Matera: A not so ordinary H5 chondrite breccia with very low density and high porosity

On the evening of February 14, 2023, at 17:58 UT, a fireball was detected by three cameras of the Italian PRISMA network (FRIPON network). The first samples of the Matera meteorite, collected 3 days after the fall, lay on the balcony of a private home. Meanwhile, four samples weighing more than 10 g (including the main mass of 46.21 g) and many minor samples (less than 10 g each) were recovered, with a total mass of 117.5 g. The analyses show that Matera is a monomict chondrite breccia, exhibiting no weathering (W0) and shock (S1). Based on the mineral compositions of olivine and low-Ca pyroxene (Fa_18.0±0.3 and Fs_17.0±0.3, respectively), the rock is an H-group ordinary chondrite. Since all low-Ca pyroxene is orthoenstatite, an H5-type classification is appropriate; although texturally, a type 4 classification could be assigned to distinct portions of the rock with well-defined chondrules. The analyzed oxygen isotopes also align with an H chondrite (δ¹⁷O‰ = 2.750 ± 0.051; δ¹⁸O‰ = 4.036 ± 0.103; Δ¹⁷O‰ = 0.650 ± 0.004). X-ray tomography and a structured light 3D scanner yielded a mean bulk density of 2.87 ± 0.04 g cm⁻³, whereas ideal gas pycnometry yielded grain densities of 3.47 ± 0.05 g cm⁻³, resulting in a porosity of 17.2 ± 1.2 vol%. The magnetic susceptibility of this meteorite is log χ = 5.46 ± 0.05. The radionuclides and fireball observations suggest that the Matera meteoroid was relatively small (with a maximum radius of 20 cm, though more likely around 15 cm). This datum is also consistent with (²¹Ne/²²Ne)_cos, which suggests the origin of Matera samples from the uppermost cm of a small meteoroid, ≤10 cm radius. Different from many other H chondrites, the transfer time in space for Matera, based on 3 He alone, is 10–12 Ma. Moreover, the Matera meteorite does not contain solar wind gases. In conclusion, the Matera meteorite is not a fairly typical ordinary chondrite, due to its low bulk density and high total porosity. The presence of ordinary chondrites with these physical characteristics must be taken into account during the asteroid modeling process, as in the case of the Didymos–Dimorphos binary system.