NASA’s James Webb Space Telescope makes first ever detection of carbon dioxide in the atmosphere of a planet outside our solar system

  • NASA’s new telescope has detected carbon dioxide on an exoplanet for first time
  • It bodes well for future James Webb studies of rocky exoplanets similar to Earth 
  • WASP-39 b is a hot gas giant which has mass roughly one-quarter that of Jupiter
  • Past studies by Hubble and Spitzer had detected water vapour on WASP-39 b

NASA’s James Webb telescope has detected carbon dioxide in the atmosphere of a planet outside our solar system for the first time.

The discovery is important because it suggests the $10 billion (£7.4 billion) observatory may be able to detect and measure the gas in the thinner atmospheres of smaller, rocky planets that could host life.

WASP-39 b is a hot gas giant orbiting a sun-like star 700 light-years away from Earth.

It has a mass roughly one-quarter that of Jupiter – about the same as Saturn – and a diameter 1.3 times greater than Jupiter’s.

The exoplanet’s extreme puffiness is related in part to its high temperature, which is about 1,600 degrees Fahrenheit, or 900 degrees Celsius.

Discovery: NASA’s James Webb telescope has detected carbon dioxide in the atmosphere of a planet outside our solar system for the first time. This illustration shows what exoplanet WASP-39 b could look like

A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near-Infrared Spectrograph (NIRSpec) revealed the first clear evidence for carbon dioxide in a planet outside the solar system


Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere. 

To understand these new worlds and what they are made of, scientists need to be able to detect what their atmospheres consist of. 

They often do this by using a technique called absorption spectroscopy. 

This form of analysis measures the light that is coming out of a planet’s atmosphere.

Every gas absorbs a slightly different wavelength of light, and when this happens a black line appears on a complete spectrum. 

These lines correspond to a very specific molecule, which indicates its presence on the planet. 

They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.

By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up the atmosphere of a planet. 

This analysis has to be done by space telescopes such as James Webb because the atmosphere of Earth would otherwise interfere. 

Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study the light before it has had chance to reach Earth. 

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 vapour, 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.

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 colours, researchers can analyse 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. 

The research team used Webb’s Near-Infrared Spectrograph (NIRSpec) for its observations of WASP-39 b. 

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 colours 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.’

The discovery has been accepted for publication in the journal Nature.

The James Webb Telescope: NASA’s $10 billion telescope is designed to detect light from the earliest stars and galaxies

The James Webb telescope has been described as a ‘time machine’ that could help unravel the secrets of our universe.

The telescope will be used to look back to the first galaxies born in the early universe more than 13.5 billion years ago, and observe the sources of stars, exoplanets, and even the moons and planets of our solar system.

The vast telescope, which has already cost more than $7 billion (£5 billion), is considered a successor to the orbiting Hubble Space Telescope

The James Webb Telescope and most of its instruments have an operating temperature of roughly 40 Kelvin – about minus 387 Fahrenheit (minus 233 Celsius).

It is the world’s biggest and most powerful orbital space telescope, capable of peering back 100-200 million years after the Big Bang.

The orbiting infrared observatory is designed to be about 100 times more powerful than its predecessor, the Hubble Space Telescope.

NASA likes to think of James Webb as a successor to Hubble rather than a replacement, as the two will work in tandem for a while. 

The Hubble telescope was launched on April 24, 1990, via the space shuttle Discovery from Kennedy Space Centre in Florida.

It circles the Earth at a speed of about 17,000mph (27,300kph) in low Earth orbit at about 340 miles in altitude. 

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