A temperate Earth-sized planet with tidal heating transiting an M6 star.

Temperate Earth-sized exoplanets around late-M dwarfs offer a rare opportunity to explore under which conditions planets can develop hospitable climate conditions. The small stellar radius amplifies the atmospheric transit signature, making even compact secondary atmospheres dominated by N2 or CO2 amenable to characterization with existing instrumentation1. Yet, despite large planet search efforts2, detection of low-temperature Earth-sized planets around late-M dwarfs has remained rare and the TRAPPIST-1 system, a resonance chain of rocky planets with seemingly identical compositions, has not yet shown any evidence of volatiles in the system3. Here we report the discovery of a temperate Earth-sized planet orbiting the cool M6 dwarf LP 791-18. The newly discovered planet, LP 791-18d, has a radius of 1.03 ± 0.04 R⊕ and an equilibrium temperature of 300-400 K, with the permanent night side plausibly allowing for water condensation. LP 791-18d is part of a coplanar system4 and provides a so-far unique opportunity to investigate a temperate exo-Earth in a system with a sub-Neptune that retained its gas or volatile envelope. On the basis of observations of transit timing variations, we find a mass of 7.1 ± 0.7 M⊕ for the sub-Neptune LP 791-18c and a mass of [Formula: see text] for the exo-Earth LP 791-18d. The gravitational interaction with the sub-Neptune prevents the complete circularization of LP 791-18d's orbit, resulting in continued tidal heating of LP 791-18d's interior and probably strong volcanic activity at the surface5,6.

Impact of the Arizona NExSS Winter School on Astrobiology Knowledge and Attitudes.

Astrobiology is an inherently interdisciplinary area of study, demanding communication across multiple fields: astronomy, geochemistry, planetary science, and so on. Successful communication requires that researchers be aware of the basic findings, open questions, and tools and techniques of allied fields and possess an appreciation and respect for what these fields consider good science. To facilitate this communication between early-career researchers, the Arizona NExSS Winter School was hosted in February 2016, bringing together graduate students and postdoctoral researchers from backgrounds spanning the field of astrobiology. Students virtually attended a scientific Workshop Without Walls and participated in lectures, discussions, field trips, and hands-on activities, culminating in the writing and review of mock proposals by interdisciplinary teams. We assess the impact of the school on interdisciplinarity using a pre- and posttest survey of 24 students, informed by National Science Foundation impact categories (Friedman et al., 2008 ) within the Impact Analysis Method (IAM) described by Davis and Scalice ( 2015 ). We demonstrate that students gained knowledge, especially in fields outside their home discipline. Furthermore, an underlying disciplinary divide between geochemists and planetary scientists on the role of life in planetary evolution is observed and interpreted. These findings demonstrate that the Arizona NExSS Winter School had measurable impact on interdisciplinarity and that the IAM rubric has utility in measuring impact. We make recommendations for further research to understand the interdisciplinary gaps in astrobiology and how best to bridge them. Key Words: Interdisciplinarity-Attitudes-Knowledge-Scientific dialogue-Training. Astrobiology 18, 365-375.

RETRACTED: Direct imaging discovery of a Jovian exoplanet within a triple-star system.

Direct imaging allows for the detection and characterization of exoplanets via their thermal emission. We report the discovery via imaging of a young Jovian planet in a triple-star system and characterize its atmospheric properties through near-infrared spectroscopy. The semimajor axis of the planet is closer relative to that of its hierarchical triple-star system than for any known exoplanet within a stellar binary or triple, making HD 131399 dynamically unlike any other known system. The location of HD 131399Ab on a wide orbit in a triple system demonstrates that massive planets may be found on long and possibly unstable orbits in multistar systems. HD 131399Ab is one of the lowest mass (4 ± 1 Jupiter masses) and coldest (850 ± 50 kelvin) exoplanets to have been directly imaged.

The onset of planet formation in brown dwarf disks.

The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub-micrometer-sized dust grains accompanied by dust settling toward the disk mid-plane. Here, we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.