Most exoplanets are discovered when they pass or move through their parent star. However, new research details the opposite scenario. When a giant planet crosses the host’s star, the specificity of its transport signature revealed new discoveries about the star itself, particularly the location that accounts for 7% of the star’s surface, and that lasted for at least seven years.
Nearly 6,000 exoplanets (planets beyond the solar system) have been identified so far. Many methods have helped to accumulate this Trove, but the most successful method is the transportation method. This technique, which helped to reveal nearly 75% of known exoplanets, measures a temporary, small reduction in star brightness as orbits pass along the line of sight between the star and the observing telescope.
Most transport signatures of the star ray are similar and consist of a single step drop. However, the planets explained in new research are rare. Known as TOI-3884 B, it is a Neptune-like world that is 33 times the mass of the Earth. When passing a star – the small M-dwarf star TOI-3884 – creates a two-bump drop in the star’s light curve.
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These asymmetric traffic, first recorded by NASA’s Exoplanet Survey Satellite (TESS), sparked the curiosity of astronomers. A 2022 study reasoned that strange transits mean that the star’s surface is not evenly bright. (Starspots – Like solar spots, but stars other than the Sun have bundles of intertwined magnetic field lines that are dimmed more lit than the surrounding light bulb.)
To determine the characteristics of this star spot, the authors of the new study, Harvard University and MIT astrophysicists – elicited both Tess observations, along with TOI3884 (including Star spot) and computational models of its planet. Their analysis revealed that Patrick Tambro, a postdoctoral researcher at Harvard University and first author of the new study, had a 76,000 miles (122,000 kilometers) radius of “about 7% of the star’s surface area,” and that the spot accounted for “about 7% of the star’s surface area.” In contrast, the largest recorded sunspot, 99,000 miles (160,000 km) in diameter, covers just 0.3% of the Earth’s Sun.
Related: The bottom of the sun is visible to humans for the first time in history (photo)
The TOI-3884 star spot is different from the solar spot that lasts its lifespan. “The longest lifespan spots last for several months on the sun,” Tambro said. However, using observational data collected by the Zwicky Transient facility in California over the past few years, researchers have shown that TOI3884’s “Pimple” has been around for at least seven years. Tambro noted that this was not surprising, as the rapidly rotating star polar spots are known to last for decades.
But how can star spots cause such a unique pattern? The 2022 survey proposed two possibilities. First, the day of TOI-3884 – the time it takes for a star to rotate about its axis – is equal (or a multiple of) the time it takes for a TO-3884 B to orbit the star once. The second possibility is that the planet is orbiting one of the poles of the star. The Star Pillar is a small center of large, long-lasting star spots.
Such spots, including M dwarves like TOI-3884, are “observed on various types of stars,” Tambro said. This latter scenario also suggests that the planet’s orbit is very inclined – perhaps even vertical, compared to the star’s equator. (In contrast, planets in the solar system have orbits below 10 degrees.)
To investigate the first scenario, the researchers estimated the rotation period for TOI3884. Using observations from TOI-3884 obtained from the Arizona-based Tierra Observatory in 2024 and 2025, researchers found that the planet rotated once every 11 days.
Data also show that TOI-3884 B passes every 4.5 days, suggesting that this is the planet’s orbital period. This means that the ratio of planetary orbital periods to star rotation periods was not integer, and we ruled out the first hypothesis.
To test the second hypothesis, the researchers relied on computational models and searched for the values of the various parameters that best describe the observations. The best explanation they discovered is that it is the TOI-3884 b orbit along the path near the chest around the star, and its location is at an 80-degree latitude. Modeling also implies that the star spot will pirouette around the star pole, likely to be visible partially or entirely to Earth-based viewers.
Regarding the vertical path of TOI-3884 B, Tambro said that either another planet or star pushed it from its original orbit, or that the disc of material from which TOI-3884 B was born is itself tilted relative to the star.
This research, which has not yet been peer-reviewed, is available as a preprint of an ARXIV server.
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