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Published online by Cambridge University Press: 01 April 2019
The Minor Planet Center, established in 1947 by the IAU, is the international repository and clearinghouse for the world’s minor planet observations. Since 1989, CCD surveys of Near Earth Objects at ground-based astronomical observatories are operational, mainly in the USA. As of 23 August, 2018, a total of 18,545 Near Earth Asteroids (NEAs) and 107 Near Earth Comets (NECs) have been registered and daily updates are made publicly available on the internet by the MPC, NASA-JPL-CNEOS and ESA-SSA-NEOCC.
Concern about the possibility of NEO impacts has been picked up by the United Nations Committee on the Peaceful Uses of Outer Space (UN-COPUOS), where the IAU has observer status, and formally expressed since 1999. This led in 2014 to the formation of two international coordinating bodies for NEO detection and NEO impact mitigation: the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG).
In support of these developments, the IAU 28th General Assembly, Session II, held in Beijing on 30 August 2012, adopted a Resolution (3B) recommending the establishment of an International NEO EarlyWarning System, as proposed by the IAU Division III (now Division F) Working Group on Near-Earth Objects. The GA recommended “… that the IAU National Members work with the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) and the International Council for Science (ICSU), to coordinate and collaborate on the establishment of an International NEO Early Warning System, relying on the scientific and technical advice of the relevant astronomical community, whose main purpose is the reliable identification of potential NEO collisions with the Earth, and the communication of the relevant parameters to suitable decision makers of the nation(s) involved. ….”
The NEO hazard issue received world-wide attention on 13 February 2013 when a NEA with an estimated size of 17 to 20 meters and an estimated mass of 11,000 tons exploded over Chelyabinsk (Russia), releasing 440 kT TNT of energy at an altitude of ∼23 km.
Subsequently, on 5 December 2014, the United Nations General Assembly adopted a Resolution (69/85, 9–10), noting “… the importance of information-sharing in discovering, monitoring and physically characterizing potentially hazardous near-Earth objects to ensure that all countries, in particular developing countries with limited capacity in predicting and mitigating a near-Earth object impact, are aware of potential threats, emphasizes the need for capacitybuilding for effective emergency response and disaster management in the event of a near-Earth object impact, .…”
In spite of all dedicated NEO surveys operational to date, the present inventory and thus our assessment of the level of threat of NEOs is severely limited by their huge number and by the available observational capabilities. E.g., while the estimated number of all NEOs larger than 40 meters in diameter is ∼700, 000, only ∼2% have been detected to date. For NEOs with sizes between 40 and 140 meters, the detection percentage amounts to less than 1% of the estimated number. Only dedicated space-based surveys, preferably in the infrared, will be able to provide the much needed orders of magnitude improvement in the detection, tracking and characterizing of NEOs. One promising project is the NASA-JPL NEOCam mission, studied since 2005 but not yet approved: a dedicated infrared observatory aiming to detect, track and characterize NEO’s from the Sun-Earth Lagrange point L1.
As Yeomans puts it: we better find them before they find us (Yeomans 2013). Traditionally, astronomers are looking back into the past, if only because of the limited speed of light. But we should realize that the clear and present danger posed by hazardous Near Earth Objects to mankind and all other life forms obliges us to look also forward, into the future. Provided with the proper means, we astronomers can do that, as a small service to society, including ourselves. The astronomical community at large should give high priority to NEO survey projects, in particular space-based surveys.
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