The challenge of detecting remote spectroscopic signatures from radionuclides

TL;DR

Detecting radionuclides in exoplanet atmospheres via remote spectroscopy could reveal planetary geology, space environment, or technosignatures, but current technology faces significant sensitivity challenges.

Contribution

This paper analyzes the feasibility and challenges of remotely detecting radionuclides in exoplanet atmospheres, highlighting current limitations and future prospects.

Findings

Detection of radionuclides requires sensitivity several orders of magnitude higher than current capabilities.

Most radionuclides attach to particles, complicating remote detection.

Current remote spectroscopic missions are not sensitive enough for radionuclide detection.

Abstract

The characterization of exoplanetary atmospheres through transit spectra is becoming increasingly feasible, and technology for direct detection remains ongoing. The possibility of detecting spectral features could enable quantitative constraints on atmospheric composition or even serve as a potential biosignature, with the sensitivity of the instrument and observation time as key limiting factors. This paper discusses the possibility that future remote observations could detect the presence of radioactive elements in the atmospheres of exoplanets. Such radionuclides could arise from cosmogenic or geologic sources, as well as from industrial sources, all of which occur on Earth. The detection of radionuclides in an exoplanetary atmosphere could reveal important properties about the planet's geology or space environment, and potentially could serve as a technosignature. However, many radionuclides, including those from industrial sources, attach to aerosol or other particles that cannot be remotely characterized. Limited experimental and theoretical spectral data exist for long-lived radionuclides, but the sensitivity required to detect the spectral features of some known radionuclides would be at least several orders of magnitude greater than required to detect the spectral features of molecular oxygen. Present-day remote spectroscopic observing mission concepts at ultraviolet to mid-infrared wavelengths are not sensitive to discern the presence of radionuclides in exoplanetary atmospheres. Interplanetary fly-by or probe missions may be more likely to provide such data in the future.