An asteroid just been discovered has a strongly undeter-mined orbit, being weakly constrained by the few avail-able astrometric observations, and there is a set of possi-ble orbits, all compatible with the observations, forminga Confidence Region (CR) in the 6-dimensional orbitalelements space. The goal of Impact Monitoring (IM) isto understand whether the CR contains subsets of initialconditions leading to a collision with the Earth in the fu-ture (Virtual Impactors, VIs) and to estimate the ImpactProbability (IP). Once defined the CR, the crucial stepsare the sampling of the uncertainty region, the propaga-tion of the so called Virtual Asteroids (VAs) searchingfor VIs and the computation of IP. Two automatic sys-tems, CLOMON2 (at University of Pisa/SpaceDyS/ESA-NEOCC) and Sentry (at JPL/NASA), have been devel-oped for this purpose. Both generate VAs by applying a1-dimensional sampling of the CR based upon the LineOf Variations (LOV), that is a differentiable curve rep-resenting a kind of spine of the uncertainty region. TheLOV method is very useful when the CR is elongated andthin, but this is not the case when the observed arc is veryshort: the uncertainty results to be wide in at least twodirections and the LOV is not a reliable representativeof the entire region. Unfortunately, this is precisely thecase of very small asteroids observed only shortly beforea close approach or an impact with the Earth (imminentimpactors). The problem has been faced recently andthree systems were developed, SCOUT (at JPL/NASA),NEORANGER (at University of Helsinki) and NEOScan(at University of Pisa/SpaceDyS): we will focus on thelatter. NEOScan consults the NEO Confirmation Page(NEOCP) of the Minor Planet Center (MPC) every twominutes, extracting data and running the algorithms basedon the Admissible Region (AR), a tool widely used alsoin the space debris orbit determination. Once an objectgoes away from the NEOCP obtaining a designation, theIM systems switch to “classical” 1-d algorithms. In thisprocedure, essentially dictated by the rules of the MPC,there is a flaw, in the sense that there are objects, witha very well-defined orbit, remaining on the NEOCP, and,on the contrary, there exist designated objects with a greatuncertainty. Thus, there are a certain number of cases thatare not properly processed. In this paper, after a reviewof the IM algorithms developed at the University of Pisa, we will present the idea of a new automatic system capa-ble, starting from the astrometric observations, to decidewhat is the right algorithm in order to reach reasonableresults for each kind of orbit.
A NEW WAY OF THINKING ABOUT IMPACT MONITORING OF NEAR-EARTHOBJECTS
G. Tommei
Primo
2019-01-01
Abstract
An asteroid just been discovered has a strongly undeter-mined orbit, being weakly constrained by the few avail-able astrometric observations, and there is a set of possi-ble orbits, all compatible with the observations, forminga Confidence Region (CR) in the 6-dimensional orbitalelements space. The goal of Impact Monitoring (IM) isto understand whether the CR contains subsets of initialconditions leading to a collision with the Earth in the fu-ture (Virtual Impactors, VIs) and to estimate the ImpactProbability (IP). Once defined the CR, the crucial stepsare the sampling of the uncertainty region, the propaga-tion of the so called Virtual Asteroids (VAs) searchingfor VIs and the computation of IP. Two automatic sys-tems, CLOMON2 (at University of Pisa/SpaceDyS/ESA-NEOCC) and Sentry (at JPL/NASA), have been devel-oped for this purpose. Both generate VAs by applying a1-dimensional sampling of the CR based upon the LineOf Variations (LOV), that is a differentiable curve rep-resenting a kind of spine of the uncertainty region. TheLOV method is very useful when the CR is elongated andthin, but this is not the case when the observed arc is veryshort: the uncertainty results to be wide in at least twodirections and the LOV is not a reliable representativeof the entire region. Unfortunately, this is precisely thecase of very small asteroids observed only shortly beforea close approach or an impact with the Earth (imminentimpactors). The problem has been faced recently andthree systems were developed, SCOUT (at JPL/NASA),NEORANGER (at University of Helsinki) and NEOScan(at University of Pisa/SpaceDyS): we will focus on thelatter. NEOScan consults the NEO Confirmation Page(NEOCP) of the Minor Planet Center (MPC) every twominutes, extracting data and running the algorithms basedon the Admissible Region (AR), a tool widely used alsoin the space debris orbit determination. Once an objectgoes away from the NEOCP obtaining a designation, theIM systems switch to “classical” 1-d algorithms. In thisprocedure, essentially dictated by the rules of the MPC,there is a flaw, in the sense that there are objects, witha very well-defined orbit, remaining on the NEOCP, and,on the contrary, there exist designated objects with a greatuncertainty. Thus, there are a certain number of cases thatare not properly processed. In this paper, after a reviewof the IM algorithms developed at the University of Pisa, we will present the idea of a new automatic system capa-ble, starting from the astrometric observations, to decidewhat is the right algorithm in order to reach reasonableresults for each kind of orbit.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
