The launch of NASA’s James Webb Space Telescope (JWST) in 2021 marked the beginning of a thrilling new era in exoplanet exploration, especially for researchers focusing on terrestrial planets orbiting stars other than our sun. However, three years into its mission, scientists have encountered obstacles that have hindered progress.
In a recent paper published in Nature Astronomy, the TRAPPIST-1 JWST Community Initiative presents a comprehensive roadmap to overcome exoplanet exploration challenges. The roadmap aims to improve data-gathering efficiency, benefiting the broader astronomy community.
“A collective effort of experts was essential to address these complex, cross-disciplinary challenges and to devise the first multiyear observational strategy, giving JWST a fighting chance at identifying habitable worlds during its mission,” says Julien de Wit, an associate professor at MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS) and a lead author of the paper.
A unique opportunity to enhance exoplanet exploration: The TRAPPIST-1 system
Located 41 light years from Earth, the TRAPPIST-1 system, with its seven planets, offers a unique opportunity to study a large system with multiple planets of different compositions, akin to our own solar system.
“It’s a dream target: Not one, but potentially three planets in the habitable zone, allowing for comparative studies within the same system,” says René Doyon from the Université de Montréal, who co-led the study with de Wit. “There are only a few well-characterized temperate rocky planets where we can hope to detect atmospheres, most of which are within the TRAPPIST-1 system.”
Astronomers like de Wit and Doyon study exoplanet atmospheres using transmission spectroscopy, which involves analyzing starlight passing through a planet’s atmosphere to identify its elements. Transmission spectra are collected when the planet transits its host star.
Due to the short orbital periods of the TRAPPIST-1 planets, their transits frequently overlap. Transit observation times are typically allotted in five-hour windows, and when scheduled correctly, nearly half of these windows can capture at least two transits. This “two-for-one” approach saves both time and money while doubling data collection.
Addressing Stellar Contamination
Stars are not uniform; their surfaces can vary in temperature, creating spots that can interfere with transmission spectra. These stellar variations can give false indications of a planet’s atmospheric composition, a problem known as “stellar contamination.” While often overlooked, the advanced capabilities of JWST have highlighted the challenges stellar contamination poses for studying planetary atmospheres.
EAPS research scientist Ben Rackham encountered these challenges during his Ph.D. research on small exoplanet exploration using the Magellan Telescopes in Chile. He now faces the same issues with the new JWST data.
“As predicted from earlier work with ground-based telescopes, the initial spectral signatures from JWST don’t align with planetary interpretations,” he says. “The features are unexpected and vary from transit to transit.”
Rackham and David Berardo, a postdoc in EAPS, are collaborating with de Wit on methods to correct stellar contamination using two approaches: improving models of stellar spectra and direct observations to derive corrections.
“By observing a star’s rotation, we can leverage JWST’s sensitivity to get a clearer picture of its surface, allowing for more accurate measurements of transiting planets’ atmospheres,” says Berardo. This, combined with back-to-back transit studies as proposed in the roadmap, provides valuable data to filter out stellar contamination from both future and past studies.
Looking Beyond TRAPPIST-1
The roadmap resulted from the TRAPPIST JWST Community Initiative’s efforts to consolidate separate programs focused on individual planets, which previously hindered optimal transit observation scheduling.
“We recognized early on that this effort required a ‘village’ to avoid the efficiency pitfalls of small observation programs,” says de Wit. “Our hope now is that a large-scale community effort guided by the roadmap can achieve timely results of Exoplanet Exploration.”
De Wit hopes this initiative could lead to identifying habitable or inhabitable worlds around TRAPPIST-1 within a decade.
Both de Wit and Doyon believe the TRAPPIST-1 system is ideal for foundational research on exoplanet atmospheres, which will extend to other systems. Doyon notes, “The TRAPPIST-1 system will be instrumental not only for its study but also for learning how to precisely correct stellar activity, benefiting many other transmission spectroscopy programs affected by stellar activity.”
“We have within reach fundamental and transformative answers with a clear roadmap to exoplanet exploration,” says de Wit. “We just need to follow it diligently.”
By improving exoplanet exploration through the JWST, scientists are paving the way for groundbreaking discoveries that could reshape our understanding of habitable worlds beyond our solar system.
