![Schematic diagram (not to scale) of the experimental apparatus used for benzene ice nucleation and growth studies (adapted from Dubois et al. (2021)). Pressure was measured with a capacitance manometer (P1) and an ion gauge (P2). The inset shows a top view of the cooled sample holder with the positions of the three K-type thermocouple gauges (red dots) used for temperature measurements. The ice sample formed on either or both sides of the silicon substrate/tholin sample (grey), which was in the path of the IR beam of the Thermo Fisher iS50. Infrared transmission spectra were collected with a liquid N2-cooled MCT/A detector. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/07/Experimental-Measurements.png?fit=1200%2C672&ssl=1)
[astro-ph.EP] The Cassini Composite Infrared Spectrometer (CIRS) revealed the presence of a benzene (C6H6) ice cloud in Titan’s autumn south polar stratosphere, following the northern spring equinox in August 2009.
This event increased the mixing ratio of benzene and raised the cloud top altitude. We present here new experimental measurements of the critical saturation (Scrit) of pure C6H6 ice at low temperature (from 13.8 at 138 K to 3.3 at 157 K), representative of Titan’s atmospheric temperatures, when deposited onto Titan aerosol analogs (tholins) produced in the NASA Ames COsmic SImulation Chamber (COSmIC).
Comparisons of Scrit values of benzene vapor deposition obtained on blank substrates versus on Titan tholins reveals the highly favorable role aerosols play as condensation nuclei.
We have included these new Scrit measurements to calculate the nucleation contact parameter from m = 2.6e-4 T + 0.9494 in the Community Aerosol and Radiation Model for Atmospheres (CARMA) to investigate the variation in size and number density of C6H6 cloud particles as a function of altitude in Titan’s southern polar atmosphere at 87 S.
We discuss how these new temperature-dependent measurements impact the microphysical modeling and result in simulated benzene clouds forming about 20 km lower than seen in previous observations.
A possible explanation for this discrepancy is that the cloud system was likely influenced by the co-condensation of more than one volatile gas species.
David Dubois, Erika Barth, Laura T. Iraci, Ella Sciamma-O’Brien, Farid Salama, Sandrine Vinatier
Comments: 33 pages, 7 figures, 3 tables, accepted for publication in the Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2607.21415 [astro-ph.EP] (or arXiv:2607.21415v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.21415
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Submission history
From: David Dubois
[v1] Thu, 23 Jul 2026 15:18:27 UTC (1,077 KB)
https://arxiv.org/abs/2607.21415
Astrobiology,
