The TRAPPIST-1 system, shown in this rendering, includes seven Earth-sized planets circling a single, relatively cool star. Credit: NASA/JPL-Caltech
Astronomers have been eager for the landmark telescope to study the TRAPPIST-1 system.
The James Webb Space Telescope (JWST) has got its first glimpse of a highly anticipated set of targets — the atmospheres of some of the seven Earth-sized planets orbiting the star TRAPPIST-1, just 12 parsecs (39 light-years) from Earth. All seven lie in or near their star’s habitable zone, where liquid water might exist, and astronomers consider them the best-known laboratory for studying what makes planets beyond the solar system suitable for life.
What researchers have seen so far is preliminary and doesn’t yet indicate what type of atmosphere these planets might actually have. But if they have dense atmospheres with intriguing molecules like carbon dioxide or methane, the $10 billion telescope will be able to spot them in the months and years to come. No other observatory was powerful enough to detect these atmospheres.
“We’re in business,” said Björn Benneke, an astronomer at the University of Montreal, Dec. 13 during a symposium on initial results from the JWST in Baltimore, Maryland.
Esteemed planets
The TRAPPIST-1 planetary system, mapped in 2017, offers astronomers multiple ways to understand the formation and evolution of Earth-sized worlds around a single star. The star is relatively faint and cool, and the seven planets nestle closer as Mercury orbits the Sun.
JWST is observing all of the planets in its first year of scientific operations, which began in June. Many of these observations have already been made, but none have been shown publicly until this week’s symposium, held at the Space Telescope Science Institute, JWST’s operations center.
The TRAPPIST-1 planets are labeled b through h, with b being closest to the star and h being furthest away.
Benneke presented the first JWST studies of TRAPPIST-1g. So far, the telescope has been able to determine that it likely doesn’t have a hydrogen-rich atmosphere — which would be relatively easy to spot because it’s so large. That could mean the planet has a denser atmosphere made up of heavier molecules like carbon dioxide, or no atmosphere at all.
JWST studies planetary atmospheres primarily by observing how they filter starlight shining through as they pass in front of the star. Which molecules make up a planet’s atmosphere can shed light on how it evolved and whether it may have life on its surface. It will take more observations and time to analyze the data collected so far before researchers know if TRAPPIST-1g has an atmosphere and, if so, what it is made of.
Creating a “Family Portrait”
TRAPPIST-1’s data is much more difficult to analyze than that of larger exoplanets, including WASP-39b, a planet closer to the size of Jupiter that JWST has studied in detail. TRAPPIST-1’s planets are much smaller, and the signal from their atmosphere is more difficult to read. Magnetic disturbances in TRAPPIST-1 can also induce signals that confuse data interpretation.
“We needed that first look to know what we were dealing with,” says Knicole Colón, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved with the work. Benneke declined to speak to reporters about the TRAPPIST-1g results, citing a paper being reviewed in a scientific journal.
In a poster presentation at the conference, Olivia Lim from the University of Montreal presented two JWST observations of the system’s innermost planet, TRAPPIST-1b. It too has not yet managed to tease out a signal that points to the planet’s atmosphere. But preliminary studies suggest that, like Planet 1g, it likely doesn’t have a bloated, hydrogen-rich atmosphere.
Lim already has several other observations of other TRAPPIST-1 planets on hand, including one taken last week that she hasn’t been able to view yet given the volume of JWST results. “It’s hectic,” she says.
But more results on the extraordinary planetary system are on the way, says Colón: “We will have a family portrait over the next year.”
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