This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

## 12 June 2012

### Various recent technical papers including on asteroid deflection and identification

Various recent technical papers including on asteroid deflection and identification.

Title: Design of a Formation of Solar Pumped Lasers for Asteroid Deflection

Abstract: This paper presents the design of a multi-spacecraft system for the deflection of asteroids. Each spacecraft is equipped with a fibre laser and a solar concentrator. The laser induces the sublimation of a portion of the surface of the asteroid. The jet of gas and debris thrusts the asteroid off its natural course. The main idea is to have a swarm of spacecraft flying in the proximity of the asteroid with all the spacecraft beaming to the same location to achieve the required deflection thrust. The paper presents the design of the formation orbits and the multi-objective optimization of the swarm in order to minimize the total mass in space and maximize the deflection of the asteroid. The paper demonstrates how significant deflections can be obtained with relatively small sized, easy-to-control spacecraft.

Title: Evidence-Based Robust Design of Deflection Actions for Near Earth Objects
Author(s): Federico Zuiani, Massimiliano Vasile, Alison Gibbings

Abstract: This paper presents a novel approach to the robust design of deflection actions for Near Earth Objects (NEO). In particular, the case of deflection by means of Solar-pumped Laser ablation is studied here in detail. The basic idea behind Laser ablation is that of inducing a sublimation of the NEO surface, which produces a low thrust thereby slowly deviating the asteroid from its initial Earth threatening trajectory. This work investigates the integrated design of the Space-based Laser system and the deflection action generated by laser ablation under uncertainty. The integrated design is formulated as a multi-objective optimisation problem in which the deviation is maximised and the total system mass is minimised. Both the model for the estimation of the thrust produced by surface laser ablation and the spacecraft system model are assumed to be affected by epistemic uncertainties (partial or complete lack of knowledge). Evidence Theory is used to quantify these uncertainties and introduce them in the optimisation process. The propagation of the trajectory of the NEO under the laser-ablation action is performed with a novel approach based on an approximated analytical solution of Gauss' Variational Equations. An example of design of the deflection of asteroid Apophis with a swarm of spacecraft is presented

Title: Characterizing Subpopulations within the Near Earth Objects with NEOWISE: Preliminary Results
Author(s): A. Mainzer, T. Grav, J. Masiero, J. Bauer, R. S. McMillan, J. Giorgini, T. Spahr, R. M. Cutri, D. J. Tholen, R. Jedicke, R. Walker, E. Wright, C. R. Nugent

Abstract: We present the preliminary results of an analysis of the sub-populations within the near-Earth asteroids, including the Atens, Apollos, Amors, and those that are considered potentially hazardous using data from the Wide-field Infrared Survey Explorer (WISE). In order to extrapolate the sample of objects detected by WISE to the greater population, we determined the survey biases for asteroids detected by the project's automated moving object processing system (known as NEOWISE) as a function of diameter, visible albedo, and orbital elements. Using this technique, we are able to place constraints on the number of potentially hazardous asteroids (PHAs) larger than 100 m and find that there are $\sim4700\pm1450$ such objects. As expected, the Atens, Apollos, and Amors are revealed by WISE to have somewhat different albedo distributions, with the Atens being brighter than the Amors. The cumulative size distributions of the various near-Earth object (NEO) subgroups vary slightly between 100 m and 1 km. A comparison of the observed orbital elements of the various sub-populations of the NEOs with the current best model is shown.

Title: Density of asteroids
Author(s): Benoit Carry

Abstract: A considerable amount of information regarding the processes that occurred during the accretion of the early planetesimals is still present among the small bodies of our solar system. A review of our current knowledge of the density of small bodies is presented here. Intrinsic physical properties of small bodies are sought by searching for relationships between the dynamical and taxonomic classes, size, and density. Mass and volume estimates for 287 small bodies are collected from the literature. The accuracy and biases affecting the methods used to estimate these quantities are discussed and best-estimates are strictly selected. Bulk densities are subsequently computed and compared with meteorite density, allowing to estimate the macroporosity within these bodies. Dwarf-planets apparently have no macroporosity, while smaller bodies can have large voids. This trend is apparently correlated with size: C and S-complex asteroids tends to have larger density with increasing diameter. The average density of each Bus-DeMeo taxonomic classes is computed. S-complex asteroids are more dense on average than those in the C-complex that in turn have a larger macroporosity, although both complexes partly overlap. Within the C-complex, B-types stand out in albedo, reflectance spectra, and density, indicating a unique composition. Asteroids in the X-complex span a wide range of densities, suggesting that many compositions are included in the complex. Comets and TNOs have high macroporosity and low density, supporting the current models of internal structures made of icy aggregates. The number of density estimates sky-rocketed during last decade from a handful to 287, but only a third of the estimates are more precise than 20%. Several lines of investigation to refine this are contemplated, including observations of multiple systems, 3-D shape modeling, and orbital analysis from Gaia astrometry.