University of California, Irvine (UCI) scientists conducting a fresh analysis of data from hundreds of exoplanets, including Earth-like planets that could potentially sustain extraterrestrial life, have discovered several cases where ‘interstellar contamination’ caused by light from nearby stars resulted in previous models overestimating a planet’s size.
Because a planet’s size is a critical component in most models predicting potential exoplanet habitability, UCI doctoral student and study lead author Te Han believes the team’s findings could eliminate several candidate exoplanets previously considered favorable places for astrobiologists to search for extraterrestrial life.
“We found that hundreds of exoplanets are larger than they appear, and that shifts our understanding of exoplanets on a large scale,” Han explained in a statement.
Analysis of TESS Exoplanets Reveals Interstellar Contamination
Since 1995, when scientists discovered the first planet outside of Earth’s solar system, newer and more powerful observation tools have increased the confirmed list of exoplanets to over 5,000. Although researchers have employed several techniques to make those discoveries, most discoveries involve measuring the dip in a star’s light as an exoplanet passes between it and Earth.
“We’re basically measuring the shadow of the planet,” explained Paul Robertson, UC Irvine professor of astronomy and study co-author.
Dubbed the transit method, this technique allowed the Transiting Exoplanet Survey Satellite (TESS) to discover more exoplanets than any other tool, including the Hubble Telescope and the James Webb Space Telescope. Along with determining an exoplanet’s likely orbit, mass, and density, the TESS data helps scientists estimate its size.
Curious if models predicting the size of an exoplanet had factored in the interstellar contamination caused by light from nearby stars, Han’s team combed through the TESS data archives. As expected, they found that light from a neighboring star can end up added to the light from a host star. If models don’t take this excess light into account, they may assume a planet is smaller than it is, since a smaller planet would block less of its host planet’s light during transit.
New Analysis Directly Affects Estimation of Earth-Like Planets
Having confirmed the interstellar contamination, Han and colleagues reexamined hundreds of previous TESS exoplanet discoveries. First, they categorized the studies based on the method of exoplanet radius measurement employed by the researchers. Han said this data allowed the UCI team to estimate how much the exoplanet’s size had been biased due to interstellar contamination. Next, the team compared the data with observations gathered by the GAIA satellite mission, which further supported the interstellar contamination findings.
“TESS data are contaminated, which Te’s custom model corrects better than anyone else in the field,” Robertson explained.
In their study, Han, Robertson, and colleagues explain how correcting for this interstellar contamination has led to significant changes in the characteristics of the exoplanets they studied. Robertson said that perhaps the study’s most significant discovery, especially for researchers searching for extraterrestrial life, is that exoplanet candidates that might be home to ET “may systematically be larger than we initially thought.”
“It raises the question: Just how common are Earth-sized planets?” Robertson asks.
One example cited by Han was the discovery of single-planet systems by TESS. According to the researcher, only three such TESS discoveries were thought to have compositions similar to Earth. After correcting for interstellar contamination, “all of them are actually bigger than we thought.”
How the Findings Affect the Search for Extraterrestrial Life
In the study’s conclusion, the research team explains how their interstellar contamination findings affect the search for Extraterrestrial life. For example, although some scientists have begun to rethink what form life outside Earth might take, most models still favor looking for places that can support liquid water, are rocky like Earth, and have a relatively similar size. If Han’s new model is correct and many planets we initially thought were Earth-like are much larger, they may not be rocky at all. Instead, they may be theoretical ‘water worlds’ covered by one giant ocean. They may also be gaseous planets like Neptune and Uranus.
“This has important implications for our understanding of exoplanets, 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,” Roberston explained.
Hoping to add to the potentially habitable exoplanet list instead of taking away from it, Han and his team plan to reexamine TESS data for candidates that were previously dismissed but now may be viable candidates for extraterrestrial life due to the inclusion of interstellar contamination in their size and composition estimates. The team also wants to let other exoplanet researchers know about the interstellar contamination phenomenon so they can correct for it in their transit models.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.