The Earth-size exoplanet TRAPPIST-1 e, depicted at the lower right, is silhouetted as it passes in front of its flaring host star in this artist’s concept of the TRAPPIST-1 system. Scientists call this event a transit, when valuable data can be gathered as the exoplanet passes between the star and the telescope and starlight illuminates the atmosphere, if one is present. NASA’s James Webb Space Telescope has made initial observations of planets b, c, d, and e during their transits, with additional observations of planet e underway. While the star’s frequent flares make it difficult to detect an atmosphere, each transit builds up more and more information for scientists to get a more complete picture of these distant worlds. Credits/Artwork: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI)
This transmission spectrum graph compares data collected by the NIRSpec (Near-Infrared Spectrograph) instrument on NASA’s James Webb Space Telescope with computer models of exoplanet TRAPPIST-1 e with (blue) and without (orange) an atmosphere. Narrower, darker colored bands show the most likely locations of data points for each model while wider, more transparent bands show areas that are less likely but still permitted by the models. The gray region shows where those two models overlap. Researchers can’t yet confidently rule out an atmosphere since many of the data points fit either scenario. As Webb makes additional observations of the exoplanet, researchers will be able to further refine and characterize the atmospheric readings. However, the existing data does indicate that the exoplanet does not have a thick, hydrogen-rich atmosphere because multiple prominent spikes would be detectable if hydrogen were present. Credits/Illustration: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI)
Scientists are in the midst of observing the exoplanet TRAPPIST-1 e with NASA’s James Webb Space Telescope. Careful analysis of the results so far presents several potential scenarios for what the planet’s atmosphere and surface may be like, as NASA science missions lay key groundwork to answer the question, “are we alone in the universe?”
“Webb’s infrared instruments are giving us more detail than we’ve ever had access to before, and the initial four observations we’ve been able to make of planet e are showing us what we will have to work with when the rest of the information comes in,” said Néstor Espinoza of the Space Telescope Science Institute in Baltimore, Maryland, a principal investigator on the research team. Two scientific papers detailing the team’s initial results are published in the Astrophysical Journal Letters.
Of the seven Earth-sized worlds orbiting the red dwarf star TRAPPIST-1, planet e is of particular interest because it orbits the star at a distance where water on the surface is theoretically possible — not too hot, not too cold — but only if the planet has an atmosphere. That’s where Webb comes in. Researchers aimed the telescope’s powerful NIRSpec (Near-Infrared Spectrograph) instrument at the system as planet e transited, or passed in front of, its star. Starlight passing through the planet’s atmosphere, if there is one, will be partially absorbed, and the corresponding dips in the light spectrum that reaches Webb will tell astronomers what chemicals are found there. With each additional transit, the atmospheric contents become clearer as more data is collected.
“Webb’s infrared instruments are giving us more detail than we’ve ever had access to before, and the initial four observations we’ve been able to make of planet e are showing us what we will have to work with when the rest of the information comes in,” said Néstor Espinoza of the Space Telescope Science Institute in Baltimore, Maryland, a principal investigator on the research team. Two scientific papers detailing the team’s initial results are published in the Astrophysical Journal Letters.
Of the seven Earth-sized worlds orbiting the red dwarf star TRAPPIST-1, planet e is of particular interest because it orbits the star at a distance where water on the surface is theoretically possible — not too hot, not too cold — but only if the planet has an atmosphere. That’s where Webb comes in. Researchers aimed the telescope’s powerful NIRSpec (Near-Infrared Spectrograph) instrument at the system as planet e transited, or passed in front of, its star. Starlight passing through the planet’s atmosphere, if there is one, will be partially absorbed, and the corresponding dips in the light spectrum that reaches Webb will tell astronomers what chemicals are found there. With each additional transit, the atmospheric contents become clearer as more data is collected.
Primary atmosphere unlikely
Though multiple possibilities remain open for planet e because only
four transits have been analyzed so far, the researchers feel confident
that the planet does not still have its primary, or original,
atmosphere. TRAPPIST-1 is a very active star, with frequent flares, so
it is not surprising to researchers that any hydrogen-helium atmosphere
with which the planet may have formed would have been stripped off by
stellar radiation. However many planets, including Earth, build up a
heavier secondary atmosphere after losing their primary atmosphere. It
is possible that planet e was never able to do this and does not have a
secondary atmosphere. Yet researchers say there is an equal chance there
is an atmosphere, and the team developed novel approaches to working
with Webb’s data to determine planet e’s potential atmospheres and
surface environments.
World of (fewer) possibilities
The researchers say it is unlikely that the atmosphere of TRAPPIST-1 e
is dominated by carbon dioxide, analogous to the thick atmosphere of
Venus and the thin atmosphere of Mars. However, the researchers also are
careful to note that there are no direct parallels with our solar
system.
"TRAPPIST-1 is a very different star from our Sun, and so the planetary system around it is also very different, which challenges both our observational and theoretical assumptions,” said team member Nikole Lewis, an associate professor of astronomy at Cornell University.
If there is liquid water on TRAPPIST-1 e, the researchers say it would be accompanied by a greenhouse effect, in which various gases, particularly carbon dioxide, keep the atmosphere stable and the planet warm.
“A little greenhouse effect goes a long way,” said Lewis, and the measurements do not rule out adequate carbon dioxide to sustain some water on the surface. According to the team’s analysis, the water could take the form of a global ocean, or cover a smaller area of the planet where the star is at perpetual noon, surrounded by ice. This would be possible because, due to the TRAPPIST-1 planets’ sizes and close orbits to their star, it is thought that they all are tidally locked, with one side always facing the star and one side always in darkness.
"TRAPPIST-1 is a very different star from our Sun, and so the planetary system around it is also very different, which challenges both our observational and theoretical assumptions,” said team member Nikole Lewis, an associate professor of astronomy at Cornell University.
If there is liquid water on TRAPPIST-1 e, the researchers say it would be accompanied by a greenhouse effect, in which various gases, particularly carbon dioxide, keep the atmosphere stable and the planet warm.
“A little greenhouse effect goes a long way,” said Lewis, and the measurements do not rule out adequate carbon dioxide to sustain some water on the surface. According to the team’s analysis, the water could take the form of a global ocean, or cover a smaller area of the planet where the star is at perpetual noon, surrounded by ice. This would be possible because, due to the TRAPPIST-1 planets’ sizes and close orbits to their star, it is thought that they all are tidally locked, with one side always facing the star and one side always in darkness.
Innovative new method
Espinoza and co-principal investigator Natalie Allen of Johns Hopkins
University are leading a team that is currently making 15 additional
observations of planet e, with an innovative twist. The scientists are
timing the observations so that Webb catches both planets b and e
transiting the star one right after the other. After previous Webb
observations of planet b, the planet orbiting closest to TRAPPIST-1,
scientists are fairly confident it is a bare rock without an atmosphere.
This means that signals detected during planet b’s transit can be
attributed to the star only, and because planet e transits at nearly the
same time, there will be less complication from the star’s variability.
Scientists plan to compare the data from both planets, and any
indications of chemicals that show up only in planet e’s spectrum can be
attributed to its atmosphere.
“We are really still in the early stages of learning what kind of amazing science we can do with Webb. It’s incredible to measure the details of starlight around Earth-sized planets 40 light-years away and learn what it might be like there, if life could be possible there,” said Ana Glidden, a post-doctoral researcher at Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, who led the research on possible atmospheres for planet e. “We’re in a new age of exploration that’s very exciting to be a part of,” she said.
The four transits of TRAPPIST-1 e analyzed in the new papers published today were collected by the JWST Telescope Scientist Team’s DREAMS (Deep Reconnaissance of Exoplanet Atmospheres using Multi-instrument Spectroscopy) collaboration.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
“We are really still in the early stages of learning what kind of amazing science we can do with Webb. It’s incredible to measure the details of starlight around Earth-sized planets 40 light-years away and learn what it might be like there, if life could be possible there,” said Ana Glidden, a post-doctoral researcher at Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, who led the research on possible atmospheres for planet e. “We’re in a new age of exploration that’s very exciting to be a part of,” she said.
The four transits of TRAPPIST-1 e analyzed in the new papers published today were collected by the JWST Telescope Scientist Team’s DREAMS (Deep Reconnaissance of Exoplanet Atmospheres using Multi-instrument Spectroscopy) collaboration.
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
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Related Links and Documents
- The science paper by N. Espinoza et al.
- The science paper by A. Glidden et al.
- JWST Telescope Science Team
