Researchers from UNSW Sydney have identified a possible new exoplanet-an extrasolar planet-through an approach called transit timing variation (TTV). This technique enabled them to detect subtle shifts in the orbital timing of a known planet, hinting at the presence of another planetary body.
Published in The Astrophysical Journal, the study, led by Scientia Senior Lecturer Ben Montet and by Simon Mansfield
Sydney, Australia (SPX) Mar 05, 2025
Researchers from UNSW Sydney have identified a possible new exoplanet-an extrasolar planet-through an approach called transit timing variation (TTV). This technique enabled them to detect subtle shifts in the orbital timing of a known planet, hinting at the presence of another planetary body.
Published in The Astrophysical Journal, the study, led by Scientia Senior Lecturer Ben Montet and PhD candidate Brendan McKee, examined transit anomalies in the orbit of the hot Jupiter TOI-2818b. The research team at the UNSW School of Physics employed simulation models that suggested a second planet could be influencing the known exoplanet's motion.
According to their findings, the newly inferred planet is estimated to be 10-16 times Earth's size and completes an orbit in less than 16 days.
"It's rare for hot Jupiters to have nearby planetary companions," said Dr. Montet. "The existence of this new planet could reshape our understanding of how these gas giants form, shedding light on planetary system development beyond our own."
Tracking exoplanets
Exoplanets are celestial bodies that orbit stars outside our solar system. While over 5,500 exoplanets have been confirmed by NASA, it is believed that trillions more exist within the Milky Way. Among these, only about 500 are classified as hot Jupiters-gas giants with close orbits around their stars. Even rarer are additional planets that share a host star with a hot Jupiter.Transit timing variation (TTV) is a method used to detect such planets by analyzing how their presence affects the observed brightness of their host star.
"A planet passing in front of its star, as seen from Earth, causes a temporary dip in the star's brightness, similar to an eclipse," explained McKee. "We can track these dips, which recur with each orbit, to determine the planet's transit timing."
Dr. Montet likened this effect to "a planet casting a shadow on its star, causing a brief dimming of its light." Since planetary orbits are expected to remain consistent, any deviation in transit timing may indicate gravitational influence from another unseen planet.
Decoding orbital disruptions
McKee examined three years of data from NASA's Transiting Exoplanet Survey Satellite (TESS). He focused on TOI-2818b, a hot Jupiter located over 1,000 light-years away in the constellation Puppis, first identified via transit observations. However, his analysis revealed an unexpected pattern-the planet's transits were occurring slightly earlier with each orbit."If TOI-2818b were a clock, it was losing time," McKee noted. "This discrepancy suggested that an external factor was influencing its orbit."
There are several possible explanations for such anomalies. One theory involves tidal interactions between a planet and its star, which could cause orbital decay, leading the planet to gradually spiral inward.
"We had to eliminate alternative explanations before concluding that another planet was responsible," Dr. Montet said. "Our models ruled out these possibilities, leaving only the presence of a secondary planet as a viable explanation."
Insights into planetary formation
Exoplanet research has evolved rapidly since the first discoveries in the 1990s. While no Earth-like, habitable exoplanets have been confirmed, scientists have identified rocky planets within the habitable zones of their stars, where conditions may allow for liquid water."Many questions about exoplanets remain unanswered," said Dr. Montet. "Each discovery presents new challenges to our understanding of planetary formation. Hot Jupiters, in particular, are still somewhat of a mystery."
Two dominant theories explain how hot Jupiters form. One involves a chaotic, unstable process that can eject other planets from the system. The other is a smoother, gradual migration toward the host star.
"If hot Jupiters often have companion planets, it would suggest a more gradual migration process," Dr. Montet explained. "If they lack companions, it implies chaotic scattering is more common. Current evidence supports a mix of both processes, but further studies are needed to determine which dominates."
Continuing the search
While the TTV method strongly indicates the presence of an additional planet around TOI-2818b, many details remain uncertain. "There are still several possible scenarios consistent with our simulations," said McKee.Future observations, particularly with the ESPRESSO instrument on the Very Large Telescope (VLT) in Chile, operated by the European Southern Observatory (ESO), will help refine the planet's characteristics.
"ESPRESSO data has already helped rule out alternative explanations, such as a brown dwarf's influence," Montet noted. "With further observations, we hope to pinpoint this hidden planet's exact nature."
As planetary research advances, new discoveries continue to reshape our understanding of the universe. "Each newly identified planetary system challenges our expectations," Montet added. "As technology improves, we'll uncover even more surprises in the coming decades."
Collaboration remains key to advancing exoplanetary science. "There are far more planets than there are astronomers," Montet emphasized. "By working together-across established research institutions and through citizen science initiatives-we can unlock some of the greatest mysteries of the cosmos."
Research Report:A Planet Candidate Orbiting near the Hot Jupiter TOI-2818 b Inferred through Transit Timing
Related Links
University of New South Wales
Lands Beyond Beyond - extra solar planets - news and science
Life Beyond Earth