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NASA’s James Webb Space Telescope has
captured the first clear evidence for carbon dioxide in the atmosphere of a
planet outside the solar system. This observation of a gas giant planet
orbiting a Sun-like star 700 light-years away provides important insights into
the composition and formation of the planet. The finding, accepted for
publication in Nature, offers evidence that in the future Webb may be able to
detect and measure carbon dioxide in the thinner atmospheres of smaller rocky
planets.
WASP-39 b is a hot gas giant with a mass
roughly one-quarter that of Jupiter (about the same as Saturn) and a diameter
1.3 times greater than Jupiter. Its extreme puffiness is related in part to its
high temperature (about 1,600 degrees Fahrenheit or 900 degrees Celsius).
Unlike the cooler, more compact gas giants in our solar system, WASP-39 b
orbits very close to its star – only about one-eighth the distance between the
Sun and Mercury – completing one circuit in just over four Earth-days. The
planet’s discovery, reported in 2011, was made based on ground-based detections
of the subtle, periodic dimming of light from its host star as the planet transits, or passes in front of the star.
Previous observations from other
telescopes, including NASA’s Hubble and
Spitzer space
telescopes, revealed the presence of water vapor, sodium, and potassium in the
planet’s atmosphere. Webb’s unmatched infrared sensitivity has now confirmed
the presence of carbon dioxide on this planet as well.
A series of light curves from Webb’s Near-Infrared Spectrograph (NIRSpec)
shows the change in brightness of three different wavelengths (colors) of light
from the WASP-39 star system over time as the planet transited the star July
10, 2022. Credits: Illustration: NASA, ESA, CSA, and L. Hustak (STScI);
Science: The JWST Transiting Exoplanet Community Early Release Science Team
Filtered Starlight
Transiting planets like WASP-39 b, whose orbits we observe edge-on rather
than from above, can provide researchers with ideal opportunities to probe
planetary atmospheres.
During a transit, some of the starlight is eclipsed by the planet
completely (causing the overall dimming) and some is transmitted through the
planet’s atmosphere.
Because different gases absorb different combinations of colors,
researchers can analyze small differences in brightness of the transmitted
light across a spectrum of wavelengths to determine exactly what an atmosphere
is made of. With its combination of inflated atmosphere and frequent transits,
WASP-39 b is an ideal target for transmission
spectroscopy.
First Clear Detection of Carbon Dioxide
The research team used Webb’s Near-Infrared
Spectrograph (NIRSpec) for its observations of
WASP-39b. In the resulting spectrum of the exoplanet’s atmosphere, a small hill
between 4.1 and 4.6 microns presents the first clear, detailed evidence for
carbon dioxide ever detected in a planet outside the solar system.
"As soon as the data appeared on my screen, the whopping carbon dioxide
feature grabbed me,” said Zafar Rustamkulov, a graduate student at Johns
Hopkins University and member of the JWST Transiting Exoplanet Community Early
Release Science team, which undertook this investigation. “It was a special
moment, crossing an important threshold in exoplanet sciences.”
No observatory has ever measured such subtle differences in brightness of
so many individual colors across the 3 to 5.5-micron range in an exoplanet
transmission spectrum before. Access to this part of the spectrum is crucial
for measuring abundances of gases like water and methane, as well as carbon
dioxide, which are thought to exist in many different types of exoplanets.
“Detecting such a clear signal of carbon dioxide on WASP-39 b bodes well
for the detection of atmospheres on smaller, terrestrial-sized planets,” said
Natalie Batalha of the University of California at Santa Cruz, who leads the
team.
Understanding the composition of a planet’s atmosphere is important because it tells us something about the origin of the planet and how it evolved. “Carbon dioxide molecules are sensitive tracers of the story of planet formation,” said Mike Line of Arizona State University, another member of this research team. “By measuring this carbon dioxide feature, we can determine how much solid versus how much gaseous material was used to form this gas giant planet. In the coming decade, JWST will make this measurement for a variety of planets, providing insight into the details of how planets form and the uniqueness of our own solar system.”
A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured
by Webb’s Near-Infrared Spectrograph (NIRSpec) July 10, 2022, reveals the first
clear evidence for carbon dioxide in a planet outside the solar system. This is
also the first detailed exoplanet transmission spectrum ever captured that
covers wavelengths between 3 and 5.5 microns. Credits: Illustration:
NASA, ESA, CSA, and L. Hustak (STScI); Science: The JWST Transiting Exoplanet
Community Early Release Science Team
Early Release Science
This NIRSpec prism observation of WASP-39 b is just one part of a
larger investigation that includes observations of the planet using multiple Webb
instruments, as well as observations of two other transiting planets. The
investigation, which is part of the Early Release Science program, was designed to provide the exoplanet research community
with robust Webb data as soon as possible.
“The goal is to analyze the Early Release Science observations quickly and
develop open-source tools for the science community to use,” explained Vivien
Parmentier, a co-investigator from Oxford University. “This enables
contributions from all over the world and ensures that the best possible
science will come out of the coming decades of observations.”
Natasha Batalha, co-author on the paper from NASA's Ames Research Center,
adds that “NASA's open science guiding principles are centered in our Early
Release Science work, supporting an inclusive, transparent, and collaborative
scientific process."
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 the Canadian
Space Agency.
Banner Image: This illustration shows what exoplanet WASP-39 b could look like, based on current understanding of the planet. WASP-39 b is a hot, puffy gas-giant planet with a mass 0.28 times Jupiter (0.94 times Saturn) and a diameter 1.3 times greater than Jupiter, orbiting just 0.0486 astronomical units (4,500,000 miles) from its star. The star, WASP-39, is fractionally smaller and less massive than the Sun. Because it is so close to its star, WASP-39 b is very hot and is likely to be tidally locked, with one side facing the star at all times. Illustration Credit: NASA, ESA, CSA, and J. Olmsted (STScI)
Source: NASA’s Webb Detects Carbon Dioxide in Exoplanet Atmosphere | NASA
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