Astronomers have found a new way to peek at the blemishes on distant stars—features known as star spots—by carefully studying planets as they cross in front of their host stars.
The method, called StarryStarryProcess, was created using data from NASA’s planet-hunting missions Kepler and TESS.
It could help scientists better understand not only the stars themselves but also the planets orbiting them, including whether those worlds might be able to support life.
Traditionally, when scientists study planets beyond our solar system, called exoplanets, they look at transits.
A transit happens when a planet passes in front of its star, briefly dimming the star’s light. The resulting dip in brightness is recorded as a light curve.
From this, astronomers can figure out the planet’s size, its orbit, and sometimes even hints about what it’s made of.
Normally, these light curves are smooth and predictable. But sometimes, they show little bumps and wiggles.
Those extra features are thought to be caused by star spots—dark, cooler patches on a star’s surface, similar to sunspots on our own Sun.
Just as sunspots follow an 11-year cycle and affect solar activity, star spots can change in number and size over time. And that variability matters, because it affects how scientists interpret the light passing through a planet’s atmosphere.
Until now, figuring out exactly where and how many star spots exist on a distant star has been tricky.
The new StarryStarryProcess model, developed by graduate student Sabina Sagynbayeva at Stony Brook University, offers a better way.
By combining information from both planetary transits and the star’s rotation, the model can map where spots are located, how dark they are, and how many there might be.
This gives astronomers a much clearer picture of the host star.
“Most models treat stars like smooth, uniform light bulbs,” Sagynbayeva explained. “But real stars are messy and complex. Our approach helps us capture that complexity.”
The team tested their method on a planet called TOI 3884 b, a gas giant about five times larger than Earth and 32 times its mass.
Discovered by TESS in 2022, this planet orbits a cool, faint star about 141 light-years away in the constellation Virgo. The analysis showed that the star has clusters of spots near its north pole, which happens to tilt toward Earth. From our perspective, that means the planet passes right over the star’s spotted pole during each transit.
Right now, the model works best with visible light data, like what Kepler and TESS provide. But upcoming missions could take it even further. NASA’s Pandora mission, set to launch soon, will focus on studying the atmospheres of exoplanets and the activity of their stars using multiwavelength observations.
By separating the signals of planets from those of their stars, tools like StarryStarryProcess will help scientists know when they’re truly detecting water vapor or other molecules in a planet’s atmosphere—a vital clue for habitability.
“The more we understand stars, the better we understand their planets,” said Brett Morris, a co-author on the study. “It’s like a feedback loop—improving one improves the other.”
With thousands of planets already discovered by TESS, and missions like Pandora on the horizon, astronomers are closer than ever to sorting out the fingerprints of stars from the signals of worlds. And that could bring us one step nearer to finding planets that look a little more like home.
Source: NASA.
