NASA's TESS Reveals Exoplanets May Be Larger Than Previously Estimated

In a significant development in the field of exoplanet research, astronomers from the University of California, Irvine (UCI) have uncovered that many exoplanets identified by NASA's Transiting Exoplanet Survey Satellite (TESS) may be larger than previously thought. This revelation, published on July 15, 2025, in the Astrophysical Journal Letters, raises important questions regarding the classification of these celestial bodies and their potential for hosting life.

The TESS mission, launched in April 2018, aims to discover new exoplanets by monitoring the brightness of stars and detecting dips in light caused by planets transiting in front of them. However, the low angular resolution of TESS can lead to light contamination from background stars, which can result in inaccurately small measurements of exoplanet radii. According to Te Han, a doctoral student at UCI and 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 study analyzed hundreds of exoplanet discoveries made by TESS, scrutinizing the methods used by various research teams to measure the radii of these planets. The researchers utilized data from the European Space Agency's Gaia satellite to develop a computer model that corrects for light contamination. "TESS data are contaminated, which the custom model corrects better than anyone else in the field," noted Professor Paul Robertson from UCI, a co-author of the study.

The implications of these findings are profound. Initially, the number of exoplanets believed to be similar in size to Earth was already low. With the new findings suggesting that all previously identified Earth-sized candidates may actually be larger, the classification of these planets could change dramatically. Instead of being rocky planets akin to Earth, they may be categorized as water worlds—planets predominantly covered by oceans—or gaseous giants similar to Uranus and Neptune.

This shift not only affects the understanding of exoplanet composition but also has significant ramifications for the search for extraterrestrial life. Water worlds, while potentially harboring life, may lack the geological features that support life as we know it. Professor Robertson emphasized the need for further observations, stating, "This has important implications for our understanding of exoplanets, including prioritization for follow-up observations with the NASA/ESA/CSA James Webb Space Telescope."

The study underscores the necessity of accurate measurements in the ongoing hunt for life beyond Earth and challenges existing paradigms in exoplanet classification. As astronomers continue to refine their methods, the quest to understand the diversity of planets in our galaxy remains a dynamic and evolving field.

This research highlights the importance of collaboration and technological advancement in astronomy, paving the way for deeper insights into the universe's many mysteries and the potential for habitable worlds beyond our solar system.