Following the success of the First Arab Impact Cratering and Astrogeology Conference (AICAC) held in Jordan in November 2009, a follow-up conference took place in Casablanca, in November 2011. The AICAC Series of meetings was initially proposed by Mr Khalil Konsul, then General Secretary of the Arab Union for Astronomy and Space Sciences, with the aims to promote research interest for impact cratering in the Arab world. The purpose of these meetings is also to provide a platform for exchange between researchers already dedicatedly pursuing impact cratering research on Earth and on other planetary surfaces, planetary scientists, and Arab geoscience.
The AICAC II conference started with a plenary session hosted by Hassan II University (Fig. 1), allowing local students to attend a selection of talks with a broad perspective. This was followed by seven sessions dedicated to various aspects of impact cratering research. These sessions were entitled “Effects of impacts on the atmosphere, landscape, life and land stability; general astrogeology; discoveries and investigations of new impact structures; geotourism and heritage conservation related to impact structures; desert meteorites, and experimental studies.” Each session was introduced by a keynote presentation. Altogether 58 abstracts were accepted. Ninety-seven participants from 16 countries, including 6 North African and Middle-East countries, attended the conference. Africa was also represented by a participant from South Africa. Twenty-one keynote and invited lectures, 14 other oral presentations, and 19 posters were given. The increasing number of abstracts and participants in comparison with AICAC I (48 participants and 47 accepted abstracts; Reimold 2010) confirms the emergence of an impact cratering community in the Arab world.
As an interesting evolution relative to AICAC I, we note a strong participation of international planetary scientists and astronomers. This opens several new opportunities for Arab researchers, such as the comparison of terrestrial impact structures with those on the surfaces of other terrestrial planets, or on asteroids, and exchanges about the diversity of instruments available for remote sensing investigations of extraterrestrial impact structures. The Ibn Battuta Center for Exploration and Field Activity in the city of Marrakech (http://www.ibnbattutacentre.org) endeavors to test the hardware and operations for the ESA missions to Mars is an example of these recent interests for planetary sciences in Morocco.
This broader perspective emphasizing the interactions between the Earth and the other objects of our solar system stimulated several debates concerning the past and present rate of formation of impact craters in the Earth–Moon system. The possible nonuniformity of the cratering rate on the Moon’s surface was also evocated. The recent or present-day rate and size distribution of bolides entering the terrestrial atmosphere is usually discussed on the basis of the lunar cratering record for youngest Apollo sites, observed bolide detonations in the terrestrial atmosphere, and more recently from the fall of meteoroids onto the Moon, which produces transient luminous events detectable from Earth. This information is critical to estimate the number of impact structures, which are yet to be discovered on our planet. Collaboration at the interface between astronomy, meteoritic, and impact science also offers the possibility to develop joint observation strategies, with the objective to track objects before their impact on Earth. The benefit of such effort is illustrated by the unique case of meteorite fall 2008 TC3 (Almahatta Sitta) in northern Sudan on October 7, 2008, 02:46 (UTC). Morocco, with its large area of arid desert environments, may represent a favorite target for the development of these techniques, which would increase the collection of meteorites available for research in the Arab world. The search for meteorites in other parts of the world was also illustrated for the Atacama Desert, in the framework of international collaborations that aim at preserving the scientific heritage of Chile. A particular emphasis was also given to the origins of objects crossing the terrestrial orbits, such as comets, leading to meteor showers, whose characteristics (peak and intensity) are now predicted with more and more accuracy.
Whereas the above topics have been largely covered by invited talks and keynote addresses, the major part of the conference was naturally dedicated to the search and confirmation of impact structures in the Arab world, and in particular in Morocco. While no impact structure has to date been confirmed in this country, it is hoped that ongoing efforts will be successful eventually. The current state of the art is summarized in Fig. 2 representing Arab and Middle East countries with their 13 known impact structures (BP and Oasis in Libya; the Amguid, Ouarkziz, Tin Bider, and Talemzane structures in Algeria; Tenoumer and Aouelloul in Mauretania; Gweni-Fada and Aorounga in Chad; Kamil in Egypt; Jebel Waqf as Suwwan in Jordan, and the Wabar craters in Saudi Arabia; cf. Earth Impact database) and several potential structures that have been presented during AICAC II (Tigraou structure, circular structures in the Ezzane volcanic province in Algeria; Raz Zeidun in Egypt; Bir Anzarane in Morroco; unnamed small structure close to the Dhiban area in Jordan). None of these potential impact structures have been confirmed to date, and Bir Anzarane has been excluded. The search for the only accepted evidence for terrestrial impact structures, such as shatter cones, shock deformation (e.g., planar deformation features, PDF; for a review, cf. e.g., French and Koeberl 2010) is naturally encouraged. However, alternative explanations must be always explored and we recall that the finding of a nonimpact related origin for an enigmatic circular structure also has an important scientific value. These research experiences are in particular useful to improve our knowledge of the diverse geological processes producing circular features on the terrestrial surface and for an efficient discrimination among morphologies that are tentatively attributed to an impact origin.
Promising impact research takes place in the Arab world, at times leading to international collaborations, fulfilling the objectives of this series of conference. For workers from other countries, AICAC II was also an occasion to present recently discovered impact structures, and also potential impact sites from around the world (e.g., Brazilian or Congolese impact structures, Karakul in Tadjikistan, Zirouki in Iran, Malami beds or Ramgarh structure in India).
Already well-known impact structures did not remain unconsidered, with presentations including talks and posters on Dhala in India, El’gygytgyn in Russia, Haughton in Canada, Oasis in Libya, as well as a review presentation on aspects of interest of the Sudbury structure in Canada. Investigations on well-known impact structures are important for a better understanding of impact processes at all scales, and evaluating their effects on the environment, as largest events can be responsible for mass extinctions—as exemplified by the Cretaceous-Paleogene boundary event (Schulte et al. 2010). We recall here, for instance, that the strain-softening effect occurring during the collapse phase of complex craters, or the mechanism responsible for the formation of shatter cones is still widely debated. All of these aspects were also covered, bridging field studies with both numerical modeling of environmental effects and shock experiments in the laboratory, particularly by several members the MEMIN research group in Germany (Multidisciplinary Experimental and Modeling Impact Research Network, http://www.memin.de/).
Another important topic was public outreach about planetary processes and impact cratering. Two presentations on the Ries Crater Museum and on the Vredefort Structure, part of which had been inscribed in 2005 by UNESCO as a World Heritage Site, illustrated the challenges and solutions linked with the dimensions of impact sites, and the current outreach activities in this field.
The conference ended with a synopsis and debate resulting in a list of recommendations, following a conference format initiated during the AICAC I event. Several outstanding questions were listed during the debate and offered research direction for future investigations by researchers in the Arab world as well as for the established impact cratering community in Europe and America. Some of these questions are reported here:
- 1 While the study of impact structures on extraterrestrial surfaces is complementary to terrestrial studies, the criteria for the identification of terrestrial structures, which require field and laboratory studies, are not applicable. How do we certify that a circular structure is an impact structure on a planet which has other active geological processes, such as Mars?
- 2 The terrestrial cratering record is still significantly incomplete due to erosion, subduction of oceanic crust, and cover of impact structures by sediment or volcanic material. Especially for those cases where the relatively limited rock volume with diagnostic shock metamorphic evidence has been removed, the development of criteria for the identification of lower shock effects in the range of 1–5 GPa is required.
- 3 Shock effects need to be documented in a large variety of lithologies (e.g., carbonate rocks and felsic/mafic volcanics)
- 4 The search for new craters is generally based on several considerations such as the geological context of a given area (e.g., age, lack of tectonic deformation), and the past and present environmental conditions (e.g., erosion rate, arid or humid conditions) that may favor or limit the preservation of impact structures. However, a better prediction of the number of highly eroded or buried impact craters (as a function of crater size) that remain to be discovered for a given area of the globe would greatly help for filling the gaps of our knowledge of the terrestrial impact record.
The Second Arab Impact Cratering and Astrogeology Conference finally agreed on the following recommendations (that, in part, repeat the recommendations of AICAC I):
- 1 Arab countries are urged to organize conferences on impact cratering, astrogeology, and meteoritics. As there are already several groups working on impact structures in Algeria, those colleagues were requested to nurture collaboration and to investigate the possibility to follow-on with an international field trip to some of these structures—as a basis for an AICAC III meeting in the near future. The possibility that an AICAC symposium could be part of the 2014 Annual Meeting of the Meteoritical Society in Casablanca was also discussed.
- 2 Students from Arab countries are strongly encouraged to attend future AICACs, and to contribute to their scientific program. Local students are also strongly encouraged to take part in the local organizing committee.
- 3 Arab universities and their lecturing staff are encouraged to include impact cratering, astrogeology, meteorite, and planetary sciences in their educational curricula.
- 4 Arab universities are urged to include in their graduate programs the fields of impact cratering, meteoritics, and planetary sciences.
- 5 Arab geoscientists are encouraged to carry out systematic search programs for new meteorites and for new impact craters in the Arab region, and should start theoretical and applied research in the fields of impact cratering, astrogeology, and meteoritics.
- 6 Meteorites found in Arab countries constitute an important natural heritage of these countries. Illegal trade in such meteorites must be curbed, and their protection for education and scientific research must be ensured.
- 7 Arab geoscientists and universities are urged to collaborate with foreign universities and research centers working in the fields of impact cratering, astrogeology, and meteoritics to develop teaching and research in these fields.
- 8 A short course, covering fundamental aspects of the physics of impact processes and/or criteria for the identification of impact structures, should be offered with the AICAC conference series.
A 5-day geological tour was organized following the conference, with 35 participants from 10 countries. With the absence of confirmed impact structures in Morocco, Prof. Hasnaa Chennaoui Aoudjehane of Hassan II University Casablanca and her team of colleagues and students provided an opportunity to sample impressions of the varied and scenic geology, with highlights on the impressive sedimentary record spanning Proterozoic to Cenozoic ages, with some of the most spectacular fossils in the world. Participants were also given the opportunity to learn about 1200 years of cultural and historical heritage of Morocco, whereby these varied experiences enhanced the interaction between conference participants. A field guide was prepared for the participants by Prof. Omar Saddaqi, André Michard, and Lahssen Baidder from Paris-Sud University, and the excursion was preceded by an introductory presentation of the geology of Morocco, given by the first author of the field guide.
The last evening of the excursion took place in the Cultural Center of the Atlas Golf of Marrakech. Prof. Zouhair Benkhaldoun of Cadi Ayad Marrakech University gave an overview of the astronomical observatories of Morocco with a description of current scientific programs including the survey and search of exoplanets, the survey and search of asteroids, and the detection of lunar flashes. His presentation was followed by a detailed presentation by Dr. Sylvain Bouley (Observatoire de Paris) of the lunar flash program, involving the Oukaimeden observatory into an emerging worldwide network of monitoring stations. Prof. Zouhair Benkhaldoun was also proud to announce, only 4 years after the inauguration of the Oukaimeden Observatory, the first asteroid detected in Morocco. This asteroid (2011 VP12) has a visual magnitude of 19.7 and a diameter of about 300 m, and has a trajectory that intersects the Earth’s orbit (it is therefore of the Amor type).
Field trip participants were finally given the opportunity to visit the 60 cm telescope of the cultural center (Fig. 3). Such excursions following AICAC conferences are and will remain essential for fostering international collaborations. However, we should not underestimate the burden it represents for the local organizing committee in any of the countries in the Arab world, given the duties associated with the preparation of the conference, and the number of academics involved locally in geosciences. To reach a high level of satisfaction, and to offer the best to future AICAC participants, it might be suggested that geological tours involve more local and international specialists of the areas selected for the field trip.