Marco Polo is a European-Japanese space mission aimed at visiting a small primitive asteroid and returning a sample to Earth for analysis in laboratory. It has been proposed to the program Cosmic Vision 2015-2025 of the European Space Agency (ESA) in June 2007 and selected for an assessment study in November 2007. This mission is proposed as a joint mission ESA-JAXA (Japan Exploration Space Agency). The in-situ investigation and sample analysis will allow us to improve our knowledge of the physical and chemical properties of a small Near-Earth Object (NEO) which is believed to have kept the original composition of the solar nebula in which planet formed. Thus, it will provide some constraints to the models of planet formation and some information on how life may have been brought to Earth. Information on the physical structure will help defining efficient mitigation strategies against a potential threatening object.
Small bodies, as primitive leftover building blocks of the Solar System formation process, offer clues to the chemical mixture from which the planets formed some 4.6 billion years ago. Current exobiological scenarios for the origin of life invoke an exogenous delivery of organic matter to the early Earth: it has been proposed that carbonaceous chondrite matter (in the form of planetesimals or dust) could have brought these complex organic molecules capable of triggering the pre-biotic synthesis of biochemical compounds on the early Earth. Moreover, collisions of NEOs with Earth pose a finite hazard to life. For all these reasons, the exploration of such objects is particularly interesting and urgent.
The principal scientific objective of the Marco Polo mission is to return unaltered materials from a NEO. Marco Polo will allow us to analyze the samples in terrestrial laboratory, and to obtain measurements that cannot yet be performed from a robotic spacecraft (e.g. dating the major events in the history of a sample: laboratory techniques can determine the time interval between the end of nucleosynthesis and agglomeration, the duration of agglomeration, time of accumulation, crystallization age, the age of major heating and degassing events, the time of metamorphism, the time of aqueous alteration, and the duration of exposure to cosmic radiation).
Moreover, the mission will allow us to:
• Determine the physical and chemical properties of the target body, which are representative of the building blocks of the terrestrial planets.
• Identify the major events (e.g. agglomeration, heating, aqueous alteration, solar wind interactions …) which influenced the history of the target.
• Determine the elemental and mineralogical properties of the target body and their variations with geological context on the surface.
• Search for pre-solar material yet unknown in meteoritic samples.
• Investigate the nature and origin of organic compounds on the target body.
• Search for organic compounds which may shed light on the origin of pre-biotic molecules.
• Understand the role of minor body impacts in the origin and evolution of life on Earth.
This NEO sample return mission will take advantage of the heritage/expertise of several European (Huygens, Philae) and Japanese (Hayabusa) missions, allowing both parties to increase their technological capabilities and thus meet a challenging objective.
NEOs are among the most accessible bodies of the Solar System. A number of possible targets of high scientific interest has been selected and covers a wide spectrum of possible launch windows in the time span 2015-2019, namely
• the C-type asteroid 1999JU3, as a representative of the numerous primitive population of the C (carbonaceous) taxonomic type asteroids; another C-type asteroid may be considered, namely 1989 UQ.
• asteroids which belong to the primitive D and T types, namely 2001 SGG286 and 2001 SK162, respectively;
• the dormant comet 4015 Wilson-Harrington (1979 VA), which can provide insights on the unknown link between asteroids and comets;
• the primitive C-type double asteroid 1996 FG3, which can provide insight into binary formation processes.
A baseline mission scenario to 199JU3 includes a launch with a Soyuz-type launcher of a Mother Spacescraft (MSC) possibly carrying a Lander, a sampling device, a re-entry capsule and scientific payloads. The Lander would perform a soft landing, anchor to the asteroid surface, and make various in situ measurements of surface/subsurface materials near the sampling site. Samples will be collected with either one or complementary techniques. Once the sampling and in-situ measurements will be completed, the MSC will start the return journey towards Earth and will release the capsule for the high-speed re-entry into Earth’s atmosphere. The capsule will be retrieved on ground at a low to mid latitude, uninhabited area, possibly in the northern hemisphere. After appropriate space quarantine and sterilization processes, samples will be taken out of the capsule in a dedicated sample curation facility to conduct initial sample characterization, prior to their distribution to designated scientists for detail analyses.
The MSC scientific payloads have to include a high resolution imaging system, visible and infrared and mid spectrometers, a LIDAR, and a dust monitor. These instruments will be operated during the approach, hovering and descent phases for science purpose, for landing site selection and for spacecraft safety during near-surface manoeuvres. The Lander would have its own payload for the characterization of the in situ measurements (e.g., close-up camera, panoramic camera, electron microscope, X-ray diffractometer, volatile detector, microbalance, mass spectrometer). Instruments on the Lander would be operated in situ through automatic and/or Earth commanded sequences. These instruments should also allow us to characterize location and surface environment on site of the sampling. The scientific objectives of the mission will be attained by the combination of the following characterisations with the analyses of the returned samples:
1. morphological surface properties;
2. environment conditions (e.g. dust, gravity field…);
3. mass, volume and bulk density;
4. mineralogical composition;
5. surface (and possibly subsurface) mineralogy and thermophysical properties (thermal inertia, conductivity, diffusivity, cohesion of the materials….);
6. surface elemental composition and distribution;
7. overall internal structure properties;
8. global topography;
9. volatile abundance.
The Marco Polo mission is innovative and would greatly contribute to:
• testing new technology developments: re-entry capsule, sampling technique, on board artificial intelligence, telecommunication, in situ energy, planetary protection.tools….;
• preparing the next generation of laboratory facilities for extraterrestrial sample analysis;
• having a pathfinder for sample returns from high gravity bodies and later on for human missions that may use asteroid resources to facilitate human exploration and the development of space.
The Marco Polo proposal has been supported by more than 400 confirmed scientists worldwide and was prepared by a joint European Japanese group.
This mission is in competition with a few other ones for the next selection phase at ESA in fall 2009. If it is selected, its study will continue until 2011. At this stage, at least one mission will be selected for a launch planned for 2017 or 2018 in the current program.
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