Wiretapping a Star: How a Naked Planet Helps Find Air express
Eavesdropping on a distant planet's atmosphere is hampered by the star's noise. In the TRAPPIST-1 system, astronomers used a planet-"bug": TRAPPIST-1 b — an airless neighbor that records only the interference. By subtracting this recording from the signal of planet TRAPPIST-1 e, we can isolate the pure voice of its air.
Initial observations by James Webb proved the idea works: on quiet days, no traces of air are seen, as expected. But the star's whims continue a game of broken telephone. The search for an atmosphere on TRAPPIST-1 e goes on — hoping to catch the star in a good mood.
Original abstract
as written by the authors arXiv:2512.07695
One of the forefront goals in the field of exoplanets is the detection of an atmosphere on a temperate terrestrial exoplanet, and among the best suited systems to do so is TRAPPIST-1. However, JWST transit observations of the TRAPPIST-1 planets show significant contamination from stellar surface features that we are unable to confidently model. Here, we present the motivation and first observations of our JWST multi-cycle program of TRAPPIST-1 e, which utilize close transits of the airless TRAPPIST-1 b to model-independently correct for stellar contamination, with the goal of determining whether TRAPPIST-1 e has an Earth-like mean molecular weight atmosphere containing CO$$_2$$. We present our simulations, which show that with the 15 close transit observations, we will be able to detect this atmosphere on TRAPPIST-1 e at $$\Delta\ln\,Z=5$$ or greater confidence assuming we are able to correct for stellar contamination using the close transit observations. We also show the first three observations of our program. We find that our ability to correct for stellar contamination can be inhibited when strong stellar flares are present, as flares can break the assumption that the star does not change meaningfully between planetary transits. The cleanest observation demonstrates the removal of stellar contamination contribution through an increased preference for a flat line over the original TRAPPIST-1 e spectrum, but highlights how minor data analysis assumptions can propagate significantly when searching for small atmospheric signals. This is amplified when using the signals from multiple planets, which is important to consider as we continue our atmospheric search.
The TRAPPIST-1 system is so compact that all its planets could fit inside Mercury's orbit. A year on TRAPPIST-1 e lasts just 6 Earth days.