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Scientific Highlight - February

Probing icy clouds in the cosmos

Scientific Highlight February 2023
Scientific Highlight February 2023
By Shaeema Zaman at Science Melting Pot.
By Shaeema Zaman at Science Melting Pot.

In a recent paper by McClure et al. in Nature Astronomy, Associate Professor Sergio Ioppolo from the Department of Physics and Astronomy at Aarhus University investigated icy regions in interstellar clouds in search of finding the fundamental building blocks of life. The team of this study includes 42 international experts in the fields of astrochemistry, astrophysics, star formation, and interstellar medium from 10 countries, who collaborated to collect and analyse data from the James Web Space Telescope’s IceAge Early Release Science program. Their results suggest that the formation of simple and complex molecules seen in our Solar System begins very early in a water-ice-rich environment.

Are the fundamental elements that make up life (as we know it on Earth) unique? To answer this question, we must track the essential molecular ingredients of life, such as carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and sulfur (S) from their formation in dense clouds in the universe and how they get incorporated into the planet-forming regions of the disks observed around young stars. These ingredients begin as elements trapped in ice layers formed on top of dust grains and then become more complex over time through a variety of chemical processes, which depend on their environmental conditions. So, how do we study this process? The answer lies in the amalgamation of new observations, cutting-edge laboratory experiments, and comprehensive chemical modelling. 

Dense molecular clouds are regions in the universe rich in gas and dust, yet still very diluted compared to terrestrial standards. Fundamental atoms and molecules (e.g. C, CO2) are locked up in ice material on the surfaces of dust grains in these clouds. The vibrational motion of these molecules can be observed by studying the absorption spectrum against the near- and mid-infrared light provided by stars located behind these clouds. Ground-based telescopes and space observatories, such as the Infrared Space Observatory, Spitzer and Akari, have probed ice-chemical evolution in young stars. However, chemical assessments of cloud ice have been limited to regions with bright stars in the background. 

In this study, researchers report the initial detections of the coldest, darkest molecular icy clouds ever observed around two faint background stars, called NIR38 and J110621, using the James Webb Space Telescope (JWST). They compare the column densities (i.e. the measure of the amount of intervening matter between an observer and the object being observed) of the detected ices for both NIR38 and J110621 with the expected cosmic abundances for C, O, N and S. This is done so that they can account for the amount of C, O, N and S in the ices, which is critical to determine the bulk amount of molecules of the stellar and planetary systems that will form within the molecular cloud. They found that at most 19% of the total O and C amounts, 13% of the total N amount, and 1% of the S amount were in ices in the dense cloud. These numbers are similar to what has been previously reported, but now we are able to trace the amounts of these elements back to their initial conditions in dense clouds well before the onset of star formation.

 The IceAge Early Release Science program and this study have provided a representative, non-proprietary inventory and additional scientific datasets that can be used by the star formation and astrochemistry communities to explore what the James Webb Space Telescope has to offer and to prepare for the next cycle of observations.

Read the paper

Other references: 

  1. http://jwst-iceage.org/
  2. American Astronomical Society, AAS Meeting #232, id. 302.03