NASA's Prima telescope will fill the infrared gap James Webb left behind

NASA has given the green light to Prima, a far-infrared space telescope designed to observe the cold, dusty regions of the universe that even the James Webb Space Telescope cannot see. The mission, short for Probe Far-infrared Mission for Astrophysics, will enter the detailed design and testing phase now, with a potential launch window in the early 2030s pending final agency approval. It represents a deliberate effort to close a gap in humanity's view of the cosmos—one that has existed since the retirement of earlier far-infrared observatories.

The blind spot Prima aims to fill sits between two existing windows on the universe. James Webb captures shorter infrared wavelengths with remarkable clarity, while ground-based radio dishes detect much longer, lower-energy signals. But the band of light in between—the far-infrared spectrum—has largely gone unwatched from space. Alexandra Pope, an astronomy professor at the University of Massachusetts, Amherst, who will lead Prima's science team, explained that Webb's success has only sharpened the questions it cannot answer. "We've uncovered all sorts of mysteries and questions that Webb can't solve because it can't see the far-infrared part of the spectrum," she said. "That's where Prima comes in."

Far-infrared light occupies a peculiar niche in the electromagnetic spectrum. Warm objects emit it—the same radiation humans feel as heat—but the wavelengths are far too long for human eyes to detect. The specific band Prima will observe ranges from about one-third the thickness of a human hair to roughly the thickness of two stacked sheets of paper. This matters because cold gas and dust glow brightly in those longer wavelengths. Cosmic dust, which blocks ordinary visible light the way smoke obscures flames, becomes transparent to far-infrared radiation. That transparency allows astronomers to peer through the dust and spot newborn stars, actively growing black holes, and the swirling disks of gas and material where planets are being born—phenomena that would otherwise remain hidden.

Observing this wavelength band from Earth presents formidable obstacles. Water vapor in the atmosphere absorbs most far-infrared light, leaving ground-based telescopes to capture only fragments of the spectrum. Any warm object, including the telescope itself, radiates infrared energy that can drown out the faint signals arriving from space. Europe's Herschel space telescope and NASA's SOFIA, which operated from a modified jumbo jet, both studied far-infrared light before being retired. Since their decommissioning, only instruments aboard high-altitude balloons and mountaintop observatories have glimpsed portions of this band. Prima will change that by operating in the cold vacuum of space with sensors chilled to hundreds of degrees below freezing.

The technological foundation for Prima emerged from an unexpected source. In 1999, Caltech physicist Jonas Zmuidzinas and NASA Jet Propulsion Laboratory engineer Rick LeDuc sketched out the concept over coffee at a Peet's shop near the Southern California campus, working through how super-cold materials could detect far-infrared light. Over subsequent years, they and their collaborators refined the design. Prima's 5.9-foot mirror and detectors will operate at extreme cold, a strategy expected to yield unprecedented sensitivity. Zmuidzinas noted that the mission could achieve roughly a thousandfold increase in sensitivity compared to previous far-infrared observations—a leap he described as rare in astronomical instrumentation.

Prima belongs to a new category of NASA missions called "Probe Explorers," a designation created to occupy middle ground between small, frequent science missions and the agency's massive flagship observatories like Webb and the recently launched Nancy Grace Roman Space Telescope. A panel of leading U.S. scientists recommended this category in 2020 to enable NASA to pursue high-impact science at lower cost. Prima's budget has been capped at $1.2 billion, excluding launch expenses—a fraction of the roughly $10 billion NASA spent on Webb.

The mission's science agenda centers on three fundamental questions. First, astronomers will study approximately 200 disks of gas and dust orbiting young stars to understand how planets acquire water and atmosphere—the ingredients necessary for habitability. Second, Prima will examine the universe's most active era, roughly 9 billion to 3 billion years ago, to trace how galaxies and their central supermassive black holes grew in tandem, since nearly every large galaxy harbors such a black hole at its core. Third, the mission will investigate cosmic dust to reconstruct how the universe's heavier elements—carbon, oxygen, and others essential to life—were forged in stars and dispersed throughout space, tracing a lineage back to the Big Bang, which produced only hydrogen and helium.

Pope is already preparing for the long commitment ahead. Her team will build the analytical tools needed to process Prima's data, a task that will require sustained staffing over the next decade. She plans to hire postdoctoral researchers and graduate students, along with what she called "a small army of undergrads" to work on discrete pieces of the science analysis. The work of understanding what Prima reveals will begin long before the telescope launches, laying groundwork for discoveries that may reshape understanding of how planets form and how the universe assembled itself.