We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016–2019 at a spatial resolution of 300–900 km (0.″1–0.″2 angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ∼0.5 m of the surface, and we find a millimeter emissivity of 0.75–0.78 and (sub)surface porosities of 10%–40%, corresponding to effective thermal inertias of 400–800 J m⁻² K⁻¹ s^−1/2. Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo’s photopolarimeter–radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ∼85% at the surface to at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5–8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (∼30–60) are generally colder than predicted; these trends are suggestive of an exogenic origin.

我们介绍了阿塔卡马大毫米波阵列（ALMA）在2016-2019年对木卫三的热观测，其空间分辨率为300-900 km（0。“ 1--0。” 2角分辨率），频率为97.5、233和343.5 GHz（3、1.3和0.87毫米的波长）；这些观测值共同涵盖了所有木卫三经度。我们使用考虑地下发射以及与深度和温度相关的热物理和介电特性的热模型，结合检索算法，确定全局热物理特性。数据对表面约0.5 m处的发射很敏感，我们发现毫米波辐射系数为0.75–0.78，（子）表面孔隙率为10％–40％，对应于有效热惯性为400–800 J m ^-2 K ^-1 s ^-1/2。结合过去的红外结果以及此处未展示的伽利略公司的光偏光计-辐射仪仪器夜间红外观测所建立的模型，多波长约束与压实曲线一致，从而孔隙率从地表的〜85％下降至深度超过数十厘米的压实长度。我们提供了来自最合适的全局模型的温度残差图，这些图表明了某些（但不是全部）黑暗地形和撞击坑的热表面特性的局部变化，这些撞击坑比模型冷了5–8K。赤道地区比模型预测的要温暖，特别是在前半球和后半球的中心附近，而中纬度（约30-60）通常比预测的要冷。这些趋势暗示了外源性起源。