High-resolution shape models of Phobos and Deimos from stereophotoclinometry

We created high-resolution shape models of Phobos and Deimos using stereophotoclinometry and united images from Viking Orbiter, Phobos 2, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter into a single coregistered collection. The best-fit ellipsoid to the Phobos model has radii of (12.95 ± 0.04) km × (11.30 ± 0.04) km × (9.16 ± 0.03) km, with an average radius of (11.08 ± 0.04) km. The best-fit ellipsoid to the Deimos model has radii of (8.04 ± 0.08) km × (5.89 ± 0.06) km × (5.11 ± 0.05) km with an average radius of (6.27 ± 0.07) km. The new shape models offer substantial improvements in resolution over existing shape models, while remaining globally consistent with them. The Phobos model resolves grooves, craters, and other surface features ~ 100 m in size across the entire surface. The Deimos model is the first to resolve geological surface features. These models, associated data products, and a searchable, coregistered collection of images across six spacecraft are publicly available in the Small Body Mapping Tool, and will be archived with the NASA Planetary Data System. These products enable an array of future studies to advance the understanding of Phobos and Deimos, facilitate coregistration of other past and future datasets, and set the stage for planning and operating future missions to the moons, including the upcoming Martian Moons eXploration (MMX) mission.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40623-023-01814-7.

MEGANE investigations of Phobos and the Small Body Mapping Tool

The MEGANE instrument onboard the MMX mission will acquire gamma-ray and neutron spectroscopy data of Phobos to determine the elemental composition of the martian moon and provide key constraints on its origin. To produce accurate compositional results, the irregular shape of Phobos and its proximity to Mars must be taken into account during the analysis of MEGANE data. The MEGANE team is adapting the Small Body Mapping Tool (SBMT) to handle gamma-ray and neutron spectroscopy investigations, building on the demonstrated record of success of the SBMT being applied to scientific investigations on other spacecraft missions of irregularly shaped bodies. This is the first application of the SBMT to a gamma-ray and neutron spectroscopy dataset, and the native, three-dimensional foundation of the SBMT is well suited to MEGANE's needs. In addition, the SBMT will enable comparisons between the MEGANE datasets and other datasets of the martian moons, including data from previous spacecraft missions and MMX's multi-instrument suite.

Planetary protection classification of samples returned from the martian moons: Summary of a review by the European Science Foundation and the National Academies of Sciences, Engineering and Medicine

This work summarizes the review undertaken by a joint committee of the European Science Foundation and the National Academies of Sciences, Engineering and Medicine into the transfer of viable organisms from the surface of Mars to its moons-Phobos and Deimos-as a consequence of a giant impact on the martian surface. The possibility that viable organisms could survive ejection from Mars and subsequent deposition on Phobos and Deimos is an important consideration in determining whether samples returned from the moons by spacecraft missions be classified as restricted or unrestricted Earth return in the consensus planetary protection guidelines maintained by the Committee on Space Research (COSPAR) of the International Council for Science. Having reviewed recent research undertaken in Europe and Japan, the joint committee recommended that samples returned from the martian moons be classified as unrestricted Earth return. This paper is not intended to be a standalone work. Rather, it should be regarded as a summary of, and advertisement for, the material presented in the joint committee's formal report, Planetary Protection Classification of Samples Return Missions from the Martian Moons (the National Academies Press, 2019).

Lacuna in the updated planetary protection policy and international law

The Planetary Protection Policy (PPP) has proclaimed the lofty ideal "All the planets, all the time." Originally formulated as Planetary Quarantine Requirements (PQR), the planetary protection policy imposed strict decontamination standards for spacecraft during the initial period of interplanetary exploration. The policy properly has been seen as a work in progress, continuously open to consideration of new data, and subject to periodic re-examination and question with a view toward improvement to better meet the goals of science. This process has led to several revisions of the PPP to improve, simplify and clarify the standards. In keeping with past practice, the policy was recently revised in light of new data and experience, and the current update is pending before the COSPAR Bureau and Council for review and approval. Specific changes to the PPP add Enceladus to the group of target bodies within the solar system subject to heightened protective measures, and modify the provisions regarding the establishment of special regions on Mars. These new updates mark another important development in the evolution of the PPP. The PQR and the PPP were based on the precept that outbound spacecraft to celestial bodies should not contaminate natural celestial environments with Earth organisms. Therefore, the policy generally requires that certain missions, particularly to target bodies that could harbor evidence of past or current alien life, take active measures to decontaminate the spacecraft. Nevertheless, recent and proposed missions demonstrate that significant gaps remain in the policy. Instead of enhancing decontamination the policy actually promotes purposely and intentionally enlarging the number of potentially contaminating Earth organisms carried by a spacecraft that could reach celestial bodies, including those bodies which are subject to active decontamination requirements. Thus, even with the new updates, the PPP may not be fully consistent with the international obligations of the Outer Space Treaty, and the continued existence of the entire PPP policy could be in jeopardy. This article discusses the flight characteristics of two specific missions, one launched and one in development, which are consistent with the PPP but nonetheless pose a substantial risk of biological contamination of celestial bodies. The manner in which the risks can be reduced is identified, and suggestions are made to close some of the gaps that remain in the PPP to comply with international law.

The transfer of unsterilized material from Mars to Phobos: Laboratory tests, modelling and statistical evaluation

Sample return missions to Phobos are the subject of future exploration plans. Given the proximity of Phobos to Mars, Mars' potential to have supported life, and the possibility of material transfer from Mars to Phobos, careful consideration of planetary protection is required. If life exists, or ever existed, on Mars, there is a possibility that material carrying organisms could be present on Phobos and be collected by a sample return mission such as the Japanese Martian Moons eXplorer (MMX). Here we describe laboratory experiments, theoretical modelling and statistical analysis undertaken to quantify whether the likelihood of a sample from Phobos material containing unsterilized material transferred from Mars is less than 10^-6, the threshold to transition between restricted and unrestricted sample return classification for planetary protection. We have created heat, impact and radiation sterilization models based on the Phobos environment, and through statistical analyses investigated the level of sterilization expected for martian material transferred to Phobos. These analyses indicate that radiation is the major sterilization factor, sterilizing the Phobos surface over timescales of millions of years. The specific events of most relevance in the Phobos sample return context are the 'young' cratering events on Mars that result in Zunil-sized craters, which can emplace a large mass of martian material on Phobos, in a short period of time, thus inhibiting the effects of radiation sterilization. Major unknowns that cannot yet be constrained accurately enough are found to drive the results - the most critical being the determination of exact crater ages to statistical certainty, and the initial biological loading on Mars prior to transfer. We find that, when taking a conservative perspective and assuming the best-case scenario for organism survival, for a 100 g sample of the Phobos regolith to be below the planetary protection requirement for unrestricted sample return, the initial biological loading on Mars must be <8.2 × 10³cfu kg^-1. For the planned MMX mission, a ∼10 g sample to be obtained from a 25-30 mm diameter core as planned would require an initial martian biological loading to be <1.6 × 10⁴cfu kg^-1, in order to remain compliant with the planetary protection threshold.

Phobos: A novel software for recording rodents' behavior during the thigmotaxis and the elevated plus-maze test

Evaluation of fear and anxiety levels offers valuable insight on the impact of experimental conditions. The elevated plus-maze and the open field (thigmotactic responce) tests are two well-established behavioral procedures for the quantification of anxiety in rodents. In this study, Phobos, a novel, effective and simple application developed for recording rodents' behavior during the elevated plus-maze and the open-field test, is being presented. Phobos is able to generate all basic locomotor-related behavioral results at once, immediately after a simple manual record of the rodent's position, along with simultaneous analysis of the experiment in 5-min periods. The efficiency of Phobos is demonstrated by presenting results from the two behavioral tests showing that animal's behavior unfolds differently in each one. Phobos manages to ease the experimenter from laborious work by providing self-explanatory characteristics and a convenient way to record the behavior of the animal, while it quickly calculates all basic locomotor-related parameters, easing behavioral studies. Phobos is freely accessible at https://sourceforge.net/projects/phobosapplication/.