Next generation near earth object surveys

Since its formation the Earth, as well as all the bodies of the Solar System, have been bombarded by cosmic debris whose size varies between a fraction of a millimiter and tens of km. The frequency of these impacts depends on the projectile's dimension and dynamical state; their computed characteristic timescales are, respectively, between minutes and hundreds of million years. In the last years the scientific community has been called to monitor all the sky, searching for objects close to Earth (Near Earth Objects, or NEOs). The work needed to discover NEOs is based on the classical astrometric techniques used to measure the position of celestial bodies: for this task we need to overcome two main obstacles, (i) the set up of a suitables observational strategy and (ii) the implementation of appropriate hardware and software. In fact, NEOs are discovered sufficiently close to the Earth to both induce an important parallax effect and to move appreciably in the telescope field of view. Consequently, the exposure times of the images have to be short enough to avoid trailing losses: this is why telescopes with very large field of view (which implies the availabilty of large format CCD and/or CCD mosaics) and short F/D ratios are best suited for this task. The most important requirement of a NEO search program is to scan large portions of the sky on a daily basis, in order to minimize the probability to lose discoveres objects in the following returns. Most of current search efforts have been conducted in the USA where during the deacde 1998-2008 NASA has funded a few dedicated surveys in the USA and Australia to scan the whole available sky twice per month to magnitude 19 and 20; the objective is to achieve 90% completeness of discovering of km-sized NEOs, the so-called Spaceyard Goal. Although such effort is currently close to been achieved at the 80% level, a survey for NEOs aiming at 90% completeness for a given size range cannot ignore that a significant fraction of the population is observable essentially only at low solar elongation, LSE, (at 90° or less). In this part of the sky effeorts have not been aggressive as in the opposition region. With telescopes larger than 1 meter in diameter, the survey work at LSE provides a number of advantages: (i) to increase the chances of discovering the largest remaining bodies in shorter amount of time; (ii) to obtain a mor unbiased inventory of the NEO population, in particular by encouraging the discovery of bodies that spend all or most of their time inside the orbit of the Earth; (iii) also, it was shown that the regions from 80 to 90°, the so called sweet spots, are thne ones where it's much more likely to discover the next Earth impactors. However, there are several penalties for such low elongation observations: (i) poorer observing conditions implying a lower limiting magnitude; (ii) shorter available observation time for each night; (iii) more difficult orbit determination. In this work I describe the current and past strategies of NEO research related to discovery and follow-up. With the help of a number of collaborations, my goal is to show that these difficulties can be overcome by suggesting the next generation surveys appropriate observing strategies. To address these issues I performed some real tests, consisting in two small scale surveys with appropriate large telescopes. In chapter 1 I go through past and existing NEO survey programs providing the results achived so far, and outline the work done in the past three years; in chapter 2 I describe the determination of the NEO population both numerical than through a orbital distribution model using also the results obtained in 5 years of activity of the Italian Campo Imperatore NEo Survey (CINEOS). In chapter 3, I describe the difficulties and the techniques used to discover and follow-up NEOs. In chapter 4 I introduce the next (second) generation NEO surveys and outline the observing strategy in order to fully exploit the potential offered by observing at LSE- The fifth chapter is used to deal with the orbital determination, including the problem of identifications, multiple solutions in order to extract all the possible information from the astrometric data. In the last part of the chapter I describe the application of the multiple solution analysis to the most important discoveries; chapter 6 is fully devoted to the problem of coordinating follow-up observations and dealing with obejcts with remote impact possibilities based on the experience gaines with the activities of the Spaceguard Central Node. In chapter 7 I complete my analysis on the results from the observing campigns conducted with the large telescopes at La SIlla and Mauna Kea and I conclude by providing a number of suggestions for the observing strategies of the next generation surveys. In the Appendix I report the most important discoveries and identifications not fully desacribed in the thesis and I outline an algorithm to address the problem of false identification dfrom different sets of data.