Measure realistic cloud–haze contact angles

Determine physically realistic microphysical contact angles between KCl cloud condensates and photochemical haze particles in sub-Neptune atmospheres by constraining the relevant condensate, haze, and interfacial surface energies.

Background

The coupled CARMA model treats the contact angle between KCl condensates and haze particles as the parameter controlling heterogeneous nucleation efficiency. Smaller contact angles produce stronger cloud–haze interactions, while larger angles approach the homogeneous-nucleation limit. Because the relevant surface and interfacial energies are poorly known for exoplanetary aerosols, the study explores a broad range of contact angles rather than adopting a physically established value.

Laboratory measurements of haze surface energies and KCl–haze contact angles could determine which of the modeled regimes—wet removal, cloud enhancement, or effectively homogeneous cloud formation—is physically relevant for warm sub-Neptunes.

References

While this contact angle is unknown in the absence of lab data, heterogeneous nucleation is the primary cloud-formation pathway across the Solar System.

— Wet Removal and Cloud Enhancement: The Microphysics of Cloud-Haze Interactions on Sub-Neptunes  (2608.19100 - Nagpal et al., 19 Aug 2026) in Figure 1 caption; Section 2.4, “Cloud-haze interactions: the role of contact angles in heterogeneous nucleation”

How cloud-haze interactions manifest in scenarios where either the clouds or hazes (or both) are aggregates remains, as of now, unclear.

— Wet Removal and Cloud Enhancement: The Microphysics of Cloud-Haze Interactions on Sub-Neptunes  (2608.19100 - Nagpal et al., 19 Aug 2026) in Section 7.3, “Effects of Haze Optical Properties and Shapes”