Beyond Webb: why astronomy needs Roman’s wider view

NASA’s latest commissioning update brings Roman closer to surveys designed to examine large areas of sky, rather than concentrate on a single target.

With Webb already studying distant galaxies, what does another space telescope add? For Roman, the answer is breadth. NASA’s 14 October update reports progress in testing its main instrument and refining its focus ahead of survey observations.

The distinction is one of observing strategy. NASA describes Webb as suited to detailed studies of selected targets, while Roman will cover much larger areas in one observation. One examines an object closely; the other helps astronomers compare populations.

Getting the optics ready

Roman’s Wide Field Instrument combines a roughly 300-megapixel camera, operating from visible to near-infrared wavelengths, with spectroscopy. Its surveys are intended to supply large samples for research including dark matter, dark energy and planets beyond the solar system.

Following adjustments, the instrument’s optical error measures 63 nanometres RMS, below a requirement of about 90 nanometres. This is a measure of optical imperfections, not the size of an object the telescope can resolve.

A complement, not a replacement

Roman has a 2.4-metre primary mirror, compared with Webb’s 6.5 metres. The different designs serve different work: broad surveys can identify patterns and targets that more concentrated observations explore in depth.

Preparation continues on Roman’s coronagraph. Camera settings and deformable mirrors still need calibration before tests of its ability to suppress starlight. The latest news concerns readiness for observation; survey discoveries must follow from the observations themselves.

Sources

• NASA — Roman commissioning update, 14 October 2026
• NASA — Roman and Webb
• NASA — Wide Field Instrument technical information