Molecular complexity observed in the HD 100546 and IRS 48 planet-forming disks

Observations from the ALMA telescope reveal the chemical composition of gas and ice in the planet-forming disks surrounding the stars HD 100546 and IRS 48. By measuring the ratios of water, methanol, and methyl formate, researchers have gained new insights into how these building blocks of planets evolve during the intermediate stages of star formation.

Star system: HD 100546 | Distance from the Sun: 359 light years

The chemical makeup of the disks surrounding young stars provides a record of the raw materials available for planet formation. By studying the presence of water, methanol, and methyl formate in the disks of HD 100546 and IRS 48, researchers are tracing how these vital molecules change as a star system matures. These molecules are essential components of interstellar ice, and their relative amounts in the gas phase indicate how ice reservoirs are processed during the period when planets are born.

Data were obtained using the Atacama Large Millimeter/submillimeter Array (ALMA), an instrument designed to detect faint radio signals from cold gas and dust in space. By analyzing specific emission lines, the team measured the abundance of these molecules within the warm, inner regions of the disks. This allows for a comparison between the chemical signatures seen in these disks and those previously observed in comets and other young star systems, effectively bridging the gap between early stellar development and later planetary systems.

In the disk of HD 100546, both water and methanol were identified, showing a ratio similar to that found in typical comets. In contrast, the IRS 48 disk appears methanol-rich but lacks detectable water vapor. Furthermore, the disk of HD 100546 shows a surprisingly high amount of methyl formate compared to younger or older systems, which suggests that gas-phase chemistry may be actively enhancing this compound during this specific stage of disk evolution.

Key findings
The HD 100546 disk shows a methanol-to-water ratio of approximately 0.02, matching the median values found in comets.
The IRS 48 disk is rich in methanol, with a methanol-to-water ratio exceeding 0.2, indicating a unique chemical environment.
A high methyl formate-to-methanol ratio of approximately 2 was found in the HD 100546 disk, exceeding values found in other known stellar systems.
The methyl formate-to-methanol ratio in the IRS 48 disk was measured at approximately 0.2.

Scientific study

An ALMA view on molecular complexity: water, methanol, and methyl formate in the HD 100546 and IRS 48 disks (external link)