NASA’s Webb Detects Carbon Dioxide in Exoplanet Atmosphere


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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.

Graphs of relative brightness of 3 different wavelengths of light versus time. Top graph forms a U-shaped valley showing a period of decreased brightness. The valley floor shows that the amount of dimming differs for the 3 different wavelengths.

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.”

Graph of amount of light blocked versus wavelength of light with data points and a model, showing a broad, prominent peak labeled “Carbon Dioxide, C O 2”.

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)

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Zig Zag Wanderer
August 26, 2022 2:10 am

Now they can obviously determine the exact climate of this planet, because CO2 is the only factor that determines planetary climates!

Reply to  Zig Zag Wanderer
August 26, 2022 3:32 am

The atmospheric CO2 concentration on this exoplanet is about 500ppm (+-99%) and its temperature is 900 deg C. Now do you understand the danger that Earth faces?

Nicholas Harding
Reply to  Mike Jonas
August 26, 2022 6:31 am

Mars 95% CO2 temp very very cold.

Now do you understand the danger that Earth faces?

Gordon A. Dressler
Reply to  Mike Jonas
August 26, 2022 8:54 am

WTF? Did you not read this statement in the above article:
“WASP-39 b orbits very close to its star – only about one-eighth the distance between the Sun and Mercury” ?

Methinks that has a LOT more to do with establishing the temperature of this exoplanet than does any possible concentration of CO2 in its atmosphere.

At Earth’s present distance from Sol, it faces NO SUCH EQUIVALENT DANGER . . . NONE!

Reply to  Gordon A. Dressler
August 26, 2022 2:50 pm

The sun has no influence on Earth’s climate, according to the IPCC. Why is this exoplanet being close to its star of any relevance at all. Clearly the 900 deg C is all because of the CO2.

Did I really need a /sarc.

Gordon A. Dressler
Reply to  Mike Jonas
August 27, 2022 10:49 am

Yes, you did.

Jim Gorman
Reply to  Mike Jonas
August 27, 2022 4:17 pm


Reply to  Mike Jonas
August 26, 2022 9:02 am

I believe the sarc is implied but some are not catching it.

Reply to  Mike Jonas
August 26, 2022 12:10 pm

Kind of like Mars, with a 100% CO2 atmosphere, the poles are covered in dry ice.

Zig Zag Wanderer
Reply to  max
August 27, 2022 3:35 am


Roughly 25x the amount of CO2 as our atmosphere. That’s why Mars is so hot!

August 26, 2022 2:40 am

If only Webb could capture evidence of extra terrestrial SUVs

Walter Sobchak
Reply to  fretslider
August 26, 2022 8:42 am

I think this is the smoking gun, as it were.

Gordon A. Dressler
Reply to  fretslider
August 26, 2022 8:59 am

Would give a whole new meaning to the name “Hot Wheels”.

Ron Long
August 26, 2022 3:14 am

Interesting spectrum peak, 4.4 micrometers, because 1 micron equals 1,000 nanometers, and the sensors common on earth top out at about 2,500 nanometers, so the 4,500 nanometers this Webb detector reads is equivalent to TV and Radio frequency energy. I’m sure they know what they are doing, however, and are not as confused as I am.

Reply to  Ron Long
August 26, 2022 4:58 am

Radio waves are much longer, ~ meter wavelength.

Reply to  Scissor
August 26, 2022 7:19 am

hmm, used to teach RADAR in the RAF. Radio wavelengths are from millimetres to thousands of kilometres. But take your point.

August 26, 2022 3:39 am

There must be human activity on this planet causing the CO2 emissions, the very fact that it is a super hot giant confirms this. Being so close to its star is mere coincidence

Reply to  Chris Ainsworth
August 26, 2022 4:09 am

Being so close to its star is mere coincidence.

Indeed it is…

Earth’s warming: how scientists know it’s not the sun”

Walter Sobchak
Reply to  Chris Ainsworth
August 26, 2022 8:44 am

Everybdody knows that the sun has no effect on the climate. It is Settled Science!

Reply to  Walter Sobchak
August 26, 2022 10:57 pm

Of course the sun has no effect on our climate. How could it? It’s 150,000,000 km away!

Joao Martins
August 26, 2022 3:48 am

NASA’s Webb Detects Carbon Dioxide in Exoplanet Atmosphere
Worse than expected!
Global Worming (sic) all over the Universe!

Reply to  Joao Martins
August 26, 2022 5:15 am

And all of it is caused by earthling CO2 emissions

Peta of Newark
August 26, 2022 3:55 am

If they’d have tipped OCO Sputnik upside down, it would have found it.

Do we say 4.1 micron = 433 Celsius?
There should be another absorption peak at around 2.7 micron

One (2 in fact) very good reason(s) how/why extra CO2 is warming the atmosphere
Not the surface, not the water, not the trees, not the urbans, not the plants and certainly not the people.
(Heaven forbid it did warm the people, they’re quite hot & bothered enough already without Sol adding to their self-inflicted plight)

i.e. CO2 is intercepting solar energy, = energy with a very potent warming potential, and heating the atmosphere

But that energy (at 4.1 and 2.7 micron) is then not reaching the surface.

In my book that would equate Global Cooling

Anyway, how long do we give this ‘Planet Wasp’ before it falls into its sun?
There’s nowhere else it can possibly go

August 26, 2022 4:28 am

When reading astronomy papers, the problem is knowing where solid science stops and mere speculation begins.

A few years ago, scientists were pointing at the existence of CO2 in a planet’s atmosphere as a sign of life. link But then, we are told that life on Earth greatly reduced the amount of CO2 in the atmosphere. link Apparently, the Earth’s early atmosphere had much more CO2 because of volcanoes. link

What to believe?

Zig Zag Wanderer
Reply to  commieBob
August 26, 2022 5:10 am

I’m pretty certain that it has been decided that aliens have noticed the massive 0.04% of CO2 in our atmosphere, and that’s why they haven’t contacted us. We’re obviously too dangerous to contact, because we are wilfully destroying our planet.

I mean, who can’t believe that?

August 26, 2022 6:16 am

On exo planet , CO2 is considered as vital gas , but on Earth, it’s poison …
That’s human Logic …

Richard Patton
Reply to  Hubert
August 26, 2022 8:58 am

They didn’t receive grant money to say that it is dangerous. Government grant money is designed to “document” a “crisis” that allows the politicians to appear to be doing something that they can point to so they can get re-elected

August 26, 2022 6:44 am

I’m sure they detected other compounds but they do publicity on this because the idea of CO2 causes US scientists full mental derangement.

Let me know when this thing produces some real useful science.

August 26, 2022 7:14 am

We must dispatch Al Gore and Greta there immediately to warn the inhabitants of the error of their ways!

Gordon A. Dressler
August 26, 2022 8:48 am

C’mon . . . is it really newsworthy that CO2 has been found in the atmosphere of an exo-solar planet???

After all, the planets Venus, Mars and Pluto (the last maybe no longer consider as a true planet) have all been found to contain significant percentages of CO2 in their atmospheres (ref: )

Good grief!

Mike McMillan
Reply to  Gordon A. Dressler
August 26, 2022 10:24 pm

Pluto is not a planet, huh?

Next thing you’ll say is that it’s got pronouns.

Gordon A. Dressler
Reply to  Mike McMillan
August 27, 2022 8:13 am

“The world was introduced to dwarf planets in 2006, when petite Pluto was stripped of its planet status and reclassified as a dwarf planet. The International Astronomical Union (IAU) currently recognizes two other dwarf planets, Eris and Ceres.”
— source: (mu underlining emphasis added)

August 26, 2022 9:06 am

Sorry but I don’t believe a word of it. I have seen pictures of stars etc. and Nasa has a whole different look to what others have seen. Is there anybody out there, should be is there really an out there. I guess maybe I’m just a nut job but the space thing doesn’t make sense to me

Zig Zag Wanderer
Reply to  HOJO
August 26, 2022 9:38 am

Did that make any sense when it was in your head?

Gordon A. Dressler
Reply to  Zig Zag Wanderer
August 26, 2022 12:28 pm

There is a WHOLE LOT to be said for the art of written communication . . . when practiced properly.

August 26, 2022 10:52 pm

That planet is doomed!

August 27, 2022 8:53 am

Wow, now they can do another measurement in a years time, fit a “trend” line and project it 100 y into the future and tell us how hot it will be !

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