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Home , 1862 Apollo, 2007 VK184, 2101 Adonis, 69230 Hermes, Chicxulub crater, Gravitational keyhole

Aeronautics and Aerospace Safety Perspective CHARACTERIZATION OF AND ANALYSIS OF THE EFFECTS OF THEIR IMPACT ON

Maria Iudicello1, Salvatore Crapanzano1, Girolamo Garreffa1,2, Massimiliano De Pasquale1, Michele Pavone3 1 Euro-Mediterranean Institute of Science and Technology (IEMEST), Palermo, Italy 2 Fondazione Potito, Campobasso, Italy 3 Independent Researcher, Montesarchio (BN), Italy

Correspondence: Received: May 4th, 2016 Revised: June 28th, 2016 Maria Iudicello ST Accepted: July 1 , 2016 e-mail: [email protected]

Abstract extended damage in the event of impact. More In this article, the authors analyze the asteroids precisely, an can become a PHO if its parameters, such as physical, chemical, structural minimum distance at the intersection of the orbit and dimensional ones, in order to predict the (MOID) with the Earth is 0.05 AU (Astronomical effect of impact on Earth. In particular, the Units) or less, and if its diameter is at least 150 authors identify those parameters that may m (i.e. absolute H of 22.0 or brighter, cause disastrous impacts on our . with assumed albedo of 13%) [3]. In fact, this size is already sufficient to cause devastating damage Keywords: Near-Earth Objects, Potentially in case of crashing into Earth. Hazardous Objects, asteroid threat to Earth, To date, more than 13,957 Near-Earth Objects asteroid properties, keyhole (NEOs) have been discovered: 13,851 asteroids and 106 , 521 of them belong to the risk Introduction list, but their number is expected to rise [4-5]. The Since the time of its formation, the Earth has number of NEAs with a diameter larger than 1 km been constantly subjected to bombardment by is estimated to be between 500 and 1,000 [6]. The objects from outer space. Such objects have a protects the Earth’s surface from the wide range of dimensions, from the smallest to majority of the NEOs, which may burn or explode the large, and they show very different rates at high altitude. Several factors may play a role in of arrival [1]. Among them, the asteroids, which enabling bodies from outer space to impact the are ancient remains of the early formation of our Earth’s surface: their size, their composition, their

Solar System, are of particular importance. They speed and their angle of approach [3]. http://www.iemest.eu/life-safety-and-security/ online at Available are older than four billion years, and are made Considering the possible negative effects of a of carbon-rich material, rock, or in some cases of NEO’s impact with the Earth, for several years metal, mainly and [2]. Their sizes vary the research centres worldwide have been from small boulders to objects with diameters of involved in finding solutions to destroy or deflect hundreds of kilometres. such asteroids, or at least in mitigating the effects For several years, asteroids have been the subject of their impact. Our ability to identify those PHO of studies and attention because of their potential well in advance, in order to accurately measure hazard if they were to slam into our planet. In their orbits and their physical properties, is general, an asteroid is considered a Potentially crucial to find the best solution. Hazardous Object (PHO) for the Earth if its orbit This article makes a physical-chemical can have close encounters with our planet and characterization and structural mechanics of if it has a sufficient size to cause substantial and the asteroids in order to identify and analyze the parameters affecting the magnitude of the

June 2016 | Volume 4 | Issue 3 | © Life Safety and Security ISSN: 2283-7604 | DOI: 10.12882/2283-7604.2016.4.3 64 disaster in the event of impact on the ground. compositions is not so deep and it is mainly derived from analyses of , remote Asteroid Chemical and Physical sensing observations from Earth and space characterization missions [10]. A Near-Earth Object (NEO) is defined as a small Near-Earth Asteroids smaller than 1 are body with perihelion distance less than 1.3 AU called Near-Earth . Meteorites, that and aphelion distance greater than 0.983 AU [7]. are meteoroids impacting the Earth’s surface, NEO’s population includes about thirteen can basically be classified into two types: those thousand Near-Earth Asteroids and more than that experience only heating (chondrites) [11] one hundred of Near-Earth Comets (NECs), which and those that experience also melting and are also serious impact threats. Comets have differentiation (achondrites, stony-, irons) densities estimated to be around 1 g/cm3 [8], [12]. Instead, silicate-rich meteorites are referred while asteroids are geologic bodies with a variety to as stony and would include all chondrites and of morphological features and different densities. achondrites [10]. Unfortunately, only qualitative mineralogical Meteorites which are similar in terms of descriptions can be given for asteroid classes, petrological, mineralogical, bulk chemical, and because quantitative analysis of asteroid isotopic properties, are separated into groups as compositions (determining the proportion well (Table 1) [10, 13-16]. and composition of different mineral species) is very difficult [9]. Since we have returned few samples from asteroids, our knowledge of their

Table 1 - Groups Groups Composition (1) Bulk Density [g/cm3] Fall percentages (2) [%] Carbonaceous chondrites CI Phyllosilicates, magnetite 1.58 0.5 CM Phyllosilicates, tochilinite, olivine 2.08-2.37 1.7 CR Phyllosilicates, pyroxene, olivine, metallic iron - 0.3 CO Olivine, pyroxene, CAIs, metallic iron 2.36-2.98 0.5 CH Pyroxene, metallic iron, olivine - Only finds CV Olivine, pyroxene, CAIs 2.60-3.18 0.6 CK Olivine, CAIs - 0.3 Enstatite chondrites EH Enstatite, metallic iron, sulfides, plagioclase, ± olivine ~3.36 0.8 EL Enstatite, metallic iron, sulfides, plagioclase ~3.36 0.7 Ordinary chondrites H Olivine, pyroxene, metallic iron, plagioclase, sulfides 3.05-3.75 34.1 L Olivine, pyroxene, plagioclase, metallic iron, sulfides 3.05-3.75 38.0 LL Olivine, pyroxene, plagioclase, metallic iron, sulfides 3.05-3.75 7.9 R chondrites Olivine, pyroxene, plagioclase, sulfides 3.05-3.75 0.1 Available online at http://www.iemest.eu/life-safety-and-security/ online at Available Primitive achondrites Acapulcoites (a) Pyroxene, olivine, plagioclase, metallic iron, sulfides - 0.1 Lodranites (a) Pyroxene, olivine, metallic iron, ± plagioclase, ± sulfides - 0.1 Winonaites Olivine, pyroxene, plagioclase, metallic iron - 0.1 Differentiated achondrites

Angrites TiO2-rich augite, olivine, plagioclase - 0.1 Aubrites Enstatite, sulfides - 0.1 Brachinites Olivine, clinopyroxene, ± plagioclase - Only finds Diogenites (b) orthopyroxene 2.99-3.29 1.2 Eucrites (b) Pigeonite, plagioclase 2.99-3.29 2.7 Howardites (b) Eucritic-diogenitic 2.99-3.29 2.1 Ureilites Olivine, pyroxene, graphite - 0,5

June 2016 | Volume 4 | Issue 3 | © Life Safety and Security ISSN: 2283-7604 | DOI: 10.12882/2283-7604.2016.4.3 65 J une suggests that most asteroids with adiameter over should beable to rotate much more rapidly, this material flung out. Since would object solid a be the gravitational force, so any loose surface inertia at the surface becomes greater than For asteroids rotating faster than this rate, the has a smaller than . 2.2 No asteroid larger than 100 meters in diameter NEAs. of continuing supply a guarantees these resonances due to the , that into other orbits. Then, new asteroids migrate into occur; asteroid in these gaps have been moved known as Kirkwood gaps, where these resonances . In the fact has gaps, the asteroid’s orbit and pushes it into the inner Jupiter. Such interaction an with Jupiter perturbs SystemSolar through resonances orbital with are moved from the Asteroid Belt into the inner asteroids Indeed, into orbits. near-Earth shifted the Solar System, new asteroids must beconstantly orbital lifetimes so short compared to the age of planet or an ejection from the Solar System. With perturbations, causing acollision with the Sun or a planetary by out eventually driven are They years. remainNEAs in their orbits for just afew million [17]. strong with strengths of approximately kbars 3.5 of 1–10 bars, while iron meteorites are extremely phyllosilicates crushing show laboratory strengths with amortar and pestle; meteorites containing meteorites can beeasily crushed into powders In terms of physical strength, most chondritic cores (irons) of differentiated bodies [10]. (pallasites),angrites), boundaries and core-mantle of crusts (howardites, eucrites, and diogenites; Many meteorites are thought to besamples 2016| (c) There are 13iron meteoritegroups plus~100ungrouped irons. (b) Howardites, eucritesanddiogenites(HEDs)appeartocomefrom thesameparent body. (a) Acapulcoites andlodranitesappeartocomefrom thesameparent body. Irons Pallasites Mesosiderites 2 : Fall percentages are calculated from the 942 classified falls 942 classified the from calculated are 2 :Fall percentages present. be may ±- inclusions. refractory –Ca-Al-rich CAIs Abbreviations: abundance. average of order decreasing in listed are components or 1 :Minerals V olume 4|I ssue Metallic iron, sulfides,schreibersite Olivine, metalliciron olivine,metalliciron Basalt-metallic iron breccia 3|©L ife S afety and S ecurity

ISSN Table 1-Meteorite Groups : 2283-7604 | Stony-irons . DOI simulations show that colliding piles are rubble 0 to ~80% [19, 20]. More than that, computer asteroids show amounts of macroporosity from similar. piles presumably are Rubble compositions internal and surface the differentiated, internally asteroids [18]. Thus, for small bodies that are not accumulation collisions debris after of between 100 meters are “rubble piles”, formed through multiplying it by the object’s volume computed a NEO (m) by using adensity of 4g/cm macroporosity, we can estimate an upper limit of between 2and 4g/cm Since most meteorites have bulk densities [21].meteorites meteorites (Pallasites, Mesosiderites), 5.7% Iron (SNC) group, Aubrites, Ureilites), 1.5% Stony iron Chassignites Nakhlites, (HED) Shergottites, group, 7.1%- Achondrites: Howardite-Eucrite-Diogenite (85.7% Chondrites: carbonaceous Enstatite and that fall to Earth are: 92.8% of Stony meteorites data, the percentage of the of meteorites types to land [10]. More specifically, according to recent Earth and a4% probability for an iron meteorite a stony or stony-iron meteorite to land on the the fall percentage, give aprobability of 94% for impacting population. Estimations, based on they are expected to beonly few percent of the since they have the highest densities. However, meteorites pose the biggest impact threat, Ir, Ni). NEOs with compositions similar to iron siderophileof (Ga, elements (“iron-loving”) Ge, They are classified according to the concentrations inclusions. silicate and schreibersite, sulfides, as with 5–20% of Nickel, plus accessory phases such Iron meteorites are composed of metallic iron more likely to merge. : 10.12882/2283-7604.2016.4.3 (Cont’d) 6.99-7.59 4.82-4.97 4.16-4.22 3 , without even, consider 4.2 0.5 0.7 3 and and 66

Available online at http://www.iemest.eu/life-safety-and-security/ J une surface compositionsurface is representative the of of much larger asteroids, it is assumed that the In since fact, can NEAs bethought to befragments the object’s density from its surface composition. Another way to derive aNEO’s mass is by estimating have average impact velocities of 55 km/s [8]. Earth is around 20 km/s [22], but some comets The average impact velocity for asteroids with (1/2)mv = the kinetic energy (E) of an incoming asteroid as E from its diameter [10]. We can then easily derive accentuated asteroids if reveal orbiting minor- Unfortunately, maybe deflection of problem the it [24] or aspacecraft encounter [25, 26]. if the object has anatural body revolving around Moreover, it is possible to determine a NEO’s mass volume. its diameter, which can beused to calculate its to Earth, radar observations [23] can determine asteroid an If is large close and enough enough Earth. from to identify characteristic absorption bands and it is hard very features. However, metallic iron does not show hydrated silicates) have characteristic absorption since many minerals (e.g. olivine, pyroxene, the best way to determine aNEO’s composition, object as a whole [10]. Reflectance spectra are 2016| 3 : In the Figure 1 “Coronos” should to be “Coronis. tobe should 1“Coronos” Figure the 3 :In Figure oftheaverage 1-Distribution distances oftheasteroids from theSun(N=asteroid number;d=distance expressed by AU) V olume 2 , where vis the velocity. 4|I ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI asteroids falling into the various spectral types It has to benoted that the proportion of known (classes). spectrum reflectance their of features and characteristics of their orbits (groups and families), Asteroids are generally classified according to the probability. NEOs only carry about 18% of the overall collision years. More than that, they estimate that known damage [22], should occur every 63,000 ±8,000 regional large-scale produce would which impact, with Earth [7], it is estimated that a1000 megaton After astudy of collision probabilities of NEOs largest body is orbited by satellites. two theyfact, constitute atriple system, where the SN263 [29] are ternary Near-Earth Asteroids. In Instead, (136617) 1994 CC [28] and (153591) 2001 [27]. its central body at an average distance of just 3km identified as S/2005 (1862) 1, which orbits about 1932 HA (1862) has aminor-planet For example, the binary Near-Earth Asteroid planet or if they are co-orbiting binaries. distance themselves from the plane of the . Generally, the orbits of the asteroids do not are easier to detect than others, biasing the totals. asteroids that are of that In some type. fact, types does not necessarily reflect the proportion of all : 10.12882/2283-7604.2016.4.3 3 . 67

Available online at http://www.iemest.eu/life-safety-and-security/ J une wobbles so much that its orientation in space may show chaotic rotation: their axis of rotation regular rotation. In afew instances, however, they bodies like , asteroids or comets show few days. Generally, the vast majority of celestial asteroids between just vary over 2hours to a irregular shapes. The rotation periods of the Ordinarily, asteroids the show elongated and asteroids, is inferior to [30]. ε=0.3 while their eccentricity, for the large majority of The average inclination of the orbits is about 10°, 2) [31]. The Apollo Asteroids are also called “Earth distance of their perihelion and aphelion (Figure on the semi-major axis of their orbit and on the asteroidsApollo Aten and asteroids depending Mostly of NEOs are classified as Amor asteroids, the ratio 3/2 with the of Jupiter. Hilda thickens is in around period whose orbit the opposite effects. In Figure 1 the group of asteroids situations, resonance a with Jupiter produce can from its original orbit. On the other hand, in certain each other, gradually moving the asteroid away by the gravitational pull of Jupiter add up one to planet. It follows that the disturbances produced of time, in an identical position with respect to the covers only one), it finds itself, at regular intervals (e.g.: asteroid covers while Jupiter three orbits is in astate of resonance with the motion of Jupiter gravitational field of Jupiter. In fact, if the asteroid gaps are due to the perturbation effects of the period of Jupiter. It is thought that Kirkwood certain relations (e.g.: 4/1, 3/1, 5/2) with the orbital gaps correspond to orbital periods that are in gaps. According to the third law of , these named after their discoverer, are called Kirkwood In the above figure we may observe ‘lacks’ which, asteroid are evenly not orbits distributed. to the Asteroid Belt (Figure 1) [30]. Within this Belt, and AU2.2 3.3 from the Sun, which corresponds maximum concentrationThe is between found between the orbits of the planets and Jupiter. It can beseen that almost all asteroids are located characteristics. Members of each group show very similar orbital into groups on the basis of orbital elements. is that many of them (almost can begathered half) Another interesting dynamic feature of asteroids YORP or perturbations effect. asteroid collisions,generated after gravitational becomes unpredictable. Chaotic rotation may be 2016| V olume 4|I ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI very threateningvery for the Earth. Instead, Atira (a the terrestrial orbit. For such reason they may be The majority of Aten and Apollo asteroids cross colour) blue (in Earth the of orbit the to compared colour) (in asteroids Aten and Amor, Apollo of orbits 2–The Figure closest to Earth. Moon, the celestial bodies whose orbits are the approaching asteroids”. In they fact, are, after the rotation asteroids of themselves temporal and method was subject to uncertainties due to the Eight-Color Asteroid Survey (ECAS) [33-35]. Such the is example An “spectrophotometry”. called distribution”energy (SED). technique This was spectra was required to build up a“spectral targeting the major features contained in asteroid measurements in several filters with bandpasses In the past, aseries of discrete photometric in initiated 1975was classification) [32]. (Spectral shape spectral colour, and on albedo, present asteroidThe based taxonomic system minerals. or meteorites, terrestrial or rocks asteroid data with laboratory data obtained from This study can becarried out by comparing the the composition of the surface reflecting the light. μm, those measurements also can beused to infer to wavelengthsespecially extending 2.5 about of classes. If sufficientspectral resolution is available, asteroids to classify used into various taxonomic between about and 0.3 1.1 micrometres (μm) -is of the amount of reflected sunlight at wavelengths measures - specifically, measurements reflectance The combination of albedos and spectral change Earth-crossing. to become immediate impact threats, but their orbits may asteroids do not cross the Earth’s orbit and are not sub-group of the Aten asteroid group) and Amor : 10.12882/2283-7604.2016.4.3 68

Available online at http://www.iemest.eu/life-safety-and-security/ J une are now routinely obtained even for asteroids visible-wavelength 0.4 to from 1.0 region μm, the covering simultaneously spectra, resolution asteroids. of High low-signal-to-noise, properties on our ability to measure the spectral-reflectance coupled-device (CCD) have had aprofound impact charge- on based Recently, spectrographs taxonomy. basis the Tholen the of formed and contains about 1000 objects) of asteroid spectra, astronomers to build an important database (ECAS conditions.variation However, sky of enabled it designations given letter been referring to specific regard to composition, many asteroid classes have without parameters astronomically observed Although asteroid taxonomy on is based resolution much higher than spectrophotometry. even low-resolution CCD spectroscopy allows conditions, avoided. be can Moreover, sky in rotation asteroids of temporal variations from or multifilterphotometry, arising from inherentthe exposure, some of the difficulties associated with By recording the entire spectral range in a single much fainter than those observed for the ECAS. X W V T S R Q P O M L K J G F E D C B A increasing wavelength. with decreasing reflectances to refers “blue” term the and wavelength increasing with increasing to reflectances refers “red” term 4 : The 4 4 4 2016| 4 Spectrum similartoE,M,orPtypes,butnoalbedoinformation. witha3 M-class visiblespectrum Distinctive 1and2 Weak UVfeature, reddish past0.4 Strong UVfeature; usuallyhas 1 Strong UVand1 Strong UVand1 Flat toslightlyred Weak UVfeature outto0.44 Flat toslightlyred, featureless moderatealbedo(0.10-0.30). spectrum; Very strong UVfeature andthenbecomingapproximately flat. Spectrum intermediatebetween SandCasteroids; usuallyassociatedwithCO3/CV3chondrites. Stronger 1 Strong UVfeature, flatpast0.4 Very weak UVfeature, flattobluishpast0.4 Flat toslightlyred, featureless highalbedo(>0.30);usuallyassociatedwithaubrites. spectrum; Very red low spectrum; albedo(usuallyaround 0.05orless). Weak UVfeature, flatto reddish past0.4 Weak UVfeature, bluepast0.4 Extremely read atwavelengths <0.7 V olume μ 4|I m feature than V types;appeartohave compositionssimilartotheHEDs. ssue μ μ 4 m feature; is349Dembowska. typespectrum chondrites. m feature; similartoordinary spectrum ,featureless low spectrum; albedo(usually around 0.05orless). μ 3|©L m features duetopyroxene; appeartohave compositionssimilartotheHEDs. μ ife m, very strong 1ųmfeature; is3628Božněmcová.m, very typespectrum μ μ μ S m, subclassofCclass;usuallyhave strong 3ųmfeatures; low albedo(<0.10). m, subclassofCtypes;low albedo(generallylessthan0.1). μ m feature, indicatingolivineand/orpyroxene; moderatealbedo(0.10–0.30). μ m absorptionfeature. afety μ m; low albedo(<0.10). m. Distinctive olivine absorptionfeatures. High albedo:0.4 and μ m; low albedo(generallylessthan0.10). μ S m, subclassofCtypes;low albedo(<0.10). ecurity

ISSN Table 2-Asteroid Classes : 2283-7604 | Class characteristics DOI of the Tholen taxonomy (Table Tholen the of 2) [36-40]. classification (2002), resulted in a modified version Belt Asteroid Spectroscopic Survey (SMASS) in 14 asteroid categories, and the Small Main- used are the Tholen classification (1984), resulted The most two widely used taxonomies now siliceous, “C” and carbonaceous): for surface compositions (e.g. “M” for metallic, “S” for • • • : 10.12882/2283-7604.2016.4.3 carbonaceous meteorites. featureless spectra, which is consistent with C-type asteroids tend to have relatively to discover observe. and than C-types, making them brighter and easier closer to the Sun and have higher albedos of classified asteroid since they tend to be asteroidsS-type are the most abundant type common asteroid type. amounts of stone. They are the third most nickel–iron either pure or mixed with small composition. Some of them are made of asteroidsM-type show partially known 69

Available online at http://www.iemest.eu/life-safety-and-security/ J une and spectral reflectances similar to the stony and S-class asteroids have moderate albedos has water present as alayer of permafrost. K- their surfaces, whereas , aG-Class, probably asteroids are known to have hydrated minerals on carbonaceous materials. precursor C-class Some by hydrothermal alteration or metamorphism of constituents their of assemblages were produced those carbonaceous of chondritic meteorites; the similar to reflectances spectral and albedos Asteroids of the F, B, C, and G classes have low Magnya (diameter about 17 [11 km ]) — to as “Vestoids”), until 2000, when asteroid (1459) asteroidsEarth-approaching (collectively referred less than 10 (6 km miles), plus afew even smaller over 16,000 Vesta-family asteroids with diameters to beconfined to the large asteroid Vesta and a major collision. The Vclass had been thought surface of aV-class that were knocked off during the from chips are museums in exhibited eucrites The match is so good that some believe that the basalticof achondritic meteorite, eucrites. the closely matching those of one particular type V-class asteroids have properties reflectance those enstatite the of achondrite meteorites. match that reflectances have spectral and albedos meteorites. The E-class asteroids have the highest achrondriteanalogous to pyroxene-olivine the with apyroxene- and olivine-rich composition has been identified as being most consistent asteroids are rare. very Their surface material silicates or both in their surface material. R-class a large fraction of carbon polymers or organic-rich mineralogical counterparts, but they may contain meteorite naturally or known no occurring P- and T-class asteroids have low albedos and 2000. January in fell represented by the Tagish Lake meteorite, which exhibited of by carbonaceous atype chondrite, spectrum the similar to spectra reflectance show minerals. D-class asteroids have low albedos and spectral features due to the presence of hydrated iron meteorites. Some M-class asteroids have nickel- the similar to reflectances spectral exhibit of nickel-iron metal in their surface material, and may haveamounts significant objects, albedo their surfaces. M-class asteroids are moderate- including the minerals olivine and pyroxene on metals, and silicates of amounts significant iron meteorites, and they are known to contain 2016| V olume 4|I ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI most important asteroids may get aname. For year, followed by an assigned designation. The Asteroids are labelled from their discovering properties. spectral long-term exposure to space, can also affect their temperature, size distribution, and the effects of their including grains, these of properties other of the bulk composition of the asteroid, but that material this surface upper is representative materials. In addition, it is generally assumed the same taxonomic class are composed of similar there is not any assurance that asteroids within are likely to becomposed of different materials, although asteroids classes different of spectral class and composition is not always reliable: However, spectral correspondence the between 10than km. diameter and only about 4with diameters greater members between 5and 10 (3 km and 6miles) in basaltic surface. There are about 100 Vesta family AU2.36 for Vesta —was discovered also to have a located at 3.15 AU from the Sun, compared with is 270 ±60 m[40]. fully compact. The estimated diameter of Apophis likely aggregates whose internal structure is not uncertainty. In bodies fact, such as Apophis are volume) the has considerableperfectly An estimate for the total mass (even knowing suggest atotal porosity of 40%. size similarities of Apophis with (25143) Itokawa macroscopic) void spaces [19]. Composition and cause any compaction of internal (microscopic or together as a “rubble pile,” but not sufficient to conglomerationto loose keep a fragments of likely to behigher, as its gravity is sufficient Macroporosity for an asteroid like Apophis is (8%) microporosity and constituent its of material. such (3.5g/cm grain as the density properties to estimate Apophis’ possible range of physical By means of ameteorite analogue, it is possible interpreted pyroxene olivineand abundances. meteorites in terms of spectral characteristics and chondrite closely resemblesmost LL ordinary an Sq-class asteroid (typical for most NEOs) that reflectance spectrum, it can be considered as With avisible to near-infrared (0.55 to 2.45 μm) [41] is aPotentially Hazardous Asteroid (PHA). example, the NEO (99942) Apophis (Table 3) : 10.12882/2283-7604.2016.4.3 70 3 )

Available online at http://www.iemest.eu/life-safety-and-security/ J une The orbit of a recently discovered NEO is calculated When entering Earth atmosphere, enteringWhen Earth relatively small Earth on impacts asteroid of effects the influence that The parameters to grow until it reaches 100%. collision trajectory with the Earth, it will continue abruptly) to zero or, if the NEO is really on a the impact probability will drop (generally quite Eventually, eliminated. are trajectories safer and grow as soon as the orbit is refined and alternative on. Therefore, the impact probability will tend to Earth then acollision cannot beruled out early if aNEO is indeed going to come near very the increase as new observations are added. In fact, probability and its associated risk will tend to the orbit is relatively well constrained, the impact particular potential persists until On the other hand, in the unlikely case where a available. become observations with aspecific NEO will decrease as additional NEO’s orbit. Most often, the threat associated reduce and observations uncertainties the the in incorporate as astronomers out ruled more be Earth. However, such early predictions can often orbits will “contemplate” future impacts with the more uncertain and it is more likely that such stemming from limited very observation sets are threateningmore than later orbits because ones Usually, first calculations of a NEO’s orbit look future. their knowledge of where the object will bein the confident become astronomers more the orbit, in observations are used to improve an object’s the object was actually observed. The more several observed times match the positions where the asteroid should have appeared in the at sky the Sun is adjusted until the predictions of where That is, the computed path of the object about best fits the available observations of the object. by finding the elliptical path about the Sun that 2016| 1949 MA(1566)Icarus 1937 UB(69230)Hermes 1998 SF36(25143)Itokawa 1936 CA(2101)Adonis 2004 MN4(99942)Apophis 1932 HA(1862)Apollo 2007 VK184 V olume 4|I ssue Asteroid 3|©L ife S afety and Table 3–ListofsomePotentially Hazardous Asteroids (PHAs) S ecurity Density [g/cm

ISSN ~2.3 ~2.0 ~2.7 ~2.0 ~2.7 ~2.0 ~2.0 : 2283-7604 | 3 ] DOI of life forms. and, in the worst scenarios, cause the extinction but global; they can involve climate, ecosystem large, the consequences of its impact are not local, an . If the size of the asteroid is very the attrition with the atmosphere, may excavate A space- body, which survives the entry and studied. are and reach subsequently surface identified and due to attrition with air. In a few cases, meteors , and suchcause phenomena as meteors NEA (which are often fragments of bigger objects) collateral effect (an anomalous abundance of the the of abundance anomalous (an collateral effect asteroid. The and ageological ago) has been linked to apossible impact with an (approximately years 65 million boundary Tertiary ) which occurred at the - the rapid extinction of many species (such as “”.to so-called the Remarkably, have similar would climateparticular, we changes distance from the point where the asteroid falls. In of the collision would bepresent even at large than ¼of mankind may perish). The aftermaths expressionthe “global more catastrophe” when sufficient to unleash a global catastrophe (we use of this size (or or two three times as large) is by 1million ton of TNT). The impact of an asteroid weapons, which corresponds produced to energy of ~50.000 Mt (energy unit used for nuclear often. Such abody releases an impact energy average every 1million years or slightly more widea 1km asteroid and our planet occurs on Given the numbers acollision of NEA, between typically close to 20 km/s. speed squared: E It depends on the mass of the impactor and the key parameter to understand the broad effects. The energy associated with the impact, E consequences long-term study nuclear a of war. of numerical simulations, similar to those used to The effects of large collisions are studied by means : 10.12882/2283-7604.2016.4.3 0.13 -1.8×10 ~4.1 ×10 Mass [kg] 4.6 ×10 5.1 ×10 3.3 x10 2.9×10 6.7×10 12 10 10 12 9 10 imp 12 =m ast v 2 imp [m/s] /2. The speed v 0.3-0.6 0.74 0.2 0.2 0.2 0.9 0.2 imp is the imp 71 is is

Available online at http://www.iemest.eu/life-safety-and-security/ J une area in Tunguska, Siberia, are still extremely extremely still are Tunguska, in area Siberia, caused extensive damage to afortunately desert Lesser events, such as the impact that in 1908 above) are perhaps 100 times more common. catastrophic events (according to the definition on average every 100 million years. However, asteroid with asize of 10 or larger, km takes place An impact of such aproportion, caused by an impact. have been identified as the likely result of the rare metal at the strata transition) of the KT few decades, and an unambiguous an and few decades, knowledge a long warning of the impact, of the order of it. To befeasible, this kind of intervention requires designeddangerous to but deviate – fragments may not beeffective given the large numbers of require amount enormous and an energy of aimed at destroying the asteroid -which would to avoid the collisions. This strategy would not be course with Earth enable us to formulate astrategy Identification and study of an asteroid on collision by means astronomical of observations. while the objects themselves are carefully studied to better evaluate the probability of collisions, dangerousmost asteroids are monitored order in colliding with our planet. The orbital paths of the assigned to large objects with high probability of danger posed by NEA; high values of this scale are predict. The “Turin scale” is used to measure the interesting, because collisions are more difficult to of years. Longer timescales are regarded as less probability of impact with Earth within a few tens The real threat of aNEA depends on both size and potentially the toorder identify dangerous ones. in contributed, strongly has community Italian the which to software, and techniques mathematical years. The discovered are NEAs studied by means of following the in smaller of objects knowledge our than by 1km 2008, and progressively increase enabled us to know at least of 90% objects larger promoted by the USA. This survey of has NEAs objects; such aprogramme has been in particular has led to undertake asystematic study of these The interest, even in practical terms, to know NEA common impression is different. impact than by an air accident, even though the has ahigher probability to bekilled by an asteroid From astatistical point of view, each individual years. hundred dangerous one even happen can and every 2016| V olume 4|I ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI accumulated is about 100 tons/ [43, 44]. Larger centimeters. A plausible estimation of the mass to small particles with size of the order of some of extraterrestrial material, ranging from dust amount great day a accumulates every Earth catastrophic event is still possible. concrete demonstration that awesome an cosmic 9 has impacted on Jupiter surface [42] giving a Earth surface. In July 1994 -Levy release agreater amount of kinetic energy on affected by atmosphere slowing down and can are massive and less zone. Larger impact objects are also related to the of the object and dramaticthe consequences, destructive which human timescales. However, conceive can one bodies with Earth are not frequent within extraterrestrial Fortunately, large collisions of knowledge. asteroids is critical, and not just amatter of basic the study of physical and collisional evolution of asteroid and its surface. This aspect explains why of physical and chemical characteristics of the (Table 4) [45]. work and data, many uncertainties still remain of colliding objects. In spite of alarge amount of most probable impact body velocities and nature conditions) boundary of known range a to identify accurate analysis of craters morphology (with all and [45-47-]. These studies performed an preserved surfaces of planets like Mars, the Moon on crater morphology, in particular on the better out, on planetary surfaces, alot of observations The main approach of these studies was to carry body. impacting the composition and target of of properties surface Energy depends upon the size, velocity, gravity, the energy range that characterize the impacts. research of understanding could provide good a scenarios of extraterrestrial body impacts. Such a validly support the evaluation of possible Results of many years of crater studies could the atmosphere. resistant enough to survive the transit through fragments of asteroids, and their structure can be (Figure 3) [45]. These are mainly orrocky metallic possible weight from few kilograms to few tons centimeters to few meters, with acorresponding year with the Earth have asize ranging from tens of that usually objects collideextraterrestrial every : 10.12882/2283-7604.2016.4.3 72

Available online at http://www.iemest.eu/life-safety-and-security/ J une 200km 100km 50km 31km 20km 12.2km 10km 7.2km 6.9km 5km 3.1km 1.8km 1.1km 1km 450m 120m 75m 35m Diameter Crater 2016| Figure locations ofterrestrial structures: of145currently 3-Distribution terrestrial structures known impact impact V olume 10km 5km 2.5km 1.5km 1km 610m 500m 360m 350m 250m 155m 90m 55m 50m 23m 6m 4m 2m Projectile Diameter Approxi mate Table 4- Terrestrial meteoriteimpactcraters:cratersizes, projectile sizes, frequencies, andcomparableterrestrial events 4|I - ssue 2.5 E+17 6.2 E+16 4.6 E+16 4.2 E+15 8.3 E+13 1.9 E+13 2.1 E+12 3.7 E+23 4.6 E+22 5.8 E+21 1.3 E+21 3.7 E+20 8.4 E+19 4.6 E+19 1.7 E+19 1.5 E+19 5.7 E+18 1.3 E+18 Energy 3|©L (J) ife 8.7 E+7MT 1.1 E+7MT 1.3 E+6MT 310000 MT 87000 MT 20000 MT 11000 MT 3700 MT 3600 MT 1400 MT 310 MT 60 MT 15 MT 11 MT 1 MT 20000 tons 4500 tons 500 tons (TNT Equiva S Energy afety lent) and S - ecurity 0.007 0.04 0.22 1.4 2.9 7.1 10 18 20 35 83 230 540 640 2700 28000 69000 250000 Frequen (No. Per Impact Whole Earth) m.y., cy

ISSN - : 2283-7604 | 4 years years 150 million years 26 million years 4.5 million 720000 years 350000 years 142000 years 100 000 years 55000 years 51000 years 28500 years 12000 years 4400 years 1900 years 1600 years 370 years 35 years 15 years pact Interval Mean Im (Tmean, Whole Earth) - DOI riment (“Snowball”; Canada,1964). Minimum (M = 5).Largestchemicalexplosionexpe damagingearthquake km). Sudbury, Canada; Vredefort, Africa;Chicxulub, . Largest known terrestrial impactstructures (original diameters200-300 Popigai, Russia (D=100km). Manicouagan, Canada(D=100km). , Sweden (D=55km). Charlevoix, Canada(D=54km). Montagnais, Canada(D=45km). Total annualenergyrelease (Heat from Earth flow, seismic, volcanic). Ries Crater, Germany (D=24 km). Rochechouart, France (D=23 km). Haughton , Canada(D=20.5km). thermal). Tambora (Indonesia, eruption 1815)(Total energy, including Oasis, Libya (D=11.5km). Bosumtwi, Ghana (D=10.5km). Lake , Sweden (D=9km). thermal). (Indonesia,Krakatoa volcano eruption 1883)(Total energy, including Largest recorded (Chile,1960;M=9.6) Goat Paddock, Australia (D=5.1km). Gardnos, Norway (D=5.0km). thermal). Mt. St. Helens, Washington (1981)(Total eruption energy, including Largest hydrogen-bomb detonation(68MT). San Francisco (1906)(M=8.4). earthquake Mt. St. Helens, Washington (1981)(blastonly). Tunguska ,Siberia, Russia (1908). , Arizona (D=1.2km). Pretoria Salt Pan, South Africa(D=1.13km). Wolfe Creek, Australia (D=0.875km). “Typical” hydrogen-bomb explosion(1MT). Atomic bombexplosion(Hiroshima, Japan, 1945). Largest chemicalexplosion(Heligoland Fortifications, 1947). : 10.12882/2283-7604.2016.4.3 Comparable TerrestrialEvent - 73

Available online at http://www.iemest.eu/life-safety-and-security/ J une As aroughAs approximation, the height of tsunami. of effects erosional equivalent distances. This splash may emulate the and fall onto the surface of the Earth over travel at high velocities for hundreds of kilometres, atmosphere volumes enormous water of that Low-trajectory asteroids can eject into the Earth. plus the location, date, and time of the impact on function of the asteroid mass and impact velocity The consequences of any impact on Earth will be a about four ringlets that ringlets four about propagate as a outwards it causes water to oscillate up and down, forming thisAs ring moves out from the centre of impact, radius the of crater. crater and forms aring whose width equals the displacedThe water piles around up pseudo- the from the pseudo-crater blasted into the ocean. displacement the height upon depends water of the impact creates atsunami wave train whose Collapse of water back into the cavity by left reach the top of the atmosphere [48]. with the ocean, sending out splashes that may of over 20 km/s, these objects burst upon contact Earth’s surface will strike the ocean. At velocities About 70% of the asteroids or comets that reach the tsunami. significant a produce to crash into the ocean without fragmenting in order large dense to enough and be must comets and initial wave height of over Most asteroids 900m. surface, it would have created atsunami with an However, had the bolides reached the ocean’s occurred over the ocean. a localized tsunami of about min 0.2 height had it surface [45]. This blast would only have generated only 0.1-0.2 megatons of energy at the ocean’s The air blast of the Tunguska bolides produced volcanoes. and energy to that of known tsunami generated by ocean can be determined by relating its kinetic waves generated by an asteroid impacting the 2016| V olume 4|I ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI the Earth’s surface basically intact is about m 40 The diameter of the smallest object that can reach [48]. 20% of its energy would reach the ocean surface If this asteroid exploded as an air-burst, then only with aforce equivalent to megatons 940 of TNT . in diameter, travelling at 25 km/s, would impact atmosphere. For example, astony asteroid 200 m tend to dissipate some of their energy in the tend to fragment in the ocean, while larger ones Stony asteroids smaller than 100m in diameter of TNT [48]. crater in Arizona –is equivalent to 12.5 megatons as that which created the 1.2 wide km Barringer 7.8 g/cm3, travelling at avelocity of 20 km/s –such iron meteorite min 40 diameter with adensity of Using the above equation, the kinetic energy of an distance from the centre of impact. site, the height upon dependent becomes then its pond). the As wave moves away from the impact ripples that form when apebble is thrown into a tsunami wave train (this process is similar to the of impact caused by NEOs of various sizes [49]. In Table 5are summarized the main consequences smaller than those produced by denser asteroids. asteroids also produce waves that are about 60% would bedepth limited in most oceans. Stony Thus, asteroids larger than 500m in diameter water.deeper smaller than in the case of the asteroid falling into In this case, the resulting tsunami is about 60% asteroid falls into water less than deep. 2000m greater than 167m will bedepth limited if the the asteroid. For example, an asteroid of diameter factor when it is less than 12 times the diameter of depth limited. In depth fact, becomes alimiting a large asteroid impacting in the ocean is also every 1000 years [45]. The tsunami created by of recurrence for a 130m stony asteroid is about and 380m for ashort-period comet. The interval for an iron meteorite, 130m for astony asteroid, : 10.12882/2283-7604.2016.4.3 74

Available online at http://www.iemest.eu/life-safety-and-security/ J une MOID (Minimum Orbit Intersection Distance): Intersection (Minimum Orbit MOID the Earth and the Sun; it is 149,597,870.7 km. Unit)AU (Astronomical nearly circles, while are others elongated. more of another celestial body. Some elliptical orbits are satellite, is elliptical if unaffected by the attraction a satellite around aplanet. The orbit of aplanet or a centre of mass, such as aplanet around the Sun or Orbit terms and Information: definitions Supplementary institutions such as ASI, ESA and NASA. international and national main with partnerships in the immediate future, is also to some start original innovative and technology. purpose, The potentially deflect dangerous asteroids of use by outcarry possible solutions that can effectively IEMEST is currently involved to investigate and innovativeat solutions efficiency energy for The Section for Aerospace research and considered potentially to Earth. hazardous deflection strategies for the asteroids that are basis to point up areasonable optimization of A precise estimation of these effects is a concrete possible impact on Earth. significant parameters related to the ofa effects been discussed with the aim to identify aclass of In this work, the main features of asteroids have Conclusions 2016| >10 10 10 10 10 10 10 10 10-10 <10 Yield 8 7 6 5 4 3 2 (Mt) -10 -10 -10 -10 -10 -10 -10 10 : path of acelestial body revolving around a 2 9 8 7 6 5 4 3 V olume - 7.2 6.6 6.0 5.4 4.8 4.2 3.6 3.0 - Interval 4|I LogT ssue 3|©L 160m 75m - - 16km 7km 3km 1.7km 700m 350m Diameter NEO : mean distance between ife S afety 3km 1.5km - - 250km 125km 60km 30km 12km 6km Diameter Crater and Table 5–Consequencesofimpactby NEOs ofvarious sizes S ecurity Irons andstonesproduce groundbursts; cometproduce airbursts. Land impactsdestroy city-sized areas; e.g., Washington, DC. Irons makecraters;stonesproduce airbursts. only irons (<3%)reach surface. Upper atmosphere detonationofstonesandcomets; Threatens survival ofalladvancedThreatens formsoflife. survival Large massextinction;e.g.,K-T-type event. ches continentalscale;e.g.,United States. Prolonged climateeffects,globalconfiguration, probably massextinction. Direct approa destruction fires. Landimpactdestroys area thesize ofalargenation;e.g., Mexico. Both landandoceanimpactsraisedust,changeclimate.Impact ejectaare global,triggeringwidespread California. ric-scale .Global Landimpactdestroys ozone destruction. area thesize ofalargestate;e.g., Land impactraisesenoughdusttoaffectclimate,freeze crop. Ocean impactsgeneratehemisphe Land impactdestroys area thesize ofamoderatestate;e.g., Virginia. Tsunamis reach oceanicscales,exceed damagefrom landimpacts. Land impactdestroys area thesize ofasmallstate;e.g.,Delaware. Impacts onlandproduce craters;oceantsunamisbecomesignificant. Impact destroys urbanareas; e.g.,New York City.

ISSN : 2283-7604 | DOI celestial bodies; it is ameasure used to assess a minimum distance between the orbits of the two whose MOID with Earth is equal or less than 0.05 PHA (Potentially Hazardous Asteroid) are considered not PHO. which are smaller than about 150 min diameter, closer to the Earth than 0.05 AU (7,500,000 km), or impact with Earth. Objects that cannot approach cause significant local damage in the event of to the Earth. Such an object is large enough to couldComet orbits make whose close approaches PHO (Potentially Hazardous Object) NEC NEA aphelion (Q) and their semi-major axis (a) [1]. according to their distance of the perihelion (q), intodivided groups (Atiras, Aten, Apollo, Amor) NEOs are asteroids (the NEAs). so-called are NEAs orbital periods Pof less than 200 years), most (those comets period havingas generally defined (NECs) Comets While Near-Earth include short- AU and aphelion distance greater than 0.983 AU. or comet, with perihelion distance less than 1.3 NEO: orbit. solar in spacecraft) a planet, comet, asteroid, or other object (e.g., a Aphelion orbit. solar in spacecraft) a planet, comet, asteroid, or other object (e.g., a Perihelion collision. future possible a for pre-alarm : 10.12882/2283-7604.2016.4.3 : Near-Earth Comet. Near-Earth : : Near-Earth Asteroid. small celestial body, for example an asteroid : the point farthest the Sun in the path of : the point nearest the Sun in the path of Consequences : Asteroid or : all asteroids - - 75

Available online at http://www.iemest.eu/life-safety-and-security/ J une to potentially several millions of years. Extinct several from range yearsComet periods orbital atmosphere as “coma” and sometimes also a“tail”. heats up and begins to outgas, displaying a visible celestial body that, when passing close to the Sun, Comet PHC considered [50]. dangerous Earth the for Objects of size less than 150 min diameter are not an (H) of 22.0 or brighter. AU (about 7,480,000 km) and characterised by the gravity of the planet continues to attract When the asteroid distances from the planet, attracts the asteroid increasing its velocity [52]. a planet (fly-by) the force of gravity of the latter In the same way, when an asteroid approaches energy. acquire also parameters of the encounter, the small body can its orbital parameters [52]. Depending on the of its kinetic energy and causing achange in with the bigger object, resulting in amodification exchanges one little the energy space objects, two assist Gravity [51].keyhole”) encounters two the (e.g.,between “7:6 resonance periods of the planet and the asteroid, respectively, Keyholes are named after the numbers of orbital including less close a intermediate encounter. keyholes, smaller with trajectories but secondary before the collision. In there fact, are even more [51]. It is also possible to have multiple encounters order to lower the probability of afuture impact to prevent the PHO from entering akeyhole, in importance fundamental of is it Therefore, planet. distance, inclination and speed respect to the previous the of encounter,geometry like specific orbital pass [3]. The impact depends upon the would collide with that planet on agiven future of apassing PHO such that the minor celestial body space where aplanet’s gravity would the orbit Keyhole planetoids. called called Asteroid Belt. The largest asteroids are also asteroids in the Solar System, especially in the so- in high-eccentricity orbit. There are millions of Asteroid asteroids. and dust and they may come to resemble small times, have lost nearly all of their volatile ices comets, which have passed close to the Sun many 2016| : Potentially: Comet. Hazardous : icy, small (less then afew tens of across) km V : Agravitational keyhole is atiny region of : orbiting the Sun, usually olume 4|I : during close: encounter a between ssue 3|©L ife S afety and S ecurity

ISSN : 2283-7604 | DOI or less [53, 54]. variation (Δv) of about few millimetres per little quantity of energy, resulting in avelocity advance may require to provide a PHO with a very preventive centuries realisedor decades action in related by the time of its interception. Therefore, a order to avoid the crash with the planet is strictly variation to provide to the potential impactor in proper mitigation strategy. In the fact, velocity It is of fundamental importance for planning a sure PHO collision with the Earth and the impact. Warning time major the experiences changes [53]. its orbit almost unchanged, while the asteroid compared intrinsic energy of to its energy, leaving respective : the planet loses little quantity and the asteroid is inversely proportional to their Indeed, the energy transfer between the planet revolution imperceptible an in orbit its and way. loses of part its energy, reducing its motion of kinetic energy is due to the that fact the planet the asteroid reducing its speed. The gain in 9. Spectral BE. mixing models of S-type 239. Arizona of University Press, Tucson, 1994; pp.221– due to Comets and Asteroids. Ed: Gehrels T, In: comets. Hazards probabilities long-period for Marsden8. BG, Steel DI. Warning times and impact 2002; 158:329–342. Icarus hazard. collision Earth albedo distribution of near Earth objects and the Tedesco EF. From magnitudes to diameters: The 7. Morbidelli Jedicke A, Bottke R, WF, Michel P, http://neo.jpl.nasa.gov/faq/6. 5. http://neo.ssa.esa.int/web/guest/risk-page Newsletter-2016-03-01 ESA-SSA-NEO-LE-0012_1_0_SSA-NEO_ OBJECTS NEAR-EARTH awareness, situational Space 4. Astrophysics, Vol408, pp. 1179-1196 AstronomyApproaches: and Theory. Analytic Chesley.(2003). Resonant Returns to Close 3. Valsecchi Milani, A. , G.B., G.F. Gronchi, S.R. www..gov.org 2. 2000 September OBJECTS. EARTH NEAR hazardous 1. NASA. of Report the Task Force on potentially References collision of aPHO with Earth. aiming methodologies of at preventing the strategyMitigation : 10.12882/2283-7604.2016.4.3 : time between the verification of a : planning: implementation and 76

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