Astronomers have made incredible strides in studying the TOI-3884 system. This fascinating red dwarf star is located roughly 140 light-years from Earth. This remarkable system is home to the planet TOI-3884b. Its size puts it in the category of super-Neptunes for such a huge planet, measuring at nearly six times the radius of Earth. A new, detailed study used state-of-the-art observational techniques to focus on the essential details of this remarkable planetary system.
The TOI-1812 research team predicted that multicolor MuSCAT3 and MuSCAT4 instruments could reveal the atmospheric spectrum diversity ululations. These instruments were installed on Las Cumbres Observatory (LCO) 2-meter telescopes to characterize the star. Through a network of LCO 1-meter telescopes, they launched a dedicated photometric monitoring campaign. This arrangement allowed them to look for vital transits and spot-crossing signals from February through March 2024. Together, their work uncovers a fascinating picture of TOI-3884 and its planetary companion.
Stellar Characteristics of TOI-3884
TOI-3884, the host star, has a stellar rotation period of 11.05 days. Though it is not rotating especially quickly compared to other stars, we do know that it displays a huge polar spot on its surface. This polar spot has a temperature as low as 3000 K, about 2000 K cooler than the surrounding stellar surface. Its equilibrium temperature is 200 K lower than the average surface temperature of 3150 K. Their persistence is remarkable since they obscure about 15% of the visible stellar disk.
Knowing these defining traits is key. They affect how astronomers interpret the star’s activity and its interaction with the planet that orbits it. These cooler regions on the surface of the star cause hot spots in brightness that can complicate transit measurements. These findings from the research team provide helpful context to what has become a hot debate about stellar activity in red dwarf stars.
Misalignment of Axes
What we found was pretty surprising and amazing! The stellar spin axis of TOI-3884 is tilted at an angle of ~62 degrees with respect to the orbital axis of TOI-3884b. This unexpected misalignment is an indication that TOI-3884 is a remarkably tilted planetary system. Such a tilt can have a relatively drastic impact on the climate and atmospheric dynamics of the orbiting planet. Tilts are unusual, in that they’re understood as common in exoplanetary systems. Defining the extent of this misalignment in TOI-3884 muddles our understanding of how these celestial bodies behave and influence one another.
Prior observational studies had released conflicting results for critical parameters of the TOI-3884 system, such as stellar inclination and rotation speed. The new observations remove the doubt and confusion that had long plagued the astronomical community. The researchers recorded brightness variations every few minutes for six months from December 2024 through March 2025. Their field measurements consistently showed distinct periodic variations that yielded much greater insight into these parameters.
Advanced Observational Techniques
The research team conducted observations utilizing four wavelength bands—g, r, i, and z. This enabled them to build light curves that helped shine a light on the complexity of the TOI-3884 system architecture. This full color approach allows us to further understand how the light is interacting with the star and the planet itself. In turn, we can build better models of what makes them unique.
Along with those big discoveries, the team was able to record the rare spot-crossing transits. This not only confirmed what we had found previously, but built upon it, providing a more holistic picture of how TOI-3884 and TOI-3884b operate as a system. These new methodologies are an important step forward in exoplanet research. They demonstrate that through collaboration and cutting-edge technology, we can make paradigm-shifting discoveries.