Planetesimal Archives

Exoplanet 29 Cygni b, seen in this artist’s concept, is a gas giant weighing about 15 times the mass of Jupiter. It orbits a type A star (shown at upper right) slightly hotter and more massive than our Sun, at an average distance of 1.5 billion miles. The star is known to possess a dusty debris disk. A hypothetical comet fragment is shown approaching the planet, while previous impacts have left dark splotches on its cloudtops, similar to what was seen from the Shoemaker-Levy 9 impact on Jupiter in our solar system. -- NASA Larger image

Astrogeology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Press Release, Stellar Cartography

Webb Redefines The Dividing Line Between Planets And Stars

by Keith CowingJune 16, 2026June 16, 2026

Planets, like those in our solar system, form in a bottom-up process where small bits of rock and ice clump together and grow larger over time. But the heftier the […]

Transition between different accretion regimes as shown by the shading and top labels. From left to right the panels show central AGN masses of 109, 108 and 107 𝑀⊙. The top row shows 𝑣frag = 1m s−1 and the bottom row shows 𝑣frag = 10 m−1 . The symbol 𝑚p gives the characteristic planetesimal mass, 𝑀HB is the transition mass between the Hill and the Bondi accretion regime, 𝑀BG is the transition mass between the Bondi and the geometric accretion regimes, and 𝑀p,iso is the pebble isolation mass. The transition between 2D and 3D accretion is also shown. In general, the objects will accrete in the 3D regime right after formation, except in the 1–10 pc range in the case 𝑣frag = 10 m/s, 𝑀SMBH = 109 𝑀⊙ (lower left). Accretion is also more efficient in the inner disk than in the outer disk, with a progression from Hill, Hill/Bondi, Bondi, and Bondi/Geometric as the central mass object decreases. The horizontal dotted black line is the hydrogen burning limit. -- astro-ph.EP

Astrogeology, Astronomy & Telescopes, Exoplanets, -moons, -comets, Status Report

Active Galactic Nucleus Tori: Potential Birthplace to Millions of Planets

by Keith CowingMay 23, 2026May 23, 2026

The outer regions of AGN disks have temperatures similar to those of circumstellar disks, permitting dust condensation. Therefore, planet formation and growth could be active in these dust tori through […]

HR diagram track of the default case (final mass of 2.2 MJ ; see Table 1), showing its surface temperature (Eqs. 12, 19 or 21, depending on the phase) and total luminosity (Eq. 6). Highlighted key moments show the start point (•), detachment (⋆), the point of maximum luminosity (▼), disk dispersal (■), and the age of Jupiter (+). Table 2 lists the corresponding values for time, mass and radius. In the ascending branch small black triangles (▲) show linearly spaced time indicators every Myr. The black dots (•) represent post-detachment intervals equally spaced in log(time). Grey reference lines show two trends: the predicted slope derived in Sect. A, evaluated with the median late-attached-phase surface density of Σpla = 1.7 g cm−2 (labelled with L ∝ T 8 ), and a constant-radius track for Rp = 1 RJ , which approximates a cooling planet in the evolutionary phase before stellar irradiation becomes relevant (last downturn). -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report, Stellar Cartography

Planetary Formation Tracks On The Hertzsprung-Russell Diagram: Visualising The Processes Of Giant Planet Growth

by Keith CowingMay 21, 2026May 21, 2026

The Hertzsprung-Russell diagram (HRD) is central to stellar astrophysics but has rarely been used to interpret planet formation.

Schematic of the model for carbonaceous chondrite formation

Astrochemistry, Astrogeology, Comets and Asteroids, Exoplanets, -moons, -comets, Meteorites & Asteroids, Status Report

Carbonaceous Chondrites Provide Evidence For Late-stage Planetesimal Formation In A Pressure Bump

by Keith CowingApril 27, 2026April 27, 2026

Carbonaceous chondrites are samples from planetesimals that formed 2-4 million years after solar system formation began.

The element abundances in the silicate Earth can be modelled as the result of accretion of three distinct components with distinct element abundances and isotope composition: A: a strongly volatile element depleted and reduced proto-Earth, B: a moderately volatile depleted and more oxidized Moon-forming impactor (Theia) and C: a near chondritic and oxidized late veneer. The absolute abundance of the siderophile and chalcophile elements was modified by core formation following accretion (after Mezger et al., 2021). -- astro-ph.EP

Astrochemistry, Astrogeology, Comets and Asteroids, Exoplanets, -moons, -comets, Gaia - Planetary Perspectives, Lava / magma ocean / Volcanic Worlds, Meteorites & Asteroids, Status Report, Water/Hycean Worlds & Oceanography

From Dust to Planets — A Chemical Perspective

by Keith CowingApril 20, 2026April 20, 2026

Chemical and chronological information preserved in meteorites permits the reconstruction of events and processes in the solar nebula from the formation of the first solids to the accretion of planetary […]

Outer disk regions become increasingly H2O ice poor as compared to dominating N2, CO, and CO2 ices over a disk’s lifetime. The leftmost pie displays the assumed initial abundances across all species that arrive in the disk frozen-out on solid particles. Individual species making up the total volatile ice composition are labeled and color-coded. Radial ice abundances from 1 to 300 au are displayed at 3 Myr in the six small pies to the right of the initial abundances. Species labels are only included in the radial 3 Myr pies if their ice abundance makes up at least 10% of the total ice composition. Displayed to the right of the 3 Myr radial ice composition pies are those of representative solar system carbon-depleted and carbon-enriched comets adapted from D. Jewitt & D. Z. Seligman (2023), which use the average of measured H2O, CO2, and CO ice production rates from a number of solar system and interstellar comets for the carbon-depleted comet, detailed in D. Z. Seligman et al. (2022), and comet C/2006 W3 (Christensen) from T. Ootsubo et al. (2012) for the carbon-enriched case. Refractory species are not considered in these pies, only volatile species. -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

Icy Volatile Enhancements in Evolving Protoplanetary Disks

by Keith CowingApril 17, 2026April 17, 2026

Protoplanetary disk ice lines shape a multitude of planet formation processes, setting the environmental composition through evolution.

Dust surface density evolution in the fiducial model without disk buildup (left) and with disk buildup taken into account (right). Time zero refers to the moment the gas disk reaches maximum mass in the model including its buildup, corresponding to the time the dust is initialized in the model without disk buildup. -- astro-ph.EP

Astrogeology, Astronomy & Telescopes, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

Dust Evolution During Protoplanetary Disk Bbuildup Enhances CO Ice Relative To Water

by Keith CowingApril 1, 2026April 1, 2026

Water ice is expected to be the dominant volatile component of bodies formed in the outer Solar System. However, recent observations of comets and trans-Neptunian objects suggest that the relative […]

Iron isotopic compositions of CI chondrites, CV chondrites, and terrestrial rocks. The μ 54Fe and μ58Fe data for different sample types (see legend) from this study (solid symbols) together with data from previous works (open symbols) (Table S1). Error bars indicate 95% confidence intervals. CV chondrites have similar μ 58Fe but elevated μ 54Fe compared to terrestrial samples. CI chondrites have similar μ 54Fe but elevated μ 58Fe compared to terrestrial samples. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Meteorites & Asteroids, Press Release

Iron Isotope Anomalies And The Origin Of The Earth

by Keith CowingMarch 30, 2026March 30, 2026

Understanding the origin of the Earth requires determining the original formation location of its building material.

Spectrally integrated line flux maps for 3I/ATLAS observed using JWST NIRSpec: (a) H2O at 2.7 µm, (b) CO2 at 4.3 µm, (c) CO at 4.7 µm. Image axes are aligned with the equatorial (RA/decl.) grid. Molecular emission has been isolated by subtracting a polynomial fit to the adjacent continuum. Spatial coordinates are with respect to the brightest pixel in each map (the pseudo-nucleus). Inset panels (upper right) show the continuum-subtracted spectra within the image integration wavelength range, spatially integrated within a 3′′ diameter circular aperture centered on the pseudo-nucleus (corresponding to 3,900 km at the 1.8 au distance of the comet from the telescope). Lower left corner shows the direction of the (sky-projected) comet-Sun (S) and nucleus velocity (v) vectors. -- astro-ph.EP

Astrochemistry, Astrogeology, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Status Report

Isotopic Evidence For A Cold And Distant Origin Of The Interstellar Object 3I/ATLAS

by Keith CowingMarch 17, 2026March 17, 2026

Interstellar objects provide the only directly observable samples of icy planetesimals formed around other stars, and can therefore provide insight into the diversity of physical and chemical conditions occurring during […]

(A) Pre and post irradiation spectra of the fiducial 10 K 2:1 benzene:ozone experiment. (B) Spectra of pure phenol ice at 10 K, (C) Spectra of a ∼ 30:1 benzene:phenol mixture at 10 K (D) Spectra of a benzene-oxide/oxepine mixture at 10 K reproduced with permission from Schleif et al. (2020). Optimized geometries representative of phenol, benzene oxide and oxepine are obtained using Gaussian 16 suite of software and are shown for reference in the corresponding panel. For clarity, only relevant spectral region are shown, full spectral data are available for download at 10.5281/zenodo.17216222 and 10.5281/zenodo.17216256 -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Status Report

Functionalization Of Benzene Ices by Atomic Oxygen

by Keith CowingJanuary 20, 2026January 20, 2026

Small aromatic molecules, including functionalized derivatives of benzene, are known to be present throughout the different stages of star and planet formation. In particular, oxygen-bearing monosubstituted aromatics, likely including phenol, […]