NASA’s Roman Telescope to Survey Vast Cosmic Frontier
In 1964, two radio astronomers at Bell Labs in New Jersey kept hearing a persistent hiss in their antenna. [1] Arno Penzias and Robert Wilson had tried everything to get rid of it. They cleaned out pigeon droppings. They checked every wire. They pointed the instrument away from known sources. The noise would not go away. It came from every direction, all the time, at the same intensity. That stubborn hiss turned out to be the cosmic microwave background - the leftover glow of the Big Bang itself. [1] It was the most important accidental discovery in modern astronomy, and it won them the Nobel Prize. [1]
That accident taught astronomers a lesson that still guides the field today: sometimes you learn the most when you are not looking for anything specific. The telescopes that followed Hubble, Webb, and their predecessors were built to stare at particular objects. They pointed at a galaxy here, a nebula there. That approach works, but it leaves most of the sky untouched. The Nancy Grace Roman Space Telescope, named after NASA’s first head of astronomy and a vital advocate for the Hubble Space Telescope, takes the opposite approach. It is built to sweep. It is built to survey. It is built to find the things nobody thought to look for.
Roman weighs as much as a Tyrannosaurus rex and is the size of a tour bus. Scientists and engineers have spent some twenty years designing and building the observatory. NASA aims to launch the telescope as early as August 30, with plans to start delivering a flood of cutting-edge astronomical data early next year. Within the mission’s first five years, scientists expect Roman to unlock mysteries about the enigmatic dark matter and dark energy that dominate our universe. It will also detect tens of thousands of alien planets, paint interactions between galaxies, and spot exploding stars.
The observatory’s superpower is its field of view. It is 100 times larger than Hubble’s. That means Roman can cover territory methodically, without specific targets, says astrophysicist Julie McEnery of NASA’s Goddard Space Flight Center in Greenbelt, Md. Hubble and Webb see only a small fraction of the sky. Roman sees vast regions at once. “Anywhere you point Roman, somebody’s going to be able to say, ‘I discovered something,’” says cosmologist Jason Rhodes of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Roman is going to touch or affect nearly all areas of astrophysics.”
The scaling principle here is simple. Hubble gave us a keyhole view of the universe. Webb gave us a window. Roman gives us a panorama. The same sharpness that Hubble used to examine a single galaxy, Roman applies to millions of galaxies at once. “Roman is going to unlock huge corners of science by really turning that sharpness over vast areas of the sky,” says astrophysicist Erik Rosolowsky of the University of Alberta in Edmonton, Canada, who is not formally affiliated with the Roman mission
The invisible glue and the invisible push
The Roman Space Telescope traces its origins to the early 2000s. At the time, cosmologists had known for a couple of decades that the matter we experience every day and observe with telescopes accounted for only a fraction of the universe’s matter. Huge amounts of so-called dark matter glue the cosmos together. The late 1990s brought a second shocking space oddity. The universe is not just expanding. It is expanding faster and faster as time passes, driven by another incomprehensible phenomenon astrophysicists dubbed dark energy.
Understanding these two mysteries has been a steep challenge because both enigmas unfold on a huge scale, says cosmologist Katarina Markovic of JPL. They call for observations of huge regions of the universe. “It requires a very new kind of astronomy which is not focused on looking at individual objects,” she says. That is exactly what Roman was built to do.
Roman will detect tiny changes in the shapes of millions of galaxies caused by dark matter passing between these objects and the telescope. Like window glass that has been warped by age, dark matter distorts distant objects. That distortion lets science map the invisible. Roman will also spot some 21,000 stellar explosions of a type so predictable that scientists can calculate their exact distance from Earth. These supernovae act as cosmic mile markers. And Roman will map billions of galaxies, stretching back in cosmic time, betraying patterns in how these objects have clumped together and spread apart over the eons.
All told, scientists hope these observations will be powerful enough to confirm or disprove current suspicions that dark energy may be more complicated than previous evidence suggested. That question carries enormous weight. The ultimate fate of the universe hangs on it. If dark energy is constant, the universe will keep expanding forever, slowly cooling and dimming. If dark energy changes over time, everything changes. Roman’s data will help decide.
The key detail here is the scale of the survey. Previous dark energy probes looked at thousands of supernovae. Roman will look at 21,000 of just one type, plus billions of galaxies for the clumping analysis. That is not a small step up. It is a leap across an order of magnitude. The statistical power of so many objects means scientists can measure subtle effects that were previously buried in noise.
Two ways to find a world
To date, scientists have identified just over 6,000 planets orbiting other stars, mostly in our own neighborhood. Roman will take that hunt to a totally new region: the Milky Way’s bulge. That is the crowded, dusty center of our galaxy, where most of the Milky Way’s stars live. It is wrapped in a haze of dust that most telescopes cannot see through. “It’s where most of the galaxy lives, and it’s just severely underexplored,” says astrophysicist Gail Zasowski of the University of Utah in Salt Lake City, who served on the committee governing Roman’s overall observation time budgeting. “All the extremes happen there
The largest trove of Roman’s exoplanets will come via transits. That is when astronomers clock the periodic dip in a star’s brightness caused by a planet passing in front of its sun. This approach has been most fruitful so far, but it is best at spotting very large planets orbiting very close to their star. Think of a planet the size of Jupiter in the orbit of Mercury. Roman could find as many as 200,000 such planets.
Roman will also excel at a second technique, called microlensing, says astrophysicist and exoplanet specialist Elisa Quintana of GSFC, who previously worked on Roman. Microlensing relies on the way large objects in space bend light around them. In the relatively rare cases when two stars align perfectly along Roman’s viewing angle, the background star briefly flares because of this phenomenon. If a planet is secretly orbiting the foreground star, it causes a second, smaller flare. From that flare, scientists can calculate the planet’s size and orbital distance. Roman will hunt down some 1,400 planets this way, farther out in their stellar systems.
The two techniques complement each other. Transits find planets close to their star. Microlensing finds planets farther out. Together, they give a complete picture of how planetary systems are arranged. Roman’s ability to see planets at such a wide range of distances from their stars should show us how typical our own solar system is. Although finding alien Jupiters may not sound as exciting as finding alien Earths, the presence and dynamics of giant planets shapes where terrestrial planets form, Quintana says. “It’s all tied together - it’s all one story
The surprises that have no name yet
Across the universe, Roman will see countless stars flare and fade and be shredded by black holes. In our own solar system, fast-moving asteroids will streak across its view, informing scientists’ evaluation of the threats to Earth posed by nearby space rocks. Roman will regularly check up on the very heart of our Milky Way galaxy, where a gigantic black hole invisibly churns. The observatory will also offer scientists their first good look at the galaxy’s bulge, which includes the majority of the Milky Way’s stars.
Of course, launch is only the next step for Roman. The telescope must fully deploy. It must trek out to its perch nearly 1.5 million kilometers away from Earth on the side opposite the sun. It must get up and running. That is a more-than-three-month-long process that mission members will be watching with bated breath.
But despite scientists’ grand agenda for Roman, they are perhaps most eager for what cannot be predicted. McEnery calls them the “absolute surprises.” She means “the things that don’t yet have a name because they haven’t yet been found.” It is these discoveries that only Roman will be able to reveal. And it is these discoveries that will shape scientists’ explorations for decades to come.
The history of astronomy is full of such moments. The cosmic microwave background was one. Dark energy itself was another - nobody predicted it before the late 1990s observations of distant supernovae. Roman is built to create more of those moments. Its surveys will produce enormous datasets that astronomers will mine for years. The telescope does not know what it will find. Neither do the scientists who built it. That is precisely the point. The instrument is not designed to answer a single question. It is designed to open a new territory, the way the first maps of a continent opened it to everyone who came after.
When the telescope starts delivering data early next year, the flood will begin. Astronomers of all stripes collaborated on Roman’s observing plan to ensure the telescope gathers widely-applicable top-tier data while optimizing for groundbreaking discoveries in three key fields: the dark universe, exoplanets, and general time-domain astronomy. Every survey is planned. Every field is chosen. But the discoveries themselves are unknown. That is the nature of a survey telescope. It does not tell you what you will find. It only promises that you will find something.
Sources
1. Bell Labs
2. NASA
3. Nancy Grace Roman Space Telescope
6. NASA’s Goddard Space Flight Center