical, mineralogical and isotopic composition of volatiles and refractories; examine the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study the development of cometary activity and the processes in the surface layer of the nucleus and in the coma; detail the origin of comets, the relationship between cometary and interstellar material and the implications for the origin of the Solar System; and characterize asteroids 2867 Steins and 21 Lutetia. This paper presents a summary of mission operations and science, focusing on the Rosetta orbiter component of the mission during its comet phase, from early 2014 up to September 2016.
This article is part of the themed issue ‘Cometary science after Rosetta’.
We highlight that the anomalous orbits of trans-Neptunian objects (TNOs) and an excess in microlensing events in the 5-year Optical Gravitational Lensing Experiment data set can be simultaneously ...explained by a new population of astrophysical bodies with mass several times that of the Earth ( M⊕ ). We take these objects to be primordial black holes (PBHs) and point out the orbits of TNOs would be altered if one of these PBHs was captured by the Solar System, inline with the Planet 9 hypothesis. Capture of a free floating planet is a leading explanation for the origin of Planet 9, and we show that the probability of capturing a PBH instead is comparable. The observational constraints on a PBH in the outer Solar System significantly differ from the case of a new ninth planet. This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH.
Abstract Jupiter Trojans (JTs) librate about the Lagrangian stationary centers L4 and L5 associated with this planet on typically small-eccentricity and moderate-inclination heliocentric orbits. The ...physical and orbital properties of JTs provide important clues about the dynamical evolution of the giant planets in the early solar system, as well as populations of planetesimals in their source regions. Here we use decade-long observations from the Catalina Sky Survey (station G96) to determine the bias-corrected orbital and magnitude distributions of JTs. We distinguish the background JT population, filling smoothly the long-term stable orbital zone about L4 and L5 points and collisional families. We find that the cumulative magnitude distribution of JTs (the background population in our case) has a steep slope for H ≤ 9, followed by a moderately shallow slope until H ≃ 14.5, beyond which the distribution becomes even shallower. At H = 15 we find a local power-law exponent 0.38 ± 0.01. We confirm the asymmetry between the magnitude-limited background populations in L4 and L5 clouds characterized by a ratio 1.45 ± 0.05 for H < 15. Our analysis suggests an asymmetry in the inclination distribution of JTs, with the L4 population being tighter and the L5 population being broader. We also provide a new catalog of the synthetic proper elements for JTs with an updated identification of statistically robust families (9 at L4, and 4 at L5). The previously known Ennomos family is found to consist of two overlapping Deiphobus and Ennomos families.
Abstract
Placing the architecture of the solar system within the broader context of planetary architectures is one of the primary topics of interest within planetary science. Exoplanet discoveries ...have revealed a large range of system architectures, many of which differ substantially from the solar system’s model. One particular feature of exoplanet demographics is the relative prevalence of super-Earth planets, for which the solar system lacks a suitable analog, presenting a challenge to modeling their interiors and atmospheres. Here we present the results of a large suite of dynamical simulations that insert a hypothetical planet in the mass range 1–10
M
⊕
within the semimajor axis range 2–4 au, between the orbits of Mars and Jupiter. We show that, although the system dynamics remain largely unaffected when the additional planet is placed near 3 au, Mercury experiences substantial instability when the additional planet lies in the range 3.1–4.0 au, and perturbations to the Martian orbit primarily result when the additional planet lies in the range 2.0–2.7 au. We further show that, although Jupiter and Saturn experience relatively small orbital perturbations, the angular momentum transferred to the ice giants can result in their ejection from the system at key resonance locations of the additional planet. We discuss the implications of these results for the architecture of the inner and outer solar system planets, and for exoplanetary systems.
The detection
of a dust disk around the white dwarf star G29-38 and transits from debris orbiting the white dwarf WD 1145+017 (ref.
) confirmed that the photospheric trace metals found in many white ...dwarfs
arise from the accretion of tidally disrupted planetesimals
. The composition of these planetesimals is similar to that of rocky bodies in the inner Solar System
. Gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies
, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a hot (about 27,750 kelvin) white dwarf, WD J091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3 × 10
grams per second. The composition of this disk is unlike all other known planetary debris around white dwarfs
, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H
O and H
S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. The orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of approximately 1 in 10,000 for spectroscopically detectable giant planets in close orbits around white dwarfs.
Most stars form in clusters where relatively close encounters with other stars are common and can leave imprints on the orbital architecture of planetary systems. In this paper, we investigate the ...inclination excitation of debris disk particles due to such stellar encounters. We derive an analytical expression that describes inclination excitation in the hierarchical limit where the stellar flyby is distant. We then obtain numerical results for the corresponding particle inclination distribution in the nonhierarchical regime using a large ensemble of N-body simulations. For encounters with expected parameters, we find that the bulk inclination of the disk particles remains low. However, a distinct high-inclination population is produced by prograde stellar encounters for particles with final pericenter distances above 50 au. The maximum extent it of the inclination distribution scales with the inclination of the encounter for massive star flybys with low incoming velocity. The inclination distribution of observed trans-Neptunian objects places constraints on the dynamical history of our solar system. For example, these results imply an upper limit on product of the number density n of the solar birth cluster and the Sun's residence time τ of the form nτ 8 × 104 Myr pc−3. Stronger constraints can be derived with future observational surveys of the outer solar system.
Deciphering the spatial and temporal evolution of chondrules allows for a better understanding of how asteroidal seeds formed, migrated, and eventually accreted into parent asteroids. Here we report ...high precision Al-Mg ages and oxygen three-isotope ratios of fifteen FeO-poor chondrules from the least metamorphosed Mighei-like (CM) and Ornans-like (CO) carbonaceous chondrites, Asuka 12236 (CM2.9), Dominion Range 08006 (CO3.01), and Yamato 81020 (CO3.05). This is the first report of Al-Mg ages of chondrules from the CM chondrite group. All but one of the fifteen chondrules exhibit a restricted range of inferred initial 26Al/27Al ratios, and all ratios are ≤ 6.0 × 10−6, which is systematically lower than those of the majority of ordinary chondrite (OC) chondrules. These observations indicate that the majority of chondrules in the outer Solar System were produced ≥2.2 Ma after the formation of Ca-Al-rich inclusions (CAIs), which postdates OC chondrule formation in the inner Solar System (≤2.2 Ma after CAI formation). We propose that the discrete chondrule-forming events in different disk regions reflect a time difference in growth and orbital evolution of planetesimals within the first 4 Ma of the Solar System.
One chondrule from Asuka 12236 has an age of 1.9 Ma after CAI formation and is therefore significantly older than the other fourteen chondrules, meaning this chondrule formed contemporaneously with the majority of OC chondrules. This old chondrule also exhibits 16O-depleted oxygen isotope characteristics compared to the other chondrules, suggesting a distinct formation region, probably inside the disk region relative to where the majority of CM and CO chondrules formed. Our results indicate that this old chondrule has migrated from the inner to the outer part of the protoplanetary disk within ∼1 Ma and then accreted into the CM parent asteroid >3 Ma after CAI formation, although its formation exterior to the accretion region of the CM parent asteroid and subsequent inward migration cannot be ruled out completely.
Northwest Africa (NWA) 6704/6693 are medium- to coarse-grained achondrites with unique petrologic and geochemical traits that are distinct from the currently established meteorite groups. Here, we ...report on the extinct 26Al-26Mg and 53Mn-53Cr systems to establish fine-scale chronology of its formation and Cr and Ti isotopic anomalies to constrain the composition of the source reservoir of NWA 6704/6693. Excesses in the neutron-rich 54Cr and 50Ti isotopes, due to nucleosynthetic anomalies, separate NWA 6704/6693 from the vast majority of established achondrites and instead resemble the excesses seen among the carbonaceous chondrites; specifically, the CR-type chondrites. The excesses in these isotopes indicate a common feeding zone during accretion in the protoplanetary disk between the source of NWA 6704/6693 and that of the carbonaceous chondrites. The 26Al-26Mg data for pyroxene and plagioclase from NWA 6704 yield a (26Al/27Al)0 = (3.15 ± 0.38)×10−7 (MSWD = 0.49) and an initial δ26Mg∗ = −0.004 ± 0.005 at the time of isotopic closure. This initial (26Al/27Al)0 translates to an absolute age of 4563.14 ± 0.38 Ma, relative to the D’Orbigny angrite. However, given the potential heterogeneity of 26Al, the D’Orbigny angrite might not be a good age anchor for the purpose of calculating 26Al-26Mg ages. The 26Al-26Mg age relative to another carbonaceous achondrite, NWA 2976, is 4562.66 ± 0.60 Ma. The 53Mn-53Cr systematics of NWA 6704/6693 indicate a (53Mn/55Mn)0 of (2.59 ± 0.34) × 10−6 (MSWD = 1.2) with an evolved initial ε53Cr of +0.14 ± 0.03. The (53Mn/55Mn)0 yields an 53Mn-53Cr age of 4562.17 ± 0.76 Ma relative to the D’Orbigny angrite. Concordant ages determined using the short-lived 26Al-26Mg and 53Mn-53Cr systems and extant 207Pb-206Pb system (4562.60 ± 0.30 Ma for NWA 6704/6693; Amelin et al., 2019) indicate rapid cooling and nearly contemporaneous closing of multiple isotope systems. The ancient crystallization ages and positive 54Cr and 50Ti anomalies of NWA 6704/6693 indicate widespread melting and differentiation processes occurring in both non-carbonaceous (NC) and carbonaceous chondrite (CC) regions of the protoplanetary disk. Additionally, we report the Cr and Ti isotopic composition for a petrologic range of CR-type materials (CR2, CR6, and achondrites). The additional Cr and Ti isotopic data for these CR-type materials indicates a range in isotopic composition not previously observed based on CR2 chondrites alone.
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