We present an optical-to-infrared transmission spectrum of the inflated sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic grism, and the Spitzer Space Telescope (Spitzer) at 3.6 μm, in addition to a Spitzer 4.5 μm secondary eclipse. The precise HST transmission spectrum notably reveals a low-amplitude water feature with an unusual shape. Based on free-retrieval analyses with varying molecular abundances, we find strong evidence for water absorption. Depending on model assumptions, we also find tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water abundance is generally ≲0.1× solar (0.001–0.7× solar over a range of model assumptions), several orders of magnitude lower than expected from planet formation models based on the solar system metallicity trend. We also consider chemical-equilibrium and self-consistent 1D radiative-convective equilibrium model fits and find that they, too, prefer low metallicities ([M/H] ≲ −2, consistent with the free-retrieval results). However, all of the retrievals should be interpreted with some caution because they either require additional absorbers that are far out of chemical equilibrium to explain the shape of the spectrum or are simply poor fits to the data. Finally, we find that the Spitzer secondary eclipse is indicative of full heat redistribution from KELT-11b’s dayside to nightside, assuming a clear dayside. These potentially unusual results for KELT-11b’s composition are suggestive of new challenges on the horizon for atmosphere and formation models in the face of increasingly precise measurements of exoplanet spectra.

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Abstract.The prioritization and improvement of ethics, planetary protection, and safety standards in the astro-sciences is the most critical priority as our scientific and exploratory capabilities progress, both within government agencies and the private sector. These priorities lie in the belief that every single science mission -crewed or non-crewed, ground-based or not -should heed strict ethical and safety standards starting at the very beginning of a mission. Given the inevitability of the private sector in influencing future crewed missions both in and beyond low-Earth orbit, it is essential to the science community to agree on universal standards of safety, mission assurance, planetary protection, and especially anti-colonization. These issues will impact all areas of space science. Examples that are particularly relevant to the Astro2020 Decadal Survey include but are not limited to: light pollution from satellites, the voices and rights of Native people when constructing telescopes on their lands, and the need to be cognizant of contamination when searching for and exploring habitable environments beyond Earth. The existence of oversight bodies to enforce planetary protection and communication between public, private, and academia is necessary for this proposal. Delegation of power and strict communication standards not only to protect the lives of the explorers, but protect the environments of wherever humanity decides to venture. Opening up the multidisciplinary approach of space exploration to international law and governance regarding planetary protection, safety, mission assurance, and creating comprehensive and ethical standards across all space faring institutions is needed for the future of space exploration. Agreement and enforcement by the United Nations Office of Outer Space Affairs (UNOOSA) and the cooperation of participating governments will also prove critical in regulating and improving standards for future science missions. Ultimately, moving international space law and domestic space policy from a reactive nature to a proactive one will ensure the future of space exploration is one that is safe, transparent, and anti-imperialist. The prioritization of safety, planetary protection, and ethical practices of space exploration and its subsets is heavily dependent on a clear, progressive, and precautionary approach to international and domestic space law.

A key item of interest for planetary scientists and astronomers is the habitable zone: the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system’s habitable zone, it is possible that one may instead observe a Venus-like planet. We define “Venus-like” as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end state of evolution for habitable worlds require an improved understanding of the Venus-like planet, specifically the distances where these planets can exist. Understanding this helps us define a “Venus zone”—the region in which Venus-like planets could exist—and assess the overlap with the aforementioned “habitable zone.” In this study, we use a 1D radiative−convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types. Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 au, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S ⊙, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.