The InSight HP3 Penetrator (Mole) on Mars: Soil Properties Derived from the Penetration Attempts and Related Activities

The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP³ to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3-5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, by precessing about a point midway along its hull, it carved a 7 cm deep and 5-6 cm wide pit and reached a depth of initially 31 cm. The root cause of the failure - as was determined through an extensive, almost two years long campaign - was a lack of friction in an unexpectedly thick cohesive duricrust. During the campaign - described in detail in this paper - the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and by direct support by the latter. The mole tip finally reached a depth of about 37 cm, bringing the mole back-end 1-2 cm below the surface. It reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the mole hull. The penetration record of the mole was used to infer mechanical soil parameters such as the penetration resistance of the duricrust of 0.3-0.7 MPa and a penetration resistance of a deeper layer ( > 30 cm depth) of 4.9 ± 0.4 MPa . Using the mole's thermal sensors, thermal conductivity and diffusivity were measured. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 2-15 kPa depending on the internal friction angle of the duricrust. Pushing the scoop with its blade into the surface and chopping off a piece of duricrust provided another estimate of the cohesion of 5.8 kPa. The hammerings of the mole were recorded by the seismometer SEIS and the signals were used to derive P-wave and S-wave velocities representative of the topmost tens of cm of the regolith. Together with the density provided by a thermal conductivity and diffusivity measurement using the mole's thermal sensors, the elastic moduli were calculated from the seismic velocities. Using empirical correlations from terrestrial soil studies between the shear modulus and cohesion, the previous cohesion estimates were found to be consistent with the elastic moduli. The combined data were used to derive a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick unconsolidated layer of sand mixed with dust and above another 10 cm of unconsolidated sand. Underneath the latter, a layer more resistant to penetration and possibly containing debris from a small impact crater is inferred. The thermal conductivity increases from 14 mW/m K to 34 mW/m K through the 1 cm sand/dust layer, keeps the latter value in the duricrust and the sand layer underneath and then increases to 64 mW/m K in the sand/gravel layer below.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11214-022-00941-z.

Donor-specific anti-HLA antibodies after bone-graft transplantation. Impact on a subsequent renal transplantation: a case report

Immunological evaluation by panel-reactive antibody (PRA) and determination of anti-HLA specificity are important phases in the evaluation of patients awaiting kidney transplantation. The main causes of immunization are previous solid organ transplantation, hemotransfusion, and pregnancy. It is also possible that immunogenicity can be triggered by vascularized tissue grafts. Immune induction by cryopreserved bone prostheses is not yet understood. A 19-year-old patient with osteosarcoma had undergone resection of the left proximal tibia with reconstruction using human bone in 1997. The donor HLA typing was as follows: A3, A29 (19); B44 (12), Bw4; DR13 (6), DR7, DR52, DR53. The patient was subsequently enrolled onto the waiting list for cadaveric donor kidney transplantation due to chronic kidney failure caused by cisplatin toxicity. Pretransplantation immunological screening using the complement-dependent cytotoxicity (CDC) technique revealed a PRA of 63%. IgG antibody specificities were detected against class I and class II donor antigens, specifically anti-A3, B44, DR7 antibodies, using flow cytometry (Tepnel Luminex). Further immunological studies using single HLA specificity analysis (LSA Class I degrees -II degrees , Tepnel-Luminex) showed direct antibodies against all donor antigen specificities. This case showed immune induction after the implantation of bone prosthesis in a kidney transplant candidate, underlining the importance of the availability of HLA typing data of donors of a human prosthesis.

[Anti-HLA antibodies after bone graft and their impact on kidney transplant programs]

Immunological evaluation by panel reactive antibody (PRA) and determination of anti-HLA specificity is an important phase in the assessment of patients awaiting kidney transplant. The main causes of immunization are previous solid organ transplants, blood transfusions, and pregnancy; immunogenicity can also be triggered by vascularized tissue grafts. Immune induction by cryopreserved bone allografts is not yet fully understood. We report the case of a 19-year-old patient with osteosarcoma who underwent resection of the left proximal tibia with reconstruction using human bone in 1997 (donor typing: A3, A29 (19) - B44 (12), Bw4 - DR13 (6), DR7, DR52, DR53). The patient was subsequently placed on the waiting list for a cadaver donor kidney transplant because of chronic kidney failure caused by cisplatin toxicity. Pretransplant immunological screening using the CDC (complement dependent cytotoxicity) technique revealed a PRA of 63% and anti-A3 and anti-A68 antibodies. The presence of IgG antibody specificity against class I and class II donor antigens (specifically anti-A3, B44, DR7 antibodies) was highlighted using flow cytometry (Tepnel-Luminex). Further immunological studies using single HLA specificity analysis (LSA Class I - II - Tepnel-Luminex) detected direct antibodies against all donor antigen specificities. This is the first reported case of immune induction after a bone graft in a kidney transplant candidate. It underlines the importance of the availability of HLA typing data of all human allograft donors.

[Preventing and reducing comorbidity in candidates for kidney transplantation for the improvement of post-operative results]

The correct and constant management of transplant waiting lists is necessary for the optimal utilization of the limited number of organs available for transplantation. The guidelines regarding placement on transplant waiting lists (absolute and relative contraindications) are well documented, even though they are in constant development. The criteria for the monitoring of patients on waiting lists, however, are not so well defined; this aspect is subject to careful evaluation on account of the widening of the criteria for transplantation suitability, the increase in the average age of patients, a rise in the number of enrolments and, as a result, prolonged waiting time (in Italy, the average time spent on a waiting list is 37 months). During the waiting period, a greater risk of clinically significant comorbidities and mortality, above all from cardiovascular events, has been noted (the annual mortality is 5-7% in the US, 1.3% in Italy). An in-depth clinical and instrumental study of patients with chronic renal failure is necessary when screening eligible candidates for transplant programs, individualizing therapeutic strategies, and identifying patients for whom the risks outweigh the potential benefits. Clinical and instrumental monitoring, as well as adequate treatment of comorbidities during the waiting period, can help improve the post-transplant outcome. This work examines the study algorithms and monitoring procedures for patients on kidney transplant waiting lists.