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If advanced technological extraterrestrial lifeforms are out there, where are they? Thus goes the Fermi paradox. This Perspective reviews various solutions and proposes that they are either not there or are deliberately hiding from us.
On Earth, technological advances required open-air combustion, which needs an oxygen partial pressure of about 18%. This threshold can help guide searches for detectable technospheres on other planets.
The habitability of a planet is defined at a fixed time. A bigger challenge is to understand how that habitability is sustained over geological timescales, and how the underlying processes compare across different planetary bodies.
A low atmospheric carbon abundance can be a ‘habiosignature’ and indicate the presence of substantial surficial liquid water, tectonic activity and/or a biomass in temperate rocky exoplanets. It can potentially be detected by JWST at 4.3 μm in a few tens of transits.
Measurements of the redshifted 21 cm line of neutral hydrogen could be a powerful tool for precision cosmology, constraining fundamental parameters and probing the cosmological dark ages. However, practical challenges must first be addressed.
An ethical approach to research in extreme environments can lay the foundations for future space exploration that respects ecologies, is founded on authentic partnerships and supports co-learning from diverse communities of non-scientists.
The exploration of small planetary bodies depends crucially on the success of anchoring robots. This Perspective takes us through the diverse challenges and technological innovations involved when making contact with unknown surfaces.
Each space launch is assessed for various risks, but not its wider impacts. This Perspective shows how the aggregate effects of space launches, plus the attendant rise of space debris, affect the darkness of our night sky now and in the future.