Observational constraints on the likelihood of ${}^{26}$Al in planet-forming environments

Abstract

Recent work suggests that ${}^{26}$Al may determine the water budget in terrestrial exoplanets as its radioactive decay dehydrates planetesimals leading to rockier compositions. Here I consider the observed distribution of ${}^{26}$Al in the Galaxy and typical star-forming environments to estimate the likelihood of ${}^{26}$Al enrichment during planet formation. I do not assume Solar-System-specific constraints as I am interested in enrichment for exoplanets generally. Observations indicate that high-mass stars dominate the production of ${}^{26}$Al with nearly equal contributions from their winds and supernovae. ${}^{26}$Al abundances are comparable to those in the early Solar System in the high-mass star-forming regions where most stars (and thereby most planets) form. These high abundances appear to be maintained for a few Myr, much longer than the 0.7 Myr half-life. Observed bulk ${}^{26}$Al velocities are an order of magnitude slower than expected from winds and supernovae. These observations are at odds with typical model assumptions that ${}^{26}$Al is provided instantaneously by high velocity mass loss from supernovae and winds. Regular replenishment of ${}^{26}$Al especially when coupled with the small age differences that are common in high-mass star-forming complexes, may significantly increase the number of star/planet-forming systems exposed to ${}^{26}$Al. Exposure does not imply enrichment, but the order of magnitude slower velocity of ${}^{26}$Al may alter the fraction that is incorporated into planet-forming material. Together, this suggests that the conditions for rocky planet formation are not rare, nor are they ubiquitous, as small regions like Taurus that lack high-mass stars to produce ${}^{26}$Al may be less likely to form rocky planets. I conclude with suggested directions for future studies.

accepted to A&A Letters

References in corpus (20)

• Binary interaction dominates the evolution of massive stars
• The lifecycle of molecular clouds in nearby star-forming disc galaxies
• How to Characterize Habitable Worlds and Signs of Life
• A water budget dichotomy of rocky protoplanets from ${}^{26}$Al-heating
• Studying the YMC population of M83: how long clusters remain embedded, their interaction with the ISM and implications for GC formation theories
• Solar system genealogy revealed by extinct short-lived radionuclides in meteorites
• Interaction of Supernova Ejecta with Nearby Protoplanetary Disks
• Age Gradients in the Stellar Populations of Massive Star Forming Regions Based on a New Stellar Chronometer
• Formation and composition of planets around very low mass stars
• A Tale of Three Cities: OmegaCAM discovers multiple sequences in the color-magnitude diagram of the Orion Nebula Cluster
• Spectral and intensity variations of Galactic 26^Al emission
• Triggered Star Formation Inside the Shell of a Wolf-Rayet Bubble as the origin of the Solar System
• Isotopic enrichment of forming planetary systems from supernova pollution
• The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264
• When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster
• Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets
• The puzzle of the CNO isotope ratios in AGB carbon stars
• Mass Functions of Giant Molecular Clouds and Young Star Clusters in Six Nearby Galaxies
• The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators
• A tale of two clusters: dynamical history determines disc survival in Tr14 and Tr16 in the Carina Nebula

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• Rapid Formation of Exoplanetesimals Revealed by White Dwarfs
• Prevalence of short-lived radioactive isotopes across exoplanetary systems inferred from polluted white dwarfs
• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk
• Theoretical Distributions of Short-Lived Radionuclides for Star Formation in Molecular Clouds
• Possible Implications of Relatively High Levels of Initial ${}^{60}$Fe in Iron Meteorites for the Non-Carbonaceous -- Carbonaceous Meteorite Dichotomy and Solar Nebula Formation
• Cosmic-Ray Bath in a Past Supernova Gives Birth to Earth-Like Planets
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