The observatory NASA sends up from Kennedy Space Center at the close of August was engineered to pursue the two greatest mysteries in physics: the dark matter holding galaxies together and the dark energy driving the cosmos apart. It may also wind up warning us which rock is headed for a city.
That second assignment never appeared in the brochure. Engineers designed the Nancy Grace Roman Space Telescope to peer through and beyond our solar system rather than at it. Yet a multi-institutional group of planetary scientists and astronomers plans to argue in September that the instrument sits in precisely the right spot, with precisely the right eye, to survey asteroids and nail down their paths, dimensions and makeup.
A 300-megapixel eye that sees 100 Hubbles wide
Roman — named for NASA’s first chief astronomer — carries a super-wide-angle infrared camera clocking in at 300 megapixels. In a single shot it swallows a slice of sky roughly 100 times wider than the Hubble Space Telescope’s view.
Everything else flows from that field of view: thousands of newly found planets, tens of thousands of exploding stars, detailed surveys of more than one billion galaxies. And all the while, its gaze runs straight through the neighborhood where the hazardous rocks reside.
The proposal, bound for the Europlanet Science Congress at The Hague in The Netherlands, attaches a figure to the idea. Between its wide view and its infrared sensitivity, Roman can single out small asteroids measuring up to 60 feet long. That size roughly matches the object that detonated above Chelyabinsk, Russia in 2013, unleashing the equivalent of 500,000 tons of TNT and sending 1,500 people to hospitals.
The origin story involves a budget fight
The planetary defense angle wasn’t born in a science meeting. It grew out of a funding scare. Last summer, the Trump administration once again floated significant cuts to Roman’s budget.
“My colleague Rick Cosentino [a planetary scientist at NASA] said to me in July 2025 that we need to show what Roman can do for planetary defense as a way to further increase the visibility of the mission with lawmakers and taxpayers,” said Bryan Holler, a researcher at the Space Telescope Science Institute in Baltimore, Maryland.
The software currently throws the asteroids away
And here sits the complication nobody puts in the press kit. Roman’s data pipeline, as currently written, files a moving rock under noise.
“Streaks, whether caused by cosmic rays or glitches or asteroids, are caught by the software and discarded,” said Andy Rivkin, a planetary scientist and planetary defense researcher at Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
Which means the telescope requires tweaking before it spots anything at all. Astronomers could dig into those discarded streaks and fish out the ones that prove to be asteroids.
It’s a support player, not a lead
Even after those adjustments, Roman won’t be an asteroid-hunting prodigy in isolation. Its worth lies in pairing with the James Webb Space Telescope, another instrument built for far-off galaxies and stars that can nonetheless lock onto an individual asteroid on request. JWST did precisely that last year, playing a key role in tracking 2024 YR4, briefly the most dangerous asteroid ever discovered.
“But Roman’s field of view is much bigger,” said Rivkin.
Meaning volume. “Roman can provide infrared observations of more asteroids than JWST could hope to observe in a reasonable amount of observing time,” said Holler.
Spot a harmless traveler and you move along. Spot something that might strike us and other telescopes, JWST among them, take the handoff and calculate the probable damage — or whether a mission to shove the object aside is warranted.
“Roman will sample such a large volume of the cosmos that we’ve long known it will offer vast opportunities for a range of additional science,” said Alise Fisher, the astrophysics communications lead at NASA Headquarters in Washington D.C.
The numbers that keep planetary defense people up at night
What chiefly worries NASA’s Planetary Defense Coordination Office and its partners around the world are asteroids 460 feet long and bigger. Roughly 25,000 of them are estimated to travel near-Earth orbits. Slightly more than half remain undiscovered.
Should one strike a city, much of it would be destroyed or irreversibly damaged in a heartbeat.
Below that sits another tier: some 230,000 asteroids around 165 feet long in orbits near Earth, of which astronomers have pinpointed less than 10 percent. An impact from one of these wouldn’t wipe out a city. It would land with the force of a large atomic bomb, minus the radiation.
Both deflection routes — slamming a spacecraft into the rock, or vaporizing it with a nuclear weapon — remain theoretically available. Neither is any use if the rock’s location is unknown. That is exactly why NASA bankrolls a network of ground-based telescopes searching for them. Those scopes deliver, but they can only sweep so much of the night sky, and Earth’s atmosphere keeps interfering.
NEO Surveyor is the one built for this
In 2027 NASA launches the Near-Earth Object Surveyor space telescope, which — unlike Roman — has no competing responsibilities. Stationing itself between Earth and the Sun allows it to catch asteroids that ground-based telescopes simply cannot see.
It also observes in infrared instead of visible light, a distinction that carries more weight than it might seem. Asteroids stand out more sharply, and infrared hands scientists a considerably better read on their size. Inside a few years it could locate 90 percent of the city-killer-size asteroids sitting in near-Earth orbits.
Nor will NEO Surveyor operate solo. It’ll coordinate with Roman and JWST — both conveniently equipped with infrared scopes — as well as the Vera Rubin Observatory, which has just begun a 10-year survey of the whole night sky from a Chilean mountaintop. Rubin’s inventory is expected to yield 89,000 near-Earth asteroids.
How the handoff actually plays out
Imagine NEO Surveyor flagging an asteroid that, based on a handful of observations, carries some chance of striking Earth. Then five more of the same. At that point every one of those orbits is deeply uncertain.
Roman swings toward the patch of sky containing all six. In a matter of days, the precision on those orbits climbs by several orders of magnitude.
Geometry lends a hand as well. Roman occupies a different region of space than either NEO Surveyor or Rubin. “Those slightly different viewing angles will also help narrow orbits down more quickly than if all objects were looking from the same place,” said Holler.
Perhaps five of the six end up cleared for the foreseeable future. The one that resists ruling out is where JWST and other telescopes get summoned for a closer inspection.
“Telescope resources, whether in space or on the ground, are typically oversubscribed and will not be available to follow up on all [near-Earth asteroids] with a non-zero impact probability when they are first discovered,” said Holler. Roman’s role is to help scientists “make sure we follow-up on the correct targets.”
Infrared tells you what the rock is made of
Size isn’t all that Roman’s infrared scope can gauge. It can tell a stony rock apart from a puffy, watery carbon-rich one, and both apart from a metallic one.
“This in turn provides strong clues to the composition and thereby the density and mass of the asteroid, which are important when estimating the impact damage or, less ghoulishly, the effort required to nudge it out of its current orbit,” said Holler.
Roman was never destined to be the telescope that saves Earth; that distinction belongs to NEO Surveyor. But while Roman busies itself cataloging supernovas and planets orbiting other stars, the streaks its software was designed to discard may prove worth holding onto.