The protoplanetary disc around the young star TW Hydrae
The discovery of the organic molecule methyl alcohol, or methanol, is the first time the compound has been found in a young planet-forming disc. An organic compound linked to the creation of the ingredients of life has been detected on a developing planet that is the closest known example to Earth.
Scientists say methanol is the only complex organic molecule as yet detected in discs that unambiguously derives from an icy form.
Its detection helps astronomers understand the chemical processes that occur during the formation of planetary systems and that ultimately lead to the creation of the ingredients for life.
The protoplanetary disc around the young star TW Hydrae is the closest known example to Earth, at a distance of about 170 light-years, making it an ideal target for astronomers to study discs.
The system closely resembles what astronomers think the Solar System looked like during its formation more than four billion years ago.
The Atacama Large Millimeter/Submillimeter Array (ALMA), which detected the compound, is the most powerful observatory in existence for mapping the chemical composition and the distribution of cold gas in nearby discs.
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A group of astronomers led by Doctor Catherine Walsh, of Leiden Observatory in Holland, investigated the chemistry of the TW Hydrae protoplanetary disc.
The ALMA observations revealed the fingerprint of gaseous methyl alcohol in a protoplanetary disc for the first time.
Dr Walsh said methanol, a derivative of methane, is one of the largest complex organic molecules detected in discs to date.
She said identifying its presence in pre-planetary objects represents a milestone for understanding how organic molecules are incorporated into new planets.
And Dr Walsh said methanol is itself a building block for more complex species of fundamental prebiotic importance, such as amino acid compounds.
As a result, methanol plays a vital role in the creation of the rich organic chemistry needed for life.
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Study lead author Dr Walsh said: “Finding methanol in a protoplanetary disc shows the unique capability of ALMA to probe the complex organic ice reservoir in discs and so, for the first time, allows us to look back in time to the origin of chemical complexity in a planet nursery around a young Sun-like star.”
She said gaseous methanol in a protoplanetary disc has a unique importance in astrochemistry.
While other species detected in space 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.
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The sharp vision of ALMA has also allowed astronomers to map the gaseous methanol across the TW Hydrae disc. They discovered a ring-like pattern in addition to significant emission from close to the central star.
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.
Study co-author Ryan Loomis added: “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.”
He said the first detection of cold gas-phase methanol in a protoplanetary disc means that astronomers have a new tool in the the hunt for life-sustaining exoplanets.