New data from the James Webb Space Telescope (JWST) on TRAPPIST-1 b, the planet in the TRAPPIST-1 solar system closest to its star, shows the complexity of studying these worlds.
In a solar system called TRAPPIST-1, 40 light years from the Sun, seven Earth-sized planets orbit a cool star.
Astronomers have obtained new data from the James Webb Space Telescope (JWST) about TRAPPIST-1 b, the TRAPPIST-1 solar system’s closest planet to its star. These new observations offer insight into how their star affects observations of exoplanets in the habitable zone of cool stars. In the habitable zone, liquid water may still exist on the surface of the orbiting planet.
The team, which includes University of Michigan astronomer and NASA Sagan Fellow Ryan MacDonald, published their study in The Astrophysical Journal Letters.
“Our observations show no signs of an atmosphere around TRAPPIST-1 b. This tells us that the planet may be bare rock, have clouds high in the atmosphere, or have a heavy very molecules like carbon dioxide that cause the atmosphere to be too small to detect,” MacDonald said in a statement. “But what we see is that the star is the largest effect that dominates our observations, and it will do the same for the other planets in the system.”
Much of the team’s research focused on what they could learn about the impact of the star from observations of the planets in the TRAPPIST-1 system.
“If we don’t know how the star is facing now, it will be much more difficult if we look at the planets in the habitable zone (TRAPPIST-1 d, e and f) to see even what atmospheric signals,” MacDonald said.
TRAPPIST-1, a smaller and cooler star than our sun located about 40 light-years from Earth, has captured the attention of scientists and space enthusiasts since the discovery of its seven Earth-sized exoplanets in 2017. These worlds, tightly wrapped around their star with three of them within its habitable zone, have raised hopes of finding potentially habitable environments beyond our solar system.
The study, led by Olivia Lim of the Trottier Institute for Exoplanet Research at the University of Montreal, used a technique called transmission spectroscopy to obtain important information about the properties of TRAPPIST-1 b. By analyzing the light from the central star after it passes through the exoplanet’s atmosphere during a transit, astronomers can see the unique imprint left by the molecules and atoms found within that atmosphere.
The main finding of the study is the significant effect of stellar activity and pollution in trying to determine the nature of an exoplanet. Stellar contamination refers to the influence of the star’s own characteristics, such as dark regions called spots and bright regions called faculae, on the dimensions of the exoplanet’s atmosphere.
The team found compelling evidence that stellar contamination plays an important role in shaping the transmission spectra of TRAPPIST-1 and, possibly, other planets in the system. The activity of the central star creates “ghost signals” that trick the observer into believing that it has detected a particular molecule in the exoplanet’s atmosphere.
This result highlights the importance of considering stellar contamination when planning future observations of all exoplanetary systems. This is especially true for systems like TRAPPIST-1, because they are centered on a red dwarf star that can be very active with stars and frequent flares.
“In addition to contamination from star spots and star faculae, we saw a stellar flare, an unpredictable event where the star appears brighter for a few minutes or hours,” Lim said. “This flare affected our measurement of the amount of light blocked by the planet. These signals of stellar activity are difficult to model, but we need to take them into account to make sure the data is interpreted correctly.”
MacDonald played a major role in modeling the star’s impact and finding atmospheres in the team’s observations, running a series of millions of models to explore the full properties of cold starpots, the active regions of stars. hot stars and planetary atmospheres that could explain the JWST observations seen by astronomers.
While TRAPPIST-1’s seven planets are tempting candidates for finding Earth-like exoplanets with atmospheres, TRAPPIST-1’s proximity to its star means that it is in harsher conditions than its counterparts. brother It receives four times as much radiation as Earth from the sun and has a surface temperature of between 120 and 220 degrees Celsius.
However, if TRAPPIST-1 b has an atmosphere, it will be the easiest to find and describe all the targets in the system. Because TRAPPIST-1 b is the closest planet to its star and therefore the hottest planet in the system, its transit generates a stronger signal. All of these factors make TRAPPIST-1 b an important but challenging observational target.
To account for the effect of stellar contamination, the team conducted two independent atmospheric retrievals, a technique to determine the type of atmosphere present in TRAPPIST-1 b, based on observations. In the first method, stellar contamination is removed from the data prior to analysis. In the second method, developed by MacDonald, the contamination of the star and the atmosphere of the planet are simultaneously modeled and adjusted.
In both cases, the results show that the TRAPPIST-1 b spectra can be fit only well by the stellar contamination model. This suggests no evidence of a significant planetary atmosphere. This result remains very valuable, as it tells astronomers what types of atmospheres are inconsistent with the observed data.
Based on observations collected from JWST, Lim and his team explored different atmospheric models for TRAPPIST-1 b, exploring various possible compositions and scenarios. They found that cloudless, hydrogen-rich atmospheres do not have high confidence. This means that there is no clear, dense atmosphere around TRAPPIST-1 b.
However, the data do not reliably rule out thinner atmospheres, such as those composed of pure water, carbon dioxide or methane, or an atmosphere similar to that of Titan, a moon of Saturn and the only moon of solar system with a significant atmosphere. These results, the first spectrum of a TRAPPIST-1 planet, are generally consistent with previous JWST observations of the dayside of TRAPPIST-1b seen in one color with the MIRI instrument.
As astronomers continue to explore other rocky planets across space, these findings will inform future observing programs at JWST and other telescopes, contributing to a broader understanding of exoplanetary atmospheres and their potential habitats.