Mercury’s tidal Love number h2 from co-registration of MLA profiles

Due to its eccentric orbit, Mercury experiences varying gravitational pull from the Sun along its orbit, leading to periodic surface deformation, called body tidal deformation. Quantifying Mercury’s tidal response allows vital insights into its deep interior. The previous measurement of Mercury’s tidal h2 by Bertone et al. (2021) is based on minimizing height differences at cross-overs of the Mercury Laser Altimeter (MLA) profiles. However, this method can suffer from significant interpolation errors for the height difference at the cross-overs. In this study, we investigate Mercury’s tidal deformation by applying an alternative approach, which is based on the co-registration of reprocessed MLA profiles. For the reprocessing, we perform a geolocation of the MLA footprints by accounting for the pointing aberration and by incorporating an updated spacecraft orbit model. Within the study region of 77°N to 84°N, we obtain a tidal h2 of 0.92±0.51 (3-σ). This value is compatible with current interior structure and rheology models, but significantly smaller than the previous estimate of 1.55±0.65 (3-σ). When combined with recent tidal k2 estimates, our measurement favors a small to medium-sized inner core.

由于水星轨道偏心率较高，其沿轨道运行时会受到太阳的变化引力作用，进而产生周期性表面形变，即星体潮汐形变（body tidal deformation）。对水星潮汐响应进行量化分析，可为其深部内部结构研究提供关键认知。Bertone等人（2021）此前对水星潮汐Love数h2的测量，基于最小化水星激光高度计（Mercury Laser Altimeter, MLA）剖面交叉点处的高度差。然而，该方法在计算交叉点高度差时可能存在显著的插值误差。本研究采用一种基于再处理MLA剖面协同配准的替代方法，对水星的潮汐形变展开研究。在再处理流程中，我们通过考虑指向像差并引入更新后的航天器轨道模型，对MLA观测足迹开展地理定位。在77°N至84°N的研究区域内，我们得到的潮汐Love数h2值为0.92±0.51（3σ）。该数值与当前的内部结构及流变学模型相符，但显著小于此前1.55±0.65（3σ）的估计值。结合最新的潮汐Love数k2估计值，本研究的测量结果更支持存在中小型内核的结论。