Astronomers find exoplanets are far larger than previously believed

Hundreds of distant planets may be far larger than scientists once believed. New research reveals that many exoplanets found by NASA’s Transiting Exoplanet Survey Satellite (TESS) might have been incorrectly sized for years. The findings have deep consequences for how astronomers view planet formation, structure, and the potential for life beyond Earth.

TESS, launched in 2018, was designed to detect exoplanets by watching thousands of stars across the sky. It does this by looking for tiny dips in starlight caused when a planet passes, or transits, in front of its star. The drop in light tells scientists how big the planet might be.

But there’s a big catch. TESS has relatively low resolution, and sometimes the light from other nearby stars mixes in with the target star’s light. This makes the planet’s shadow look smaller than it truly is—and causes scientists to underestimate the planet’s size.

A new study led by Te Han, a doctoral student at the University of California, Irvine, has uncovered how serious this problem really is. Han and his team reviewed hundreds of TESS planet discoveries and found that many planet sizes have been underestimated by around 6.1%. That may not seem like much, but because density is calculated using both size and mass, a small error in radius results in a much bigger mistake in density—about 20% too high.

“These biases are widespread in the literature,” Han said. “They’ve shaped how we view exoplanet populations, and not always in the right way.”

To get a better handle on the problem, Han built a custom computer model that corrected for the extra light from background stars. He combined TESS data with observations from another satellite, Gaia, which can more precisely measure star positions and brightness.

By comparing results from many published studies and applying his corrections, Han discovered that over 200 known exoplanets are likely significantly larger than earlier reports suggested.

“This means we may have actually found fewer Earth-like planets so far than we thought,” Han explained. That’s because many planets that once appeared to be rocky, Earth-sized worlds may now be reclassified as larger and less Earth-like.

Paul Robertson, a UC Irvine astronomy professor and co-author on the study, helped lead the analysis. “We’re basically measuring the shadow of the planet,” he said. “And TESS data are contaminated, which Te's custom model corrects better than anyone else in the field.”

When an exoplanet blocks light from its host star, astronomers use that drop in brightness to determine the planet’s radius. If other stars nearby brighten the scene, the drop appears smaller, and the calculated radius shrinks. That leads to incorrect assumptions about the planet’s nature.

Han sorted published results based on how each team estimated the planet radius. Then, using his corrections, he reassessed the data to determine just how much TESS’s results had been biased by the extra starlight. His work found a clear pattern: planets were consistently larger than past estimates.

The implications stretch far beyond simple numbers. “What we find in this study is that these planets may systematically be larger than we initially thought,” Robertson said. “It raises the question: Just how common are Earth-sized planets?”

Before this discovery, only three planets found by TESS were believed to be similar in size and structure to Earth. Han’s corrections now show that all three are actually bigger. That’s a major change for astronomers who search for planets where life might exist.

Rather than rocky Earth-like worlds, the revised planets may be water-rich “ocean worlds,” completely covered by deep global seas. Others could be even larger, with thick gas layers like Uranus or Neptune. These types of planets might still support life, but they lack many of the stable features found on rocky planets like Earth.

“This has important implications for our understanding of exoplanets,” Robertson said, “including among other things prioritization for follow-up observations with the James Webb Space Telescope, and the controversial existence of a galactic population of water worlds.”

Han’s results suggest that the actual number of Earth-sized planets in our galaxy may be even smaller than earlier studies claimed. That doesn’t mean life elsewhere is impossible. But it does mean astronomers need to rethink where they look—and how they measure what they find.

The new research doesn’t just correct earlier mistakes. It opens up fresh opportunities. Han’s team now plans to revisit planets that were once considered too large to be habitable. With their corrected sizes, some of these worlds might move back into the spotlight as possible homes for alien life.

Han also wants to alert fellow scientists. He hopes that other teams using TESS data will adopt similar methods to avoid drawing wrong conclusions. “TESS is an incredible tool,” Han said. “But we have to be careful with the data it gives us.”

With support from NASA, this study marks a turning point in how exoplanet measurements are reviewed. By using improved models and better data, researchers can now refine the planet radius measurements that shape much of what we believe about planets beyond our solar system.

Smaller radius errors have led to big misunderstandings about density, structure, and what these planets are made of. With corrected sizes, the field can build more accurate models about planet formation, composition, and potential for life. The study also points out that satellites like TESS are only the first step in exploring other worlds.

Tools like the James Webb Space Telescope will help take the next steps by directly observing planet atmospheres and conditions. But getting those follow-up targets right depends on understanding their true size and nature. For now, scientists will need to revise earlier models and think again about where they might find Earth’s twin—or if one even exists in the neighborhood of stars TESS has already explored.

Research findings are available online in The Astrophysical Journal Letters.

Note: The article above provided above by The Brighter Side of News.

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