accretion Archives

Core-mantle boundary core- (left) and mantle-side (right) temperature change in accretionary collisions compared to our scaling-law fits (blue surfaces) as a function of specific impact energy QS and impact angle θi, color-coded by the final angular momentum in units of LEM (the angular momentum of the Earth-Moon system). The shape of the data point markers indicates the size of the initial target planet in the simulation: • – moon mass (0.01M⊕), ✚ – Mars (0.1M⊕), × – half-Earths (0.5M⊕), ⋆ – proto-Earths (0.91M⊕), and ▲ – super-Earths (1.3M⊕). Residuals for these fits are depicted in Supplementary Figure 23. -- astro-ph.EP

Thermal And Rotational Effects Of Giant Impacts During Terrestrial Planet Accretion

by Keith CowingJune 25, 2026June 25, 2026

Terrestrial planets likely experienced one or more giant impacts during their formation that inflicted large thermal, chemical, and rotational perturbations.

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 […]

Left: E(KS −W3) vs. E(KS −W4) color excess plot for our targets. Full disks, transitional disks, evolved disks and debris disks are shown as red circles, orange squares, cyan triangles and blue diamonds, respectively. The newly discovered Peter Pan disks are highlighted with additional blue pluses. The solid lines display the boundaries used to classify our targets into different categories (Esplin et al. 2014, 2018). Right: similar as the left panel, but shows the E(KS − W2) vs. E(KS − W3) color excess plot. -- astro-ph.GA

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

LAMOST Reveals Long-lived Protoplanetary Disks

by Keith CowingJanuary 9, 2025January 9, 2025

While both observations and theories demonstrate that protoplanetary disks are not expected to live much longer than ∼10 Myr, several examples of prolonged disks have been observed in the past.

Four stages of planet formation via core accretion and its schematic diagram. Top: Sequential accretion of gas and solid divides the mass growth of planets into four stages. In Stage I, planetary cores form by solid accretion. As time goes on, solid accretion rates decrease, and gas accretion becomes dominated. One conservative estimate of a characteristic solid accretion rate is 10M⊕/1 Myr ∼ 10−5M⊕ yr−1 as denoted by the black dash-dotted line. Once the solid accretion rate becomes lower the value, gas accretion comes into play. In Stage II, accretion of both gas and solids occurs. The gas accretion rate is regulated by cooling of accreted gas (i.e., M˙ XY,KH denoted by the blue solid line). In Stage III, gas accretion is controlled by disk evolution. The corresponding rate becomes very high (i.e., M˙ XY,hydro denoted by the green dotted line), and it is the main channel of forming sub-giants. In Stage IV, gas accretion is reduced due to planet-disk interaction and the resulting gap formation in gas disks (i.e., M˙ XY,gap denoted by the yellow dashed line). This is the final stage of giant plane formation. Mathematical expressions of accretion rates are summarized in Appendix A. Bottom: Sequential accretion of gas and solid can be idealized by the onion-like model. As we show below, bulk and atmospheric metallicities can be used to trace when gap formation in both planetesimal and gas disks occurs, which corresponds to Stages III and IV, respectively. The purple and light salmon trapezoids represent gas and planetesimals disks, respectively. The brown circles denotes solids and the circular rings represent envelope gas. -- astro-ph.EP

Astrochemistry, Astrogeology, Exoplanets, -moons, -comets, Status Report

Bulk and Atmospheric Metallicities as Direct Probes of Sequentially Varying Accretion Mechanisms of Gas and Solids Onto Planets

by Keith CowingSeptember 17, 2024September 17, 2024

Core accretion is the standard scenario of planet formation, wherein planets are formed by sequential accretion of gas and solids, and is widely used to interpret exoplanet observations. However, no […]

Analog Studies, Astrogeology, Exoplanets, -moons, -comets, Status Report

Comparisons Of The Core And Mantle Compositions Of Earth Analogs From Different Terrestrial Planet Formation Scenarios

by Keith CowingFebruary 22, 2023February 22, 2023

The chemical compositions of Earth’s core and mantle provide insight into the processes that led to their formation. N-body simulations, on the other hand, generally do not contain chemical information, […]

accretion

Thermal And Rotational Effects Of Giant Impacts During Terrestrial Planet Accretion

Webb Redefines The Dividing Line Between Planets And Stars

LAMOST Reveals Long-lived Protoplanetary Disks

Bulk and Atmospheric Metallicities as Direct Probes of Sequentially Varying Accretion Mechanisms of Gas and Solids Onto Planets

Comparisons Of The Core And Mantle Compositions Of Earth Analogs From Different Terrestrial Planet Formation Scenarios

Atmospheric Evolution Through Outgassing And Escape On Young Molten Rocky Exoplanets

The Exozodi Spectral Effect: Residual Habitable Zone Dust May Bias ExoEarth Characterization

The Majority Of Hot Jupiters Formed Beyond The Water Ice Line

Sulfur Photochemistry Observationally Traces Mantle Redox States Of Rocky Planets

Tracing The Source Of Carbon Oxides On The Large Moons Of Uranus