Our solar system's central star has reached approximately the midpoint of its existence, indicating that Earth shares a similar timeline. When stars deplete their hydrogen fuel, they undergo dramatic expansion, potentially swallowing nearby planets. While this event remains billions of years away for our world, scientists have identified a possible glimpse into this future scenario.
Researchers Edward Bryant from the University of Warwick and Vincent Van Eylen of University College London analyzed data from the Transiting Exoplanet Survey Satellite (TESS). They compared planetary systems around stars in their prime—similar to our sun—with those orbiting older stars nearing the end of their life cycles.
"We saw that these planets are getting rarer [as stars age]," Bryant stated. This observation suggests that planets gradually vanish as their host stars grow older. The comparison between younger and older stellar systems indicates this phenomenon isn't due to planets never forming initially, but rather that aging stars become increasingly destructive.
"We're fairly confident that it's not due to a formation effect," Bryant explained, "because we don't see large differences in the mass and [chemical composition] of these stars versus the main sequence star populations."
Complete planetary engulfment represents just one method by which giant stars eliminate their companions. As these stars expand, they generate powerful tidal forces that can degrade planetary orbits, strip away atmospheres, and even tear worlds apart completely. Bryant and Van Eylen focused on orbital decay in their model of planetary destruction.
"We're looking at how common planets are around different types of stars, with number of planets per star," Bryant said. The team identified nearly 457,000 post-main sequence stars in TESS data, finding only 130 planets and candidates in close orbits. "The fraction [of stars with planets] gets significantly lower for all stars and shorter-period planets, which is very much in line with the predictions from the theory that tidal decay becomes very strong as these stars evolved."
TESS detects exoplanets by observing the slight dimming that occurs when planets pass in front of their host stars—a phenomenon called a transit. This method works best for large planets in tight orbits, making these systems quite different from our own solar system. Studying planets around aging stars presents additional difficulties.
"If you have the same size planet but a larger star, you have a smaller transit," Bryant noted. "That makes it harder to find these systems because the signals are much shallower."
Despite these challenges, the researchers emphasized that stars in their sample share similar masses with our sun, which is the most crucial factor. Stars with solar-like masses will experience identical life cycles and eventual demise, providing valuable insights into our solar system's distant future.
"The processes that take place once the star evolves [past main sequence] can tell us about the interaction between planets and host star," said Sabine Reffert, an astronomer at Universität Heidelberg not involved in the study. "We had never seen this kind of difference in planet occurrence rates between [main sequence] and giants before because we did not have enough planets to statistically see this difference before. It's a very promising approach."
Challenges in Studying Aging Star Systems
Exoplanet research has achieved remarkable success in recent decades, with astronomers confirming thousands of worlds beyond our solar system. However, investigating planets orbiting post-main sequence stars presents unique obstacles.
One complication involves stellar age and composition. Older stars typically contain fewer heavy elements—a property astronomers call "metallicity." Observations have revealed connections between higher metallicity and greater exoplanet abundance.
"A small difference in metallicity…could potentially double the occurrence rate," Reffert commented, noting that while the study's general conclusions remain valid, more precise metallicity data would refine the details.
Future observations measuring metallicity through spectroscopy, along with improved stellar and planetary mass data, could enhance the model. Additionally, the European Space Agency's Plato Mission, scheduled for launch in late 2026, will provide more sensitive data to complement TESS observations.
Earth's fiery destiny remains billions of years away, but researchers have made significant progress in understanding how dying stars consume their planetary companions. With additional data from TESS and future missions like Plato, scientists might even detect the subtle orbital changes that signal a planet's final spiral toward destruction—a catastrophic end for that world, but a valuable discovery for our comprehension of how planets and stars evolve together.
