Young Disk Research Articles

Thermal evolution of protoplanetary disks: from β-cooling to decoupled gas and dust temperatures

Aims. We explore the long-term evolution of young protoplanetary disks with different approaches to computing the thermal structure determined by various cooling and heating processes in the disk and its surroundings. Methods. Numerical hydrodynamics simulations in the thin-disk limit were complemented with three thermal evolution schemes: a simplified β-cooling approach with and without irradiation, where the rate of disk cooling is proportional to the local dynamical time; a fiducial model with equal dust and gas temperatures calculated taking viscous heating, irradiation, and radiative cooling into account; and a more sophisticated approach allowing decoupled dust and gas temperatures. Results. We found that the gas temperature may significantly exceed that of dust in the outer regions of young disks thanks to additional compressional heating caused by the infalling envelope material in the early stages of disk evolution and slow collisional exchange of energy between gas and dust in low-density disk regions. However, the outer envelope shows an inverse trend, with the gas temperatures dropping below that of dust. The global disk evolution is only weakly sensitive to temperature decoupling. Nevertheless, separate dust and gas temperatures may affect the chemical composition, dust evolution, and disk mass estimates. Constant-β models without stellar and background irradiation fail to reproduce the disk evolution with more sophisticated thermal schemes because of the intrinsically variable nature of the β-parameter. Constant-β models with irradiation more closely match the dynamical and thermal evolution, but the agreement is still incomplete. Conclusions. Models allowing separate dust and gas temperatures are needed when emphasis is placed on the chemical or dust evolution in protoplanetary disks, particularly in subsolar metallicity environments.

Low lordosis is a common finding in young lumbar disc herniation patients

PurposeThe sagittal alignment of the lumbar spine and pelvis can be classified into several subtypes. It has been suggested that the risk of developing certain pathologies, such as a lumbar disc herniation (LDH) is affected by spinal sagittal profiles. The main aim of this study was to investigate the sagittal profile in young patients surgically treated for a lumbar disc herniation and if a discectomy would alter the sagittal parameters.MethodsSixteen active young patients (mean age 18.3 ± 3.2 SD) with a lumbar disc herniation having a discectomy were included. A classification according to Roussouly of the sagittal parameters was made by two senior spinal surgeons, both pre-operatively and post-operatively on radiographs. The distribution of sagittal parameters and spinopelvic profiles were analysed and compared to a previous established healthy normal population.ResultsThis series of active young patients with LDH exhibited a low lumbar lordosis dominance, with Roussouly sagittal profiles type 1 and type 2 accounting for more than 75% of the examined patients. An analysis of the erect radiographs revealed no significant changes in the post-operative sagittal profile.ConclusionsThis study showed that sagittal spinal alignment according to Roussouly in a young population with LDH is skewed compared with a normal population cohort. Furthermore, the lack of post-operative correction is suggestive of a non-ephemeral response to a LDH. Roussouly type 2 spinal sagittal profile may be a risk factor in young individuals suffering a disc herniation.

Nearby Quintuple Systems κ Tucanae and ξ Scorpii

Abstract Architecture and parameters of two wide, nearby hierarchical systems containing five solar-type stars each, κ Tuc and ξ Sco, are studied. Using Gaia astrometry and photometry, masses are determined from visual orbits and isochrones, and effective temperatures from spectra or colors. Both systems are ∼2 Gyr old. Their spatial motion corresponds to a young disk but does not match any known kinematic group. Internal proper motions relative to the center of mass and radial velocities show that wide ∼8 kau outer pairs are bound. No correlation between orbit orientations in the inner subsystems is observed. All masses except one are confined to the narrow range from 0.8 to 1.5 solar. Strongly correlated masses and wide orbits can be explained if those systems formed by fragmentation in relative isolation and their components accreted gas from a common source, as expected in a hierarchical collapse. Young moving groups could be formed in similar environments, and many of them contain high-order hierarchies.

On the settling of small grains in dusty discs: analysis and formulae

ABSTRACT Instruments achieve sharper and finer observations of micrometre-in-size dust grains in the top layers of young stellar discs. To provide accurate models, we revisit the theory of dust settling for small grains, when gas stratification, dust inertia, and finite correlation times for the turbulence should be handled simultaneously. We start from a balance of forces and derive distributions at steady state. Asymptotic expansions require caution since limits do not commute. In particular, non-physical bumpy distributions appear when turbulence is purely diffusive. This excludes very short correlation times for real discs, as predicted by numerical simulations.

Accretion in low-mass members of the Orion Nebula Cluster with young transition disks

Context.Although the Orion Nebula Cluster is one of the most studied clusters in the solar neighborhood, the evolution of the very low-mass members (M* < 0.25 M⊙) has not been fully addressed due to their faintness.Aims.Our goal is to verify if some young and very low-mass objects in the Orion Nebula Cluster show evidence of ongoing accretion using broadband VLT/X-shooter spectra.Methods.For each target, we determined the corresponding stellar parameters, veiling, observed Balmer jump, and accretion rates. Additionally, we searched for the existence of circumstellar disks through available on-line photometry.Results.We detected accretion activity in three young stellar objects in the Orion Nebula Cluster, two of them being in the very low-mass range. We also detected the presence of young transition disks with ages between 1 and 3.5 Myr.

Spitzer’s debris disk legacy from main-sequence stars to white dwarfs

The Spitzer Space Telescope enabled the detection and characterization of infrared excess — attributed to thermal emission from circumstellar dust — towards more than 1,000 main-sequence stars and more than 40 white dwarfs. These systems have been dubbed ‘debris disks’ because they are believed to be planetary systems in which the observed dust is generated by collisions among otherwise undetected planetesimals, planetary embryos and planets. With its superb sensitivity and good spatial resolution, Spitzer revolutionized the study of debris disks, increasing the number of known systems by an order of magnitude and providing detailed disk demographics and properties for a substantial sample for the first time. In doing so, Spitzer set the stage for detailed characterization of the dust using Herschel, the Atacama Large Millimeter/submillimeter Array and high-contrast imaging instruments such as the Hubble Space Telescope’s NICMOS and STIS, the Very Large Telescope’s SPHERE, and the Gemini Planet Imager. Spitzer played a vital role in demonstrating that planetary systems are present and active around white dwarfs. Specifically, it showed that the origin of pollution in white dwarfs is circumstellar material. Finally, Spitzer’s longevity enabled time-domain studies of young debris disks that are actively forming terrestrial planets and rejuvenized the study of dusty white dwarfs. Spitzer’s legacy will endure into the next decade with discoveries expected from new instruments on SOFIA, the James Webb Space Telescope and SPHEREx. The Spitzer Space Telescope made huge advances in the study of debris disks around main-sequence stars and white dwarfs, increasing their number by an order of magnitude, and leading the way for the next generation of space-based infrared missions.

Global Simulations of Self-gravitating Magnetized Protoplanetary Disks

Abstract In the early stages of a protoplanetary disk, turbulence generated by gravitational instability (GI) should feature significantly in the disk’s evolution. At the same time, the disk may be sufficiently ionized for magnetic fields to play some role in the dynamics. In this paper, we report on global three-dimensional magnetohydrodynamical simulations of a self-gravitating protoplanetary disk using the meshless finite mass Lagrangian technique. We confirm that GI spiral waves trigger a dynamo that amplifies an initial magnetic field to nearly thermal amplitudes (plasma β < 10), an order of magnitude greater than that generated by the magnetorotational instability alone. We also determine the dynamo’s nonlinear back reaction on the gravito-turbulent flow: the saturated state is substantially hotter, with an associated larger Toomre parameter and weaker, more “flocculent” spirals. But perhaps of greater import is the dynamo’s boosting of accretion via a significant Maxwell stress; mass accretion is enhanced by factors of several relative to either pure GI or pure magnetorotational instability. Our simulations use ideal MHD, an admittedly poor approximation in protoplanetary disks, and thus, future studies should explore the full gamut of nonideal MHD. In preparation for that, we exhibit a small number of ohmic runs that reveal that the dynamo, if anything, is stronger in a nonideal environment. This work confirms that magnetic fields are a potentially critical ingredient in gravito-turbulent young disks, possibly controlling their evolution, especially via their enhancement of (potentially episodic) accretion.

Dust dynamics and vertical settling in gravitoturbulent protoplanetary discs

Abstract Gravitational instability (GI) controls the dynamics of young massive protoplanetary discs. Apart from facilitating gas accretion on to the central protostar, it must also impact on the process of planet formation: directly through fragmentation, and indirectly through the turbulent concentration of small solids. To understand the latter process, it is essential to determine the dust dynamics in gravitoturbulent flow. For that purpose, we conduct a series of 3D shearing box simulations of coupled gas and dust, including the gas’s self-gravity and scanning a range of Stokes numbers, from 10 −3 to ∼0.2. First, we show that the vertical settling of dust in the mid-plane is significantly impeded by gravitoturbulence, with the dust scale height roughly 0.6 times the gas scale height for centimetre grains. This is a result of the strong vertical diffusion issuing from (i) small-scale inertial-wave turbulence feeding off the GI spiral waves and (ii) the larger scale vertical circulations that naturally accompany the spirals. Second, we show that at R = 50 au concentration events involving submetre particles and yielding order 1 dust-to-gas ratios are rare and last for less than an orbit. Moreover, dust concentration is less efficient in 3D than in 2D simulations. We thus conclude that GI is not especially prone to the turbulent accumulation of dust grains. Finally, the large dust scale height measured in simulations could be, in the future, compared with that of edge-on discs seen by ALMA, thus aiding detection and characterization of GI in real systems.

Chemical abundances of 1111 FGK stars from the HARPS-GTO planet search sample

Context. Elemental abundances are of prime importance to help us reconstruct the origin and evolution of stars and galaxies in our Universe. Sulfur abundances have not been as heavily studied as other elements, so some details regarding their behaviour are still unclear. Aims. We aim to investigate [S/Fe] ratios in stars of the solar neighbourhood in order to analyse the chemical evolution of sulfur and probe for possible differences in abundances of planet host and non-planet host stars. Methods. We used the code MOOG to perform spectral synthesis and derive v sin i values and [S/Fe] ratios for 719 FGK stars with high-resolution (R ~ 115 000) and high-quality spectra from the HARPS-GTO programme. We found the best fit and corresponding parameter values by performing χ2 minimisation of the deviation between synthetic profiles and observational spectra. Results. Our results reveal that sulfur behaves as a typical α-element, with low abundances in young thin disc stars and high abundances in old thick disc stars, following what was expected from our understanding of the Galactic chemical evolution (GCE). Nevertheless, further studies into the abundances of sulfur in very metal-poor stars are required as our sample only derived sulfur abundances of stars with metallicity as low as [Fe/H] = − 1.13 dex. High-α metal rich stars are more enhanced in sulfur compared to their thin disc counterparts at the same metallicity. We compare our results to GCE models from other authors in the [S/Fe] versus [Fe/H] plane. The [S/Fe]-age relationship is a good proxy for time, just as is the case with other α-elements. We report no differences in the abundances of sulfur between stars with and without planetary companions in the metallicity range [Fe/H] ≥−0.3 dex.

Polarized emission by aligned grains in the Mie regime: Application to protoplanetary disks observed by ALMA

Context. The azimuthal polarization patterns observed in some protoplanetary disks by the Atacama Large Millimetre Array (ALMA) at millimeter wavelengths have raised doubts about whether they are truly produced by dust grains that are aligned with the magnetic field lines. These conclusions were based on the calculations of dust polarized emission in the Rayleigh regime, that is, for grain sizes that are much smaller than the wavelength. However, the grain size in such disks is typically estimated to be in the range of 0.1−1 mm from independent observations. Aims. We study the dust polarization properties of aligned grains in emission in the Mie regime, that is, when the mean grain size approaches the wavelength. Methods. By using the T-MATRIX and DustEM codes, we computed the spectral dependence of the polarization fraction in emission for grains in perfect spinning alignment for various grain size distributions. We restricted our study to weakly-elongated oblate and prolate grains of astrosilicate composition that have a mean size ranging from 10 μm to 1 mm. Results. In the submillimeter and millimeter wavelength range, the polarization by B-field aligned grains becomes negative for grains larger than ∼250 μm, meaning that the polarization vector becomes parallel to the B-field. The transition from the positive to the negative polarization occurs at a wavelength of λ ∼ 1 mm. The regime of negative polarization does not exist for grains that are smaller than ∼100 μm. Conclusions. When using realistic grain size distributions for disks with grains up to the submillimeter sizes, the polarization direction of thermal emission by aligned grains is shown to be parallel to the direction of the magnetic field over a significant fraction of the wavelengths typically used to observe young protoplanetary disks. This property may explain the peculiar azimuthal orientation of the polarization vectors in some of the disks observed with ALMA and attest to the conserved ability of dust polarized emission to trace the magnetic field in disks.

Galactic warp from the kinematics of OB stars

The warp in Milky Way seen through the young stellar disk shows the complex structures. Its spatial distribution reveals the asymmetry in the vertical distance to the galactic midplane, whereas the kinematics shows the os- cillating motion. We analyze the warp using about 25,000 OB stars from Gaia Data Release 2, with Galactocentric azimuth (φ) range from 135◦ to 225◦ . We detect the warp from two distinctive regions. First region (warp down) lies on 100◦ < l < 150◦ and second regions (warp up) lies on 150◦ < l < 220◦ . The vertical position towards the Galactic midplane (Z) from all samples shows the line-of-nodes of the warp is on φ = 174◦ ± 2◦ . The maximum deviation in warp down region reachs 0.1 kpc and 0.2 kpc in warp up region. The vertical velocity (VZ) from both regions are dominated by negative VZ . From the kinematics dis- tribution, it can be concluded that there is an oscillati1ng motion. Considering with the previous study, the oscillating motion was caused by the gravitational interaction with the Galaxy satellites. From this, we can constrain the origin of the warp is developing from the tidal interaction between Milky Way and its satellites.

Star formation at the Galactic Centre: coevolution of multiple young stellar discs

ABSTRACT Studies of the Galactic Centre suggest that in situ star formation may have given rise to the observed stellar population near the central supermassive black hole (SMBH). Direct evidence for a recent starburst is provided by the currently observed young stellar disc (2–7 Myr) in the central 0.5 pc of the Galaxy. This result suggests that star formation in galactic nuclei may occur close to the SMBH and produce initially flattened stellar discs. Here, we explore the possible build-up and evolution of nuclear stellar clusters near SMBHs through in situ star formation producing stellar discs similar to those observed in the Galactic Centre and other nuclei. We use N-body simulations to model the evolution of multiple young stellar discs and explore the potential observable signatures imprinted by such processes. Each of the five simulated discs is evolved for 100 Myr before the next one is introduced in the system. We find that populations born at different epochs show different morphologies and kinematics. Older and presumably more metal-poor populations are more relaxed and extended, while younger populations show a larger amount of rotation and flattening. We conclude that star formation in central discs can reproduce the observed properties of multiple stellar populations in galactic nuclei differing in age, metallicity, and kinematic properties.

Thoracic spinal kinematics is affected by the grade of intervertebral disc degeneration, but not by the presence of the ribs: An in vitro study

BACKGROUND CONTEXTThoracic spinal three-dimensional kinematics is widely unknown. For the evaluation of surgical treatments and the complete validation of numerical models, however, kinematic data of the thoracic spine are essential. PURPOSETo identify possible effects of rib presence and grade of intervertebral disc degeneration on thoracic spinal kinematics including three-plane helical axes and instantaneous centers of rotation. DESIGN/SETTINGRadiological grading of intervertebral disc degeneration and in vitro tests using n=8 human thoracic functional spinal units of the segmental levels T1–T2, T3–T4, T5–T6, T7–T8, T9–T10, and T11–T12, respectively, were performed with as well as without ribs to analyze the specific kinematic properties. METHODSSpecimens were loaded with pure moments of 5 Nm and constant loading rates of 1°/s in flexion/extension, lateral bending, and axial rotation. Optical motion tracking was performed to visualize helical axes and instantaneous centers of rotation on three-plane X-rays and to evaluate primary ranges of motion (ROMs) and coupled motions. RESULTSMotion segments with no or mild disc degeneration showed reproducible kinematics in all motion planes, whereas medium or severely degenerated specimens offered high variations and shifts of the rotational axes to the distal direction as well as lower ROM. Coupled motions were generally not detected. CONCLUSIONSWith progressing disc degeneration, the rotational axes show higher variation and tend to shift in distal direction, especially in flexion/extension with a shift to the anterior direction, whereas rib resection does not affect thoracic spinal kinematics but its stability. Rib resections as part of spinal deformity treatment destabilize the thoracic spine, but do not alter its kinematics. Young and healthy discs, however, could be affected by surgical treatments of the thoracic spine regarding thoracic spinal kinematics.

Inflammaging determines health and disease in lumbar discs: evidence from differing proteomic signatures of healthy, aging and degenerating discs

BACKGROUND CONTEXT The true understanding of aging and disc degeneration (DD) is still elusive. MRI has not helped our attempts to understand the health and disease status of the discs as it reflects mainly the end morphological changes and not the changes at a molecular level. Understanding degeneration at a molecular level through proteomics might allow differentiation from normal aging and also aid in the development of biomarkers for early diagnosis and preventive therapies. PURPOSE To utilize proteomics to understand the molecular basis of healthy, aging and degenerating discs and conclusively differentiate normal aging and degeneration. STUDY DESIGN Proteomic analysis of human intervertebral disc samples. METHODS L4-L5 disc samples from three groups were acquired and subjected to proteomic analysis. Samples from individuals aged in the 2nd, 3rd, and 4th decades were used to represent young healthy discs (Group A). Those from MRI normal donors aged in the 5th, 6th and 7th decades represented normal aging (Group B). Five degenerated discs obtained from patients at surgery represented degeneration (Group C). The entire proteome map and alteration in protein expressions were further analyzed using bioinformatics analysis. This was a self-funded project. RESULTS There were 84 common proteins. Specific proteins numbered 225 in A, 315 in B and 283 in C. By gene ontology biological process identification, Group A predominated with extracellular matrix organization, cytoskeletal structural and normal metabolic proteins. Group B differed in having additional basal expression of immune response, complement inhibitors and senescence proteins. Group C was different, with up regulation of proteins associated with oxidative stress response, positive regulators of apoptosis, innate immune response, complement activation and defense response to gram positive bacteria indicating ongoing inflammaging. CONCLUSIONS Our study documented diverse proteome signatures between the young, aging and degenerating discs. Inflammaging was the main differentiation between normal biological aging and DD. CLINICAL SIGNIFICANCE Multiple inflammatory molecules unique to DD were identified, allowing the possibility of developing specific biomarkers for early diagnosis and thereby provide evidence-based metrics for preventive measures rather than surgical intervention and also to monitor progress of the disease. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. The true understanding of aging and disc degeneration (DD) is still elusive. MRI has not helped our attempts to understand the health and disease status of the discs as it reflects mainly the end morphological changes and not the changes at a molecular level. Understanding degeneration at a molecular level through proteomics might allow differentiation from normal aging and also aid in the development of biomarkers for early diagnosis and preventive therapies. To utilize proteomics to understand the molecular basis of healthy, aging and degenerating discs and conclusively differentiate normal aging and degeneration. Proteomic analysis of human intervertebral disc samples. L4-L5 disc samples from three groups were acquired and subjected to proteomic analysis. Samples from individuals aged in the 2nd, 3rd, and 4th decades were used to represent young healthy discs (Group A). Those from MRI normal donors aged in the 5th, 6th and 7th decades represented normal aging (Group B). Five degenerated discs obtained from patients at surgery represented degeneration (Group C). The entire proteome map and alteration in protein expressions were further analyzed using bioinformatics analysis. This was a self-funded project. There were 84 common proteins. Specific proteins numbered 225 in A, 315 in B and 283 in C. By gene ontology biological process identification, Group A predominated with extracellular matrix organization, cytoskeletal structural and normal metabolic proteins. Group B differed in having additional basal expression of immune response, complement inhibitors and senescence proteins. Group C was different, with up regulation of proteins associated with oxidative stress response, positive regulators of apoptosis, innate immune response, complement activation and defense response to gram positive bacteria indicating ongoing inflammaging. Our study documented diverse proteome signatures between the young, aging and degenerating discs. Inflammaging was the main differentiation between normal biological aging and DD.

The Concentration and Growth of Solids in Fragmenting Circumstellar Disks

Abstract Due to the gas-rich environments of early circumstellar disks, the gravitational collapse of cool, dense regions of the disk form fragments largely composed of gas. During formation, disk fragments may attain increased metallicities as they interact with the surrounding disk material, whether through particle migration to pressure maxima or through mutual gravitational interaction. In this paper, we investigate the ability of fragments to collect and retain a significant solid component through gas-particle interactions in high-resolution 3D self-gravitating shearing-box simulations. The formation of axisymmetric perturbations associated with gravitational instabilities allows particles of intermediate sizes to concentrate through aerodynamic drag forces. By the onset of fragmentation, the masses of local particle concentrations within the fragment are comparable to that of the gas component and the subsequent gravitational collapse results in the formation of a solid core. We find that these cores can be up to several tens of Earth masses, depending on grain size, before the fragment center reaches temperatures that would sublimate solids. The solid fraction and total mass of the fragment also depend on the metallicity of the young parent protoplanetary disk, with higher initial metallicities resulting in larger fragments and larger solid cores. Additionally, the extended atmospheres of these soon-to-be gas giants or brown dwarfs are occasionally enriched above the initial metallicity, provided no solid core forms in the center, and are otherwise lacking in heavier elements when a core does form.

Fullerenes in the IC 348 star cluster of the Perseus Molecular Cloud

Abstract We present the detection of fullerenes C60 and C70 in the star-forming region IC 348 of the Perseus molecular cloud. Mid-IR vibrational transitions of C60 and C70 in emission are found in Spitzer IRS spectra of individual stars (LRLL 1, 2, 58), in the averaged spectrum of three other cluster stars (LRLL 21, 31 and 67) and in spectra obtained at four interstellar locations distributed across the IC 348 region. Fullerene bands appear widely distributed in this region with higher strength in the lines-of-sight of stars at the core of the cluster. Emission features consistent with three most intense bands of the C$_{60}^+$ and with one of C$_{60}^-$ are also found in several spectra, and if ascribed to these ionized species it would imply ionization fractions at 20 and 10 %, respectively. The stars under consideration host protoplanetary disks, however the spatial resolution of the spectra is not sufficient to disentangle the presence of fullerenes in them. If fullerene abundances in the cloud were representative of IC 348 protoplanetary disks, C60, the most abundant of the two species, could host ∼ 0.1 % of the total available carbon in the disks. This should encourage dedicated searches in young disks with upcoming facilities as JWST. Fullerenes provide a reservoir of pentagonal and hexagonal carbon rings which could be important as building blocks of prebiotic molecules. Accretion of these robust molecules in early phases of planet formation may contribute to the formation of complex organic molecules in young planets.

Radiation pressure clear-out of dusty photoevaporating discs

Theoretical models of protoplanetary disc dispersal predict a phase where photoevaporation has truncated the disc at several AU, creating a pressure trap which is dust-rich. Previous models predicted this phase could be long-lived (~Myr), contrary to the observational constraints. We show that dust in the pressure trap can be removed from the disc by radiation pressure exerting a significant acceleration, and hence radial velocity, on small dust particles that reside in the surface layers of the disc. The dust in the pressure trap is not subject to radial drift so it can grow to reach sizes large enough to fragment. Hence small particles removed from the surface layers are replaced by the fragments of larger particles. This link means radiation pressure can deplete the dust at all particle sizes. Through a combination of 1D and 2D models, along with secular models that follow the disc's long-term evolution, we show that radiation pressure can deplete dust from pressure traps created by photoevaporation in ~1e5 years, while the photoevaporation created cavity still resides at 10s of AU. After this phase of radiation pressure removal of dust, the disc is gas-rich and dust depleted and radially optically thin to stellar light, having observational signatures similar to a gas-rich, young debris disc. Indeed many of the young stars (~<10 Myr old) classified as hosting a debris disc may rather be discs that have undergone this process.

ALMA observations require slower Core Accretion runaway growth

ABSTRACT Due to recent high-resolution ALMA observations, there is an accumulating evidence for presence of giant planets with masses from ${\sim } 0.01 \, {\rm {M}}_{\rm {J}}$ to a few $\, {\rm {M}}_{\rm {J}}$ with separations up to 100 au in the annular structures observed in young protoplanetary discs. We point out that these observations set unique ‘live’ constraints on the process of gas accretion on to sub-Jovian planets that were not previously available. Accordingly, we use a population synthesis approach in a new way: we build time-resolved models and compare the properties of the synthetic planets with the ALMA data at the same age. Applying the widely used gas accretion formulae leads to a deficit of sub-Jovian planets and an overabundance of a few Jupiter mass planets compared to observations. We find that gas accretion rate on to planets needs to be suppressed by about an order of magnitude to match the observed planet mass function. This slower gas giant growth predicts that the planet mass should correlate positively with the age of the protoplanetary disc, albeit with a large scatter. This effect is not clearly present in the ALMA data but may be confirmed in the near future with more observations.

Inflammaging determines health and disease in lumbar discs—evidence from differing proteomic signatures of healthy, aging, and degenerating discs

BACKGROUND CONTEXTThe true understanding of aging and disc degeneration (DD) is still elusive. MRI has not helped our attempts to understand the health and disease status of the discs as it reflects mainly the end morphologic changes and not the changes at a molecular level. Understanding degeneration at a molecular level through proteomics might allow differentiation from normal aging and also aid in the development of biomarkers for early diagnosis and preventive therapies. PURPOSETo utilize proteomics to understand the molecular basis of healthy, aging, and degenerating discs and conclusively differentiate normal aging and degeneration. STUDY DESIGNProteomic analysis of human intervertebral disc samples. METHODSL4–L5 disc samples from three groups were acquired and subjected to proteomic analysis. Samples from individuals aged in the second, third, and fourth decades were used to represent young healthy discs (Group A). Those from MRI normal donors aged in the fifth, sixth, and seventh decades represented normal aging (Group B). Five degenerated discs obtained from patients at surgery represented degeneration (Group C). The entire proteome map and alteration in protein expressions were further analyzed using bioinformatics analysis. This was a self-funded project. RESULTSThere were 84 common proteins. Specific proteins numbered 225 in A, 315 in B, and 283 in C. By gene ontology biological process identification, Group A predominated with extracellular matrix organization, cytoskeletal structural and normal metabolic proteins. Group B differed in having additional basal expression of immune response, complement inhibitors, and senescence proteins. Group C was different, with upregulation of proteins associated with oxidative stress response, positive regulators of apoptosis, innate immune response, complement activation and defense response to gram positive bacteria indicating ongoing inflammaging. CONCLUSIONSOur study documented diverse proteome signatures between the young, aging and degenerating discs. Inflammaging was the main differentiator between normal biological aging and DD. CLINICAL SIGNIFICANCEMultiple inflammatory molecules unique to DD were identified, allowing the possibility of developing specific biomarkers for early diagnosis and thereby provide evidence-based metrics for preventive measures rather than surgical intervention and also to monitor progress of the disease.

Extreme Debris Disk Variability: Exploring the Diverse Outcomes of Large Asteroid Impacts During the Era of Terrestrial Planet Formation

Abstract The most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescales of up to 100–200 Myr, when violent impacts occur between large planetesimals of sizes up to protoplanets. Such events are marked by the production of large amounts of debris, as has been observed in some exceptionally bright and young debris disks (termed extreme debris disks). Here we report five years of Spitzer measurements of such systems around two young solar-type stars: ID8 and P1121. The short-term (weekly to monthly) and long-term (yearly) disk variability is consistent with the aftermaths of large impacts involving large asteroid-sized bodies. We demonstrate that an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometry effects, can produce short-term modulation in the disk light curves. The long-term disk flux variation is related to the collisional evolution within the impact-produced fragments once released into a circumstellar orbit. The time-variable behavior observed in the P1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor condensates as the dominant impact product. Two distinct short-term modulations in the ID8 system suggest two violent impacts at different times and locations. Its long-term variation is consistent with the collisional evolution of two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders. The bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique opportunity to study violent events during the era of terrestrial planet formation.