NASA Warns 3-Billion-Year Oxygen Gap Could Blind HWO to Life

1 articles · Updated · spacedaily.com · Jul 26

3 billion years of inhabited Earth would have looked lifeless to an oxygen-based search, even though life existed by at least 3.5 billion years ago and oxygen became a reliable remote signal only in the past 500 million years.
That history complicates NASA’s Habitable Worlds Observatory, a proposed flagship telescope meant to directly image Earth-like planets and read spectra for gases such as water vapour, oxygen, ozone, methane and carbon dioxide.
A 2026 modelling study found visible-light spectra at resolving power 140 could detect recent Earth-like oxygen, but Proterozoic-level oxygen would need detector dark current more than 10 times lower than the baseline assumption.
HWO remains an early-stage concept: NASA awarded technology contracts in January 2026, but the coronagraph performance, optical stability, final design and launch timetable are still unsettled.
The broader lesson is that HWO must judge chemical patterns rather than a single gas, because oxygen can yield false positives and its absence can still hide a living world.