The Astrophysical Journal: The effect of a strong pressure bump in the Sun’s natal disk: Terrestrial planet formation via planetesimal accretion rather than pebble accretion

The effect of a strong pressure bump in the Sun’s natal disk: Terrestrial planet formation via planetesimal accretion rather than pebble accretion

André Izidoro, Bertram Bitsch, Rajdeep Dasgupta


Mass-independent isotopic anomalies of carbonaceous and noncarbonaceous meteorites show a clear dichotomy suggesting an efficient separation of the inner and outer solar system. Observations show that ring-like structures in the distribution of millimeter-sized pebbles in protoplanetary disks are common. These structures are often associated with drifting pebbles being trapped by local pressure maxima in the gas disk. Similar structures may also have existed in the Sun’s natal disk, which could naturally explain the meteorite/planetary isotopic dichotomy. Here, we test the effects of a strong pressure bump in the outer disk (e.g., ~5 au) on the formation of the inner solar system. We model dust coagulation and evolution, planetesimal formation, as well as embryo growth via planetesimal and pebble accretion. Our results show that terrestrial embryos formed via planetesimal accretion rather than pebble accretion. In our model, the radial drift of pebbles fosters planetesimal formation. However, once a pressure bump forms, pebbles in the inner disk are lost via drift before they can be efficiently accreted by embryos growing at gap1 au. Embryos inside ~0.5–1.0 au grow relatively faster and can accrete pebbles more efficiently. However, these same embryos grow to larger masses so they should migrate inwards substantially, which is inconsistent with the current solar system. Therefore, terrestrial planets most likely accreted from giant impacts of Moon to roughly Mars-mass planetary embryos formed around gap1.0 au. Finally, our simulations produce a steep radial mass distribution of planetesimals in the terrestrial region, which is qualitatively aligned with formation models suggesting that the asteroid belt was born low mass.


Izidoro, A., Bitsch, B. & Dasgupta, R. (2021). The effect of a strong pressure bump in the Sun’s natal disk: Terrestrial planet formation via planetesimal accretion rather than pebble accretion. The Astrophysical Journal 915, 62. doi:10.3847/1538-4357/abfe0b

JGR Atmospheres: Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2

Laurence Y. Yeung, Lee T. Murray, Asmita Banerjee, Xin Tie, Yuzhen Yan, Elliot L. Atlas, Sue M. Schuaffler, and Kristie A. Boering

doi: 10.1029/2021JD034770


Tropospheric 18O18O is an emerging proxy for past tropospheric ozone and free-tropospheric temperatures. The basis of these applications is the idea that isotope-exchange reactions in the atmosphere drive 18O18O abundances toward isotopic equilibrium. However, previous work used an offline box-model framework to explain the 18O18O budget, approximating the interplay of atmospheric chemistry and transport. This approach, while convenient, has poorly characterized uncertainties. To investigate these uncertainties, and to broaden the applicability of the 18O18O proxy, we developed a scheme to simulate atmospheric 18O18O abundances (quantified as ∆36 values) online within the GEOS-Chem chemical transport model. These results are compared to both new and previously published atmospheric observations from the surface to 33 km. Simulations using a simplified O2 isotopic equilibration scheme within GEOS-Chem show quantitative agreement with measurements only in the middle stratosphere; modeled ∆36 values are too high elsewhere. Investigations using a comprehensive model of the O-O2-O3 isotopic photochemical system and proof-of-principle experiments suggest that the simple equilibration scheme omits an important pressure dependence to ∆36 values: the anomalously efficient titration of 18O18O to form ozone. Incorporating these effects into the online ∆36 calculation scheme in GEOS-Chem yields quantitative agreement for all available observations. While this previously unidentified bias affects the atmospheric budget of 18O18O in O2, the modeled change in the mean tropospheric ∆36 value since 1850 C.E. is only slightly altered; it is still quantitatively consistent with the ice-core ∆36 record, implying that the tropospheric ozone burden increased less than ∼40% over the twentieth century.

Plain-language summary

Oxygen in the air is constantly being broken apart and remade. Its constituent atoms are shuffled around by light-induced chemical reactions, which cause changes in the number of heavy oxygen atoms that are bound together. The number of these heavy-atom “clumps” is sensitive to air temperatures and the presence of air pollution; hence, their variations are being used to understand past high-altitude temperatures and atmospheric chemistry. This study incorporates oxygen clumping into an atmospheric chemistry model and compares the results to measurements of oxygen clumping in the atmosphere. We find that the model can explain all the modern-day measurements (from the surface to 33 km altitude), but only if the broader fates of oxygen atoms―i.e., their incorporation into other molecules beyond O2―are considered. Simulations of the preindustrial atmosphere are also generally consistent with snapshots of the ancient atmosphere obtained from O2 trapped in ice cores. The developments described herein will thus enable models to simulate heavy oxygen-atom clumping in past cold and warm climates and enable simulated high-altitude atmospheric changes to be evaluated directly against ice-core snapshots of the ancient atmosphere.

IEEE TPDS: Planetary Normal Mode Computation: Parallel Algorithms, Performance, and Reproducibility

Shi, J., Li, R., Xi, Y., Saad, Y. and de Hoop, M. V., 2021. Planetary normal mode computation: Parallel algorithms, performance, and reproducibility. IEEE Transactions on Parallel and Distributed Systems32(11), pp.2609-2622.


Notes: This article has been awarded a “Results Reproduced (ROR-R)” badge.



This article is an extension of work entitled “Computing planetary interior normal modes with a highly parallel polynomial filtering eigensolver.” by Shi et al., originally presented at the SC18 conference. A highly parallel polynomial filtered eigensolver was developed and exploited to calculate the planetary normal modes. The proposed method is ideally suited for computing interior eigenpairs for large-scale eigenvalue problems as it greatly enhances memory and computational efficiency. In this article, the second-order finite element method is used to further improve the accuracy as only the first-order finite element method was deployed in the previous work. The parallel algorithm, its parallel performance up to 20k processors, and the great computational accuracy are illustrated. The reproducibility of the previous work was successfully performed on the Student Cluster Competition at the SC19 conference by several participant teams using a completely different Mars-model dataset on different clusters. Both weak and strong scaling performances of the reproducibility by the participant teams were impressive and encouraging. The analysis and reflection of their results are demonstrated and future direction is discussed.

Sedimentology: Timescale dependent sedimentary record during the past 130 kyr from a tropical mixed siliciclastic–carbonate shelf edge and slope: Ashmore Trough (southern Gulf of Papua)

Authors: Gianni Mallarino, Jason M. Francis, Stephan J. Jorry, James J. Daniell, André W. Droxler, Gerald R. Dickens, Luc Beaufort, Samuel J. Bentley, Bradley N. Opdyke, Larry C. Peterson

Abstract: In tropical and sub‐tropical mixed siliciclastic–carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea‐level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea‐level fluctuations. Export of neritic carbonate to the slopes was initiated during re‐flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea‐level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea‐level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic–skeletal sand resumed at the shelf edge during the subsequent stepwise sea‐level rise of the last deglaciation. Contemporaneous, abrupt siliciclastic input from increased precipitation and fluvial discharge illustrates that climate controlled deglacial sedimentation. Siliciclastic input persisted until ca 8.5 ka. Carbonate accumulation waned at the shelf edge after ca 14 ka, whereas it increased on the slopes since ca 11.5 ka, when previously exposed reef and bank tops were re‐flooded. When comparing the last sea‐level cycle sedimentation patterns of the southern Gulf of Papua with other coeval mixed systems, sea level and shelf physiography emerge as primary controls on deposition at the 100 kyr scale. At the millennial scale, siliciclastic input was also controlled by climate change during the unstable atmospheric and oceanic conditions of the last deglaciation.

First published: 16 March 2021

Nature Geoscience: Rates of protoplanetary accretion and differentiation set nitrogen budget of rocky planets

Authors: Damanveer S. Grewal, Rajdeep Dasgupta, Taylor Hough, Alexandra Farnell

Abstract: The effect of protoplanetary differentiation on the fate of life-essential volatiles like nitrogen and carbon and its subsequent effect on the dynamics of planetary growth is unknown. Because the dissolution of nitrogen in magma oceans depends on its partial pressure and oxygen fugacity, it is an ideal proxy to track volatile re-distribution in protoplanets as a function of their sizes and growth zones. Using high pressure-temperature experiments in graphite-undersaturated conditions, here we show that the siderophile (iron-loving) character of nitrogen is an order of magnitude higher than previous estimates across a wide range of oxygen fugacity. The experimental data combined with metal-silicate-atmosphere fractionation models suggest that asteroid-sized protoplanets, and planetary embryos that grew from them, were nitrogen-depleted. However, protoplanets that grew to planetary embryo-size before undergoing differentiation had nitrogen-rich cores and nitrogen-poor silicate reservoirs. Bulk silicate reservoirs of large Earth-like planets attained nitrogen from the cores of latter type of planetary embryos. Therefore, to satisfy the volatile budgets of Earth-like planets during the main stage of their growth, the timescales of planetary embryo accretion had to be shorter than their differentiation timescales, i.e., Moon- to Mars-sized planetary embryos grew rapidly within ~1-2 Myrs of the Solar System’s formation.

Grewal, D.S., Dasgupta, R., Hough, T. et al. Rates of protoplanetary accretion and differentiation set nitrogen budget of rocky planets. Nat. Geosci. (2021).

Paleoceanography and Paleoclimatology: Size‐fraction‐specific stable isotope variations as a framework for interpreting early Eocene bulk sediment carbon isotope records

Carbon isotope (δ13C) records from marine sediments have been extensively used in Cenozoic chemostratigraphy. The early Paleogene interval in particular has received exceptional attention because negative carbon isotope excursions (CIEs) documented in the sedimentary record, e.g. at the Paleocene Eocene Thermal Maximum (PETM), ca ∼56 Ma, are believed to reflect significant global carbon‐cycle perturbations during the warmest interval of the Cenozoic era. However, while bulk carbonate δ13C values exhibit robust correlations across widely separated marine sedimentary basins, their absolute values and magnitude of CIEs vary spatially. Moreover, bulk carbonates in open‐marine environments are an ensemble of different components, each with a distinct isotope composition. Consequently, a comprehensive interpretation of bulk‐δ13C record requires an understanding of co‐evolution of these components. In this study, we dissect sediments, from early Paleogene interval, at ODP Site 1209 (Shatsky Rise, Pacific Ocean) to investigate how a temporally varying bulk carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for δ13C and δ18O compositions, as bulk and individual size fractions. We find a significant increase in coarse‐fraction abundance across PETM, driven by a changing community structure of calcifiers, modulating the size of CIE at Site 1209 and thus making it distinct from those recorded at other open‐marine sites. These results highlight the importance of biogeography in marine stable‐isotope record, especially when isotope excursions are driven by climate‐ and/or carbon‐cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as conventional proxy for carbonate dissolution.

JGR: Source-to-Sink Terrestrial Analogs for the Paleoenvironment of Gale Crater, Mars

Michael T. Thorpe, Joel A. Hurowitz, and Kirsten L. Siebach

doi: 10.1029/2020JE006530


In the Late Noachian to Early Hesperian period, rivers transported detritus from igneous source terrains to a downstream lake within Gale crater, creating a stratified stack of fluviolacustrine rocks that is currently exposed along the slopes of Mount Sharp. Controversy exists regarding the paleoclimate that supported overland flow of liquid water at Gale crater, in large part because little is known about how chemical and mineralogical paleoclimate indicators from mafic‐rock dominated source‐to‐sink systems are translated into the rock record. Here, we compile data from basaltic terrains with varying climates on Earth in order to provide a reference frame for the conditions that may have prevailed during the formation of the sedimentary strata in Gale crater, particularly focusing on the Sheepbed and Pahrump Hills members. We calculate the chemical index of alteration for weathering profiles and fluvial sediments to better constrain the relationship between climate and chemical weathering in mafic terrains, a method that best estimates the cooler limit of climate conditions averaged over time. We also compare X‐ray diffraction patterns and mineral abundances from fluvial sediments in varying terrestrial climates and martian mudstones to better understand the influence of climate on secondary mineral assemblages in basaltic terrains. We show that the geochemistry and mineralogy of most of the fine‐grained sedimentary rocks in Gale crater display first‐order similarities with sediments generated in climates that resemble those of present‐day Iceland, while other parts of the stratigraphy indicate even colder baseline climate conditions. None of the lithologies examined at Gale crater resemble fluvial sediments or weathering profiles from warm (temperate to tropical) terrestrial climates.


Nature Astronomy: A very early origin of isotopically distinct nitrogen in inner Solar System protoplanets

Authors: Damanveer S. Grewal, Rajdeep Dasgupta, & Bernard Marty

Abstract: Understanding the origin of life-essential volatiles such as nitrogen (N) in the Solar System and beyond is critical to evaluate the potential habitability of rocky planets. Whether the inner Solar System planets accreted these volatiles from their inception or had an exogenous delivery from the outer Solar System is, however, not well understood. Using previously published data of nucleosynthetic anomalies of nickel, molybdenum, tungsten and ruthenium in iron meteorites along with their 15N/14 N ratios, here we show that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct N. While the Sun and Jupiter captured N from nebular gas6, concomitantly growing protoplanets in the inner and outer disk possibly sourced their N from organics and/or dust—with each reservoir having a different N isotopic composition. A distinct N isotopic signature of the inner Solar System protoplanets coupled with their rapid accretion suggests that non-nebular, isotopically processed N was ubiquitous in their growth zone between 0 and ~0.3 Myr after Solar System formation. Because the 15N/14N ratio of the bulk silicate Earth falls between that of the inner and outer Solar System reservoirs, we infer that N in the present-day rocky planets represents a mixture of both inner and outer Solar System material.


Grewal, D.S., Dasgupta, R. & Marty, B. A very early origin of isotopically distinct nitrogen in inner Solar System protoplanets. Nat Astron (2021).

PLoS ONE: Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina

Stable isotope (C, N, O, and H) study of a comprehensive set of feathers from two Setophaga citrina

Samiksha Deme, Laurence Y. Yeung, Tao Sun, and Cin-Ty A. Lee, PLoS ONE 16 (2021): e0236536.


Oxygen, hydrogen, carbon and nitrogen stable isotopes were measured on a comprehensive sampling of feathers from two spring Hooded Warblers (Setophaga citrina) in Texas to evaluate isotopic variability between feathers and during molt. Isotopic homogeneity within each bird was found across all four isotopic systems, supporting the hypothesis that molt in these neotropical migrants is fully completed on the breeding grounds. This homogeneity suggests that the isotopic composition of a single feather is may be representative of the whole songbird. However, each bird was found to have one or two outlier feathers, which could signify regrowth of lost feathers after prebasic molt.

doi: 10.1371/journal.pone.0236536

RiMG: Climbing to the Top of Mount Fuji: Uniting Theory and Observations of Oxygen Triple Isotope Systematics

Laurence Y. Yeung and Justin A. Hayles

Rev. Mineral. Geochem. 86 (2021) 97-137


Are current theoretical methods sufficiently accurate to benchmark oxygen triple-isotope
geochemistry? In this review and synthesis article, we first cover basic concepts and notation relevant to oxygen triple-isotope geochemistry. Second, we examine what theory predicts for oxygen triple-isotope variability in chemical processes. Third, we examine the systematic biases that may be present in theoretical approaches, with special attention paid to first-principles electronic structure calculations. Fourth, we will consider the current limits of analytical accuracy and the complications introduced by physical effects in real systems. Finally, we revisit the triple-isotope mass dependence of carbonate acid digestion as a case study of how theory and experiment can work together to improve both each other and ultimately also our understanding of a process that is vital for the emerging area of carbonate-based paleohydrology.

doi: 10.2138/rmg.2021.86.03