Italian Lunar Science Studies and Possible Missions a.k.a. The Moon: an Italian Approach. Angioletta Coradini Istituto Nazionale di Astrofisica

Transcription

1 Italian Lunar Science Studies and Possible Missions a.k.a. The Moon: an Italian Approach Angioletta Coradini Istituto Nazionale di Astrofisica

2 Goals of the Study The primary goal of the present study is to improve our knowledge of the Moon, by identifying top priority scientific problems that need to be solved in order understand the evolution of the Solar System The secondary goals are: to identify if there are resources that can be exploited by mankind to identify potential risks for men and instruments in case of a systematic exploration.

3 Primary Scientific themes What is the internal structure of the Moon? Is it the Moon differentiated? Is it the Moon Geophysically Active? What are the main events characterising lunar history? What is the Geochemical Evolution of the Moon? What is the Chemical / Mineralogical Composition of the Moon? What is the geomorphology structure of the Moon surface? What are the resources? What is the Interaction Surface / Environment? What is the Hazard for Robotic and Human Exploration?

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7 Outcome of the study A common set of prioritized science goals -to be addressed via a series of orbital, landed or sample return missions - has been identified. It has been recognized whether individual goals are most amenable to orbital measurements, in situ analysis,, or terrestrial analysis via sample return.

8 Top Priority Science Origin, Internal evolution, catastrophic event, further differentiation

9 Why the Moon? Origin of the Solar System The Moon is an ancient body, whose primordial differentiation stopped about 3.2 (TBC!) billion years ago, when most of the lunar mare basalt was formed. The Origin of the Moon is tied to the earliest evolutionary stages of the Earth.

10 Why the Moon: planetary differentiation The Moon preserves the remnants of primordial crust and early differentiated mantle, therefore, on the Moon we can find track of processes that characterized the primordial solar system, and that now, are cancelled on more active planetary bodies. In particular : The Moon has retained a record of the nearpost accretional impact history of the inner solar system. The Moon provides a type-locality for surface processes on airless-planetary body.

11 Moon Origin: the current scenario The Moon and the Earth are similar from isotopic point of view, particularly as far as the most important element is concerned: Oxygen

12 Forming the Earth-Moon System Impact by Mars-sized or larger planetesimal with young Earth 4.6 to 4.4 billion years ago ejected large quantity of hot material, and formed the Moon

13 Problems 1. The bulk composition of Earth and Moon are different 2. The depletion of volatile on the Moon cannot simply be attributed to the partial volatilization of terrestrial materials 3. The 128Hf-182W systematic indicate that the Moon is older than the Earth Core formation of the Moon must have predated the core formation of the earth. More extensive laboratory analyses on different lunar sample is requested.

14 Key Measurements The present Moon has several attributes that might serve as record of it past history: Accurate analysis of the lunar figure and differentiation can give an insight on past contraction (or expansion) history of the satellite as whole. The absence of records of extensive (opposite that on Mercury) contractions Therefore we have the hope to see these records by studying the moon surface extensively at high spatial resolution, and identifying areas that are old enough to be representative of the original thermal history. Another constraint on the lunar thermal history is the timing of the volcanism that gave rise to the Maria on the moon. The way in which the basalt volcanism was generated is still debated. For this reason it is extremely important to determine it extension, performing accurate mineralogical investigations from orbit. Moreover it will be extremely important to confirm that this volcanic event was localized in time, having a typical age of 3.5 Ga.

15 Second Phase: the Magma Ocean A second important phase of the lunar evolution was the large scale bombardment that happened about 3.5 b.a. ago. The Moon, after accretion, underwent a new extensive phenomenon of melting (Lunar Magma Ocean), that gave rise to the highlands, anorthositic in composition. Measurements of the depth of the anorthositic crust are needed to infer the extension of the original ocean (250 - to 1000 Km deep, according to different models). Therefore detailed gravimetric measurements are needed, with a resolution that allow to identify the highlands depth at planet size. Lunar structure. Estimates mineralogical composition of the crust and mantle. Significant crustal asymmetry (KREEP, mare basalts) that reflects very early differentiation processes. Therefore geochemical mineralogical measurements are needed

16 Thermal and Magmatic History of the Moon Was there a lunar magma ocean? If there was a magma ocean, what was its nature? Is the magma ocean the dominate process by which all of the terrestrial planets differentiate? How does lunar magmatism change with time? How does this change in magmatism reflects mantle processes and evolution? How does the lunar volcanic asymmetry reflect asymmetry in mantle processes? How does lunar heat flow change with lunar geography and time?

17 Needed Measurements Limitations of current data: Apollo seismic data is ambiguous and regional. Apollo heat flow data is regional Basalts are primarily samples from PKT. Examples of required data: High-quality, Moon-wide topography and geophysics Extensive, Moon-wide seismic network. Heat-flow measurements and thickness of regolith. Samples collected in relevant places

18 Further evolution:bombardment Once the crust was formed, by crystallisation of a magma ocean, the major events in the Moon's history were: 1) intense meteoritic bombardment, where the original Highland crust was broken up by large impacts during the heavy bombardment period (megaregolith formation), 2) development of the mare lavas, where the basins formed by impacts were flooded by basaltic lava, and 3) light bombardment with a uniform cratering and small impacts that formed the soil-like regolith and the fewer craters on the maria. On the Moon 2 populations were identified: Population 1 is responsible for the Late Heavy Bombardment (LHB), which took place b.y. ago Population 2 is made up of largely New Earth Objects, and is responsible for the bombardment, starting about 3.8 b.y. ago.

19 Scientific Importance Was there a substantial increase in the intensity of impact flux in the inner solar system at 3.9 billion years ago? challenge or confirm the Nice model If it occurred, what role did this increasein impact flux have on the evolution of life on Earth? What is the impact flux after 3.9 GA? Does the composition of impactor population change with time? Does the impact flux change within the inner solar system? What is effect of catastrophic impacts on planetary evolution?

20 Bombardment History of the Inner Solar System Examples of required data: High-quality, Moon-wide topography, imaging and gravitational field data sets. Sampling and dating of impact melt sheets associated with large basins and craters suspected to be products of the 3.9 billion year cataclysm. Sampling and dating of impact melt sheets associated with craters suspected to be products impact after 3.0 billion year.

21 Moon composition The knowledge of lunar composition is largely based on two sources: the lunar samples and the lunar meteorites. Unfortunately, all six sites of the Apollo are clustered in a small area of the nearside near the equator. Lunar meteorites exhibit a larger variability then the lunar samples, testifying that the mineralogical distribution is yet to be discovered. The mineralogical evolution of a surface can be inferred on the basis of remotely sensed data, accompanied by the analysis of samples collect in regions never sampled

22 Lunar Volcanism The main question is to identify the age of the last Lunar eruptive cycles. Other relevant aspects are: More detailed studies are needed for lava flows, volcanic domes and pyroclastic deposits. New determination of relative composition and aging of different volcanic episodes Needed measurements: Mineralogical studies Spectroscopy Geo-morphological studies and crater counting Relative ( from orbit) and absolute ( on returned samples) dating of subsequent units

23 AURUS LITTROW WEST WALL OF CRATER NORTH WALL OF CRATER HORTY CRATER 30M 5KM QuickTime and a Photo CD Decompressor are needed to use this picture YROCLASTICS LOW-TI MARE BASALT 25KM 50µ SCULPICCIUS GALLES ILEWG REGION October 2007 SW EDGE SERENITATIS BASIN Pyroclastic Glass deposits NASA PHOTOS

24 Open problems Constrain the initial thermal state of the Moon after its formation by a giant impact with the formation and crystallization of a magma ocean; Describe the differentiation process in order to explain the crust formation Describe an up to date internal structure of the Moon, that is quite different from that of the Earth even if crust, mantle and core are present. The size of the metallic core, for example, is highly uncertain ranging from 100 t0 400 km. The Moon does not have much of a magnetic field, so the lunar core is not generating magnetism the way Earth s core is. Nevertheless it did in the past, because lunar rocks are magnetized and this is an intriguing problem for lunar science.

25 Key Measurements The determination of elemental abundances is one of the science objectives of lunar missions. Such multi-element abundances, ratios, or maps should include results for elements that are diagnostic or important in lunar processes, including heat- producing elements (such as K and Th), important incompatible elements (Th( and rare earth elements), hydrogen (for polar deposits and regolith maturity), and key variable elements in major lunar provinces (such as Fe and Ti in the Maria). Both neutron (NS) and gamma-ray spectroscopy (GRS) can be used to infer elemental abundances; the two complement each other as in Lunar Prospector (LP).

26 Key Measurements Lunar Prospector gamma-ray and neutron spectrometers determine the concentrations of Fe, Ti, Th, K, H, Sm, and Gd. Fe and Ti data provide an independent check on the concentrations determined by reflectance spectroscopy. The ability to measure neutrons with thermal (E < 0.1 ev), epithermal (E ~ ev), and fast (E ~ MeV) energies maximizes the scientific return, being especially sensitive to both hydrogen (using epithermal neutrons) and thermal-neutron-absorbing elements is essential.

27 What we will learn from orbit? (1) What is the bulk composition of the Moon? yes What are the structural, compositional, and thickness variations of the lunar crust? Yes Are there distinct crustal and mantle structural domains? If so, do they mimic surface terranes and are the transitions between them abrupt or gradational? Yes Is garnet present in the middle and deep mantle? (Model Dependent) What is the lunar core made of, and how extensive is it? Yes Do plastic zones persist in the lunar core and mantle (i.e., are parts of the Moon still hot)? Yes

28 What we will learn from orbit? (2).What are the dominate volatiles in the lunar interior? NO What are the volatile reactions that drive magmatic volcanic processes? NO How extensive are the lunar pyroclastic deposits? NO Are Volatiles present on the lunar surface? YES Do H2O ice deposits exist at the lunar poles? What is the lateral extent of these deposits? What is the vertical extent of these deposits? Over what period of time are these deposits formed?

29 Requirements for Orbital Measurements and Scientific Experiments 1.Uniform and Global high resolution morphology 2.Uniform and Global high resolution mineralogical/compositional mapping 3.Uniform global gravity field and positioning control network A fundamental step in such a direction is a deeper characterisation, through a gravimetry experiment, of the Moon s s gravitational field together with an accurate measurement of its rotational state.

30 Requirements for Orbital Measurements and Scientific Experiments (2) 4 Characterisation of lunar polar regions 5 Uniform global regolith characterization

31 Possible Scenario One or two orbital missions, a geophysical lander, mobility

32 Orbital Measurements Given the previous constraints, we can summarise here the needed orbital measurements: Geophysics. On the basis of all the previous discussions, we can identify among the highest priorities the following components, since they permit a study of the internal structure of the Moon, its differentiation and its geological history. Ka-band Gradiometers Stereo-camera Laser altimeters Geochemistry. Among the main goals, we have identified the geological evolution of the Moon, the identification of the presence of water and recognition of the distribution of lunar resources. The highest priority experiments are: Multispectral cameras γ, X, UV and IR spectrometers radio and radar measurements

33 A Possible Scenario We summarise possible scenarios for a sequence of lunar missions that are affordable for a single nation or for cooperative efforts. During several meetings and discussions, we have verified that the limitations do exist for a national mission.

34 Constraints Mission duration 9 months Possible payload 50 Kg Reference orbit 100 Km on the lunar surface Possible further orbit 50 Km on the lunar surface Second orbiter elongated orbit

35 Orbital Measurements (1) Geophysics. On the basis of all the previous discussions, we can identify among the highest priorities the following components, since they permit a study of the internal structure of the Moon, its differentiation and its geological history. K-band Gradiometers Stereo-camera Laser altimeters

36 Orbital Measurements (2) Geochemistry. Among the main goals, we have identified the geological evolution of the Moon, the identification of the presence of water and recognition of the distribution of lunar resources. The highest priority experiments are: Multispectral cameras γ, X, UV and IR spectrometers radio and radar measurements

37 Orbital Measurements (3) Given the previous priorities, we can assume that the scientific requirements can be satisfied by means of a series of missions, starting with one or more orbital missions followed by one or more lander missions. As far as the orbital missions are concerned, we can think either to concentrate all of the measurements in one large satellite (case 1), or to split them into two smaller orbiters (case 2).

38 Case 1 This hypothesis foresees the need to use one large satellite (600Kg dry mass) which is able to host a complex geophysical/geochemical payload. Advantages In this case, taking into account that there will be only one launch, the launch cost will be less expensive then a dual launch. Only one spacecraft will be operated, thus reducing the cost of the operations. The information coming from different payloads will be better integrated. Disadvantages Complexity in the integration and operation of several complex experiments Less reliability in overall system Higher data rate (due to the number of instruments) and the necessity to include a large mass memory

39 Case 2 In this case, we consider the possibility to operate two different satellites. One satellite will be mainly devoted to the study of lunar geophysics, and the other mainly devoted to the geochemistry. Advantages Higher reliability and lower launch risk Higher flexibility in the selection of the orbital strategy and easier orbital optimisation Possibility to build a small orbital network during the lifetime of the two satellites Wider choice of launchers of smaller cost Possibility to dilute the spending profile over a wider time-span. Optimisation of human resources Possibility to start sooner with a small national mission achieving a prestigious goal and attracting the public interest (High E/PO) Disadvantages The lifetime of the two satellites should be long enough to permit one to operate both spacecraft jointly for at least for a certain time span The cost of the launch and operations are higher