NASA’s James Webb Space Telescope just scored another first: a molecular and chemical profile of a distant world’s skies.
While Webb and other space telescopes, including NASA’s
Hubble and Spitzer, previously have revealed isolated ingredients of this
broiling planet’s atmosphere, the new readings from Webb provide a full menu of
atoms, molecules, and even signs of active chemistry and clouds.
The latest data also gives a hint of how these clouds might
look up close: broken up rather than a single, uniform blanket over the planet.
The telescope’s array of highly sensitive instruments was
trained on the atmosphere of WASP-39 b, a “hot Saturn” (a planet about as
massive as Saturn but in an orbit tighter than Mercury) orbiting a star some
700 light-years away.
The findings bode well for the capability of Webb’s
instruments to conduct the broad range of investigations of all types of
exoplanets – planets around other stars – hoped for by the science community.
That includes probing the atmospheres of smaller, rocky planets like those in
the TRAPPIST-1 system.
“We observed the exoplanet with multiple instruments that,
together, provide a broad swath of the infrared spectrum and a panoply of
chemical fingerprints inaccessible until [this mission],” said Natalie Batalha,
an astronomer at the University of California, Santa Cruz, who contributed to
and helped coordinate the new research. “Data like these are a game changer.”
The suite of discoveries is detailed in a set of five new
scientific papers, three of which are in press and two of which are under
review. Among the unprecedented revelations is the first detection in an
exoplanet atmosphere of sulfur dioxide (SO2), a molecule produced from chemical
reactions triggered by high-energy light from the planet’s parent star. On
Earth, the protective ozone layer in the upper atmosphere is created in a
similar way.
“This is the first time we see concrete evidence of
photochemistry – chemical reactions initiated by energetic stellar light – on
exoplanets,” said Shang-Min Tsai, a researcher at the University of Oxford in
the United Kingdom and lead author of the paper explaining the origin of sulfur
dioxide in WASP-39 b’s atmosphere. “I see this as a really promising outlook
for advancing our understanding of exoplanet atmospheres with [this mission].”
This led to another first: scientists applying computer
models of photochemistry to data that requires such physics to be fully
explained. The resulting improvements in modeling will help build the
technological know-how to interpret potential signs of habitability in the
future.
“Planets are sculpted and transformed by orbiting within the
radiation bath of the host star,” Batalha said. “On Earth, those
transformations allow life to thrive.”
The planet’s proximity to its host star – eight times closer
than Mercury is to our Sun – also makes it a laboratory for studying the
effects of radiation from host stars on exoplanets. Better knowledge of the
star-planet connection should bring a deeper understanding of how these
processes affect the diversity of planets observed in the galaxy.
To see light from WASP-39 b, Webb tracked the planet as it
passed in front of its star, allowing some of the star’s light to filter through
the planet’s atmosphere. Different types of chemicals in the atmosphere absorb
different colors of the starlight spectrum, so the colors that are missing tell
astronomers which molecules are present. By viewing the universe in infrared
light, Webb can pick up chemical fingerprints that can’t be detected in visible
light.
Other atmospheric constituents detected by the Webb
telescope include sodium (Na), potassium (K), and water vapor (H2O), confirming
previous space and ground-based telescope observations as well as finding
additional fingerprints of water, at these longer wavelengths, that haven’t
been seen before.
Webb also saw carbon dioxide (CO2) at higher resolution,
providing twice as much data as reported from its previous observations. Meanwhile,
carbon monoxide (CO) was detected, but obvious signatures of both methane (CH4)
and hydrogen sulfide (H2S) were absent from the Webb data. If present, these
molecules occur at very low levels.
To capture this broad spectrum of WASP-39 b’s atmosphere, an
international team numbering in the hundreds independently analyzed data from
four of the Webb telescope’s finely calibrated instrument modes.
An infographic titled "Hot Gas Giant Exoplanet Wasp-39
B Atmosphere Compositions" that shows four graphs from Webb's different
instruments.
The atmospheric composition of the hot gas giant exoplanet
WASP-39 b has been revealed by NASA’s James Webb Space Telescope. This graphic
shows four transmission spectra from three of Webb’s instruments operated in
four instrument modes. At upper left, data from NIRISS shows fingerprints of
potassium (K), water (H2O), and carbon monoxide (CO). At upper right, data from
NIRCam shows a prominent water signature. At lower left, data from NIRSpec
indicates water, sulfur dioxide (SO2), carbon dioxide (CO2), and carbon
monoxide (CO). At lower right, additional NIRSpec data reveals all of these molecules
as well as sodium (Na).Credits: NASA, ESA, CSA, J. Olmsted (STScI)
Download the full-resolution image from the SpaceTelescope
Science Institute.
“We had predicted what [the telescope] would show us, but it
was more precise, more diverse, and more beautiful than I actually believed it
would be,” said Hannah Wakeford, an astrophysicist at the University of Bristol
in the United Kingdom who investigates exoplanet atmospheres.
Having such a complete roster of chemical ingredients in an
exoplanet atmosphere also gives scientists a glimpse of the abundance of
different elements in relation to each other, such as carbon-to-oxygen or
potassium-to-oxygen ratios. That, in turn, provides insight into how this
planet – and perhaps others – formed out of the disk of gas and dust
surrounding the parent star in its younger years.
WASP-39 b’s chemical inventory suggests a history of
smashups and mergers of smaller bodies called planetesimals to create an
eventual goliath of a planet.
“The abundance of sulfur [relative to] hydrogen indicated
that the planet presumably experienced significant accretion of planetesimals
that can deliver [these ingredients] to the atmosphere,” said Kazumasa Ohno, a
UC Santa Cruz exoplanet researcher who worked on Webb data. “The data also
indicates that the oxygen is a lot more abundant than the carbon in the
atmosphere. This potentially indicates that WASP-39 b originally formed far
away from the central star.”
In so precisely parsing an exoplanet atmosphere, the Webb
telescope’s instruments performed well beyond scientists’ expectations – and
promise a new phase of exploration among the broad variety of exoplanets in the
galaxy.
“We are going to be able to see the big picture of exoplanet
atmospheres,” said Laura Flagg, a researcher at Cornell University and a member
of the international team. “It is incredibly exciting to know that everything
is going to be rewritten. That is one of the best parts of being a scientist.”
The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe 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).