Webb makes the first discovery of the important carbon molecule in a planet-forming disc

Science and Exploration

26/06/2023
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An international team of scientists used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect a molecule [1] known as methyl cation (CH3+) for the first time, found in the protoplanetary disc surrounding a young star. They accomplished this work through a cross-disciplinary expert review, including key input from laboratory spectroscopists.

This simple molecule has a unique property: it reacts relatively poorly with the most abundant element in our Universe (hydrogen) but readily reacts with other molecules and therefore initiates the growth of more complex carbon-based molecules. The chemistry of carbon is of particular interest to astronomers because all known life is based on carbon. The important role that CH3+ plays in interstellar carbon chemistry was predicted in the 1970s, but Webb’s unique capabilities made it possible to observe it — in a region of space where life-capable planets may eventually develop. develop.

Carbon compounds [2] form the foundations of all known life, and as such are of particular interest to scientists trying to understand both how life evolved on Earth, and how it might have evolved elsewhere in our Universe. Because of this, interstellar organic chemistry [3] is an area of ​​great interest to astronomers who study the places where new stars and planets form. Molecular ions [4] Carbon-containing ones are especially important, because they react with other small molecules to form more complex organic compounds even at low interstellar temperatures. [5].

The methyl cation (CH3+) is one of the carbon-based ions. CH3+ has been assumed by scientists to be of particular importance since the 1970s and 1980s. This is due to an amazing property of CH3+, that it reacts with a wide range of other molecules. This small cation is significant enough that it is thought to be the foundation of interstellar organic chemistry, but until now it has not been identified. The unique properties of the James Webb Space Telescope have made it the perfect instrument to search for this crucial cation — and now, a group of international scientists have observed it on Webb for the first time. Marie-Aline Martin of Paris-Saclay University, France, a spectroscopist and member of the science team, explains: “This discovery of CH3+ not only confirms James Webb’s incredible sensitivity but also proving the fundamental importance of CH3+ in interstellar chemistry.”

The Orion Bar region (upscaled MIRI image)

The CH3+ signal was detected in the star-protoplanetary disc [6] system known as d203-506, located about 1350 light years away, in the Orion Nebula. Although the star in d203-506 is a small red dwarf star, with a mass of only about a tenth of the Sun, the system is bombarded with strong ultraviolet radiation from nearby hot, young, massive stars. Scientists believe that most of the planet-forming protoplanetary disks passed through a period of such intense ultraviolet radiation, because stars tend to form in clusters that often include massive ultraviolet-producing stars. Interestingly, evidence from meteorites suggests that the protoplanetary disc that formed our Solar System was also subject to a great deal of ultraviolet radiation — emitted by a companion star to our Sun that has long since died (the large ones burn brightly star and die off much faster than less massive stars). The confusing factor in all this is that ultraviolet radiation has long been considered purely destructive to the formation of complex organic molecules – but there is clear evidence that the only life-supporting planet we know of was born from a disc that overexposed to it.

The team that conducted this research may have found the solution to this conundrum. Their work predicts that the presence of CH3+ is in fact connected to ultraviolet radiation, which provides the necessary energy source to form CH3+. Furthermore, the period of ultraviolet radiation experienced by some disks seems to have a profound effect on their chemistry. For example, Webb’s observations of protoplanetary disks that are not subject to intense ultraviolet radiation from a nearby source show a large abundance of water — in contrast to d203-506, where the team could not detect water. The lead author, Olivier Berné of the University of Toulouse, France, explained, “This clearly shows that ultraviolet radiation can completely change the chemistry of a proto-planetary disc. It can actually play a critical role in the early chemical stages of the origin of life by helping to produce CH3+ — something that was probably underestimated before.”


The Orion Bar region (Slider)

Although research published in the early 1970s predicted the importance of CH3+, it was previously almost impossible to detect. Many molecules in protoplanetary discs are observed using radio telescopes. However, for this to be possible the molecules in question must have a so-called ‘permanent dipole moment’, that is, the geometry of the molecule is such that its electric charge is permanently unbalanced, giving the molecule a positive and negative ‘end’. CH3+ is symmetrical, and therefore its charge is balanced, and thus lacks the permanent dipole moment required for observations with radio telescopes. In this theory, it is possible to observe the spectroscopic lines emitted by CH3+ in the infrared, but the Earth’s atmosphere makes them impossible to observe from Earth. Thus, it was necessary to use a sufficiently sensitive space-based telescope that could observe infrared signals. The instruments NIRSpec, part of the European contribution to Webb’s, and MIRI, half of which was contributed by Europe, are ideal for the job. In fact, a CH3+ detection used to be so difficult that when the team first saw the signal in their data, they weren’t sure how to detect it. Remarkably, the team was able to interpret their result in four short weeks, by drawing on the expertise of an international team with a diverse range of expertise.

The discovery of CH3+ was only possible through the collaboration of observational astronomers, astrochemical modellers, theoreticians, and experimental spectroscopists, who combined the unique capabilities of JWST in space and Earth-based laboratories to successfully investigate and provide meaning the composition of our local universe and evolution. Marie-Aline Martin added: “Our discovery was only possible because astronomers, modellers and spectroscopists joined forces in the laboratory to understand the unique features observed by James Webb.”
The results of the PDRs4ALL ERS team were published today at Nature.

Stars
[1] A molecule is a particle made up of two or more atoms held together by chemical bonds.
[2] A compound is a molecule that includes more than one element. So, all compounds are molecules but not all molecules are compounds. For example, the hydrogen molecule (H2) is a molecule but not a compound, whereas the water molecule (H2O) is also a compound.
[3] Organic chemistry refers to the chemistry of carbon-based molecules and compounds. It can also be called carbon chemistry.
[4] An ion is an atom or molecule that has a total electric charge, due to an excess or deficiency in the number of negative electrons compared to the number of positive protons in the ion. A cation is an ion with a net positive charge (hence a deficit of electrons).
[5] A complex organic molecule is a molecule with many carbon atoms.
[6] A protoplanetary disc is a rotating disc of gas and dust that forms around young stars, and from which planets can eventually form.

Additional information
Webb is the largest, most powerful telescope ever launched into space. Under an international cooperation agreement, ESA provided the telescope launch service, using the Ariane 5 launch vehicle. In collaboration with partners, ESA is responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the Arianespace launch service. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in collaboration with JPL and the University of Arizona .

Webb is an international collaboration between NASA, ESA and the Canadian Space Agency (CSA).

Please contact:
ESA Media relations
[email protected]

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