Table 1: Measured interior and orbital characteristics of Saturn’s mid-sized moons, and moon-specific physical input parameters.

Observed characteristics are for the present day, except where noted. In the last column are listed the conditions under which simulations are deemed to match measurements.

Parameter	Mimas	Enceladus	Tethys	Dione	Rhea	Condition for match
Observed characteristics
Mean radius R (km)a	198.2	252.0b	531.0	561.4	763.5	Within 5%
Mass M (kg)c	3.75 × 1019	1.08 × 1020	6.17 × 1020	1.10 × 1021	2.30 × 1021	N/A (model input)
Bulk density ρ (kg m−3)	1149	1611	985	1478	1237	Within 5%
Core density ρc (kg m−3)d	1200–3300e	~2400f	Unknown	1940–3120	1240–2100	Within range
		2450g
Corresponding core radius Rc (km)h	82–181	190–192h	Unknown	344–450j	463–758k	Within range
		180–185i
		183–199j
Present-day ocean?	Maybe e	Yesf,g,i,j	Unknown	Maybej	Unknown	Presence or absence
Past near-surface heat flux (mW m−2)l	Not estimated	≈150m	60p	20–60q	s15	Within 20%
		110–400n		60p
Semi-major axis (km)	185539	237948	294660	377400	527040	Within 20%
(Saturn radii)	3.19	4.09	5.06	6.48	9.05
Eccentricity	0.0196	0.0047	0.0001	0.0022	0.0010	Range overlaps
Assumed quantities
Porosity-free radius (km)	186.5	252.0	507.7	556.5	762.2
Initial radius with 20% bulk porosity (km)	200.9	271.5	546.9	599.5	821.1
Porosity-free bulk density (kg m−3)	1378	1611	1127	1517	1267
Surface temperaturet	76	68	68	70	72
Case with initial Q = 80000, initial e = 0.016
Time of formation (Myr after CAIs)u	3450	primordial	primordial	primordial	primordial
Initial semi-major axis (km)u	160000	165000	155000	354000	520000
Case with constant Q = 2452.8, initial e = 0.016
Time of formation (Myr after CAIs)u	4470	4140	4760	2280	primordial
Initial semi-major axis (km)u	160000	160000	160000	160000	478000

^aThomas⁴⁵.

^bThomas et al.¹³.

^cJacobson et al.⁴⁶.

^dEstimated from gravity and libration measurements; the determination of interior models is non-unique. For Dione and Rhea, densities are calculated from reported core radii.

^eRange of densities explored by Tajeddine et al.¹¹.

^fless et al.⁴⁷.

^gMcKinnon¹⁰.

^hCalculated as R_c = R [(ρ − ρ_i)/(ρ_c − ρ_i)]^1/3 assuming an ice shell density ρ_i = 985 kg m⁻³.

ⁱČadek et al.⁹.

^jBeuthe et al.⁸.

^kTortora et al.¹².

^lInferred from analyses of surface topography and crater relaxation.

^mBland et al.⁴⁸.

ⁿBland et al.^17,49; Giese et al.⁵⁰.

^pWhite et al.⁵¹.

^qHammond et al.⁵².

^sNimmo et al.⁵³.

^tEffective temperatures, assumed constant over time; Enceladus’ surface temperature is equated to that of Tethys (see Methods).

^uEstimated based on Saturn’s Q (Fig. 1) and refined as needed to account for orbital evolution driven by the rings and tidal dissipation inside the moons.

CAIs: Ca-Al-rich inclusions, the oldest known remaining solar system solid material that set the “time zero” of solar system history.