UC Irvine Study Reveals Exoplanets Larger Than Previously Estimated

Irvine, California, July 14, 2025 — A groundbreaking study conducted by astronomers at the University of California, Irvine (UCI) has revealed that over 200 known exoplanets are considerably larger than previously estimated. This research, published in the *Astrophysical Journal Letters*, marks a significant shift in understanding the potential habitability of these distant worlds, as many of them may not be the rocky planets akin to Earth that researchers had hoped to find.

According to Te Han, a doctoral student at UCI and the lead author of the study, "We found that hundreds of exoplanets are larger than they appear, and that shifts our understanding of exoplanets on a large scale." The research suggests that the number of Earth-like exoplanets may be even smaller than initially believed, raising questions about the criteria used to identify potentially habitable planets in the universe.

Astronomers face the challenge of observing exoplanets indirectly. They can only detect these distant bodies when they transit in front of their host stars, leading to a measurable decrease in the star's brightness. Paul Robertson, a professor of astronomy at UCI and co-author of the study, explained, "We're basically measuring the shadow of the planet." The data analyzed in this study came from NASA's Transiting Exoplanet Survey Satellite (TESS), which has been instrumental in cataloging exoplanets.

One of the key findings of Han’s team is that the light from neighboring stars can interfere with the light from the star being studied. This contamination can cause planets to appear smaller than they truly are, as smaller planets block less light than their larger counterparts. To assess the degree of this light contamination, Han compiled observations from numerous studies involving exoplanets cataloged by TESS and utilized a sophisticated computer model to estimate the biases in the measurements of the exoplanets' sizes.

The team corroborated their findings using data from another satellite mission, Gaia, which helped to quantify the extent of the contamination affecting TESS observations. "TESS data are contaminated, which Te's custom model corrects better than anyone else in the field," noted Robertson. The implications of this research are profound, as it suggests that many planets previously thought to be similar in size to Earth might instead be categorized as larger, possibly oceanic worlds or even gas giants like Uranus or Neptune.

With the number of exoplanets considered potentially Earth-like already limited, the revised understanding indicates that none of the three single-planet systems discovered by TESS are Earth-sized. The study raises critical considerations regarding the search for extraterrestrial life, as while water worlds may support life, they often lack the geological features conducive to flourishing ecosystems.

This research could significantly impact future observations with the James Webb Space Telescope and the ongoing discourse regarding the existence of a galactic population of water worlds. The findings may also prompt researchers to re-evaluate previously classified uninhabitable planets based on their sizes.

The research was supported by funding from NASA and illustrates UCI's commitment to advancing our understanding of the universe. Founded in 1965, UCI is recognized for its academic excellence and innovative research initiatives, contributing substantially to the scientific community's knowledge of astrophysics and exoplanet studies. The next steps for Han and his team involve leveraging this new data to guide future research and refine methodologies for interpreting satellite observations, ensuring that scientists approach the study of exoplanets with heightened caution.

As the quest for identifying habitable worlds continues, the findings from UC Irvine's research herald a new chapter in exoplanet exploration, encouraging a more nuanced perspective on the potential for life beyond Earth.