'Our new work suggests that what really matters is the ultraviolet radiation field generated by the star accreting matter from the disk,' he said. This represents the evolution of small dust over time.Ībout 20 years ago, researchers realized that the chemistry of the gaseous disk is governed by chemistry operating on shorter timescales and powered by sources such as cosmic rays and X-rays, said Edwin Bergin, principal investigator, professor and chair of astronomy. 'If we have a carbon-rich environment paired with a UV-rich environment due to the evolution of the small solids in planet forming regions, we can produce complex organics in the gas and reproduce these observations,' she said. To account for the observed brightness, Calahan adjusted her model to decrease the mass of the small dust population - which typically blocks UV photons - to allow more UV photons to penetrate deep into these coldest regions of the disc. As the planet-forming disk evolves over time, the changing environment affects the chemistry within. The planet-forming disk has three main components, a pebble-rich dusty midplane, a gas atmosphere and a small dust population coupled to the gas. These molecules should add to an icy coating on the grains, so they cannot be observed in the gas. These molecules are emitting from regions that are minus-400 degrees Fahrenheit, and at these temperatures they're thought to be frozen onto tiny solids that astronomers label as dust grains, or for the later mm-to-cm-sized solids as pebbles. 'This bright emission has been puzzling because we expect these molecules to be frozen out at these temperatures, not in the gas where we can observe them.' 'It has been shown that there are bright, complex organic molecules present in the coldest and densest parts of planet-forming disks,' Calahan said.

Jenny Calahan, a doctoral student in astronomy and first author of the paper, which appears in Nature Astronomy, said the discovery was part happy accident, part building on previous work. New research from the University of Michigan Department of Astronomy suggests that chemistry in late-stage planet development is fueled by ultraviolet rays, rather than cosmic rays or X-rays, and this new understanding provides a chemical signature that helps researchers trace exoplanets back to their cosmic nurseries in the planet-forming disks.

Mark disk