Models Of Solar System Formation Research Articles

Abundant molecular oxygen in the coma of comet 67P/Churyumov-Gerasimenko.

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov-Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.

Nucleosynthetic isotope anomalies in meteorites—clues for solar system origin

The solar system was previously thought to have evolved from a hot and well‐mixed solar nebula, until the discovery of nucleosynthetic isotope anomalies in meteorites flew in the face of this popular model. These anomalies have been found to exist at the grain‐size level but not at the planetary‐scale, thus indicating the mixing and homogenization of presolar dust within the solar nebula over time as the planets formed. The use of nucleosynthetic isotope anomalies as tracers of the manner, efficiency and timing of this mixing provides an invaluable tool for planetary science. Today the field is more exciting than ever and the discoveries continue to mount up. As such, models of solar system formation are being refined and improved.

Evaluating the carbon depletion found by the Stardust mission in Comet 81P/Wild 2

The low abundance of refractory carbonaceous material in samples collected by Stardust in comet 81P/Wild 2 coma was completely unexpected. If these results are universal to other comets, this necessitates a reformulation of current models of solar system formation. A polarimetric imaging analysis demonstrates that dust is not uniformly distributed within cometary coma, and that the circumnucleus halo region where the dust samples were collected must contain a low population of carbonaceous particles. Such regions are seen in other comets, suggesting that comet 81P/Wild 2 is not unusual and that the anomalous lack of carbon is not necessarily representative of the entire coma.

OSS (Outer Solar System): a fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt

The present OSS mission continues a long and bright tradition by associating the communities of fundamental physics and planetary sciences in a single mission with ambitious goals in both domains. OSS is an M-class mission to explore the Neptune system almost half a century after flyby of the Voyager 2 spacecraft. Several discoveries were made by Voyager 2, including the Great Dark Spot (which has now disappeared) and Triton's geysers. Voyager 2 revealed the dynamics of Neptune's atmosphere and found four rings and evidence of ring arcs above Neptune. Benefiting from a greatly improved instrumentation, it will result in a striking advance in the study of the farthest planet of the Solar System. Furthermore, OSS will provide a unique opportunity to visit a selected Kuiper Belt object subsequent to the passage of the Neptunian system. It will consolidate the hypothesis of the origin of Triton as a KBO captured by Neptune, and improve our knowledge on the formation of the Solar system. The probe will embark instruments allowing precise tracking of the probe during cruise. It allows to perform the best controlled experiment for testing, in deep space, the General Relativity, on which is based all the models of Solar system formation. OSS is proposed as an international cooperation between ESA and NASA, giving the capability for ESA to launch an M-class mission towards the farthest planet of the Solar system, and to a Kuiper Belt object. The proposed mission profile would allow to deliver a 500 kg class spacecraft. The design of the probe is mainly constrained by the deep space gravity test in order to minimise the perturbation of the accelerometer measurement.

RETENTION OF A PRIMORDIAL COLD CLASSICAL KUIPER BELT IN AN INSTABILITY-DRIVEN MODEL OF SOLAR SYSTEM FORMATION

The cold classical population of the Kuiper belt exhibits a wide variety of unique physical characteristics, which collectively suggest that its dynamical coherence has been maintained through out the solar system's lifetime. Simultaneously, the retention of the cold population's relatively unexcited orbital state has remained a mystery, especially in the context of a solar system formation model, that is driven by a transient period of instability, where Neptune is temporarily eccentric. Here, we show that the cold belt can survive the instability, and its dynamical structure can be reproduced. We develop a simple analytical model for secular excitation of cold KBOs and show that comparatively fast apsidal precession and nodal recession of Neptune, during the eccentric phase, are essential for preservation of an unexcited state in the cold classical region. Subsequently, we confirm our results with self-consistent N-body simulations. We further show that contamination of the hot classical and scattered populations by objects of similar nature to that of cold classicals has been instrumental in shaping the vast physical diversity inherent to the Kuiper belt.

EARLY DYNAMICAL EVOLUTION OF THE SOLAR SYSTEM: PINNING DOWN THE INITIAL CONDITIONS OF THE NICE MODEL

In the recent years, the "Nice" model of solar system formation has attained an unprecedented level of success in reproducing much of the observed orbital architecture of the solar system by evolving the planets to their current locations from a more compact configuration. Within the context of this model, the formation of the classical Kuiper belt requires a phase during which the ice giants have a high eccentricity. An outstanding question of this model is the initial configuration from which the Solar System started out. Recent work has shown that multi-resonant initial conditions can serve as good candidates, as they naturally prevent vigorous type-II migration. In this paper, we use analytical arguments, as well as self-consistent numerical N-body simulations to identify fully-resonant initial conditions, whose dynamical evolution is characterized by an eccentric phase of the ice-giants, as well as planetary scattering. We find a total of eight such initial conditions. Four of these primordial states are compatible with the canonical "Nice" model, while the others imply slightly different evolutions. The results presented here should prove useful in further development of a comprehensive model for solar system formation.

The formation of Uranus and Neptune in solid-rich feeding zones: Connecting chemistry and dynamics

The core accretion theory of planet formation has at least two fundamental problems explaining the origins of Uranus and Neptune: (1) dynamical times in the trans-saturnian solar nebula are so long that core growth can take >15 Myr and (2) the onset of runaway gas accretion that begins when cores reach ∼10 M ⊕ necessitates a sudden gas accretion cutoff just as Uranus and Neptune’s cores reach critical mass. Both problems may be resolved by allowing the ice giants to migrate outward after their formation in solid-rich feeding zones with planetesimal surface densities well above the minimum-mass solar nebula. We present new simulations of the formation of Uranus and Neptune in the solid-rich disk of Dodson-Robinson et al. (Dodson-Robinson, S.E., Willacy, K., Bodenheimer, P., Turner, N.J., Beichman, C.A. [2009]. Icarus 200, 672–693) using the initial semimajor axis distribution of the Nice model (Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A. [2005]. Nature 435, 466–469; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R. [2005]. Nature 435, 462–465; Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F. [2005]. Nature 435, 459–461), with one ice giant forming at 12 AU and the other at 15 AU. The innermost ice giant reaches its present mass after 3.8–4.0 Myr and the outermost after 5.3–6 Myr, a considerable time decrease from previous one-dimensional simulations (e.g. Pollack, J.B., Hubickyj, O., Bodenheimer, P., Lissauer, J.J., Podolak, M., Greenzweig, Y. [1996]. Icarus 124, 62–85). The core masses stay subcritical, eliminating the need for a sudden gas accretion cutoff. Our calculated carbon mass fractions of 22% are in excellent agreement with the ice giant interior models of Podolak et al. (Podolak, M., Weizman, A., Marley, M. [1995]. Planet. Space Sci. 43, 1517–1522) and Marley et al. (Marley, M.S., Gómez, P., Podolak, M. [1995]. J. Geophys. Res. 100, 23349–23354). Based on the requirement that the ice giant-forming planetesimals contain >10% mass fractions of methane ice, we can reject any Solar System formation model that initially places Uranus and Neptune inside of Saturn’s orbit. We also demonstrate that a large population of planetesimals must be present in both ice giant feeding zones throughout the lifetime of the gaseous nebula. This research marks a substantial step forward in connecting both the dynamical and chemical aspects of planet formation. Although we cannot say that the solid-rich solar nebula model of Dodson-Robinson et al. (Dodson-Robinson, S.E., Willacy, K., Bodenheimer, P., Turner, N.J., Beichman, C.A. [2009]. Icarus 200, 672–693) gives exactly the appropriate initial conditions for planet formation, rigorous chemical and dynamical tests have at least revealed it to be a viable model of the early Solar System.

Water on Planets

AbstractWater is an abundant molecule in the Cosmos. It has exploitable and unique spectroscopic and physical properties and has been found to be ubiquitous in places that we would expect in the standard model of solar system formation and nebular condensation: beyond the snow line in outer solar system planets, moons, asteroids, and comets. However, water is also an important constituent of planetary bodies (dominating at least one of their surfaces) in the inner solar system, likely indicating significant mixing between inner and outer solar system reservoirs of water during planetary accretion and the early history of the solar system. Water has played a critical role in the differential evolution of the terrestrial planets Venus, Earth, and Mars, and the concept of the “habitable zone” where liquid water could be stable on an Earth-like planet provides a starting point for assessing the habitability of worlds in our solar system and beyond. Examples of potentially habitable environments outside this zone in our own solar system warn us that this concept should only be a guide, however-important exceptions will no doubt occur. Recent discoveries of past liquid water and abundant present subsurface ice on Mars, of water reservoirs in unexpected places like the poles of Mercury and the Moon and the subsurface of Enceladus, of water in circumstellar disks and in the atmospheres of extrasolar planets, and the expectation of the discovery of water on Earth-like worlds in the habitable zones around other stars make this an exciting time in the study of water on planets both in our own solar system, and beyond.

Interaction of Supernova Ejecta with Nearby Protoplanetary Disks

The early Solar System contained short-lived radionuclides such as 60Fe (t1/2 = 1.5 Myr) whose most likely source was a nearby supernova. Previous models of Solar System formation considered a supernova shock that triggered the collapse of the Sun's nascent molecular cloud. We advocate an alternative hypothesis, that the Solar System's protoplanetary disk had already formed when a very close (< 1 pc) supernova injected radioactive material directly into the disk. We conduct the first numerical simulations designed to answer two questions related to this hypothesis: will the disk be destroyed by such a close supernova; and will any of the ejecta be mixed into the disk? Our simulations demonstrate that the disk does not absorb enough momentum from the shock to escape the protostar to which it is bound. Only low amounts (< 1%) of mass loss occur, due to stripping by Kelvin-Helmholtz instabilities across the top of the disk, which also mix into the disk about 1% of the intercepted ejecta. These low efficiencies of destruction and injectation are due to the fact that the high disk pressures prevent the ejecta from penetrating far into the disk before stalling. Injection of gas-phase ejecta is too inefficient to be consistent with the abundances of radionuclides inferred from meteorites. On the other hand, the radionuclides found in meteorites would have condensed into dust grains in the supernova ejecta, and we argue that such grains will be injected directly into the disk with nearly 100% efficiency. The meteoritic abundances of the short-lived radionuclides such as 60Fe therefore are consistent with injection of grains condensed from the ejecta of a nearby (< 1 pc) supernova, into an already-formed protoplanetary disk.

Composition of Titan's surface from Cassini VIMS

Titan's bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite's dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan's solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan's history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission's visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 μm were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan T a encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79 μm in the poorly understood 2.8-μm methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-μm methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8 μm that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface.

Multi-correlation analyses of TOF-SIMS spectra for mineralogical studies

A time-of-flight mass spectrometer (TOF-SIMS, COSIMA experiment) has been launched by ESA the 2nd March 2004, on board the comet bound spacecraft “ROSETTA”. The scientific objectives of COSIMA are the determination of the compositions of cometary grains as well as the molecular analyses of their exposed organic compounds. These analyses will provide inorganic and organic data for pristine solar system material, which are crucial for models of solar system formation and evolution. The challenge is, from a mass spectrum, to determine the mineral(s) analysed, to trace back the origin and formation processes of the grains which will be ultimately analysed in situ in the comet by COSIMA. To prepare the interpretation of COSIMA spectra, we have evaluated a correlation algorithm between TOF-SIMS spectra, to estimate how the information can be used to characterise the mineral phase(s) analysed. As a first step in this work, we used mineralogical samples representative of minerals found on earth and in the solar system, silicate grains. These different minerals have rather similar mass spectrum, but experienced different formation conditions in the solar nebula. We will present this correlation algorithm, allowing an accurate study of the elements responsible for the correlation, and a rapid comparison with the classical principal component analysis (PCA) method.

Multi-correlation analyses of TOF-SIMS spectra for mineralogical studies

A time-of-flight mass spectrometer (TOF-SIMS, COSIMA experiment) has been launched by ESA the 2nd March 2004, on board the comet bound spacecraft “ROSETTA”. The scientific objectives of COSIMA are the determination of the compositions of cometary grains as well as the molecular analyses of their exposed organic compounds. These analyses will provide inorganic and organic data for pristine solar system material, which are crucial for models of solar system formation and evolution. The challenge is, from a mass spectrum, to determine the mineral(s) analysed, to trace back the origin and formation processes of the grains which will be ultimately analysed in situ in the comet by COSIMA. To prepare the interpretation of COSIMA spectra, we have evaluated a correlation algorithm between TOF-SIMS spectra, to estimate how the information can be used to characterise the mineral phase(s) analysed. As a first step in this work, we used mineralogical samples representative of minerals found on earth and in the solar system, silicate grains. These different minerals have rather similar mass spectrum, but experienced different formation conditions in the solar nebula. We will present this correlation algorithm, allowing an accurate study of the elements responsible for the correlation, and a rapid comparison with the classical principal component analysis (PCA) method.

Short-lived radionuclides in the early solar system — A meteoritic perspective of the solar system formation

This paper reviews the evidence for short-lived radionuclides in the early solar system and evaluates the models of their origin. The stellar model requires that some freshly-nucleosynthesized radionuclides were injected into the proto-solar cloud shortly before it began to collapse. The spallation theory suggests that these nuclides were the products of interaction between energetic particles and gas/dust in the proto-solar cloud or solar nebula. A brief discussion is given to a new theory for the X-wind model of solar system formation.

Direct N-body Simulations of Rubble Pile Collisions

There is increasing evidence that many kilometer-sized bodies in the Solar System are piles of rubble bound together by gravity. We present results from a project to map the parameter space of collisions between kilometer-sized spherical rubble piles. The results will assist in parameterization of collision outcomes for Solar System formation models and give insight into disruption scaling laws. We use a direct numerical method to evolve the positions and velocities of the rubble pile particles under the constraints of gravity and physical collisions. We test the dependence of the collision outcomes on impact parameter and speed, impactor spin, mass ratio, and coefficient of restitution. Speeds are kept low (<10 m s −1, appropriate for dynamically cool systems such as the primordial disk during early planet formation) so that the maximum strain on the component material does not exceed the crushing strength, assuming sufficient granularity. We compare our results with analytic estimates and hydrocode simulations. We find that net accretion dominates the outcome in slow head-on collisions while net erosion dominates for fast off-axis collisions. The dependence on impact parameter is almost equally as important as the dependence on impact speed. Off-axis collisions can result in fast-spinning elongated remnants or contact binaries while fast collisions result in smaller fragments overall. Clumping of debris escaping from the remnant can occur, leading to the formation of smaller rubble piles. In the cases we tested, less than 2% of the system mass ends up orbiting the remnant. Initial spin can reduce or enhance collision outcomes, depending on the relative orientation of the spin and orbital angular momenta. We derive a relationship between impact speed and angle for critical dispersal of mass in the system. We find that our rubble piles are relatively easy to disperse, even at low impact speed. This may provide a way of constraining the energy dissipation parameter and related properties of the initial planetesimal population.

A new look at the jovian planets.

The Infrared Space Observatory was launched by the European Space Agency in November 1995. For two and a half years, the craft gathered a wealth of data on the jovian planets: Jupiter, Saturn, Uranus, and Neptune. In their Perspective, BA©zard et al . discuss some of the important results, recently presented at workshops in Wisconsin and Paris. Among them were a new determination of the deuterium/hydrogen ratio in these bodies, which has implications for models of solar system formation; new findings on hydrocarbon photochemistry in the jovian planets; and the unexpected detection of water vapor in the stratospheres of the giant planets.

Does debris from the formation of other planetary systems impact earth?

We calculate the expected flux of small and large particles impacting the Earth using model size distributions for the ejected debris from extrasolar planet formation. The flux of extrasolar impactors of large meteorite size and smaller at Earth should be detectable given likely size distributions, if the standard Solar System formation model is applicable to other planetary systems. We propose that the report of impactors with extrasolar velocities at the Long Duration Exposure Facility (LDEF) and by the Kharkov radar may be due to these particles, and that a number of recovered meteorites may be extrasolar. Conversely, if it can be determined that no meteorites or small meteoroids are extrasolar planetary debris, then the standard Solar System formation model will be constrained.

Chemical Fractionation in Gas Rings and the Formation of the Solar System

AbstractThe anomalously high density of the planet Mercury and the higher-than-solar rock-to-ice ratio in Jupiter’s moons Ganymede and Callisto cannot be explained by the conventional disc models of solar system formation. It is shown here that the unusual chemical signature of these bodies is the outcome of a process of chemical fractionation and orbital focussing which is peculiar to gas ring models of planet and regular satellite formation. Good numerical agreement with the observational data is obtained if the temperature of condensation of the planetary system closely followed the law Tn ≃ 680[R⊕/Rn]0.9 K, where Rn denotes the radial distance from the Sun.

Age of the sun

The age of the sun is deduced to be 4.49 + or - 0.04 Gyr. This determination is based on the ages of the oldest meteorites, current models of solar system formation, and the premain-sequence evolution of a 1-solar-mass star from T Tauri phase to the ZAMS. Prior to this it was common to use an age of 4.7 Gyr for the sun. Comparing a solar model evolved to 4.5 Gyr with a model evolved to 4.7 Gyr shows that the 200 Myr difference in their ages has very little effect on the helium abundance and mixing-length parameters of the solar models. 16 refs.

Origin of the Solar System

The current status of the classical model of solar-system formation is surveyed, reviewing the results of recent observational and theoretical investigations. Topics addressed include interstellar clouds, the collapse of interstellar gas, the primitive solar nebula, the formation of the sun, planetesimal accumulation, planetary accumulation, major planetary collisions, the development of planetary atmospheres, and comets. The relative merits of conflicting theories on many key problems are indicated, with reference to more detailed reviews in the literature.

Models of solar system formation

Models of solar system formation