News Summary Archives

ALMA Reveals Thermal and Non-thermal Desorption of Methanol Ice in the HD 100546 Protoplanetary Disk

By Keith Cowing

Status Report

astro-ph.EP

March 4, 2025

Filed under ALMA, astro-ph.EP, astrochemistry, biochemistry, formaldehyde, Herbig Ae disk HD 100546, Interstellar, Methanol, organic chemistry, Protoplanetary Disk, Spectroscopy

ALMA Reveals Thermal and Non-thermal Desorption of Methanol Ice in the HD 100546 Protoplanetary Disk — Azimuthally-averaged radial profiles for the four unblended CH3OH lines (top row) and all H2CO lines (bottom row) in order of decreasing peak intensity. These four CH3OH lines are those which show both an inner compact and outer ringed component of emission. The latter coincides with the position of the dust ring, which peaks between approximately 180 − 220 au; the radial ranges of the peaks of the two dust rings seen in the 0.9 mm continuum emission between ∼ 20 − 31 au and ∼ 180 − 220 au are denoted by the grey shaded regions. Note that the o-H2CO profile at 231.38 GHz contains contributions from two lines with equal transition properties: one at 291.380 GHz and one at 291.384 GHz. The horizontal bar shows the Full-Width at Half Maximum (FWHM) of the synthesised beam. — astro-ph.EP

Methanol (CH₃OH) and formaldehyde (H₂CO) are chemically coupled organic molecules proposed to act as an intermediate step between simple molecules and more complex prebiotic compounds.

Their abundance distributions across disks regulate the prebiotic potential of material at different disk radii. We present observations of multiple methanol and formaldehyde transitions toward the Herbig Ae disk HD 100546 obtained with ALMA, building upon the previous serendipitous detection of methanol in this source.

We find that methanol has a higher rotational temperature (Trot) than formaldehyde towards both the centrally concentrated emission component in the inner disk (0−110 au) and a radially separate dust ring farther out in the disk (180−260 au).

Trot decreases for methanol and formaldehyde from the inner (152+35−27 K and 76+9−8 K) to the outer disk (52+8−6 K and 31+2−2 K), suggesting that we are tracing two different chemical environments. Trot for both species in the inner disk is consistent with thermal desorption as the origin, while the outer disk reservoir is driven by non-thermal desorption.

The CH₃OH/H₂CO column density ratio decreases from 14.6+5.2−4.6 in the inner disk to 1.3+0.3−0.2 in the outer disk, consistent with modelling predictions. The CH₃OH/H₂CO column density ratio for the inner disk is consistent with the median value in the range of column density ratios compiled from Solar System comets which would have formed at a similar distance.

This supports the notion that interstellar ice is inherited and preserved by protoplanetary disks around solar-mass and intermediate-mass stars as we are seeing ‘fresh’ ice sublimation, as well as providing more evidence for the presence of prebiotic precursor molecules in planet-forming regions.

Lucy Evans, Alice S. Booth, Catherine Walsh, John D. Ilee, Luke Keyte, Charles J. Law, Margot Leemker, Shota Notsu, Karin Öberg, Milou Temmink, Nienke van der Marel

Comments: 35 pages, 16 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2502.04957 [astro-ph.EP] (or arXiv:2502.04957v2 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2502.04957
Focus to learn more
Related DOI:
https://doi.org/10.3847/1538-4357/adb287
Focus to learn more
Submission history
From: Lucy Evans
[v1] Fri, 7 Feb 2025 14:22:17 UTC (23,010 KB)
[v2] Fri, 28 Feb 2025 15:10:01 UTC (22,994 KB)
https://arxiv.org/abs/2502.04957
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

Follow on Twitter