Most exoplanets, or planets outside our solar system, are found using the transit method. This involves measuring slight dips in a star’s brightness as a planet passes in front of it. So far, we’ve identified nearly 6,000 exoplanets this way. A new study, however, flips the script by revealing insights about a star from the transit of a giant planet, TOI-3884 b.
TOI-3884 b is interesting for a couple of reasons. It has 33 times the mass of Earth and orbits a small star known as an M-dwarf. Instead of the usual single-drop transit pattern, this planet creates a two-bump drop in its star’s light, which raised some eyebrows among astronomers.
Initially observed by NASA’s Transiting Exoplanet Survey Satellite (TESS), these unusual transits suggested something interesting was happening on the star’s surface. It was hypothesized that this star had a significant spot—similar to sunspots—but much larger. These spots are cool areas where magnetic fields disrupt normal brightness.
The research team, mainly from Harvard and MIT, analyzed data and found a starspot that covers about 7% of TOI-3884’s surface. For context, the largest sunspots on our Sun cover only 0.3% of its area.
Unlike sunspots that usually last for just a few months, this one has endured for at least seven years. “Such long-lasting spots have been seen on rapidly rotating stars,” noted Patrick Tamburo, a lead author of the study. This adds to our understanding of how different stars behave compared to our own Sun.
What makes this study noteworthy is the way the starspot was inferred. The researchers utilized advanced modeling techniques to analyze TOI-3884’s light patterns and its planet’s transits. They concluded that TOI-3884 b’s unusual orbit is tilted at almost a right angle compared to the star’s equator. This could mean something else, perhaps another planet, altered its path over time.
Interestingly, this peculiar starspot and its impact on transit shapes might open doors to discovering other planetary systems with unique characteristics. As astrophysicist Patrick Tamburo put it, “This is the first time we’ve inferred a polar starspot through a transiting planet.” Such insights challenge our current understanding of how exoplanets interact with their stars.
For those interested in this field, the study adds a fresh perspective on how exoplanets can inform us about their host stars, potentially leading to more discoveries in the future.
