Methane precipitation in ice giant atmospheres | Astronomy & Astrophysics (A&A)

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Volume 694 (February 2025)

A&A, 694 (2025) A81

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Table 1

Microphysical model parameters.

Parameter	Equation	Reference
Saturation vapor pressure	$\log (p_{sat}) = A_{0} + \sum_{i = 1}^{4} A_{i} / T^{i}$ $\log \left( {{p_{{\rm{sat}}}}} \right) = {A_0} + \mathop \sum \limits_{i = 1}^4 {A_i}/{T^i}$	(1)
	A₀ = 10.51, A₁ = −1.1 × 10 × 10³,
	A₂ = −4.341 × 10³, A₃ = +1.035 × 10⁵,
	A₄ = −7.910 × 10⁵

Methane ice density (ρ_s)	425 kg m⁻³	(2)

Activation energy for desorption	0.1519 × 10⁻¹⁹ J molecule⁻¹	(3)

Contact parameter	0.99	(3)

Methane latent heat (∆H_V)	∆H_V = 7.08 ⋅ (1 − T_r)^0.354 + 10.95 ⋅ ω ⋅ (1 − T_r)^0.456 ⋅ R ⋅ T_c	(4)

	where T_r = T/T_c, T_c = 190.4 K, ω = 0.011

Thermal conductivity (K) of H₂	K = A + BT + CT² + DT³	(4)
	A = 8.099 × 10⁻³, B = 6.689 × 10⁻⁴,
	C = −4.158 × 10⁻⁷, D = 1.562 × 10⁻¹⁰

Surface tension (σ)	$σ = P_{c}^{2 / 3} T_{c}^{1 / 3} Q {(1 - T_{r})}^{11 / 9}$ $\sigma = P_c^{2/3}T_c^{1/3}Q{\left( {1 - {T_r}} \right)^{11/9}}$	(4)
	where T_c = 190.4 K, p_c = 46, T_r = T/111.6 and
	Q = 0.1196 ⋅ [1 + (T_br ⋅ In(P_c/1.01325))/(1 − T_br)] − 0.279

Notes. (1) Fray & Schmitt (2009); (2) Yarnall & Hudson (2022); (3) Rannou et al. (2019); (4) Reid et al. (1987).

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