James Webb Space Telescope's first spectrum of a TRAPPIST-1 planet

Seven Earth-sized planets orbit a frigid star in the TRAPPIST-1 solar system, around 40 light years from our sun.

New information on TRAPPIST-1 b, the planet in the TRAPPIST-1 solar system nearest to its star, has been made available to astronomers by the James Webb Space Telescope (JWST). These new discoveries shed light on how measurements of exoplanets in the habitable zone of cold stars might be impacted by the star. Liquid water can still be found on the surface of the circling planet in the habitable zone.

Researchers Ryan MacDonald, a NASA Sagan Fellow and astronomer at the University of Michigan, and his team published their findings in the journal The Astrophysical Journal Letters.

"We found no evidence of an atmosphere surrounding TRAPPIST-1 b in our observations. This indicates that the planet may be made entirely of rock, have clouds high in the sky, or have an atmosphere that is too thin to be detected due to a highly heavy chemical like carbon dioxide, according to MacDonald. "However, we do observe that the star is by far the most significant factor influencing our observations, and this will have the same effect on other planets within the system."

The main objective of the team's research was to determine how much information could be gleaned about the star's influence on planet observations in the TRAPPIST-1 system.

"It will be much, much harder to detect any atmospheric signals when we look at the planets in the habitable zone—TRAPPIST-1 d, e, and f—if we don't figure out how to deal with the star now," MacDonald stated.

After seven Earth-sized exoplanets were discovered in 2017 in the potential exoplanetary system TRAPPIST-1, a star about 40 light-years distant from Earth that is considerably smaller and colder than our sun, astronomers and space enthusiasts alike have been interested in this system. These planets, which are closely clustered around their star and three of which are in its habitable zone, have raised expectations for the discovery of possibly habitable planets outside of our solar system.

Utilizing a method known as transmission spectroscopy, Olivia Lim of the Trottier Institute for Research on Exoplanets at the University of Montreal conducted the investigation and provided crucial information about the characteristics of TRAPPIST-1 b. Astronomers can detect the distinct imprint that the molecules and atoms in the exoplanet's atmosphere leave behind by examining the light emitted by the central star after it has traveled past it during a transit.

Michael Meyer, an astronomy professor at the University of Montreal, stated, "These observations were made with the NIRISS instrument on JWST, built by an international collaboration led by René Doyon at the University of Montreal, under the auspices of the Canadian Space Agency over a period of nearly 20 years." Being a part of this partnership was an honor, and it was really thrilling to witness discoveries like these, which characterize varied planets orbiting neighboring stars because to NIRISS's unique capabilities.

Know your planet and star.

The study's main discovery was the importance of pollution and star activity in determining an exoplanet's composition. The term "stellar contamination" describes how the star's natural properties, including as brilliant areas known as faculae and dark regions known as spots, might affect measurements of an exoplanet's atmosphere.

The researchers discovered strong evidence that the transmission spectra of TRAPPIST-1 b and, probably, the other planets in the system are significantly shaped by stellar pollution. The activity of the central star can produce "ghost signals" that could lead an observer to believe they have found a certain chemical in the exoplanet's atmosphere.

This finding emphasizes how crucial it is to take stellar pollution into account while organizing upcoming observations of any exoplanetary system. This is particularly true for systems like TRAPPIST-1, which revolve around a red dwarf star that exhibits periodic flare outbursts and starspot activity.

Lim stated, "We observed a stellar flare, an erratic event during which the star looks brighter for several minutes to hours, in addition to the contamination from stellar spots and faculae." "Our assessment of the quantity of light blocked by the planet was impacted by this flare. Although these stellar activity characteristics are challenging to model, we must take them into consideration to make sure that the data is appropriately interpreted."

Running a series of millions of models to explore the full range of properties of cool starspots, hot star active regions, and planetary atmospheres that could explain the JWST observations the astronomers were seeing, MacDonald played a crucial role in modeling the impact of the star and looking for an atmosphere in the team's observations.

Nothing noteworthy to observe about TRAPPIST-1 b

The quest for Earth-sized exoplanets with an atmosphere has made all seven of the TRAPPIST-1 planets intriguing prospects; nevertheless, TRAPPIST-1 b faces more challenging circumstances than its siblings due to its close closeness to its star. Its surface temperature ranges from 120 to 220 degrees Celsius, and it gets four times as much solar energy as Earth.

Nonetheless, of all the candidates in the system, TRAPPIST-1 b would be the simplest to identify and characterize if it had an atmosphere. A greater signal is produced during TRAPPIST-1 b's transit since it is the hottest planet in the system and the planet nearest to its star. Because of all these things, TRAPPIST-1 b is an important but difficult observation target.

The researchers carried out two separate atmospheric retrievals, a method to ascertain the type of atmosphere present on TRAPPIST-1 b, based on observations, to account for the influence of stellar pollution. Before the data were examined, star pollution was eliminated in the first method. MacDonald's second method involved modeling and fitting both the planetary atmosphere and stellar pollution at the same time.

The results showed that the predicted stellar pollution alone might match TRAPPIST-1 b's spectra in both scenarios. This implies that there isn't any proof of a substantial atmosphere on the planet. This kind of conclusion is still highly significant since it indicates to astronomers the kinds of atmospheres that don't fit the data that have been seen.

Lim and her colleagues investigated a variety of atmosphere models for TRAPPIST-1 b, looking at many probable compositions and situations based on their accumulated JWST data. High trust was placed on the exclusion of atmospheres rich in hydrogen and devoid of clouds. This indicates that TRAPPIST-1 b does not seem to have a distinct, prolonged atmosphere.

The information, however, was insufficient to definitively rule out thinner atmospheres, such as ones made entirely of water, carbon dioxide, or methane, as well as atmospheres like to Titan's, Saturn's moon and the only moon in the solar system with a sizable atmosphere. These findings, the first spectrum of a TRAPPIST-1 planet, are in general in agreement with earlier JWST observations of the dayside of TRAPPIST-1 b, which the MIRI instrument saw in a single hue.

These discoveries will guide next JWST and other telescope observation programs, advancing our knowledge of exoplanetary atmospheres and possible habitability as astronomers continue to study more rocky planets in the vastness of space.