An international team of scientists have used data collected by the NASA/ESA/CSA James Webb Space Telescope to detect for the first time ever a molecule known as methyl cation (CH3+), located in the protoplanetary disc surrounding a young star. They accomplished this feat with interdisciplinary expert analysis, including key input from laboratory spectroscopists.
This simple molecule has a unique property: it reacts relatively inefficiently with the most abundant element in our universe (hydrogen) but reacts readily with other molecules and therefore initiates the growth of more complex carbon-based molecules.
Image made of three panels. The largest on the left shows the NIRCam image of a nebula with two bright stars. A skewed box in the top-right points to a second panel on the right, with a MIRI image of that area. A tiny box in the centre of that panel is blown up in a third panel below, with a zoomed-in, combined MIRI and NIRCam image of a yellow and orange blob.] Credit: ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb), the PDRs4All ERS Team
Carbon chemistry is of particular interest to astronomers because all known life is carbon-based. The vital role of CH3+ in interstellar carbon chemistry was predicted in the 1970s, but Webb's unique capabilities have finally made observing it possible - in a region of space where planets capable of accommodating life could eventually form.
Western University astrophysicists Els Peeters and Jan Cami are core members of the international collaboration with Peeters serving as co-lead investigator of Webb's Photodissociation Regions for All (PDRs4All ID 1288), an Early Release Science Program on radiative feedback from massive stars.
Els Peeters
"While we have hypothesized for some time methyl cation existed in the universe, it was purely theoretical until now," said Peeters, a physics and astronomy professor and expert on interstellar molecules and the formation of stars. "And we can only now prove its existence thanks to the awesome capabilities of the James Webb telescope. This is a remarkable discovery."
The PDRs4All team first spotted the previously undetected molecule's spectroscopic fingerprint while poring over data captured by Webb. Its cameras have such fine spatial resolution and infrared technologies that every pixel of every image captured contains a near-endless amount of mineable data.
Jan Cami
Cami made the first rudimentary simulation of how CH3+ would look through Webb's Optical Telescope Element - basically its eye - and it looked very much like the actual observations.
"The team looked in vain through catalogues and databases of molecular spectra to find a match, but the mystery species had apparently not been properly measured in the lab yet at this wavelength. I realized we could use Webb's exquisite data to characterize the molecule and that's how we zoomed in on CH3+."
These latest results from the PDRs4ALL team, which also includes Western researchers Ameek Sidhu, Ryan Chown, Bethany Schefter, Sofia Pasquini and Baria Kahn, were published today by the high impact journal Nature.
A nebula made of many layers of cloudy, colourful material. The top-left side of the image is brightly lit, filled with wispy, thin material in pale shades of pink and blue. A thick bar of denser, cloudier material crosses diagonally at the bottom right. It begins as orange and grows darker and sparser down to the corner. Two very bright stars, with very long diffraction spikes, lie in this sparse area. Credit: ESA/Webb, NASA, CSA, M. Zamani (ESA/Webb), the PDRs4All ERS Team
Fascinating to astronomers
Carbon compounds form the foundations of all known life, and as such are of particular interest to scientists working to understand both how life developed on Earth, and how it could potentially develop elsewhere in our universe. As such, interstellar organic chemistry is an area of keen fascination to astronomers who study the places where new stars and planets form.
Molecular ions containing carbon are especially important, because they react with other small molecules to form more complex organic compounds even at low interstellar temperatures. The methyl cation (CH3+) is one such carbon-based ion. CH3+ has been posited by scientists to be of particular importance since the 1970s and 1980s. This is due to a fascinating property of CH3+, which is that it reacts with a wide range of other molecules.
This little cation is significant enough that it has been theorized to be the cornerstone of interstellar organic chemistry, yet until now it has never been detected. The unique properties of Webb made it the ideal instrument to search for this crucial cation - and already, a group of international scientists have observed it for the first time.
The Orion Nebula has been studied by astronomers for hundreds of years, and it has been a frequent target of the Hubble Space Telescope since its launch. This comparison shows the striking difference in views afforded by a visible-light telescope, such as Hubble, and an infrared telescope like Webb. In Webb's image on the left, near-infrared light is able to penetrate the dust, but the heated gas also emits its own infrared light, making for a colourful scene with filaments and cavities. On the right in the Hubble image, which was taken during 2004 and 2005, bubbles of gas appear to float in front of the thick, smoky clouds of the nebula. Numerous new stars, some with protoplanetary discs, are visible across both images. Credit: NASA & ESA
"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 Marie-Aline Martin, a spectroscopist and science team member at Paris-Saclay University in France.
The CH3+ signal was detected in the star-protoplanetary disc system known as d203-506, which is located about 1350 light years away, in the Orion Nebula. While the star in d203-506 is a small red dwarf star, with a mass only about a tenth of the Sun's, the system is bombarded by strong ultraviolet radiation from nearby hot, young, massive stars. Scientists believe that most planet-forming protoplanetary discs go through a period of such intense ultraviolet radiation, since stars tend to form in groups that often include massive, ultraviolet-producing stars.
Evidence from meteorites suggest that the protoplanetary disc that went on to form our Solar System was also subject to a vast amount of ultraviolet radiation - emitted by a stellar companion to our Sun that has long since died (massive stars burn brightly and die much faster than less massive stars). The confounding factor in all this is that ultraviolet radiation has long been considered to be purely destructive to the formation of complex organic molecules - and yet there is clear evidence that the only life-supporting planet that we know of was born from a disc that was heavily exposed to it.
The team that performed 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 source of energy for CH3+ to form.
The period of ultraviolet radiation experienced by certain discs also seems to have a profound impact on their chemistry. For example, Webb observations of protoplanetary discs 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 at all.
"This clearly shows that ultraviolet radiation can completely change the chemistry of a proto-planetary 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," said lead author Olivier Berné of the University of Toulouse in France.
