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).
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