A celestial body’s radius serves as a crucial indicator deciphering its material makeup and potential for life. Precise delineations of planetary radii are predominantly obtained by quantifying the reduction in stellar radiance when a planet traverses the face of its parent star. NASA’s Transiting Exoplanet Survey Satellite (TESS) has been instrumental in identifying numerous new exoplanets; however, its limited angular resolution poses a challenge, as the luminescence from a star harboring a transiting exoplanet can become intermingled with discernible emissions from background stars. If this extraneous light is not adequately accounted for, it can attenuate the transit signature, leading to an underestimation of the planet’s actual radius. Through an examination of TESS-identified exoplanets, researchers affiliated with the University of California, Irvine, have posited that systematically erroneous planet radii are prevalent within scientific discourse.
An artist’s impression of a gas-giant exoplanet and its parent red dwarf star. Image credit: Sci.News.
“Our findings indicate that a substantial number of exoplanets are in fact larger than initially perceived, thereby necessitating a recalibration of our broad understanding of these celestial entities,” stated Te Han, a doctoral candidate at the University of California, Irvine.
“Consequently, it is plausible that the count of Earth-analogous planets identified to date may be less than previously estimated.”
Direct observation of exoplanets remains beyond our current capabilities. Astronomers must await the infrequent event wherein a planet intercepts the path of its host star, at which point they meticulously measure the minuscule diminution in stellar luminosity.
“Essentially, we are observing the celestial body’s shadow,” commented Professor Paul Robertson of the University of California, Irvine.
Within the scope of their investigation, the authors meticulously analyzed observational data pertaining to hundreds of exoplanets cataloged by TESS.
It was determined that luminary contributions from proximate stellar sources can ‘contaminate’ the light spectrum originating from the target star under scrutiny.
This phenomenon can create the illusion that a transiting planet is smaller than its true dimensions, given that lesser volumes of light are occluded by more diminutive celestial bodies.
The research team meticulously compiled an extensive corpus of academic publications detailing exoplanets discovered by the TESS mission.
These exoplanets were systematically categorized based on the methodologies employed by various research cohorts in determining their radii, facilitating an estimation, augmented by computational modeling, of the extent to which these measurements might be skewed due to radiative ingress from neighboring stars.
Data procured from the European Space Agency’s Gaia satellite were leveraged to ascertain the degree of light contamination impacting TESS observations.
“TESS data are subjected to contamination, a situation our bespoke computational model addresses with unparalleled efficacy within the field,” Professor Robertson remarked.
“The central conclusion of our investigation is that these celestial bodies may, in a systematic fashion, possess larger radii than our initial assessments suggested.”
“This discovery prompts a pertinent query: to what extent do Earth-sized planets populate the cosmos?”
The cohort of exoplanets considered comparable in size to Earth was already relatively limited.
“Among the single-planet systems exclusively identified by TESS thus far, a mere trio were initially believed to exhibit compositional similarities to Earth,” Han elaborated.
“With the advent of this new finding, the actual sizes of all these planets exceed our prior estimations.”
This implies that, rather than being terrestrial planets akin to Earth, these exoplanets are more likely to be classified as so-called water worlds (celestial bodies predominantly covered by a singular, expansive ocean, which tend to be larger than Earth) or even more substantial, gaseous entities comparable to Uranus or Neptune.
Such revelations could significantly influence the ongoing endeavor to detect extraterrestrial life on distant worlds, as while water worlds might indeed harbor life, they may also lack the specific environmental characteristics conducive to the flourishing of life as observed on Earth.
“These findings carry profound implications for our comprehension of exoplanetary systems, impacting, among other aspects, the prioritization for subsequent observational campaigns utilizing the NASA/ESA/CSA James Webb Space Telescope, and the ongoing debate surrounding the existence of a galactic population of water worlds,” Professor Robertson articulated.
This research endeavor was formally published in the esteemed journal, the Astrophysical Journal Letters.
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Te Han et al. 2025. Hundreds of TESS Exoplanets Might Be Larger than We Thought. ApJL 988, L4; doi: 10.3847/2041-8213/ade794
