With Webb, scientists make first detection of carbon molecule in protoplanetary disk

by Haygen Warren

With new data collected by the joint NASA/European Space Agency/Canadian Space Agency James Webb Space Telescope, an international team of scientists has — for the first time ever — detected a carbon molecule within the protoplanetary disk of a star located in the Orion Nebula. The molecule, called methyl cation (CH3+), is quite unique. The molecule doesn’t react to hydrogen all that efficiently but can react with other common molecules. This reaction allows for the creation and growth of more complex carbon-based molecules  — like life.

CH3+’s potential importance in universal carbon chemistry has been predicted by scientists since the 1970s. However, until Webb officially began operations in 2022, telescopes before and since have all been unable to detect the molecule in the universe. Webb’s incredibly sensitive suite of infrared instruments allowed the team, led by Olivier Berné of the French National Centre for Scientific Research in Toulouse, to detect the molecule.

Located approximately 1,350 light-years away in the Orion Nebula, protoplanetary disk d203-506 was the focus of Webb’s observations and Berné et al.’s research. Webb observed the nebula with its near-infrared camera (NIRCam) and mid-infrared instrument (MIRI). While just a spec in a vast area of swirling gas, dust, rock, and other cosmic materials, the team was able to identify and analyze Webb’s d203-506 data to discover CH3+ in the disk.

Annotated graphic of Webb’s Orion Nebula image that shows d203-506. (Credit: ESA/Webb/NASA/CSA/M. Zamani (ESA/Webb)/PDRs4All ERS Team)

Carbon compounds have long been known to form the basis for all life forms on Earth. Without carbon, life and many other vital environmental processes wouldn’t be possible. Because of their importance to life and the formation of life, scientists are constantly searching the universe for different signs and forms of carbon — a field known as interstellar organic chemistry. Scientists who search for carbon in the universe typically search for carbon-containing molecular ions, as they can react with a plethora of other elements and molecules to form more complex structures.

CH3+ is one of these molecular carbon ions that are capable of reacting with other elements/molecules and forming complex structures. For several decades, scientists have searched for the molecule throughout the universe due to its importance in the formation of complex structures and life forms. CH3+ has long been referred to as the “cornerstone of interstellar organic chemistry.”

However, how do you detect carbon molecules in a protoplanetary disk several thousand light-years away?

When trying to observe molecules in protoplanetary disks, scientists will typically use radio telescopes and attempt to detect a molecule’s “perfect dipole moment” — a molecular characteristic that means that a molecule’s electric charge is permanently off balance due to its geometry (this gives the molecule a positive and negative “end”). Given that CH3+ is perfectly balanced, it doesn’t have a perfect dipole moment and, thus, can’t be detected using traditional radio telescopes. Instead, scientists try to detect the spectroscopic lines that CH3+ emits in the infrared. Since Earth’s atmosphere would interfere with infrared observations, a space-based infrared telescope would be needed.

MIRI’s image of d203-506’s (center) location within the Orion Nebula. (Credit: ESA/Webb/NASA/CSA/M. Zamani (ESA/Webb)/PDRs4All ERS Team)

When Webb — the world’s newest space-based infrared telescope — officially began scientific operations in mid-2022, using the revolutionary telescope to detect CH3+ was at the top of many scientists’ to-do lists. Webb’s immense sensitivity to the near-infrared and mid-infrared regions of the electromagnetic spectrum allows it to see molecules and structures that are typically hidden from the view of instruments in visible and X-ray telescopes. Furthermore, Webb’s incredible size and massive mirror allow it to see more of the universe than any other telescope that came before it. These qualities made Webb the perfect tool to detect CH3+.

While scientists expected Webb to eventually detect CH3+, many were shocked that the telescope and Berné et al. detected it as soon as they did (Webb is still in the midst of its first year of scientific observations). In fact, it took Berné et al. just four weeks to interpret the CH3+ signal, which they didn’t even know how to identify when they saw it for the first time.

“This detection of CH3+ not only validates the incredible sensitivity of James Webb but also confirms the postulated central importance of CH3+ in interstellar chemistry,” said spectroscopic and co-author Marie-Aline Martin of the Paris-Saclay University in France.

Given its age and location in the Orion Nebula, d203-506, which is located around a small red dwarf star, is constantly bombarded by strong ultraviolet radiation from surrounding young stars. Many scientists currently believe that most star systems experience this period of intense ultraviolet radiation exposure.

Interestingly, though, previous data suggest that ultraviolet radiation can kill compounds necessary for the formation of complex structures. However, CH3+ — a molecule capable of producing complex structures — was detected in a protoplanetary disk being perpetually exposed to ultraviolet radiation. What’s happening here?

In their study, Berné et al. explain that CH3+ may need ultraviolet radiation to exist. If this is true, the ultraviolet radiation would be serving as a source of energy for the CH3+ in the protoplanetary disk. If a disk experiences a period of intense ultraviolet radiation exposure, the radiation appears to significantly alter the chemistry within the disk. To confirm this, Webb observed a disk that had not been exposed to intense ultraviolet radiation, in which it found abundant amounts of water. However, in d203-506 (which was exposed to radiation), Berné et al. were not able to detect any water in the disk or surrounding areas.

“This clearly shows that ultraviolet radiation can completely change the chemistry of a protoplanetary disc. It might actually play a critical role in the early chemical stages of the origins of life by helping to produce CH3+ — something that has perhaps previously been underestimated,” Berné explained.

Berné et al.’s results were published in the journal Nature on June 26.

“Our discovery was only made possible because astronomers, modelers, and laboratory spectroscopists joined forces to understand the unique features observed by James Webb,” said Martin.

(Lead image: Webb’s image of the Orion Nebula. Credit: ESA/Webb/NASA/CSA/M. Zamani (ESA/Webb)/PDRs4All ERS Team)

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