Just as Saturn is ringed by hundreds of globe-shaped moons, giant planets across the Milky Way might be surrounded by exotic exomoons, including some that are habitable, astronomers predict. (Photo by Space Frontiers/Hulton Archive/Getty Images)
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Astronomers are eagerly anticipating the deployment of the recently launched Roman Space Telescope to survey the Milky Way for potentially habitable alien moons, according to one of the telescope’s lead scientists.
Professor B. Scott Gaudi, who leads the NASA Roman Galactic Exoplanet Survey team, explained that the galaxy likely harbors trillions of moons, with some situated in the temperate zones of their host stars, making them potential candidates for supporting life.
“In our own Solar System, all of the giant planets possess numerous moons,” Gaudi noted, adding that NASA estimates the Milky Way contains approximately 400 billion star systems.
Using the most advanced camera ever deployed in space, this forthcoming galactic survey could identify up to 200,000 planets, Gaudi predicts. This includes rogue planets and moons that have been ejected from their original star systems.
Gaudi, the Thomas Jefferson Professor for Discovery and Space Exploration at The Ohio State University, stated that his team will focus on identifying habitable moons within nearby sectors of the galaxy.
Recognized for his exceptional leadership as the ExoPlanet Program Analysis Group Chairperson, Gaudi was awarded the NASA Outstanding Public Leadership Medal. He is poised to be at the forefront of these critical astronomical searches.
In a groundbreaking paper titled “Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. III. Detectability of Giant Exomoons of Wide Separation Giant Planets,” Gaudi and his co-authors noted: “The presence of an exomoon may impact the habitability of its host planet and exomoons may themselves be habitable.”
Gaudi explained that Earth’s Moon enhances our planet’s habitability by stabilizing its axial spin.
Without this stabilizing effect, a wobbly axis could lead to severe climatic shifts, potentially triggering ice ages and rendering the planet less hospitable to life.
However, Gaudi acknowledged a counter-argument: over the past 4 billion years, the Moon has gradually slowed Earth’s rotation.
Early in its history, Earth is estimated to have spun much faster, completing a full rotation in roughly 10 hours. This rapid rotation would have provided significant gyroscopic stability.
“The detection of moons with masses similar to the giant moons in our Solar System is possible with Roman,” Gaudi stated, highlighting the telescope’s advanced capabilities.
As space-based telescopes grow more powerful and sophisticated, astronomers anticipate they will be able to identify life-friendly moons orbiting nearby stars, reminiscent of the fictional moon Pandora from the blockbuster film Avatar.
“If Pandora existed, we potentially could detect it and study its atmosphere in the next decade,” astrophysicist Lisa Kaltenegger said in a press release from the Harvard-Smithsonian Center for Astrophysics, where she was formerly based.
“If Pandora existed, we potentially could detect it and study its atmosphere in the next decade,” said astrophysicist Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University. Shown here is the fantastical moon-world Pandora, from the blockbuster firm Avatar, recreated by Walt Disney in Florida. (Photo by Gustavo Caballero/Getty Images)
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Kaltenegger, currently the director of the Carl Sagan Institute at Cornell University, added, “So far, planet searches have spotted hundreds of Jupiter-sized objects in a range of orbits.”
She explained, “Gas giants, while easier to detect, could not serve as homes for life as we know it. However, scientists have speculated whether a rocky moon orbiting a gas giant could be life-friendly, if that planet orbited within the star’s habitable zone.”
Comparing them to the giant satellites orbiting Jupiter, Kaltenegger predicted that alien Jupiters and Saturns could also be orbited by massive moons.
“Some of those may be Earth-sized and able to hold onto an atmosphere,” she noted.
Furthermore, Kaltenegger explained that the atmospheres of these alien moons could be studied using a telescope’s spectrograph. This instrument can detect life-related chemical signatures such as oxygen, ozone, methane, and water vapor.
She suggested that astronomers initiate these surveys at Alpha Centauri, the closest star system at just four light-years away and the fictional home of the Avatar moon Pandora.
In her paper, “Characterizing Habitable Exo-Moons,” Kaltenegger forecasted that astronomers would soon begin identifying habitable moons. “Transmission spectroscopy of Earth-like exomoons is a unique potential tool,” she wrote, “to screen them for habitability in the near future, especially for M [dwarf] stars.”
Despite the confirmation of over 6,000 exoplanets and the recent detection of 10,000 more candidate planets, Gaudi emphasized that comparatively little is known about their companion moons.
Professor Scott Gaudi says despite the discovery of thousands of exoplanets, comparatively little is known about their companion moons. Shown here is an artist’s conception of habitable-zone planets similar to Earth. (Photo by: Universal History Archive/ Universal Images Group via Getty Images)
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He noted that the moons of the icy giants in the outer Solar System have “orbits that are roughly circular and coplanar to the equator of the planet, likely indicating that they were formed concurrently with the planet in a circumplanetary disk.”
The Roman Space Telescope’s upcoming survey of the Milky Way, he added, could rapidly expand our understanding of the physical processes governing planet and moon formation throughout the cosmos.
Gaudi explained that Roman Telescope scientists will employ a variety of methods to detect exoplanets and exomoons, including observing transit events where planets cross in front of their host stars, creating repeated patterns of partial light eclipses.
Nearby planets may also be directly imaged using the Roman Telescope’s cutting-edge 300-megapixel camera.
Additionally, some astronomers will utilize the more experimental technique of gravitational microlensing, a concept derived from Albert Einstein’s General Theory of Relativity.
Einstein hypothesized that massive objects—such as a cluster of galaxies, a single galaxy, or even a lone star—warp the fabric of spacetime. This warping can act as a natural lens, magnifying stellar systems aligned behind them.
These massive, naturally occurring lenses, fortuitously distributed throughout the cosmos, enable astronomers to detect and map distant, gravitationally magnified galaxies.
On a smaller scale, individual stars can be utilized in gravitational microlensing to search for planets and moons that align with and pass in front of a background star.
Gaudi indicated that the majority of searches will rely on detecting transits within star-planet-moon systems. Transits occurring in relatively nearby galactic sectors may allow scientists to use spectrographs to analyze the atmosphere of a passing planet, characterizing its chemical composition and searching for potential biomarkers like oxygen and H2O.
While transit searches to date have primarily detected giant planets in close proximity to their stars, Gaudi noted that the Roman Space Telescope, coupled with microlensing techniques, will be capable of identifying smaller, rocky planets—and potentially their moons—that orbit at greater distances from their host stars.
When asked if it might be possible to directly capture images of a super-sized moon using the telescope’s massive camera:
Launch of the Roman Space Telescope aboard a SpaceX Falcon Heavy rocket. (Photo by Joel Kowsky/NASA via Getty Images)
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Gaudi predicted that directly imaging giant moons might be achievable with the next-generation Habitable Worlds Observatory.
A notable feature of the Roman Space Telescope’s galactic survey, Gaudi mentioned, is that its continuous stream of data and images will be openly released to the scientific community in real time as it is collected.
While conducting his own research, Gaudi plans to utilize an array of artificial intelligence tools to filter and characterize the most promising planet and moon candidates from the raw imagery.
If the Roman Space Telescope’s mission is extended after five years, it could provide opportunities for more refined searches for giant moons orbiting giant planets during the galactic survey, he explained.
This extension, however, will depend on the telescope’s remaining fuel. Gaudi noted that it might be possible to robotically refuel the observatory—which is already equipped with a docking mechanism for servicing missions—potentially extending its operational lifetime into the 2030s.
Through a series of increasingly sophisticated space telescopes and surveys, NASA’s ultimate goal is to identify habitable planets by searching for biosignatures (traces of life) and technosignatures (indicators of advanced civilizations), explained Dr. Bertrand Mennesson, the Roman Telescope’s Deputy Project Scientist, in a recent interview.
Dr. Mennesson, who earned a doctorate in astrophysics and space techniques from the University of Paris VII, has spent decades spearheading the search for extraterrestrial life.
Since 2000, he has helped guide NASA’s Jet Propulsion Laboratory in developing a succession of cutting-edge observatories.
In addition to assisting with the Roman Telescope’s launch preparations, he serves as the science co-chair of the Habitable Worlds Observatory Technical Assessment Group.
An artist’s illustration of a transiting exoplanet and exomoon about to partially eclipse their star. (Photo by Future Publishing via Getty Images)
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According to NASA scientists, the next-generation Habitable Worlds Observatory will focus on discovering Earth-like planets located within the habitable zones of their respective stars.
This advanced observatory will have the capability to directly image nearby Earth analogs as photons from their host stars reflect off their surfaces and pass through their atmospheres.
During its galactic survey, the Habitable Worlds Observatory will aim to determine “the fraction of the planets being habitable, and the fraction of these habitable planets being actually inhabited,” Dr. Mennesson stated.
“We will design future missions to objectively answer whether life as we understand it is rare or common in the solar neighborhood,” he added.
The Habitable Worlds Observatory, Dr. Mennesson concluded, will actively search for biosignatures “that may indicate that life, as we understand it, exists.”