Plan 9: Detecting Atmospheric Deterrence Against Interstellar Monsters

Abstract

Exoplanet atmospheres are usually discussed as tracers of climate, chemistry, and habitability, but they may also preserve signatures of planetary defense. We consider three folklore-motivated deterrents against monsters: reduced organosulfur gases as anti-hematophage repellents, argentiferous reflective aerosols as anti-lycanthropic countermeasures, and haline aerosols as a counting problem for specters. We show that globally-mixed garlic-smelly levels of DMS/DMDS could produce observable mid-infrared transmission features, that silver hazes would show up as anomalous optical brightening, and that sea-salt lofting sustained by strong near-surface winds appears as muted spectra. None of these signatures is unique, which is precisely the observational challenge. A defended world may first appear merely sulfur-rich, bright, or hazy. Therefore, some atmospheres may encode not only biosignatures, but also evidence that the local biosphere has stopped being afraid of the dark.

Figures (5)

• Figure 1: The 16 oz of pharmacy-grade dimethyl sulfoxide DR's mother-in-law recommends. Not shown: strong garlic smell with skin contact.
• Figure 2: Conceptual mid-infrared transmission spectra for a hydrogen-rich sub-Neptune with increasing sulfur-defense abundance. The shared DMS/DMDS absorption complex appears between 6.8–8 µm, with broader secondary features near 9–10 µm for DMS and 10–11 µm for DMDS. The plotted cases correspond to 0.1, 1, and 10 ppb sulfur loading, giving schematic transit-depth modulations of 5, 12, and 24 ppm relative to a cloudy baseline. The 0.1–1 ppb range marks the adopted olfactory repulsion threshold for space vampires.
• Figure 3: Conceptual geometric albedo spectra for a baseline cloudy atmosphere, a sulfur-haze comparison motivated by Gao2017, and an argentiferous (silver-bearing) haze atmosphere. The sulfur case reproduces the characteristic short-wavelength absorption turnover and bright optical plateau expected for sulfur hazes, while the argentiferous case is shown schematically as a smoother, modest broadband enhancement to the reflectivity of an otherwise cloudy atmosphere.
• Figure 4: Specter counting rate as a function of near-surface wind speed, $U_{10}$, for several minimum countable grain sizes $d_{\min}$ and log-normal size-distribution widths $\sigma_g$. The counting rate $\dot N_{>d_{\min}}$ is computed from a wind-driven salt loading model (Eq. 1–5) assuming a ghost cross-sectional area of $A_{\rm g}=1~\mathrm{m^2}$. Horizontal dashed line indicates maximum sustainable counting rate (5 s$^{-1}$) above which specters become throughput-limited.
• Figure 5: Still frame from Plan 9 from Outer Space (1959; dir. Ed Wood) detailing an invasion of Earth by extraterrestrial vampires and featuring a flying saucer that is totally not a tin plate attached to a string. Via Wikimedia Commons, marked public domain in the United States PlanNine02_WikimediaCommons