1. Vladimir Rubtsov, Reconstruction of the Tunguska Event of 1908: Neither an Asteroid, Nor a Comet Core, arXiv:1302.6273
    The Tunguska explosion occurred in the morning of June 30, 1908, in Central Siberia, some 800 km NNW from Lake Baikal. It devastated the forest area of 2150 sq. km, flattening and scorching some 30 million trees. Before this, a luminous body flew overhead in the cloudless sky. The air waves from the explosion were recorded as far as in London. The object that flew that morning over Siberia is usually designated as the Tunguska meteorite or - more cautiously - the Tunguska space body (TSB). Certainly, this body was dangerous: the taiga was leveled over an area twice as large as New York City. The whole number of Tunguska hypotheses reaches a hundred, or so. But few of them have been built according to the standards of science and with due consideration of empirical data. There is also a serious methodological problem that is, as a rule, overlooked: the need to take into consideration all empirical data and to reconstruct the Tunguska event before building any models of it. Such a reconstruction is essential - since the consequences of this event are many and varied. The main Tunguska traces may be grouped and listed as follows: (a) material traces; (b) instrumental traces; (c) informational traces. To be sure that a proposed theory is correct, the scientist must check it against all the three types of Tunguska evidence. Having reconstructed the Tunguska event with due attention to all the evidence, we have to conclude that it could not have been an asteroid or a comet core. There seems to exist in space another type of dangerous space objects, whose nature still remains unknown.
  2. P.Michel, Physical properties of Near-Earth Objects that inform mitigation, Acta Astronautica, Volume 90, Issue 1, September 2013, Pages 6-13, https://doi.org/10.1016/j.actaastro.2012.07.022

    Various methods have been proposed to avoid the collision of a Near-Earth Object (NEO) with the Earth. Each of these methods relies on a mitigation concept (deflection or fragmentation), an energy source (e.g. kinetic, gravitational, solar, thermal, etc.) and a mode of approach (e.g. remote station and interaction). The efficiency of each method depends on the physical properties of the considered NEO that influence the way the body will respond to the considered energy source. While the knowledge of properties such as the mass, spin rate and obliquity as well as the shape is generally required for all mitigation methods, there are other properties that are important to know for some methods and that have no great influence for other ones. This paper summarizes the current knowledge of main physical properties of NEOs and their importance for the most usual mitigation strategies that have been proposed, i.e. the kinetic impactor, the gravity tractor, strategies based on anchoring or depositing material on the surface, and strategies aimed at modifying the thermal properties of the NEO in order to either modify or cancel the Yarkovsky effect, or cause surface vaporization.