The future Habitable Worlds Observatory (HWO) telescope could detect life with much lower spectral resolution than previously thought.
A new study indicates that it won't need extreme performance to spot biosignatures. This surprising finding changes the game for engineers tasked with its design. To achieve this, researchers calculated the minimum specifications needed to identify Earth-like atmospheres from different eras.
Spectral resolution refers to a telescope's ability to distinguish between similar colors of light. The higher it is, the more detailed the atmospheric fingerprint, but at the cost of longer observation times and increased noise. Engineers must therefore strike a balance between precision and feasibility. The study results indicate that moderate resolution is sufficient for key biosignatures, simplifying the design. This reduces technical constraints and allows focus on other aspects.
The future Habitable Worlds Observatory (HWO).
Image: NASA To estimate the necessary capabilities, researchers modeled what HWO would see while observing Earth at different geological epochs. Earth's atmosphere has changed radically: the oxygen-free Archean, the low-oxygen Proterozoic, and the Phanerozoic with 20% oxygen. Each period leaves a unique spectral signature. The telescope must be able to recognize these different configurations to avoid missing a biosphere. These models allow testing of the instrument's sensitivity in realistic scenarios. The study shows that even early Earth would have been detectable with modest resolution.
The key numbers are remarkably low: for detecting molecular oxygen, the required resolution in the visible is 140. For ozone in the ultraviolet, only 7. In the near-infrared, a resolving power of 70 is recommended to distinguish carbon dioxide from carbon monoxide, avoiding mistaking a dead volcanic planet for a living one. These values are well within current technical limits.
How did they arrive at these numbers? The study, available on the
arXiv platform, generated synthetic observations from HWO for resolving powers up to 5,000, then analyzed each spectrum with inversion algorithms. They accounted for detector noise, exposure time, and anti-biosignatures—those atmospheric characteristics that argue against the presence of life. This realistic simulation allows evaluation of what can actually be deduced from the atmosphere. The results confirm that modest resolutions suffice.
The study's authors remain cautious, however. Their estimates of exposure times have an uncertainty margin of about 20%. Crucially, detecting oxygen, ozone, methane, and water in an exoplanet atmosphere is not definitive proof of life. The universe hosts non-biological processes capable of producing these gases. HWO's role is to identify promising candidates, not to conclude on its own. It is a selection tool for future, more in-depth observations. This nuance is essential for interpreting the results.
The study thus provides a precise set of specifications: a resolution of at least 140 in the visible, 7 in the ultraviolet, and 70 in the near-infrared. These are the specifications for a telescope capable, in principle, of finding signs of life on another planet. With these numbers in hand, engineers can move forward confidently.