http://www.caymanunterborn.com/new-page-1 daily 0.75 2020-07-02 http://www.caymanunterborn.com/new-page daily 1.0 2026-02-16 https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/68cb9cf9-8f09-490d-83bc-71bc3b1495cf/IMG_6703.png Home http://www.caymanunterborn.com/science daily 0.75 2023-05-17 https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1582590991225-O16PRFEI3DEY5D7ET9I2/Fig.png Science How Rocky Exoplanets Are (Left): Mg, Fe and Si stellar compositions for Sun-like stars taken from the Hypatia catalog. Overlaid are contours of the predicted core mass fraction of any planets should a planet form with a bulk refractory composition the same as the stellar abundance which provide a baseline to test the hypothesis that host-star refractory composition is approximately that of the orbiting rocky exoplanet. It also outlines the diversity of compositions relative to the Solar System rocky planets. From Unterborn & Panero, 2019 JGR-Planets How Rocky Exoplanets Were (Center): The TRAPPIST-1 planets have densities consistent with having ∼7 wt% surface water oceans and lacking a substantial extended atmosphere. They also likely migrated inward to there current orbital positions. Here, I show the orbital radius of a modeled water snow line (blue, red lines) in the protoplanetary disk of the TRAPPIST-1 M-dwarf system as a function of time of planet formation. As the disk cools, the ice-line moved inwards. The black dashed lines represent the minimum pre-migration orbital radius of TRAPPIST-1d if it formed outside the ice line in order to gain its water-rich compositions. This plot shows that if TRAPPIST-1d formed quickly (<3 Myr) it would have had to migrate farther to its current orbit. This represents a case where exoplanet composition can be used to analyze how and when rocky exoplanets formed. From Unterborn et al., 2018 Nature Astronomy How Rocky Exoplanets Will Be (Right): Active degassing from a rocky exoplanet’s interior is a first-order constraint on whether it can sustain a temperate atmosphere over geologic timescales. Here are calculated times when degassing rates fall below 10% of Earth value as function of the total amount of the planet’s bulk K abundance relative to the Earth across observed stellar K abundances. This shows that the more potassium a stagnant-lid exoplanet contains directly affects how long it is able to degas. The degree of which K volatilizes during planet formation is a key parameter then on a planet’s potential to be habitable and for how long it can do so. As TRAPPIST-1 is ∼8 Gyr old, it may in fact be too old to sustain this critical process. From Unterborn et al., in review http://www.caymanunterborn.com/pagecv daily 0.75 2023-04-13 http://www.caymanunterborn.com/media daily 0.75 2017-12-07 http://www.caymanunterborn.com/code daily 0.75 2023-05-17 http://www.caymanunterborn.com/astronomy daily 0.75 2016-10-06 http://www.caymanunterborn.com/dynamics-mineralogy-and-structure-of-exoplanets daily 0.75 2017-11-16 https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1510851647615-SMCU29EYPWPK18OTDGRZ/Chi_x_sub.jpg Dynamics, Mineralogy and Structure of Exoplanets Modeled chi-squared goodness-of-fit for the TRAPPIST-1 planets as a function of the relative water fraction in weight percent added to the system. Mass-radius-composition curves were created using the ExoPlex calculator. From Unterborn et al., in review https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1510851690243-MLAEC75PF7CCL75F8736/UM.jpg Dynamics, Mineralogy and Structure of Exoplanets Using the Sun's composition to reverse engineer the Earth. From Unterborn, Dismukes & Panero, 2016. https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1510851710890-QYXUZQSUIZI0QUMKCLTN/image-asset.png Dynamics, Mineralogy and Structure of Exoplanets Contours of constant mass (black, in Earth masses) and constant mantle radius fraction (MRF = (R—Core Radius)/R, blue-dashed) vs. planetary radius and [Si/Fe]. Contours were calculated adopting a three-layer planetary model with an Fe core with 6% density deficit due to 8.5 wt% Si and 1.6 wt% O, brigmanite/periclase lower mantle and pyroxene/olivine upper mantle with Mg/Si = 1.25. Our calculated model for Kepler-36b is shown as a red diamond. Earth and Venus (adopting Mg/Si = 1.25; open square, and Mg/ Si = 1.35; solid square) are shown as well. If stellar composition is a proxy for planetary composition and Kepler-36b is indeed "Earht-like," this model predicts a [Si/H] abundance for Kepler-36 of ∼−0.32. https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1510851731528-KFF17T3MGODQU6MIN13X/image-asset.png Dynamics, Mineralogy and Structure of Exoplanets Stellar Th/Si as a function of average Si abundance. Stars with observed planets are shown as closed squares and without as unfilled squares. The Sun is represented by a triangle. The Sun is depleted relative to the rest of this sample, suggesting some planets may have a greater heat budget than the Earth. https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1510851748104-DOGT7CQM86KXY4OLP3W4/C.png Dynamics, Mineralogy and Structure of Exoplanets Ternary diagram for the C–(Mg+2Si+Fe)–O system. The Earth is shown as a blue cross and HD 19994 as a red diamond. The exact position of the diamond/no diamond line on the core-free side of the ternary depends on the specific Fe/(Mg+2Si+Fe) ratio, in which planets with more Fe relative to the other cations are able to stabilize more FeCO3, and thus reduce the amount of diamond present in the mantle. http://www.caymanunterborn.com/dynamics-and-chemistry-of-planet-formation daily 0.75 2016-10-31 https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1477902804676-YFJTGHAN3ECSVE7U764U/image-asset.png Dynamics and Chemistry of Planet Formation Mg and Si phase diagrams for condensation sequence calculations adopting the Solar composition of Asplund et al. (2005) as input. Both figures are on the same scale for comparison. Higher temperature condensed solids are shown as dashes. https://images.squarespace-cdn.com/content/v1/5717bb294c2f853190e29054/1477902832548-7B4CEIHAJR915HP8RPGW/image-asset.png Dynamics and Chemistry of Planet Formation The percentage of oxygen condensed in refractory phases as a function of Mg/Si for independent changes in both Mg (crosses) and Si (squares). The Sun (circle; Asplund et al. 2005) is included for reference. Results of the stoichiometric determination of the core mass fraction (assuming only Fe-Ni alloy) and mantle mineralogy are appended for the Sun and each end-member.