UV-målinger er vigtige for den næste generation af rumteleskoper

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The Importance of UV Capabilities for Identifying Inhabited Exoplanets with Next Generation Space Telescopes

The strongest remotely detectable signature of life on our planet today is the photosynthetically produced oxygen (O₂) in our atmosphere. However, recent studies of Earth’s geochemical proxy record suggest that for all but the last ~500 million years, atmospheric O₂ would have been undetectable to a remote observer–and thus a potential false negative for life. During an extended period in Earth’s middle history (2.0 – 0.7 billion years ago, Ga), O₂ was likely present but in low concentrations, with pO₂ estimates of ~0.1 – 1% of present day levels. Although O₂ has a weak spectral impact at these low abundances, O₃ in photochemical equilibrium with that O₂ would produce notable spectral features in the UV Hartley-Huggins band (~0.25 um), with a weaker impact in the mid-IR band near 9.7 um. Thus, taking Earth history as an informative example, there likely exists a category of exoplanets for which conventional biosignatures can only be identified in the UV. In this paper, we emphasize the importance of UV capabilities in the design of future space-based direct imaging telescopes such as HabEx or LUVOIR to detect O₃ on planets with intermediate oxygenation states. We also discuss strategies for mitigating against ‘false positives’–that is, O₃ produced by abiotic processes. More generally, this specific example highlights the broad implications of studying Earth history as a window into understanding potential exoplanet biosignatures.

Jorden har kun haft oxygen fra fotosyntese i atmosfæren de seneste 500 millioner år. O₂ i fotokemisk ligevægt med det lave indhold af O₂ vil producere absorption ved 0.25 μm. Forfatterne diskuterer også muligheder for at gardere sig mod O₃ produceret ved abiotiske processer.

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