If the James Webb Space Telescope is the most audacious space observatory mission of the 2020s — surrounded by both hype over its capabilities and controversy over its controversial namesake — then the Nancy Grace Roman Telescope mission is our cosmic dark horse.
Named for a renowned astronomer dubbed the “Mother of Hubble,” it’s intended to hunt for two elusive beasts: exoplanets and dark energy, which comprises about 70 percent of the known universe but we’ve never actually observed. Its story is one of spies and supernovae.
“Its data will be so powerful that we will glean insights into the universe that at the moment aren’t even in our minds for conceptualizing,” NASA astrophysicist Dominic Benford tells Inverse.
In 2010, NASA scientists were having trouble making all the pieces of a major space telescope project fit. The U.S. National Research Council Decadal Survey committee recommended an ambitious observatory called Wide-Field Infrared Survey Telescope (WFIRST). It became a top priority project with exacting specifications, Benford says.
WRST was renamed to become the Nancy Grace Roman Space Telescope, expected to launch in May 2027. Its journey to a new name and a new purpose was a twisty one, complicated by global politics and the Covid-19 pandemic. Its total lifecycle cost is estimated to be $4.3 billion.
That may seem steep but compared to flagship missions like the James Webb Space Telescope, a $10 billion juggernaut that finally launched on December 25 after decades of development, it’s considered a reasonable price tag. That’s on purpose and a critical part of its story: This telescope has to contain its vast potential into a mirror just 1.5 meters in diameter and launch under budget.
NASA spent a good amount of time in 2011 and 2012 trying to balance those attributes, Benford tells Inverse, but “we couldn’t easily see a way to keep all the scientific ability we’d want, and that the decadal survey had asked us to produce, and yet keep that cost.”
Then a key puzzle piece came through from an unexpected source.
The National Reconnaissance Office came calling — the U.S. government agency tasks with overseeing American intelligence satellites. It had a deal to offer: an old space telescope for free.
From spyglass to sky glass
The Hubble Space Telescope launched in 1990 aboard the space shuttle Discovery. It packed a 2.4-meter mirror, the largest ever in a space telescope at the time. It also came with a suite of capabilities — infrared, visible light, ultraviolet — and after a major servicing mission, it was ready to go.
Hubble seemed so unique, but it wasn’t quite the case. While it peered out into the universe, some unknown number of its kin were peering down at Earth to gather geopolitical intelligence. Some were just as big as Hubble.
“The fact is that 2.4-meter mirrors have been made for [Department of Defense] purposes, for National Reconnaissance Office purposes, for years,” David DeVorkin, senior curator emeritus of astronomy and space sciences at the National Air and Space Museum, tells Inverse.
Among the many spy scopes were a few under the guidance of the still-classified Future Imagery Architecture, or FIA, program. It was a mysterious Department of Defense program that needed a certain set of capabilities. One of those was infrared, which is good for both night vision and heat mapping. It’s also great for astronomy.
“About all I can tell is that it was an attempt to produce very high-powered but wide-field cameras in space that would look down not in the visual part of the spectrum, but in the infrared part of the spectrum,” DeVorkin says.
The mirrors from the FIA program, despite its veil of secrecy, finally came to NASA in 2012.
When it did, NASA realized they might just have what it takes to build WFIRST.
Nancy Grace Roman Space Telescope vs. Hubble
NASA didn’t immediately assign the FIA mirrors to WFIRST.
“There were other useful, scientifically productive things we could have done with those telescope components,” Benford says. The space agency went through a methodical process to consider its options.
One such alternative proposal would see WFIRST continue with a 1.5-meter mirror as originally planned, and the gifted primary mirror used for a complimentary space telescope.
“We designed an ultraviolet optimized telescope with the assumption that WFIRST, in some form, would also exist to take over the near-infrared portions of Hubble,” Benford says.
Ultimately NASA settled on WFIRST as the best use for the new mirrors, and Benford joined the team in 2013 to help complete the concept study for the project, which was approved in 2016.
In the meantime, NASA was already working on the acquisition of necessary items such as the infrared detectors for the telescope while making some subtle adjustments to the mirrors.
“We received mirrors from the National Reconnaissance Office, but they weren’t exactly what we wanted them to be,” Benford says. “So we refigured them, changing their shape very, very slightly — literally less than a millimeter — to make the images we wanted for our infrared camera purposes.”
While the primary mirror of the FIA telescope is the same size as Hubble, it’s more advanced. DeVorkin says they weigh less than Hubble’s mirrors, and thus make for a lighter launch and are easier to get into higher orbits — for instance, stable orbital points called Lagrangian points, where the teeter-totter between the hefty Sun and much smaller Earth reach a sort of equilibrium or stalemate.
The newer mirror also enables a wider field of view than Hubble, a wider field of view than even the James Webb Space Telescope with its 6-meter diameter primary mirror, Roeland van der Marel tells Inverse.
Van der Marel is the lead of scientific operations for the telescope project at the Space Telescope Science Institute in Baltimore.
According to van der Marel, Hubble’s field of view is about 1/10th of the full moon — it stitches together larger images from multiple observations. The FIA telescope’s field of view is 100 times bigger than either Hubble’s or Webb’s, he says, so that it could take a picture of the full moon in a single shot. “That’s why it’s a survey telescope — really aimed at surveying large areas of the sky.”
It can also view 100 million stars at once by taking pictures of the same patch of sky every 15 minutes, and capture details of seven patches around it. That kind of wide-field view has unrivaled agility.
“We can cover about 200 times as much sky in a single picture, but we can also take the pictures substantially faster,” he says. In the first month, Benford says, it will take more images of the sky than Hubble has during its entire lifetime.
Once the development of WFIRST was well underway, it was given a new name in 2020 — the Nancy Grace Roman Space Telescope.
Who was Nancy Grace Roman?
The namesake of the telescope — Nancy Grace Roman — was one of the leading champions of a space telescope from the earliest days of NASA.
An astronomer who earned her Ph.D. at the University of Chicago in a time when few women had doctorates in astronomy (or any science discipline, for that matter), Roman worked at the Yerkes Observatory and Naval Research Laboratory before NASA hired her as its first program director for astronomy in 1959. Founded the year prior, the nascent space agency tasked her with getting astronomers interested in working at NASA.
But Roman became instrumental in pushing NASA to consider telescope projects, from the balloon-borne Stratoscope II telescope to NASA’s three Orbiting Astronomical Observatory satellites that operated from 1966 through 1972, and finally to the Hubble itself. Retiring from NASA in 1979, one of her last achievements was the formation of the Space Telescope Science Institute to manage the science of the Hubble mission.
Roman passed away in 2018, before the 2020 rechristening of WFIRST with her name, but DeVorkin, who interviewed Roman many times, said she would have been pretty happy about the telescope that now bears her name.
“Considering the legacy of the telescope she worked on for so many years, that the Hubble Space Telescope will be continued,” he says, “I think she would have been delighted.”
But there was a chance Nancy Grace Roman would not have had a telescope to be delighted by. The Trump administration’s Fiscal Year 2019 budget recommended slashing funding for the telescope, along with other NASA science programs and its office of education. Congress ultimately bucked the former president and not only declined to axe the space telescope, but gave NASA an 8 percent overall budget increase.
What are the Nancy Grace Roman Space science missions?
Roman is now WFIRST’s namesake, but its mission is the same, beginning with the investigations of dark energy.
The telescope's large, wide-field optics and electronics make up one of its two instruments, the Wide Field Instrument, which will be used in three ways to search for more information about dark energy:
The first method is to look at distant supernovae, van der Moral says, observations of which are what initially led to the concept of dark energy. Supernovae are an explosive end of life for certain stars, with a characteristic, intrinsic brightness, which can help “determine the distance and thereby map the geometry of the universe,” he says.
The second method is called weak gravitational lensing, a more subtle application of the gravitational lensing technique that uses a celestial object’s gravity field to view a more distant object behind it.
A large object’s mass distorts the space around it, which in turn bends the path of light from other objects passing around it. A distant galaxy, for instance, can act as a magnifying lens, bending and focusing the light from more distant galaxies behind it and bringing the distant object into clearer view, making it appear brighter or even resulting in multiple images of the distant object, according to van der Marel.
But in weak gravitational lensing, the foreground object’s gravity isn’t strong enough to increase the brightness or result in multiple images of a more distant object, such as another galaxy. Instead, “there is just a very subtle shearing of the background object shape,” van der Marel says. “Imagine as if a galaxy was drawn on cloth and you would slightly pull the cloth in one direction.”
The orientations of galaxy shapes should be random, he says, so subtle similarities should tell scientists about the shape of the universe rather than the galaxies themselves, and that shape is believed to be influenced by the presence of dark energy.
The third method the Nancy Grace Roman telescope will use to hunt for dark energy is known as baryon acoustic oscillations. The telescope will measure the “redshift” of distance galaxies, whose light is stretched into longer — and hence redder — wavelengths as they speed away from Earth’s point of view.
Accurate redshift measurements give the distances of galaxies, and “that gives you another measure of the distribution of the galaxies in the universe,” van der Marel says. Variations in the distribution of normal, “baryonic” matter in the universe, such as galaxies are the aforementioned acoustic osicllations, and are “directly tied to the geometry of the universe, which is tied to the dark energy presence in the universe,” he says.
But Roman isn’t just hunting for signs of dark energy, Benford notes: It’s also an exoplanet hunter.
How will the Nancy Grace Roman Space Telescope find exoplanets?
NASA’s Kepler and the Transiting Exoplanet Survey Satellite (TESS) space telescope were designed as dedicated exoplanet hunters, watching distant stars carefully to catch any dimming in their brightness caused by an orbiting exoplanet passing in front of, or transiting the stars face in relation to the telescope.
It’s a technique that has some drawbacks, Benford says. It can be very difficult to differentiate subtle differences in the perceived brightness of distant stars due to a transiting planet from the ordinary but similarly subtle changes in brightness the stars undergo all the time.
The Nancy Grace Roman Space Telescope will hunt for exoplanets using a powerful technique called microlensing. Rather than watch for signs of an exoplanet is passing in front of its star, the telescope will look for stars or planets passing in front of other stars in the background.
“The gravity of the foreground star, as we know from Einstein’s General Theory of relativity, will bend the light of the background star and act like a lens to focus the light of the background star on to us,” Benford says.
The result is that the foreground star — and its potential planets — will grow temporarily brighter during such an alignment, and the time it takes them to dim again is related to the foreground object’s mass.
“For a star lensing another star, it lasts for months,” Benford says. “But for a planet lensing a star, it lasts for days, or sometimes even an hour.”
This allows scientists to convert a hard problem — measuring the relative brightness of faint and distant objects — into the easier one of measuring time. It’s a technique that should be able to detect planets the size of Jupiter but possibly even smaller objects the size of Mercury, Benford says. The Nancy Grace Roman can watch 100 million stars at once for just such microlensing opportunities.
The other component of the Nancy Grace Roman telescope’s exoplanet-hunting mission relies on a different instrument, a coronagraph, an instrument designed to block out a bright object, such as a star, so you can see the fainter objects, namely exoplanets, nearby.
“If you want to see something like the Earth next to a star, the Earth would be a factor 10 billion less bright than the star next to it,” van der Marel says. “It's sort of like from a distance looking in a lighthouse and trying to see the firefly next to it, which is really, really hard.”
The Nancy Grace Roman telescope’s coronagraph won’t quite achieve the degree of contrast necessary to study an Earth-like world in detail, but it will still be able to detail some of the most distant exoplanets we’ve ever spotted. “That’s much better than what’s been done before,” he says. “It allows you to study somewhat brighter planets than Earth — think hot Jupiters and things like that.”
The future of looking into the distant past
In many ways, the new telescope-to-be serves as a way to look into the past without breaking the laws of physics. “All telescopes are ultimately time machines because light has a finite travel speed,” Benford says. “So the further you look, the further back in time you see.”
Taken together, Nancy Grace Roman’s two instruments and wide field of view will work synergistically with the James Webb Space Telescope to look wider and deeper into the cosmic past than ever before. Roman will scan for objects of interest, and Webb will zoom in on them.
“It’s one of the things we very much hope to do,” Benford says, “That Roman will serve to find objects that are the rare, very, very distant objects, and the Webb will teach us about them.”
“What makes me happiest about Roman is that it’s not a single-purpose type of instrument,” Benford says. “It’s really a survey that’s designed to serve the whole community in some many ways from the same dataset that wasn’t possible with Hubble or Webb before it.”
Rather than individual scientists booking telescope time to study one distant object, Nancy Grace Roman will use its wide field of view to study many objects at once, Benford adds, with the datasets made immediately available to all scientists and the public to study as they wish.
“We are going to try to usher in a new era, a new paradigm for astrophysics at these wavelengths, that’s never been possible before,” he says.
But what Benford says he is truly excited about isn’t the answers to longstanding questions the Nancy Grace Roman Space Telescope will provide.
It’s that “Roman will answer so many questions that we don’t even know to ask yet,” he says.