Space instrumentation

Abstract:

The formation mechanisms, extent, and compositions of red spots on the lunar surface have intrigued the lunar community for decades. By identifying a new dome and another silicic crater in the highlands nearby, we find that the silicic volcanism in the Gruithuisen region extends beyond the three major domes. Our observations indicate that the Gruithuisen domes have low iron and titanium contents. They are enveloped by ejecta from surrounding regions and host silica-rich material excavated by the young craters consistent with previous work. Our boulder maps of the Gamma dome display a high boulder count and indicate that the Diviner rock abundance maps are only sensitive to boulders larger than ∼2 m. The H-parameter values are sensitive to presence of rocks and may be a better indicator of rocks at submeter scales. The Delta dome has gentle slopes, lower rock abundance, and one young crater, and it could serve as a safe and scientifically valuable site for landing and exploration of the domes and nearby region. The dome also displays anomalously high H-parameter in the same region as the crater, indicating the potential presence of pyroclastic materials. We observe up to 200 ppm of OH/H2O on the domes and nearby mare despite the presence of a weak magnetic field to the south of Delta dome, further supporting the potential presence of pyroclastics in the region. This study could potentially aid in logistical and scientific decisions of the future NASA missions in the region.

Abstract:

Asteroids with diameters less than about 5 km have complex histories because they are small enough for radiative torques (that is, YORP, short for the Yarkovsky–O’Keefe–Radzievskii–Paddack effect)1 to be a notable factor in their evolution2. (152830) Dinkinesh is a small asteroid orbiting the Sun near the inner edge of the main asteroid belt with a heliocentric semimajor axis of 2.19 au; its S-type spectrum3, 4 is typical of bodies in this part of the main belt5. Here we report observations by the Lucy spacecraft6, 7 as it passed within 431 km of Dinkinesh. Lucy revealed Dinkinesh, which has an effective diameter of only 720 m, to be unexpectedly complex. Of particular note is the presence of a prominent longitudinal trough overlain by a substantial equatorial ridge and the discovery of the first confirmed contact binary satellite, now named (152830) Dinkinesh I Selam. Selam consists of two near-equal-sized lobes with diameters of 210 m and 230 m. It orbits Dinkinesh at a distance of 3.1 km with an orbital period of about 52.7 h and is tidally locked. The dynamical state, angular momentum and geomorphologic observations of the system lead us to infer that the ridge and trough of Dinkinesh are probably the result of mass failure resulting from spin-up by YORP followed by the partial reaccretion of the shed material. Selam probably accreted from material shed by this event.