NASA’s Roman Telescope could reveal 100,000 hidden worlds and rewrite what we know about planets across the Milky Way.
NASA’s Nancy Grace Roman Space Telescope is expected to dramatically expand humanity’s catalog of worlds beyond our solar system. Known as exoplanets, these distant planets number nearly 6,300 discoveries so far through NASA missions and other observatories. Scientists estimate Roman could add around 100,000 more to that total.
What makes the mission especially exciting is where it will look. Most of the planets Roman discovers are expected to be located in regions of the Milky Way that have received little attention from previous exoplanet surveys.
“Our galaxy is home to a variety of different environments, but when it comes to hunting for exoplanets, we’ve really only 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 for Roman’s exoplanet transit observations. “Roman will extend the search far enough to encompass other galactic habitats, which could help us learn how planet formation varies across different regions of the Milky Way.”
Most known exoplanets orbit stars within a few thousand light-years of Earth. Roman, however, will look much farther. One of the telescope’s primary surveys will examine stars throughout the Milky Way’s densely packed central bulge and continue all the way toward the outer reaches of the galaxy’s far side.
Searching the Galaxy for New Worlds
Roman will monitor millions of stars and watch for changes in their brightness.
One technique involves detecting slight dips in starlight when a planet passes in front of its host star. These events are known as transits. Another approach relies on a phenomenon called microlensing, in which the gravity of a star and its planets briefly magnifies the light from a more distant star, making it appear brighter.
Each method is particularly effective at finding different kinds of planets.
Using the transit method, Roman is expected to discover around 100,000 planets. This technique works especially well for large, extremely hot planets because they block more starlight and cross in front of their stars more often.
Microlensing is expected to uncover more than 1,000 additional planets. It is particularly useful for finding worlds that orbit farther from their stars, including planets with arrangements more similar to those found in our own solar system. Because microlensing can separate a planet’s gravitational influence from that of its host star, it can detect worlds as small as Earth or Mars.
The technique can also find planets within a star’s habitable zone and even farther out. Many of these distant worlds are nearly impossible to detect using other methods and remain largely unexplored beyond our solar system.
Together, the transit and microlensing surveys will provide a broader view of how planets form and evolve throughout the Milky Way, including in the region where our own solar system may have originated.
Exploring Earth’s Cosmic Origins
Today, the solar system sits about 27,000 light-years from the center of the Milky Way. Scientists believe it formed roughly 10,000 light-years closer to the galactic center before gradually moving outward to its current location.
Evidence for that migration comes largely from the Sun’s chemical composition.
Astronomers refer to all elements heavier than hydrogen and helium as heavy elements. Hydrogen and helium formed shortly after the birth of the universe, while heavier elements were created inside stars. As generations of stars live and die, these heavier elements become more abundant.
Stars located in the outer parts of the Milky Way generally contain fewer heavy elements. By contrast, stars in the galactic bulge tend to be older and richer in elements such as silicon, oxygen, and magnesium.
Those chemical differences may have a major impact on the planets that form around those stars. Some planetary systems may produce larger planets, rockier worlds, or different numbers of planets altogether.
Astronomers have already found evidence that stellar composition influences planet formation.
“Stars with more heavy elements tend to host more planets, especially giant ones,” said Robby Wilson, a postdoctoral fellow at NASA Goddard, who led a study about Roman’s expected transiting planet yield.
By examining entirely different populations of stars and planets, Roman could significantly deepen scientists’ understanding of how common planetary systems like our own are throughout the galaxy.
“Roman will be especially powerful because it will observe hundreds of millions of distant stars, letting scientists compare faraway planet populations to those found nearby,” said Wilson. “All of that data will give us a lot to comb through, so we’re prepping by creating synthetic data, detecting simulated planets, and using machine learning to filter out false positives. That way we’ll be ready to go right away when real data comes pouring in.”
All data collected by Roman will be publicly available, allowing professional astronomers and citizen scientists alike to participate in the search for new worlds.
Studying Alien Weather and Atmospheres
Beyond discovering planets, Roman may also provide information about the atmospheres of several thousand transiting worlds.
“Roman won’t analyze atmospheres in the same in-depth way as missions like NASA’s James Webb Space Telescope, but it will gather different information on a much larger scale,” Wilson said.
While telescopes such as Webb focus on detailed chemical studies of individual planets, Roman will look at broader atmospheric trends across thousands of worlds. Researchers will be able to compare temperatures, climate patterns, and other atmospheric characteristics on a scale that has never been possible before.
The telescope’s infrared instruments will be particularly useful for studying so-called hot Jupiters. These giant planets are similar in size to Jupiter, which is around 11 times as wide as Earth, but orbit their stars in just a few days. Their high temperatures cause them to emit detectable infrared radiation.
When a hot Jupiter passes in front of its star, astronomers observe a dip in brightness. A second, smaller dip occurs when the planet moves behind the star and its own light is temporarily blocked.
“That secondary dip tells us how bright, and therefore how hot, the planet is,” said Wilson. “By tracking how the planet’s brightness changes over its orbit, Roman can also see differences between the day side and night side, and even detect shifts in where the hottest region is on the planet. That tells us about atmospheric winds and heat circulation.”
Building the Next Exoplanet Revolution
Astronomers believe Roman could have an impact similar to that of NASA’s Kepler Space Telescope, which transformed exoplanet science more than a decade ago.
“NASA’s now-retired Kepler mission’s survey of 100,000 stars revolutionized the field of exoplanets over a decade ago, and taught us that planets are even more common than stars in our galaxy,” said Jorge Martínez-Palomera, an astronomer at NASA Goddard who is helping prepare for Roman’s exoplanet data. “Roman’s galactic bulge survey will observe around 100 million stars and probe underexplored areas of our galaxy, which will provide a foundational dataset that will likewise revolutionize what we know about other worlds and our place in the universe.”
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