Seven Earth-sized planets orbit a frigid star in the TRAPPIST-1 solar system, 40 light years from the sun.
New information about TRAPPIST-1 b, the planet in the TRAPPIST-1 solar system that is closest to its star, was discovered by astronomers using the James Webb Space Telescope (JWST). These fresh discoveries shed light on the potential influence of the star on observations of exoplanets in cold stars’ habitable zones. Liquid water can still exist on the surface of the circling planet in the habitable zone.
Ryan MacDonald, a NASA Sagan Fellow and astronomer at the University of Michigan, was a member of the team that published the findings in The Astrophysical Journal Letters.
“We found no evidence of an atmosphere surrounding TRAPPIST-1 b in our observations. This suggests that the planet could be a barren rock, have clouds located high in the sky, or contain an extremely heavy molecule like carbon dioxide that would render the atmosphere too thin to be detected, according to MacDonald. But from what we can tell, the star is clearly the dominant factor in our observations, and this will have a similar impact on the other planets in the system.
The majority of the team’s research was concentrated on what they could discover about the star’s influence on observations of the planets in the TRAPPIST-1 system.
“If we don’t figure out how to deal with the star now, it’s going to make it much, much harder when we look at the planets in the habitable zone—TRAPPIST-1 d, e, and f—to see any atmospheric signals,” MacDonald said.
A promising exoplanetary system
Transmission spectroscopy was a method utilized in the study, which was directed by Olivia Lim of the Trottier Institute for Research on Exoplanets at the University of Montreal, to gather crucial knowledge on TRAPPIST-1 b’s characteristics. Astronomers can detect the distinct fingerprints left by the molecules and atoms contained within the exoplanet’s atmosphere by examining the light from the central star after it has passed through the exoplanet’s atmosphere during a transit.
Transmission spectroscopy was a method utilized in the study, which was directed by Olivia Lim of the Trottier Institute for Research on Exoplanets at the University of Montreal, to gather crucial knowledge on TRAPPIST -1’s characteristics. Astronomers can detect the distinct fingerprints left by the molecules and atoms contained within the exoplanet’s atmosphere by examining the light from the central star after it has passed through the exoplanet’s atmosphere during a transit.
According to Michael Meyer, an astronomy professor at the University of Michigan, “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 sponsorship of the Canadian Space Agency, over a period of nearly 20 years.” It was an honor to take part in this partnership, and it was quite exciting to see discoveries like these, which came from NIRISS’s special capacity, describing different worlds around close stars.
Know thy star, know thy planet
The study’s main conclusion was that star activity and contamination have a major impact on our ability to characterize an exoplanet. Stellar contamination is the term used to describe how the star’s own characteristics, such as bright regions known as faculae and dark regions known as spots, affect measurements of an exoplanet’s atmosphere.
The scientists discovered strong proof that star contamination is essential in forming TRAPPIST -1’s transmission spectrum and, most likely, the transmission spectra of the other planets in the system. The activity of the central star can produce “ghost signals” that could lead the observer to believe they have found a certain molecule in the exoplanet’s atmosphere.
This finding emphasizes how crucial it is to take stellar contamination into account when organizing your observations of all exoplanetary systems in the future. Since TRAPPIST-1 revolves around a red dwarf star that can be very active with starspots and frequent flare outbursts, this is particularly true for systems like TRAPPIST-1.
We observed a stellar flare, an unforeseen event during which the star appears brighter for several minutes to hours, in addition to contamination by stellar spots and faculae, Lim said. “This flare influenced how much light was blocked by the planet when we measured it. Although it is challenging to simulate these signs of star activity, we must take them into consideration in order to properly understand the data.
In order 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 ran a series of millions of models, which he used to model the impact of the star and search for an atmosphere in the team’s observations.
No significant atmosphere on TRAPPIST-1 b
Although all seven of the TRAPPIST-1 planets have been intriguing possibilities in the hunt for Earth-sized exoplanets with atmospheres, TRAPPIST-1 b is in more hostile circumstances than its siblings because of its close closeness to its star. It has a surface temperature between 120 and 220 degrees Celsius and receives four times as much solar energy as the Earth does.
However, of all the candidates in the system, TRAPPIST-1 b would be the simplest to identify and describe if it had an atmosphere. TRAPPIST-1 b produces a stronger signal during its passage because it is the hottest planet in the system and is closest to its star. These and other elements combine to make TRAPPIST-1 b an important but difficult observational target.
The researchers performed two separate atmospheric retrievals, a method to identify the type of atmosphere present on TRAPPIST-1 b based on observations, to account for the effects of stellar pollution. In the initial method, star pollution was eliminated from the data prior to analysis. The planetary atmosphere and stellar contamination were both modeled and fit simultaneously in MacDonald’s second method.
The outcomes in both situations suggested that the modeled stellar pollution alone might provide a good match to TRAPPIST -1’s spectra. This means that there isn’t any proof that the planet has a sizable atmosphere. Such a finding is nonetheless extremely significant since it reveals to astronomers which kinds of atmospheres are incompatible with the data that have been observed.
Lim and her colleagues investigated a variety of atmospheric models for TRAPPIST-1 b, looking at several potential compositions and situations based on their accumulated JWST observations. They discovered that there was a high degree of confidence in ruling out hydrogen-rich, cloudless atmospheres. This indicates that there doesn’t seem to be a distinct, extensive atmosphere surrounding TRAPPIST-1 b.
The results, however, could not reliably rule out thinner atmospheres, such as ones made of pure water, carbon dioxide, or methane, nor one that is comparable to Titan’s atmosphere, the only substantial atmosphere in the solar system and a moon of Saturn. These findings—the first spectrum of a TRAPPIST-1 planet—are generally in line with earlier JWST observations of TRAPPIST-1 b’s dayside made with the MIRI instrument and viewed in a single hue.
These discoveries will guide future observing programs on the JWST and other observatories, advancing knowledge of exoplanetary atmospheres and their potential habitability as scientists continue to investigate more rocky planets in the vastness of space.
