What Cosmic Secrets Will The Roman Telescope Reveal?

In 2025, the Roman Space Telescope will be launched to space to explore our galaxy and exoplanets, picking up where its predecessor Hubble left off.
Matthew S. Williams
Spitzer Space Telescope's view of the Milky Way's centerNASA/JPL-Caltech

In 2025, NASA will be stepping up its space-based astronomy game when it launches the Nancy Grace Roman Space Telescope - or Roman Space Telescope (RST) for short. Once it establishes a stable orbit at the Sun-Earth L2 Lagrange Point, it will join a host of other space observatories (some old, some new) that are similarly dedicated to searching for answers to the mysteries of the Universe.

For instance, the James Webb Space Telescope (JWST), scheduled to launch by October 31st, 2021, will work in tandem with Roman to investigate parts of the Universe that are only visible in the infrared wavelength. It will also join the three "Great Observatories" that are still in operation, including the Chandra X-Ray Observatory and the Compton Gamma Ray Observatory (CGRO).

But most importantly, the Roman Space Telescope will be joining its predecessor, the venerable Hubble Space Telescope. The RST was designed to be the designated successor mission to Hubble and build on the foundation its predecessor established.

The Roman incorporates a 2.4-meter (94.5-inch) primary mirror (same as Hubble), a multi-band camera capable of capturing light in the visible and near-infrared parts of the spectrum - the Wide-Field Instrument (WFI) - and a high-contrast camera/spectrometer equipped with starlight-suppression technology - the Coronagraphic Instrument (CGI). 

This combination of tried and true optics and cutting-edge technology will allow the NST to study the Universe with the same image sharpness as Hubble but with a field of view 100 times larger. So exactly what phenomena will Roman use these next-generation capabilities to study? What secrets is it expected to reveal?

An honored name

Initially, NASA was planning on calling this next-generation telescope the Wide-Field Infrared Space Telescope (WFIRST). The name was fitting, as it encapsulated the observatory's greatest features. However, on May 20th, 2020, NASA announced that they were going in a new direction and giving the WFIRST a proper name.

Like its predecessors, Hubble, Kepler, Spitzer, the Neil Gehrels Swift Observatory, and the soon-to-be-launched James Webb, NASA wanted a name that would reflect the nature of its mission while also paying homage to scientists who helped make it a reality. Since WFIRST would be the natural successor to Hubble, they appropriately decided to name it after the "Mother of Hubble."

The name honors Nancy Grace Roman, NASA’s first Chief Astronomer, a tireless educator and advocate for women in STEM, and the scientist who laid the groundwork for space telescopes. For her efforts, Roman was nicknamed "the mother of Hubble."

Born in Nashville, Tennessee, in 1925, Roman demonstrated an aptitude for astronomy early in life and decided to pursue astronomy as a career. Despite encountering resistance from countless people who told her, "girls don't become astronomers," she followed her dream to Swarthmore College, where she studied astronomy and worked at the Sproul Observatory. 

In 1946, she began her graduate work at the University of Chicago while researching at the Yerkes and McDonald Observatories (in Wisconsin and Texas), eventually earning a position as an assistant professor. But due to the lack of tenured positions available to women, she took a position at the Naval Research Laboratory (NRL) in 1954.

Within three years, Roman became the head of the ARLs microwave spectroscopy section due to her contributions to the emerging field of radio astronomy. She also traveled extensively to lecture about her research, which garnered the attention of the newly-formed National Aeronautical and Space Administration (NASA).

In 1959, she joined NASA, just six months after the agency was established, and became the Head of their Observational Astronomy program. As she would later write in a memoir published in 2018, "the chance to start with a clean slate to map out a program that I thought would influence astronomy for fifty years was more than I could resist."

By the 1960s, she became the first Chief of Astronomy in NASA's Office of Space Sciences (OSS). She traveled extensively across the US to speak directly to astronomy students and promote NASA programs. She also established a committee dedicated to realizing a space telescope that would be unfettered by atmospheric disturbances or weather.

During the many speeches and lectures she delivered over the years, she would challenge students to join a STEM field to satisfy their inborn curiosity. "If you enjoy puzzles," she once said, "science or engineering may be the field for you because scientific research and engineering is a continuous series of solving puzzles."

What Cosmic Secrets Will The Roman Telescope Reveal?
Nancy Roman at NASA. Credit: NASA/ESA

Her efforts eventually convinced NASA and the US Congress to make a space telescope a priority. In 1990, her dream was realized with the launch of the most revolutionary space telescope ever built - the Hubble Space Telescope. Because of the role she played in its creation, Dr. Roman earned the nickname "the Mother of Hubble."

As Hubble's designated successor, it seemed only natural that the WFIRST mission should be named in honor of Dr. Nancy Grace Roman - who passed away in 2018.

The Space Telescope Science Institute (STScI), located in Baltimore, which oversees Hubble's science operations, will also oversee the James Webb and Roman telescopes once they are in service. Dr. Kenneth Sembach, the director of the STSI, had this to say about the choice of name:

"Dr. Nancy Grace Roman was an accomplished scientist and leader, as well as a staunch advocate of Hubble and NASA’s other Great Observatories. She also strongly backed the creation of STScI. We thought of her as a colleague and friend, and were delighted to welcome her to the Institute for our annual spring science symposium in 2017...

"We are honored to be part of her continuing legacy. Our entire team stands ready to support the astronomical community and ensure that the Roman Space Telescope will achieve its full scientific potential."

A fitting successor

As noted, the RST will have the sensitivity and ability to cover a larger viewing area, effectively giving it the surveying power of "100 Hubbles." This is made possible by the telescope's 18 square detectors, each with 4096×4096 pixels, which allow the RST to cover an area roughly 1.33 times the size of a Full Moon (whereas Hubble covered an area of around 1% the diameter of a Full Moon).

The WFI relies on a 300-megapixel camera to capture images in the multi-band near-infrared part of the spectrum. The CGI, meanwhile, will suppress light coming from distant stars that would otherwise obscure the detection of smaller, dimmer objects. Taken together, these instruments will allow Roman to see parts of the Universe that would otherwise be invisible.

Another advantage the RST will have is its halo orbit at the Sun-Earth L2 Lagrange Point, about 1.6 million km (1 million mi) from Earth. This will give it an unobstructed view of the cosmos and the ability to conduct observations in an almost continuous fashion.

The RST is expected to collect about 20 petabytes (PB) of data during its five-year mission - that's 2.0×1016 bytes! To put that in perspective, the US Library of Congress (one of the largest libraries in the world) contains an estimated 15 terabytes (TB) of data - or 1.5×1013. This means that Roman will gather the equivalent of over 2,666 Libraries of Congress worth of data a year!

All told, the RST is expected to make multiple discoveries that will lead to advances in many fields of astrophysics. This will include discovering thousands of planets beyond the Solar System and characterizing them, which will help complete the growing census of exoplanets.

There's also the way it will enable astronomers to study comets, asteroids, dwarf planets, and "Ocean Worlds" right in our own backyard. Beyond all that, the RST will pierce the veil of the cosmic "Dark Ages" and reveal what was happening during the earliest epochs of the Universe.

In short, astronomers hope the RST will address some of the deepest and most daunting questions about our Universe - are we alone? How and when did it all begin? How has it evolved since? When did the first galaxies form? What do we really know about it all?

Objects closer to home

Roman's observations are expected to reveal a great deal about the Solar System and the types of objects it contains. This is particularly true of the Kuiper Belt, the massive ring of debris and iceteroids that resides at the edge of the Solar System. Using its IR filters, which will allow the telescope to image much of the near-infrared K band, which extends from 2.0 to 2.4 microns, Roman will be able to study these small, dark objects and get a better idea of their composition.

Much like the Main Asteroid Belt and the many other asteroid families in the Solar System, objects in this region are essentially leftover material from the protoplanetary disk that orbited our Sun roughly 4.5 billion years ago. This material, consisting of gases, silica, and heavier elements, was itself leftover material from the birth of the Sun.

Over the next few hundred million years, this material accreted to form the planets of our Solar System. Whereas denser, more rocky asteroids are found today in the Main Belt (or around various planets), the Kuiper Belt is thought to consist mainly of objects with higher volatile content (e.g., water, ammonia, methane, carbon dioxide, etc.). 

Since Kuiper Belt Objects (KBOs) have remained largely unchanged since the early days of the Solar System, studying them will reveal how our system formed and evolved. The study of this region would also provide greater insight into long-period comets, which are known to originate here and are believed to have played a vital role in the distribution of water throughout the Solar System.

It could also reveal more in the way of Trans-Neptunian Objects (TNOs), some of which could be large enough to be classified as Dwarf Planets (or Planetoids). Since the early 2000s and the discovery of TNOs comparable in size to Pluto (Sedna, Eris, Haumea, Makemake, etc.), scientists have wondered how many more of these smaller planets might be out there.

Objects next door

One of the most exciting things Roman will be able to do is directly image small, rocky planets that orbit closer to their stars. This is where "Earth-like" planets that orbit within a star's circumsolar habitable zone (HZ) are expected to be found. However, imaging these planets is rather difficult given the limits of current instruments.

This where Roman's advanced optics and coronograph technology will make all the difference. With the necessary sensitivity to resolve individual planets and block out the obscuring light of parent stars, as well as the interstellar dust and gas that absorbs visible light, the RST will be able to characterize their atmospheres, determine their chemical makeup, and identify potential signs of life (aka. "biosignatures.")

It will also work in concert with other observatories by using its infrared camera suite and its wide field of view to identify diverse objects for follow-up studies. Observatories like the JWST or Hubble will conduct these, taking advantage of their different range of imaging capabilities - e.g., the JWST can see more of the infrared spectrum.

Roman will also allow for exoplanet surveys using the Gravitational Microlensing method. This method takes advantage of an effect predicted by Einstein's General Theory of Relativity, where light from a distant source is amplified (or "lensed") by the gravitational force of an intervening object.

In this case, astronomers will use a "lens star" passing between their line of sight and a more distant "source star" to magnify the light coming from the latter. This allows them to detect orbiting planets based on the amplified light reflected by their atmospheres and surfaces.

Roman will also use the transit method. This is when the light from a star dims periodically because there is a planet crossing its face. By employing these two methods, NASA estimates that Roman could detect 100,000 exoplanets.

Roman's advanced IR suite will also allow it to study circumstellar debris disks. According to the most widely accepted theory, planets form from matter accreting from these disks. Unfortunately, such disks are very hard to visualize in visible light, but radiate brightly in the infrared spectrum. By viewing more of these systems, Roman will witness planetary systems that are still in the early phases of formation.

In the past, direct imaging and microlensing were rarely used for the sake of exoplanet research. Thanks to Roman's sensitivity and instruments, it will be able to complete the exoplanet census that Kepler began and gain a more comprehensive understanding of the architecture of planetary systems - which will yield clues about planetary formation and habitability.

At the heart of the Milky Way

Another part of the Universe that the Roman will shed light on is the center of our own galaxy. Right now, astronomers have a hard time observing the heart of the Milky Way because of the Interstellar Medium (ISM). Made up of dust and gas clouds that drift between stars, the ISM causes light to become scattered and absorbed.

Since the Solar System is embedded in the Milky Way's disk, we view the center of our galaxy edge-on. By the time that light has traveled from the heart of the galaxy to reach Earth (roughly 26,000 light-years), it is scattered to the point of being useless to our instruments. However, infrared light can pass more freely through these clouds because it travels in longer waves.

Roman’s IR filters will be able to pick up this light through dust clouds up to three times denser than before, which will help us learn more about the structure and population of the Milky Way. In particular, astronomers are looking forward to observing the center of our galaxy for brown dwarfs - a class of "failed stars" that weren't massive enough to undergo nuclear fusion.

It is well-known that when stars undergo gravitational collapse at the end of their lives (and explode in a supernova), they seed their surroundings with new elements that formed inside them over time. This process is believed to affect the formation of stars and planets near the galactic center.

What Cosmic Secrets Will The Roman Telescope Reveal?
Artist's rendering of the Nancy Grace Roman Space Telescope (RST). Source: NASA

By studying the compositions of brown dwarfs in this region, astronomers will learn more about objects near the heart of our galaxy and draw comparisons to those located in the spiral arms. Once again, this will provide valuable insight into how galaxies like ours evolve.

The "dark" universe

The RST will also observe billions of star systems and galaxies to map out their 3-D positions, which will allow astronomers to measure how their distribution has changed over time. In so doing, Roman will provide another means for measuring the rate at which the cosmos has been expanding (aka. the Hubble-Lemaitre Constant) over the past 13 billion years.

This could clear up discrepancies with previous measurements and allow astronomers to place tighter constraints on Dark Energy. It will also survey supernovae and galaxy clusters, mapping the distribution of galaxies in three dimensions. These studies will place tighter constraints on the role Dark Energy has played in cosmic evolution.

Roman will also use a technique known as weak gravitational lensing, where galaxies will alter the curvature of spacetime around them, causing light to bend as it passes by. This technique will be instrumental in measuring the mass of galaxies, providing new opportunities to test General Relativity and determine how much of them is Dark Matter.

According to current cosmological models, Dark Matter and Dark Energy account for 95% of the total mass–energy content of the Universe. Though these phenomena have been inferred from extensive observations and tests involving General Relativity, the full extent of its role in the evolution of the Universe remains uncertain.

To the beginning of time!

Roman's IR suite will allow it to observe light at frequencies ranging from the visible (V band) to the near-infrared K band. This corresponds to wavelengths of 0.5 to 2.3 microns (µm) and temperatures of up to 773 °C (1425 °F). As George Helou, the director of the Infrared Processing and Analysis Center (IPAC) at Caltech, explained:

"Roman will see things that are 100 times fainter than the best ground-based K-band surveys can see because of the advantages of space for infrared astronomy. It’s impossible to foretell all of the mysteries Roman will help solve using this filter."

In addition to fainter stars, debris disks, and brown dwarfs, these capabilities will allow Roman to study the Universe as it appeared just half a billion years after the Big Bang (thought to be about 4% of its current age). This coincides with the cosmic “Dark Ages,” when the first stars and galaxies formed, gradually dispelling the hot plasma that permeated the Universe. 

As the first galaxies formed, they released enough photons to dispel this plasma, which is what makes the early Universe "dark." By studying these structures as they emerged from the darkness, Roman will be able to study how these galaxies have evolved since and how matter is structured and distributed throughout the cosmos.

Exciting times ahead

As you may have gathered, the Roman Space Telescope has some ambitious goals to fulfill. On top of that, it has some rather big shoes to fill - coming as it is on the heels of Hubble and Kepler. Nevertheless, big things are expected for this aptly-named observatory, and what it is poised to reveal will be nothing short of groundbreaking.

After years (or decades) of waiting, scientists will finally be able to answer the kinds of questions that have kept them up at night. Questions like:

  • How did life begin in our Solar System?
  • Are there more habitable planets out there?
  • What lies at the heart of the Milky Way Galaxy?
  • How have galaxies evolved in the past 13 billion years?
  • What role has Dark Matter and Dark Energy played in cosmic evolution?

The RST is one of several next-generation observatories that will be taking to space in this decade. Several ground-based telescopes equipped with the latest optics and cutting-edge technology will also become operational before the 2020s are over. Combined with improvements in data sharing and analysis, it's unlikely any part of the Universe will be "dark" to us for long!

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