NASA’s Nancy Grace Roman Space Telescope is expected to dramatically expand the search for planets outside our solar system, known as exoplanets. Scientists estimate that the mission will discover about 100,000 previously unknown worlds, a significant increase compared to the approximately 6,300 exoplanets discovered to date through NASA missions and other observatories.
What’s especially exciting about Roman is where it shows up. Most exoplanet discoveries to date have come from relatively nearby regions of the galaxy. However, Roman will explore a largely unexplored region of the Milky Way galaxy and provide a broader view of planetary systems across the galaxy.
“There are many environments in our galaxy, but when it comes to searching for exoplanets, we’ve only really explored one: our own neighborhood,” said Elisa Quintana, an exoplanet researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Quintana leads a team focused on building software and simulations to help prepare Roman for exoplanet transit observations. “Roman plans to expand his research to other galactic habitats, which could help us learn how planet formation varies in different regions of the Milky Way.”
Currently, most known exoplanets are located within a few thousand light years of Earth. One of Roman’s major investigations will extend far beyond that range, examining stars through the Milky Way’s dense central bulge, to the far side of the galaxy.
Explore the Milky Way and find new worlds
Roman will continuously monitor stars across a wide swath of the Milky Way, looking for changes in their brightness.
One technique relies on transits of planets. When a planet passes in front of a star from our perspective, it blocks a small amount of starlight, temporarily dimming the star.
The telescope also uses a second technology called microlensing. In these phenomena, the gravitational pull of the foreground star and its accompanying planet magnifies the light of more distant background stars, making them appear temporarily brighter.
Each method corresponds to different types of planets.
This transit technique is expected to discover around 100,000 worlds and is particularly effective at detecting large, extremely hot planets. These planets are easier to spot because they block more light from the star and complete their orbits more frequently.
Microlensing, which is expected to reveal more than 1,000 worlds, excels at finding planets far from stars, including systems similar to our solar system. It can detect not only planets in the habitable zone but also planets as small as Earth or Mars far away from the star. Many of these worlds are very difficult or impossible to find using other detection methods.
Combining these complementary approaches will allow scientists to investigate how planets form throughout the galaxy, including the region where our solar system may have originated.
Clues to the origin of the earth
Currently, our solar system is approximately 27,000 light-years from the center of the Milky Way galaxy. Researchers believe it likely formed about 10,000 light-years closer to the galaxy’s center and then gradually moved outward to reach its current location.
Evidence for this idea comes primarily from the chemical composition of the Sun.
Astronomers use the term heavy elements to describe all elements other than hydrogen and helium that were created shortly after the formation of the universe. Heavier elements are produced inside stars, and more elements are produced over time as stars live and die through successive generations.
Stars in the outer regions of galaxies generally contain few heavy elements. In contrast, stars within the galactic bulge tend to be older and rich in elements such as silicon, oxygen, and magnesium.
These chemical differences can affect the types of planets that form around stars. Some systems may produce larger planets, more rocky worlds, or perhaps more planets overall. In some cases, a star’s composition can even influence whether planets form.
Astronomers have already found evidence that such relationships exist between nearby stars.
“Stars with heavier elements tend to host more planets, especially giant planets,” said Robbie Wilson, a postdoctoral researcher at NASA Goddard who led the study on Roman’s expected abundance of transiting planets.
By examining disparate populations of stars and planets across the Milky Way, Roman could greatly extend these studies and help reveal how planetary systems like ours actually have something in common.
“Roman will be particularly powerful because it will observe hundreds of millions of distant stars, allowing scientists to compare populations of distant planets with populations of planets found nearby,” Wilson said. “All of this data requires us to scrutinize, so we’re preparing by creating synthetic data, detecting simulated planets, and using machine learning to filter out false positives so we can react quickly when real data comes in.”
All data collected by Roman will be made available to the public, allowing researchers and citizen scientists alike to participate in exploring new worlds.
Studying alien atmosphere and weather
Roman also has the potential to provide atmospheric information for the thousands of transiting planets it discovers.
“While Roman won’t analyze the atmosphere in the same detailed way as missions like NASA’s James Webb Space Telescope, it will collect a much larger variety of information,” Wilson said.
While the James Webb Space Telescope focuses on detailed chemical analyzes of individual planets, Roman will investigate broader temperature and climate patterns across thousands of worlds. This large statistical dataset can identify important trends and help guide future observations by Webb and other observatories.
One of the focuses is Hot Jupiter, a giant planet roughly the same size as Jupiter that orbits extremely close to the star. Jupiter is about 11 times the width of Earth, so these worlds are huge and often complete one orbit in just a few days. High temperatures emit detectable infrared radiation.
Roman’s infrared instruments will be able to observe these glowing planets and study how their brightness changes over time.
When hot Jupiter passes in front of the star, astronomers observe a slight decrease in brightness. The second small dip occurs when the planet moves behind the star, temporarily blocking its light.
“This secondary dip tells us how bright the Earth is, and therefore how hot it is,” Wilson said. “By tracking how the planet’s brightness changes throughout its orbit, Roman can also see the difference between its day and night sides and detect changes in where the hottest regions on Earth are. This can tell us about wind and heat circulation in the atmosphere.”
A new era of exoplanet discovery
NASA’s Kepler mission transformed exoplanet science by monitoring nearly 100,000 stars and demonstrating that planets are extremely common throughout the Milky Way.
“NASA’s now-retired Kepler mission’s survey of 100,000 stars revolutionized the field of exoplanets more than a decade ago and taught us that planets are even more common than stars in our galaxy,” said Jorge Martínez Palomera, a NASA Goddard astronomer who is helping prepare Roman’s exoplanet data.
Roman is expected to build on that tradition. The Galactic Bulge survey alone will observe approximately 100 million stars while exploring a largely uncharted region of the Milky Way.
“Roman’s Galactic Bulge survey will observe approximately 100 million stars and explore an unexplored region of the Milky Way. It will provide a foundational data set that will revolutionize our knowledge of other worlds and our place in the universe as well.”
