This artist’s impression shows the closest known protoplanetary disc, around the star TW Hydrae in the huge constellation of Hydra (The Female Watersnake). The organic molecule methyl alcohol (methanol) has been found by the Atacama Large Millimeter/Submillimeter Array (ALMA) in this disc. This is the first such detection of the compound in a young planet-forming disc. Credit: ESO/M. Kornmesser
The protoplanetary disc around young star TW Hydrae is the closest known example to Earth, at ~170 light-years. As such it is an ideal target for astronomers to study discs. This system closely resembles what astronomers think the Solar System looked like during its formation more than four billion years ago. The ALMA Array is the most powerful observatory for mapping the chemical composition and the distribution of cold gas in nearby discs.
ALMA observations have revealed the fingerprint of gaseous methyl alcohol, or methanol (CH3OH), in a protoplanetary disc for the first time. Methanol, a derivative of methane, is one of the largest complex organic molecules detected in discs to date. Identifying its presence in pre-planetary objects represents a milestone for understanding how organic molecules are incorporated into nascent planets. It is a building block for more complex species of fundamental prebiotic importance, like amino acid compounds. As a result, methanol plays a vital role in the creation of the rich organic chemistry needed for life.
While other species detected are formed by gas-phase chemistry alone, or by a combination of both gas and solid-phase generation, methanol is a complex organic compound which is formed solely in the ice phase via surface reactions on dust grains. The observation of methanol in the gas phase, combined with information about its distribution, implies that methanol formed on the disc’s icy grains, and was subsequently released in gaseous form. This first observation helps to clarify the puzzle of the methanol ice-gas transition, and more generally the chemical processes in astrophysical environments.
Ryan A. Loomis, adds: “Methanol in gaseous form in the disc is an unambiguous indicator of rich organic chemical processes at an early stage of star and planet formation. This result has an impact on our understanding of how organic matter accumulates in very young planetary systems.”
This successful first detection of cold gas-phase methanol in a protoplanetary disc means that the production of ice chemistry can now be explored in discs, paving the way to future studies of complex organic chemistry in planetary birthplaces. In the hunt for life-sustaining exoplanets, astronomers now have access to a powerful new tool. http://www.eso.org/public/news/eso1619
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