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V-Type Near-Earth Asteroids: Dynamics, Close Encounters and Impacts with Terrestrial Planets†

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V-Type Near-Earth Asteroids: Dynamics, Close Encounters and Impacts with Terrestrial Planets† Received: 4 July 2016 Revised: 12 September 2016 Accepted: 6 October 2016 DOI: 10.1002/asna.201613273 ORIGINAL ARTICLE V-type near-Earth asteroids: Dynamics, close encounters and impacts with terrestrial planets† M. A. Galiazzo1,2,3*† E. A. Silber1,2 D. Bancelin3,4 1Department of Physics and Astronomy, The University of Western Ontario, London, ON, Background: Asteroids colliding with planets vary in composition and taxonomical Canada type. Among Near-Earth Asteroids (NEAs) are the V-types, basaltic asteroids that 2Centre for Planetary Science and Exploration are classified via spectroscopic observations. (CPSX), The University of Western Ontario, London, ON, Canada Materials and Methods: we performed numerical simulations and statistical analy- 3Institute of Astrophysics, University of Vienna, sis of close encounters and impacts between V-type NEAs and the terrestrial planets Vienna, Austria over the next 10 Myr. We study the probability of V- type NEAs colliding with Earth, 4IMCCE, Paris Observatory, UPMC, CNRS, UMR8028, Paris, France Mars and Venus, as well as the Moon. We perform a correlational analysis of possi- ble craters produced by V-type NEAs, using available catalogs for terrestrial impact *Correspondence M. A. Galiazzo, Department of Physics and craters. Astronomy, The University of Western Ontario, Results: The results suggest that V-type NEAs can have many close encounters London, Ontario N6A 3K7, Canada. below 1 LD and even some of them impacts with all the terrestrial planets, the Earth Email: [email protected]; [email protected] in particular. There are four candidate craters on Earth that were likely caused by †Data from Dr. Mattia A. Galiazzo. V-type NEAs. Conclusion: At least 70% of the V-type NEAs can have close encounters with the terrestrial planets (and 58% with the Moon) . They can collide with all the terrestrial planets. In particular for the Earth the average rate is one every ∼12 Myr. The two craters with the highest probability of being generated by an impact with a basaltic impactor are: the Strangways crater (24 km diameter) in Australia and the Nicholson crater (12.5 km diameter) in Canada. KEYWORDS asteroids – planets – impacts 1 INTRODUCTION position (being only basaltic asteroids coming from peculiar bodies, e.g., 4 Vesta). In case of impacts, V-NEAs can pro- V-type near-Earth asteroids (V-NEAs) are basaltic asteroids duce a wide range of crater sizes and impact material (e.g., with a perihelion less than 1.3 au. Dynamically speaking, this was shown, in part, with some V-NEAs in Galiazzo, these objects exist as NEAs in a chaotic region; however, 2013). Some of V-NEAs are in a resonance, for example, they are peculiar, because they originated from specific aster- (7899) 1994 LX and (137052) Tjelvar in M4:3 (mean motion oid families, mainly from the Vesta family (Carruba, Roig, with Mars), (1981) Midas (which is also the largest V-NEA) Michtchenko, Ferraz-Mello, & Nesvorný, 2007; Delisle & in J3:2 (mean motion with Jupiter), and (4688) 1980 WF Laskar, 2012; Galiazzo, Souami, Eggl, & Souchay, 2012; in the 6 secular resonance, which creates one of the most Sears, 1997) in the main asteroid belt, even though some unstable interactions (see Bottke et al., 2002; Migliorini, V-type asteroids can be found in other families (Eunomia, Michel, Morbidelli, Nesvorný, & Zappalá, 1998). Close plan- Magnya, Merxia, Agnia, Eos, and Dembowska) (Carruba, etary encounters strongly influence the dynamics of bodies Huaman, Domingos, Dos Santos, & Souami, 2014; Hua- in the NEA space. The dynamics in the NEA region is man, Carruba, & Domingos, 2014), albeit in significantly therefore the result of a complicated interplay between res- smaller numbers. Compared to other NEAs, V-NEAs can onant dynamics and close encounters (Michel, Morbidelli, have different orbits, size distribution, and, of course, com- & Bottke, 2005). Known V-NEAs are currently confined in Astron. Nachr. / AN, 2017; 1–10 www.an-journal.org © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 2 GALIAZZO ET AL. V-NEA size distribution in a vs i these ranges of osculating elements (present semi-major axis E4:3 M3:2 E1:2 J5:1 M2:3 J3:1J11:4 J5:2 M4:3 J6:1 J4:1 M2:1 J8:3 a0, eccentricity e0, and inclination i0, as listed in Table 1): 50 0.825 < a0 < 2.824 au (between resonances with the Earth, 45 ◦ E4:3, and with Jupiter, J5:2), 0.29 < e0 < 0.90 and 2 < 40 ◦ i0 < 49 . Furthermore, V-NEAs typically have a semi-major 35 < . > . 30 axis a ∼ 1 8au and e ∼ 0 4. This is different from, for 25 example, the Hungarias E-type NEAs, which preferentially ν6 have 1.92 < a < 2.04 au and 0.32 < e < 0.38, as shown in Inclination i 20 Galiazzo, Bazsó, and Dvorak 2013. 15 Figure 1 shows the (a, i) (with the size distribution) and 10 (a, e) plane for V-NEAs, where it is evident that the largest 5 > ◦ 0 asteroids reside at high inclinations, i ∼ 20 . Their size ranges 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 from ∼60 m to ∼3.1 km. These quantities are computed using Semi-major axis a [au] 1 E4:3 M3:2 E1:2 J5:1 M2:3 M2:1J3:1J11:4 J5:2 a standard albedo for basaltic asteroids and their absolute 1 M4:3 J6:1 J4:1 J8:3 magnitude (Tedesco, Veeder, Fowler, & Chillemi, 1992). 0.9 This work aims to investigate whether present-day basaltic 0.8 TV or V-NEAs can impact terrestrial planets (specifically, Venus, 0.7 Earth and its satellite, and Mars) within the time span of TE 0.6 10 million years (Myr). 0.5 NEAs Furthermore, we aim to perform the following: TM 0.4 Eccentricity 1. Establish the probability of close encounters, the impact 0.3 probability for each V-NEA (assuming the number of 0.2 impacts among all its clones), the rate of impacts, and 0.1 the size of craters produced by V-NEAs that collide with 0 planetary surfaces. 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 2. Examine whether some asteroids could impact planetary Semi-major axis a [au] surfaces at high velocities. Compared to slow-velocity FIGURE 1 Location and size distribution of the V-type near-Earth objects, high-velocity asteroids can generate a tremendous asteroids (V-NEAs) in the (a, i)and(a, e) planes. Circles (in the upper plot) amount of kinetic energy upon collision with a planetary are proportional to the V-NEA size: the smallest asteroid is 62 m in diameter surface. Such impacts might cause catastrophic events, and the largest is 3.4 km. The blue, violet, and green vertical lines represent similar to disruptive events usually made by comets (Jef- the mean motion resonances with Earth, Mars, and Jupiter, respectively. The green dot is Earth, and the red dot is Mars. The semi-dotted curves are fers, Manley, Bailey, & Asher, 2001). the Tisserand curves for the respective terrestrial planets. 3. Perform a statistical analysis of close encounters and impacts between present (observed and synthetic popula- 2 MODEL tions of) V-NEAs and the terrestrial planets. For impacts, we primarily aim to establish the impact energy and size 2.1 Numerical simulations of the V-NEA orbits and of impact craters on planetary surfaces, particularly the analysis Earth. We also aim to identify possible candidate craters on the Earth, using past geological studies on the material The orbital evolution of each V-NEA, including its 49 clones, of the impactor, in addition to our constraints on the crater has been computed using its real orbit. The clones of each sizes obtained through our results coming from orbital asteroid were generated with these elements: a = a0 ± simulations and crater formation simulations. 0.005, e = e0 ± 0.003, and i = i0 ± 0.01, where elements with 0 are the initial osculating elements of the V-NEAs. We performed numerical computations of orbits and also This range was selected based on Horner, Evans, and Bai- simulated crater formation on planetary surfaces. ley (2004), who showed that the aforementioned intervals of The paper is organized as follows: Section 2 describes the osculating elements are reasonable to perform orbital simu- model, subdivided in two subsections, one for the numerical lations for minor bodies in such chaotic orbits. Therefore, we simulation of the impacts and one for the simulation of the propagated 1450 V-NEAs orbits. Each clone was integrated orbital evolution of the V-NEAs. In Section 3, we revisit over the time span of 10 Myr into the future using the Lie the numerical results. Finally, our conclusions are given in integrator (Bancelin, Hestroffer, & Thuillot, 2012; Eggl & Section 4. Dvorak, 2010; Hanslmeier & Dvorak, 1984) with an accuracy parameter set to 1013. The code was upgraded by a subrou- 1The average of the known NEAs is 0.33. tine designed to compute encounter velocity, deflection of GALIAZZO ET AL. 3 the orbit, impact angle, and impact velocity after an impact 2.2 Hydrocode modeling of impacts is identified (see Galiazzo, Bazso, & Dvorak, 2014). Orbits For numerical simulations of impact crater processes, we were taken from the HORIZONS web interface2 at Epoch employ iSALE-2D, a multi-material, multi-rheology shock 2453724.5 JDTBT (Epoch Julian Date, Barycentric Dynam- physics hydrocode (Collins, Melosh, & Ivanov, 2004; Wun- ical Time). NEAs with a V-type spectrum were taken from nemann, Collins, & Melosh, 2006). We use the ANEOS Xu, Binzel, Burbine, and Bus (1995), Binzel, Harris, Bus, equation of state (EoS) for basalt to approximate the V-type and Burbine (2001), Bus and Binzel (2002), Dandy, Fitzsim- asteroid material, as well as the crustal material of Venus.
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