The radius of a planet is a crucial factor in understanding its composition and characteristics. Accurate radius measurements are generally obtained by analyzing the percentage of starlight blocked as the planet transits its host star. NASA’s Transit Exoplanet Survey Satellite (TESS) has identified hundreds of new exoplanets; however, its low angular resolution can lead to the mixing of light from stars hosting exoplanets with that of background stars. If not entirely corrected, this additional light may dilute the transit signal, leading to an underestimation of the planetary radius. In their analysis of the planet Tess, astronomers from the University of California, Irvine revealed that systematically incorrect planetary radii are frequently reported in scientific literature.

Artistic impression of a gas giant exoplanet and its parent red dwarf star. Image credit: Sci.News.

“We have discovered that many exoplanets are larger than previously thought, which shifts our understanding of exoplanet characteristics on a wide scale,” states Tae Han, a doctoral student at the University of California, Irvine.

“This suggests that we may have actually identified Earth-like planets that are fewer than we initially believed.”

Astronomers cannot directly observe exoplanets; they rely on the planets passing in front of their host stars to measure the subtle decrease in starlight.

“Essentially, we are measuring the shadows cast by planets,” remarks Paul Robertson, a professor at the University of California, Irvine.

In their study, the authors examined the observations of hundreds of exoplanets detected by TESS.

They found that light from neighboring stars could “contaminate” the light emitted by the stars under study.

This results in planets transiting in front of their stars appearing smaller than their actual size, receiving less light compared to larger planets.

Astronomers have conducted numerous studies explaining the characteristics of planets discovered by TESS.

They categorized the planets based on how different research teams measured their radii and used computer models to estimate the extent of bias resulting from light interference from adjacent stars.

Data from the ESA Gaia satellite was utilized to assess the impact of light contamination on TESS observations.

“TESS data is indeed contaminated, and our custom models perform better than any existing methods in the field,” stated Professor Robertson.

“What we discovered in this study is that these planets could be systematically larger than we initially assumed.”

“This raises the question: How common are Earth-sized planets?”

Previously, it was thought there were fewer planets resembling Earth in size.

“Among the single-planet systems identified by TESS, only three were believed to have a composition similar to Earth,” Han noted.

“This new finding indicates that all of them are larger than we previously thought.”

This implies that instead of rocky planets like Earth, they are more likely to be water worlds (planets entirely covered by vast oceans that are often larger than Earth) or larger gas giants like Uranus or Neptune.

This could have significant implications for the search for life on distant worlds, as water worlds may harbor life but lack the specific conditions necessary for life to thrive as it does on Earth.

“These insights have important consequences for our understanding of exoplanets, including prioritizing follow-up observations with the NASA/ESA/CSA James Webb Space Telescope and assessing the prevalence of water worlds in our galaxy,” concluded Professor Robertson.

The study was published in Astrophysical Journal Letters.

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Tae Han et al. 2025. Hundreds of TESS exoplanets may be larger than previously thought. ApJL 988, L4; doi: 10.3847/2041-8213/ade794