Icarus 408 (2024) 115844 Contents lists available at ScienceDirect Icarus journal homepage: www.elsevier.com/locate/icarus Research Paper Oort cloud perturbations as a source of hyperbolic Earth impactors Eloy Peña-Asensio a,b ,∗, Jaakko Visuri c , Josep M. Trigo-Rodríguez b,d , Hector Socas-Navarro e,f , Maria Gritsevich g,h , Markku Siljama c , Albert Rimola a a Departament de Química, Universitat Autònoma de Barcelona, Carrer dels Til⋅lers, Bellaterra, 08193, Catalonia, Spain b Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/ de Can Magrans S/N, Cerdanyola del Vallès, 08193, Catalonia, Spain c Finnish Fireball Network, Ursa Astronomical Association, Kopernikuksentie 1, Helsinki, 00130, Finland d Institut d’Estudis Espacials de Catalunya (IEEC), Carrer del Gran Capità, 2, Barcelona, 08034, Catalonia, Spain e Instituto de Astrofísica de Canarias, Avda Vía Láctea S/N, La Laguna, 38205, Tenerife, Spain f Departamento de Astrofísica, Universidad de La Laguna, Avda Vía Láctea S/N, La Laguna, 38205, Tenerife, Spain g Finnish Geospatial Research Institute, Vuorimiehentie 5, Espoo, 02150, Finland h Faculty of Science, University of Helsinki, Gustaf Hällströmin katu 2a, Helsinki, 00014, Finland ARTICLE INFO ABSTRACT Keywords: The observation of interstellar objects 1I/’Oumuamua and 2I/Borisov suggests the existence of a larger Meteorites population of smaller projectiles that impact our planet with unbound orbits. We analyze an asteroidal Meteors grazing meteor (FH1) recorded by the Finnish Fireball Network on October 23, 2022. FH1 displayed a likely Meteoroids hyperbolic orbit lying on the ecliptic plane with an estimated velocity excess of ∼0.7 km s−1 at impact. Comets FH1 may either be an interstellar object, indicating a high-strength bias in this population, or an Oort Oort cloud Minor planets cloud object, which would reinforce migration-based solar system models. Furthermore, under the calculated Asteroids uncertainties, FH1 could potentially be associated with the passage of Scholz’s binary star system. Statistical Interstellar evaluation of uncertainties in the CNEOS database and study of its hyperbolic fireballs reveals an anisotropic geocentric radiant distribution and low orbital inclinations, challenging the assumption of a randomly incoming interstellar population. Orbital integrations suggest that the event on March 9, 2017 (IM2) from CNEOS may have experienced gravitational perturbation during the Scholz fly-by, contingent upon velocity overestimation within the expected range. These findings suggest that apparent interstellar meteors may, in fact, be the result of accelerated meteoroid impacts caused by close encounters with massive objects within or passing through our solar system. 1. Introduction objects and interlopers can be found in Jewitt and Seligman (2023) and Seligman and Moro-Martín (2023). In 2017, the Pan-STARRS1 telescope observed for the first time When an object impacts the atmosphere at hypervelocity, friction the reflected sunlight from a metric (∼100 m) interstellar interloper, with air particles progressively ablates the outer layers, radiating large 1I/’Oumuamua (Meech et al., 2017). Two years later, the second amounts of energy (Ceplecha et al., 1998; Silber et al., 2018; Trigo- discovery of a large object (0.4–1 km) not gravitationally bound to Rodríguez, 2019). This luminous phase is known as a meteor or fireball, the Sun, comet 2I/Borisov, was announced (Guzik et al., 2020). The discoverer of 2I/Borisov himself estimated that a spherical volume of and its detection with ground-based or satellite instruments allows both 50 au radius may have 50 bodies of more than 50 meters in diameter the physicochemical analysis and the determination of the heliocentric (Borisov and Shustov, 2021). The Pan-STARRS survey’s detection of orbit (Jenniskens et al., 2009; Trigo-Rodríguez et al., 2006; Dmitriev 1I/’Oumuamua allows the calculation of a number density of 0.1 au−3 , et al., 2015; Brown et al., 2016; Devillepoix et al., 2019; Borovička corresponding to 104 similar objects within Neptune’s orbit and an et al., 2020; Colas et al., 2020; Peña-Asensio et al., 2021a). Recently, influx of 3 objects per day (Jewitt et al., 2017). By the expected power the first detections of interstellar meteors were claimed from the flashes laws of object size distribution, a much more abundant population spotted by the U.S. Department of Defense (DoD) satellite sensors of smaller interstellar objects is expected to cross our solar system, and published on the NASA-JPL Center for NEOs Studies (CNEOS) which may eventually collide with the Earth. A review of interstellar ∗ Corresponding author at: Departament de Química, Universitat Autònoma de Barcelona, Carrer dels Til⋅lers, Bellaterra, 08193, Catalonia, Spain. E-mail addresses: eloy.pena@uab.cat, eloy.peas@gmail.com (E. Peña-Asensio). https://doi.org/10.1016/j.icarus.2023.115844 Received 2 May 2023; Received in revised form 12 October 2023; Accepted 19 October 2023 Available online 26 October 2023 0019-1035/© 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). E. Peña-Asensio et al. Icarus 408 (2024) 115844 website (Tagliaferri et al., 1994): the so-called IM1 occurred in 2014- 2. Methodology 01-08 (Siraj and Loeb, 2022a) and IM2 in 2017-03-09 (Siraj and Loeb, 2022b), the latter being first identified as an interstellar candidate For the meteor science performed in this work, we use our veri- by Peña-Asensio et al. (2022). fied Python pipeline 3D-FireTOC (Peña-Asensio et al., 2021a,b) which: In the early 20th century, the field of meteor science was pre- performs the meteor positional reduction from the stellar astrometry dominantly focused on determining whether most meteors originated accounting for asymmetric radial lens distortions (Borovicka et al., from interstellar or interplanetary sources (Hughes, 1982). However, 1995) and atmospheric refraction by a revised Bennett’s model (Wil- it was not until the 1950s that the optical observations of fireballs son, 2018), employs the plane intersection method to reconstruct the generated by meteoroids exhibiting hyperbolic were reported (Opik, atmospheric trajectory (Ceplecha, 1987), and computes the heliocentric 1950; Almond et al., 1951, 1952), in addition to subsequent meteor orbit using the N-body orbital dynamics integrator REBOUND and radar echoes detection of interstellar micrometeoroid impacts (Weryk REBOUNDx packages considering the gravitational harmonics (J2, J4) and Brown, 2004; Froncisz et al., 2020) and interstellar dust incoming of the Earth and the Moon (Rein and Spiegel, 2015; Tamayo et al., flux measurements (Meisel et al., 2002a,b). Multiple automated meteor 2020). Uncertainties are calculated by generating 1000 clones from the networks have detected numerous hyperbolic Earth impactors, most of astrometry error fits assuming a normal distribution. which are pointed out as the result of the instrument and method limi- For mass estimation and event classification, it is necessary to tations (Štohl, 1970; Hajduková, 2008; Musci et al., 2012). Hajdukova calibrate the light curve. Using the visual magnitude of the same et al. (2020) reported that, of the total number of recorded events, reference stars as in astrometry, we perform aperture photometry by 12.5% for CAMS, 11.9% for SonotaCO, and 5.4% for EDMOND were subtracting the local background of each one. In this way, a logarithmic apparently hyperbolics. These events are clearly associated with low- fit is conducted to relate pixel values with magnitudes. We correct the quality detection and low angular elongation, so these large datasets atmospheric extinction and calculate the absolute magnitude of the cannot be used to discern hyperbolic impactors properly, and truly meteor (as observed at 100 km at the zenith). interstellar projectiles could remain hidden within the error bars. The The pre-atmospheric velocity is a critical quantity for orbit estima- identification of meteors with extra-solar provenance is a significant tion and cannot be directly measured by optical devices. It is necessary challenge and statements about the interstellar origin of IM1 and to derive it from the distance traveled, for which a smooth function fit IM2 cannot be conclusive if the uncertainties of the data are not of the observed points is usually performed. For this purpose, we apply provided (Vaubaillon, 2022). Recent studies have even suggested that the function proposed by Whipple and Jacchia (1957) that allows the IM1 could be consistent with a common chondritic impactor assuming velocity to be obtained straightforwardly from its derivative. However, a lower atmospheric entry velocity (Brown and Borovička, 2023). for high-altitude grazing meteors, this model does not perform properly Peña-Asensio et al. (2022) and Brown and Borovička (2023) iden- as it cannot represent the velocity end. What is expected for the tified hyperbolic fireballs recorded by the United States Government atmospheric entry of a meteoroid with these characteristics is a non- (USG) satellite sensors, representing ∼1% of total meter-sized im- appreciable deceleration. For that reason, we assume that, within the pactors, events that are potentially meteorite-droppers. In contrast, error margins of the measurements, the pre-atmospheric and terminal there is no evidence of any recovered meteorite with a different compo- velocities are virtually the same as a first approximation. Nevertheless, sition from that of our solar nebula.1 This fact opens several hypotheses: as we do not adjust the trajectory for the influence of gravity, we opt (1) CNEOS hyperbolic fireballs are spurious data; (2) There is a viable to analyze the initial third of the observed data points, conducting way for nearby stellar systems to be isotopically homogeneous so a linear fit with the mean value as the most likely velocity. The extra-solar objects do not have distinctive non-chondritic elemental standard deviation of the fit serves as a measure of velocity uncertainty. and isotopic compositions. The interstellar material exchange would As the entire trajectory can be used for velocity estimation without be enough to smooth out any differences in the initial inventory of applying a deceleration model, this results in a smaller margin of elements; (3) Incoming interstellar objects are biased towards low- error than expected for regular meteor velocity estimation from optical strength properties and do not survive either the interstellar medium observations (Egal et al., 2017). or the ablation process during the atmospheric entry; (4) There is an Assuming the radiated energy by the meteor is proportional to the efficient mechanism by which objects that belong to our solar nebula loss of kinetic energy in the form of mass loss (Ceplecha, 1966), which acquire hyperbolic orbits. is only theoretically valid for atmospheric flight with no decelera- In this work, we present evidence supporting the latter hypothesis, tion (Gritsevich and Koschny, 2011), the initial meteoroid mass can be assuming that the former remains unverified, a matter still awaiting computed from clarification. We show that apparent interstellar meteors may actually 2 be the result of accelerated projectile impacts due to gravitational 𝑚0 = 𝐼(𝑡)𝑑𝑡, (1) ∫ 𝜏(𝑣)𝑣2 perturbations induced by massive objects (stars, free-floating brown where 𝜏 is the luminous efficiency, 𝑣 is the velocity, 𝑡 is the time, dwarfs, rogue planets, sub-stellar or sub-Jovian mass perturbers, pri- 𝐼 = 𝐼0 10−0.4𝑀 is the radiated energy, 𝐼0 = 1300 W is the zero-magnitude mordial black holes...) shaping or visiting the outer part of our solar radiant power for high-speed meteors (Weryk and Brown, 2013), and system. In particular, we analyze a likely hyperbolic asteroid-like graz- 𝑀 the absolute magnitude. The luminous efficiency in percent is taken ing meteor recorded in Finland in 2022 exhibiting no deceleration, from Ceplecha and McCrosky (1976): log 𝜏 = −1.51 + log 𝑣 when 𝑣 ≥ which could be associated with Scholz passage. Additionally, we dis- 27 km s−1 . However, Borovička et al. (2022) note that contemporary cuss the IM2 hyperbolic fireballs of the CNEOS database, which may luminous efficiency models lead to ∼7 times less mass for velocities belong either to the Oort cloud or to a hypothetical Oort-like Scholz’s above 27 km s−1 , so our initial meteoroid mass may be overestimated cloud if its velocity is overestimated by 22%. All events exhibit non- by one order of magnitude. For example, using the Revelle and Ce- cometary compositions and probably are not of extra-solar provenance, plecha (2001) updated model where ln 𝜏 = −1.53 + ln 𝑣 for 𝑣 ≥ 25.372 which has profound implications for solar system formation models. km s−1 , larger average luminous efficiency of are achieved. In case they were truly interstellar in origin, the bias towards a high- Following Ceplecha and McCrosky (1976), meteors can be classified strength composition of the incoming interstellar population would be according to the so-called 𝑃𝐸 criterion: reinforced. 𝑃𝐸 = log 𝜌𝑒 − 0.42 log 𝑚0 + 1.49 log 𝑣∞ − 1.29 log cos 𝑧𝑅 , (2) 1 On the other hand, whenever a meteorite is recovered it is attributed to where 𝜌𝑒 is the air density at terminal height, 𝑣∞ is the pre-atmospheric our solar system by default. velocity, and cos 𝑧𝑅 is the apparent radiant zenith distance. 2 E. Peña-Asensio et al. Icarus 408 (2024) 115844 A more physical, dimensionless form of this criterion exists Table 1 Longitude, latitude, and altitude of the station recording the FH1 meteor. (Moreno-Ibáñez et al., 2020), however, as the analyzed event presents challenges in uniquely determining their atmospheric flight parameters, Station Lon. (◦ ) Lat. (◦ ) Alt. (m.a.s.l.) we turn to the original PE criterion form. From the classical third-order Nyrola 25.5097 62.3425 203 system describing the meteor body deceleration, numerous efforts have Vaala 26.7317 64.3917 130 Tampere 23.7931 61.5119 171 been made to define a height-velocity relation (Kulakov and Stulov, Sastamala 23.0024 61.3826 63 1992; Gritsevich and Stulov, 2006; Gritsevich, 2007, 2008, 2009; Turchak and Gritsevich, 2014; Lyytinen and Gritsevich, 2016; Sansom et al., 2019a; Boaca et al., 2022; Peña-Asensio et al., 2023). Following these works, the dynamics of a meteor can be characterized from the 902H; 768 × 576 px; 3.8 mm f/0.8), and Sastamala (NIKON D750; analytical solution using two dimensionless parameters, namely the 6016 × 4016 px; 14 mm f/4.0). These observations have been used ballistic coefficient 𝛼 and the mass loss parameter 𝛽. It is possible in this study (Table 1). Fig. 1 shows two blended images of FH1 from to express 𝛼 in terms of the meteoroid bulk density 𝜌𝑚 , the pre- the videos recorded by the Sastamala and Nyrola stations. atmospheric shape factor 𝐴0 , the drag coefficient 𝑐𝑑 , the atmospheric The luminous phase of FH1 started at an altitude of 126.55 ± 0.03 density at the sea level 𝜌0 , the height of the homogeneous atmosphere km (24.3104 ± 0.0008◦ E, 63.6677 ± 0.0002◦ N), traveling a distance of ℎ0 = 7.16 km, the meteoroid mass 𝑚, and the slope of the trajectory 409.47 ± 0.09 km until ablation ended at 112.60 ± 0.04 km altitude with the horizon 𝛾: (18.558 ± 0.002◦ E, 61.2358 ± 0.0005◦ N). The flight angle with respect to the local horizon (i.e., the slope) was 3.588 ± 0.013◦ , with an azimuth 1 𝑐𝑑 𝐴0 𝜌0 ℎ0 𝛼= . (3) of 229.915 ± 0.007◦ (zero being north and positive in clockwise direc- 2 𝑚1∕3 𝜌2∕3 sin 𝛾 0 𝑚 tion). Fig. 2 shows the 3D scaled atmospheric flight reconstruction. The Assuming that the ablation of the body due to its rotation is uniform geocentric radiant, namely the corrected meteor anti-apex, is calculated over the entire surface of the meteoroid (Bouquet et al., 2014), the mass outside of the gravitational influence field of the Earth and the Moon loss parameter can be calculated directly from the ablation coefficient (at 10 times the Earth’s Hill sphere), being the right ascension 𝛼𝑅 = 𝜎 and the entry velocity: 117.160 ± 0.009◦ and the declination 𝛿𝑅 = 19.444 ± 0.020◦ . The best convergence angle between the observations is ∼50◦ (for Sastamala and 1 2 𝛽= 𝜎𝑣 . (4) Vaala stations), where plane intersections with angles smaller than 5◦ 6 ∞ are excluded (only for Sastamala and Tampere stations). Table 5 in We selected a uniformly distributed range of values for the ablation the Appendix shows the position vectors of the initial and final points coefficient between 0.014 s2 km−2 and 0.042 s2 km−2 suitable for of FH1’s luminous path in the Earth-centered Earth-fixed coordinate a rocky body based on both the classical single-body ablation and system, as recorded by each of the four stations. contemporary mass-loss models (Ceplecha et al., 1998; Vida et al., Fig. 3 shows the apparent point-to-point velocities, together with 2018). the fitted (73.7 ± 0.6 km s−1 ) and the parabolic velocity threshold for Due to the high altitudes and velocities of the atmospheric flight this specific atmospheric trajectory (∼73 km s−1 ). For 0.2 s intervals, with an enhanced mass loss under the condition of minimal decel- Nyrola detection has 71% of all instant velocity measurements above eration, standard dynamical fits, such as 𝛼 − 𝛽, may not perform this threshold, while for Vaala it is 64%. Nyrola and Vaala stations properly as they are often organized as a function of velocity and record at 25 fps, Tampere at 2.5, and Sastamala is an image of 5 s are not primarily intended for high-height grazers, that is, for non- of exposure. Note that the apparent dispersion of the point-to-point decelerating flights. Nevertheless, we can use the asymptotic form of velocities depends on the time interval selected and, paradoxically, the the solution obtained to describe meteor trajectories at large values of smaller the interval, the greater the dispersion, but the more accurate the mass loss parameter given the formal fulfillment of the condition the final result. In the Appendix, Tables 6 and 7 offer the detected ln(2𝛼𝛽) < ℎ𝑒 ∕ℎ0 < ∞, where ℎ𝑒 is the end (terminal) height (Stulov, positions of FH1 for each frame, represented in a horizontal coordinate 1997, 1998; Gritsevich and Popelenskaya, 2008; Stulov, 2004; Moreno- system comprising azimuth and elevation. Ibáñez et al., 2015). To account for the possible change in velocity We are aware that the plane intersection method may not be ap- at the end of the luminous trajectory, we use the latest modification propriate for long-duration grazing events (Borovicka and Ceplecha, of this solution (Moreno-Ibáñez et al., 2015; Gritsevich et al., 2016; 1992; Sansom et al., 2019b; Shober et al., 2020). Still, for this work, Moreno-Ibáñez et al., 2017): the approach described above is sufficient given the high velocity, ( )1∕2 brief duration (5.56 s), negligible atmospheric drag, and no dark flight ln(1 − 2𝛼𝛽𝑒−ℎ𝑒 ∕ℎ0 ) 𝑣𝑒′ = 𝑣∞ +1 . (5) calculations are required as no terminal mass is expected. Nonetheless, 𝛽 utilizing the fundamental equations of motion, we calculate the descent Using FireOwl analysis software (Visuri et al., 2020; Visuri and of an object due to gravitational acceleration under these conditions to Gritsevich, 2021), a Finnish Fireball Network tool that performs nu- be 147 m. merical integration of the meteoroid trajectory (Moilanen et al., 2021; From the inbound velocity, we estimate the heliocentric osculating Kyrylenko et al., 2023), we recompute and contrast all the results. orbital elements at impact to be the following: semi-major axis 𝑎 = - Finally, we check the dynamic association with some meteoroid stream 8 ± 5 au, eccentricity 𝑒 = 1.07 ± 0.06, inclination 𝑖 = 177.18 ± 0.04◦ , or parent body by means of the well-known 𝐷𝐷 orbital dissimilarity the longitude of the ascending node 𝛺 = 30.10390 ± 0.00010◦ , argu- criterion proposed by Drummond (1981). ment of periapsis 𝜔 = 16.1 ± 0.8◦ , and true anomaly 𝑓 = 343.9 ± 0.8◦ . The orbit shows no close encounters with any planets. Fig. 4 illustrates 3. Results the obtained heliocentric hyperbolic orbit. Fig. 5 shows the meteoroid absolute magnitude for every frame On October 23, 2022, at 19:38:34 (UTC), a very fast grazing meteor, from Nyrola and Vaala stations, which are in good agreement with hereafter FH1, flew through the sky of Finland and terminated over the each other. FH1 curve light has a mean luminous efficiency of 𝜏 = Gulf of Bothnia. The event was observed by 3 stations of the Finnish 2.278 ± 0.018%, a peak brightness of 𝑀 = −3.0 ± 0.5, and yields a Fireball Network (FFN) (Gritsevich et al., 2014; Trigo-Rodríguez et al., photometric initial mass of 𝑚 = 1312 ± 50 𝑔. Using the Revelle and 2015; Lyytinen and Gritsevich, 2016; Visuri and Gritsevich, 2021; Ceplecha (2001) updated model yields an average luminous efficiency Moilanen et al., 2021) and 1 image observation from the public: Nyrola of 15.96 ± 0.13%. Note that the meteoroid underwent a smooth and (Sony IMX291; 1280 × 720 px; 4 mm f/0.95), Tampere (Hikvision gradual ablation without any flares or catastrophic disruption, resulting DS-2CD2T87G2-L; 3840 × 2160 px; 2.8 mm f/1.0), Vaala (Watec in the absence of saturated pixels in all recordings. 3 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Fig. 1. Blended image of the FH1 videos recorded by Sastamala station with (top) and Nyrola station (bottom). The green illuminated area is an aurora borealis. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 2. 3D scaled atmospheric flight reconstruction of the FH1 meteoroid by using the Python software 3D-FireTOC. For FH1 meteor we obtain 𝑃𝐸 = −4.173 ± 0.009. Ceplecha and Mc- fireballs. This is consistent also with similar works (Subasinghe et al., Crosky (1976) classified meteors as type I when 𝑃𝐸 > −4.6, which Ce- 2017; Drolshagen et al., 2021a,b). In any case, the FH1 meteoroid has plecha et al. (1998) assigned to ordinary chondrites. Note that the a consistency equal to or greater than ordinary chondrites, tending photometric mass used for 𝑃𝐸 classification must be computed using towards high-strength materials. luminous efficiency from Ceplecha and McCrosky (1976) in Eq. (2). Conservatively, taking an asteroid-like bulk density of 3700 kg m−3 , The obtained value is in good agreement with our estimated luminous we compute an initial meteoroid diameter of 8.75 ± 0.12 cm, which in efficiency as Revelle and Ceplecha (2001) found that asteroidal fireballs contrast may be 4.59 ± 0.06 cm in diameter based on modern luminous should be around 5.57% and 1.35% for carbonaceous chondrite-like efficiency models. Given the inferred meteoroid size and bulk density, 4 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Fig. 3. Apparent velocity points of FH1 derived from Nyrola and Vaala observations computed at intervals of 0.2 s, fitted velocity, and the parabolic threshold. The error bars are multiplied by a factor of 10. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Fig. 4. Osculating heliocentric orbit of the FH1 meteoroid (J2000). The arrow at the bottom right shows the direction to the point of the vernal equinox. an asteroidal origin seems likely (Blum et al., 2006; Trigo-Rodríguez We corroborate with the FireOwl pipeline that an asteroid-like me- and Llorca, 2006), although it could also be compatible with rocky teoroid with no catastrophic disruption and the estimated character- pebbles ejected by cometary disintegration during inner solar system istics would behave in agreement with the observations. However, trips (Trigo-Rodríguez and Blum, 2022). From Eq. (3), we obtain a differences between compositions are almost marginal as the projectile experiences a low air drag during its ∼5.56 s of flight. Therefore, on value of 𝛼 of 444 ± 4 or 855 ± 7 depending on the initial photometric this occasion, the dynamic models cannot provide conclusive results mass estimates previously calculated, and 𝛽 = 25 ± 7, far away from concerning the meteoroid density. being a meteorite-dropper event (Gritsevich et al., 2012; Sansom et al., The two candidates are the Taurids swarm and the comet P/2015 2019a; Boaca et al., 2022). Eq. (5) yields a velocity decrease over 5 A3, with a 𝐷𝐷 = 0.160 and 𝐷𝐷 = 0.177, respectively. These values m s−1 and 10 m s−1 , which is below the resolution of the measurements are well above the typically accepted threshold (Galligan, 2001), so and within the uncertainty margin estimated for the velocity along the this event is definitely not associated with any known parent body or flight. meteoroid stream. 5 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Fig. 5. Photometry of FH1 from Nyrola and Vaala stations. The mean uncertainty of the magnitude is 0.44 and 0.55 respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) In summary, FH1 was a non-cometary centimeter-sized meteoroid Table 2 Atmospheric flight, photometric, physical, and heliocentric orbital (J2000) computed in an inbound retrograde likely hyperbolic orbit lying almost on the parameters of FH1 grazing meteor. The values with two results correspond to the ecliptic plane. It exhibits no close encounter with any known planet and luminous efficiency models considered: Ceplecha and McCrosky (1976) on the left and a velocity excess at impact of ∼0.7 km s−1 with respect to the barycenter Revelle and Ceplecha (2001) on the right. of the solar system. Photometry of the meteor phase yields an asteroid- Parameter Value like (or higher) bulk density. FH1 is the first likely hyperbolic event Reference time (UTC) 𝑡0 2022-10-23 19:38:34 detected by the FFN since the beginning of the year 2004, with over Velocity (km s−1 ) 𝑣∞ , 𝑣0 , 𝑣𝑒 73.7 ± 0.6 2000 manually analyzed meteors. All computed parameters can be Initial latitude (◦ ) 𝜑0 63.6677 ± 0.0002N found in Table 2. Initial longitude (◦ ) 𝜆0 24.3104 ± 0.0008E Initial height (km) ℎ0 126.55 ± 0.03 Final latitude (◦ ) 𝜑𝑒 61.2358 ± 0.0005N 4. Discussion Final longitude (◦ ) 𝜆𝑒 18.558 ± 0.002E Final height (km) ℎ𝑒 112.60 ± 0.04 The distinctive attributes of FH1, primarily its remarkably high Duration (s) 𝛥𝑡 5.56 eccentricity, could conceivably prompt conjectures regarding its inter- Length (km) 𝛥𝑙 409.47 ± 0.09 Slope (◦ ) 𝛾 3.588 ± 0.013 stellar origin. Notably, such speculations have been posited recently in Azimuth (◦ ) 𝐴 229.915 ± 0.007 the context of certain hyperbolic fireball events cataloged in the CNEOS Peak brightness 𝑀 −3.0 ± 0.5 database. However, a critical observation emerges when analyzing or- Luminous efficiency (%) 𝜏 2.278 ± 0.018 ∣ 15.96 ± 0.13 bital inclination, which appears as a key indicator that urges to exercise Ablation coef. (s2 km−2 ) 𝜎 0.014 ∣ 0.042 caution before leaping to interstellar suppositions. We need first to Initial phot. mass (g) 𝑚0 1312 ± 54 ∣ 187 ± 7 P𝐸 criterion 𝑃𝐸 −4.173 ± 0.009 investigate more plausible scenarios, including the possibility that these Meteoroid density (kg m−3 ) 𝜌𝑚 3700 intriguing projectiles are either indigenous to our solar system, subject Initial diameter (cm) 𝐷 8.75 ± 0.12 ∣ 4.59 ± 0.06 to measurement inaccuracies, or potentially subjected to gravitational Geo. velocity (km s−1 ) 𝑣𝑅 72.7 ± 0.6 accelerations. Geo. radiant (RA) (◦ ) 𝛼𝑅 117.160 ± 0.009 Geo. radiant (Dec) (◦ ) 𝛿𝑅 19.444 ± 0.020 In this section, due to the similarity with FH1, we discuss the Hyp. excess (km s−1 ) 𝛥𝑣 ∼0.7 possible interstellar origin of some CNEOS fireballs considering their Hel. velocity (km s−1 ) 𝑣𝐻 43.0 ± 0.6 uncertainties from events detected independently by ground-based sta- Semi-major axis (au) 𝑎 −8 ± 5 tions. Additionally, we put forth the hypothesis that hyperbolic Earth Eccentricity 𝑒 1.07 ± 0.06 impactors may be celestial bodies native to our solar nebula, which Inclination (◦ ) 𝑖 177.18 ± 0.04 Long. of the asc. node (◦ ) 𝛺 30.10390 ± 0.00010 have been perturbed by close encounters with massive objects. More Argument of periapsis (◦ ) 𝜔 16.1 ± 0.8 precisely, we propose that IM2’s trajectory aligns exceptionally well in Periapsis distance (au) q 0.9748 ± 0.0008 time and direction with the Scholz system fly-by when considering an True anomaly (◦ ) 𝑓 343.9 ± 0.8 overestimated velocity. Ballistic coef. 𝛼 444 ± 4 ∣ 855 ± 7 Mass-loss parameter 𝛽 25 ± 7 Deceleration (m s−2 ) a 0.94 ± 0.01 ∣ 1.817 ± 0.015 4.1. CNEOS ‘interstellar’ fireballs As of October 2023, the CNEOS public database includes ∼956 fire- balls starting from 1988. Among them, 6 events have hyperbolic orbits cos 𝑖. This implies that the random likelihood that 𝑛 orbital inclinations (see Table 3). These interstellar candidates have orbital inclinations fulfill ∣ 𝑖 ∣≤ 𝜃 ◦ where 𝑖 ∈ [−𝜋∕2, 𝜋∕2] is (1 − cos 𝜃)𝑛 . Consequently, lower than 25◦ (with an average of 12 ± 9◦ ). As interstellar interlopers the orbits of 1I/’Oumuamua and 2I/Borisov had a likelihood of being may originate from any part of the sky, the expected inclination should lower than ∣ −58◦ ∣ (the largest inclination which is 1I/Omumuamu’s) be an isotropic probability density function, which follows a sinusoidal of ∼22%. By comparison, the likelihood of detecting six interstellar distribution (Engelhardt et al., 2017) and, therefore, is uniform in objects with inclination orbits smaller than 25◦ is ∼0.00007%. This 6 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Table 3 CNEOS hyperbolic fireballs with geocentric radiant, heliocentric velocity, semi-major axis, eccentricity, and orbital inclination. Date (UTC) 𝛼𝑅 (◦ ) 𝛿𝑅 (◦ ) Vℎ (km s−1 ) a (au) e i (◦ ) 2022-07-28 01:36:08 276.5 14.8 46.9 −1.98 1.44 23.47 2021-05-06 05:54:27 62.5 12.2 44.1 −2.64 1.15 6.05 2017-03-09 04:16:37 (IM2) 170.6 34.1 50.1 −1.22 1.57 24.03 2015-02-17 13:19:50 339.3 −9.6 44.0 −1.45 1.10 1.12 2014-01-08 17:05:34 (IM1) 88.9 13.3 61.1 −0.46 2.42 10.05 2009-04-10 18:42:45 107.8 4.5 45.5 −1.91 1.33 6.52 Table 4 Comparison of 17 fireballs detected by USG sensors and published on CNEOS website with independent ground-based analysis. The geocentric radiant in right ascension and declination, the entry velocity, the radiant position angle deviation, and the velocity deviation are shown. The papers used as a reference are listed in the last column. Some of the geocentric parameters have been calculated from the apparent atmospheric data. Event Date 𝛼𝑅𝑈 𝑆𝐺 𝛿𝑅𝑈 𝑆𝐺 𝑣𝑈𝑒 𝑆𝐺 𝛼𝑅𝑅𝐸𝐹 𝛿𝑅𝑅𝐸𝐹 𝑣𝑅𝐸𝐹 𝑒 𝛥𝑅 𝛥𝑣𝑒 Reference (UTC) (◦ ) (◦ ) (km s−1 ) (◦ ) (◦ ) (km s−1 ) (◦ ) (%) 2008 TC3 2008-10-07 02:45:45 351.6 9.06 13.3 316.8 7.2 12.42 34.49 7.09 Scheirich et al. (2010) Buzzard Coulee 2008-11-21 00:26:40 184.8 50.8 12.9 300 75 18.6 47.24 30.65 Milley (2010) Kosice 2010-02-28 22:24:47 114.5 33.5 15.1 114.3 29 15 4.5 0.67 Borovička et al. (2013b) Chelyabinsk 2013-02-15 03:20:21 334.5 −1.5 18.6 328.28 0.28 19.03 6.47 2.26 Borovička et al. (2013a) Kalabity 2015-01-02 13:39:11 53.8 33.5 18.1 64.3 51.7 15.4 19.73 17.53 Devillepoix et al. (2019) Romania 2015-01-07 01:05:59 118.7 6.1 35.7 113.8 10.13 27.76 6.31 28.6 Borovička et al. (2017) Sariçiçek 2015-09-02 20:10:30 61.1 45.2 21.1 264.8 59.4 13.0 73.6 62.31 Unsalan et al. (2019) Baird Bay 2017-06-30 14:26:45 273.6 −16.1 15.2 272.14 −12.5 15.1 3.87 0.66 Devillepoix et al. (2019) Crawford Bay 2017-09-05 05:11:27 203.7 1.8 14.7 205.12 3.13 16.5 1.94 10.91 Hildebrand et al. (2018) 2018 LA 2018-06-02 16:44:12 248.7 −9.7 11.8 244.19 −10.32 12.375 4.48 4.65 Jenniskens et al. (2021) Ozerki 2018-06-21 01:16:20 310.6 44.5 14.4 307.51 43.11 14.9 2.63 3.36 Kartashova et al. (2020) Viñales 2019-02-01 18:17:10 325.4 −42.8 16.3 324.72 −41.43 16.9 1.46 3.55 Zuluaga et al. (2019) 2019 MO 2019-06-22 21:25:48 217.2 −16.1 9.6 237.3 −15.6 9.3 19.33 3.23 JPL Horizons (2023) Flensburg 2019-09-12 12:49:48 183.1 −21.3 14.6 183.5 −18.55 14.77 2.78 1.15 Borovička et al. (2021) Novo Mesto 2020-02-28 09:30:34 332 2.0 21.5 330.92 2.32 22.098 1.13 2.71 Vida et al. (2021) Ådalen 2020-11-07 21:27:04 359.2 47.3 12.4 358.1 47.6 13.5 0.8 8.15 Kyrylenko et al. (2023) 2022 EB5 2022-03-11 21:22:46 157.5 38.1 13.2 157.0 37.6 13.0 0.64 1.54 JPL Horizons (2023) is without considering that all 6 events are in prograde orbits, which Eliminating the fireballs that appear as outliers based on the radiant should be expected in the 50% of extra-solar visitors and would further position and velocity errors (2008 TC3, Buzzard Coulee, Kalabity, reduce the likelihood. Therefore, multiple options can be inferred: Romania, Sariçiçek, 2019 MO), deviations become Gaussian where there are shortcoming data in the CNEOS database, these hyperbolic the radiant would be reduced to 1.9◦ in right ascension and 1.7◦ in fireballs belonged to our solar system, or they came from sources with declination, and a 3.6% deviation in velocity, which is the scenario we a directional bias. assume for the study of the CNEOS fireballs. Therefore, this assumption As the error bars are not provided by USG sensors, it is necessary to remains valid solely under the condition that the hyperbolic CNEOS narrow down the uncertainties and determine the frequency of spurious events are part of the same distribution as the events characterized by data in the database. Devillepoix et al. (2019) reported that CNEOS elliptical orbits in Table 4. Hence, if these events are indeed outliers, fireball radiants are off for most events, sometimes by only a couple of the presented results here should be ignored. Consequently, 65% of degrees but other times as much as 90◦ . They compared the radiants of CNEOS events provide measurements accurate enough for a rough 9 events recorded simultaneously by ground-based stations and found estimation of heliocentric orbits. However, this also implies that the that the velocity vector of 4 of them was incorrectly measured by results for two out of the six hyperbolic fireballs will be inaccurate, the USG sensors: Buzzard Coulee (2008-11-21 00:26:44), 2008 TC3 rendering these estimated errors inapplicable. Note that there is a lack (2008-10-07 02:45:45), DN150102 - Kalabity (2015-01-02 13:39:11), of a significant correlation between the velocity error and the actual and Crawford Bay (2017-09-05 05:11:27). As we calculate a different velocity value. When a linear fit is performed, it yields a coefficient of radiant for Crawford Bay event based on CNEOS data and, as pointed determination as low as 0.027. In principle, we should not assume that in Peña-Asensio et al. (2022), 2008 TC3 was missing a minus sign in the the faster hyperbolic ones will necessarily exhibit larger errors z velocity component, we decide to recompute the mean radiant posi- These hyperbolic events, 2009-04-10 18:42:45, 2014-01-08 tion and velocity deviations of CNEOS fireballs including also the recent 17:05:34 (IM1), 2017-03-09 04:16:37 (IM2), and 2021-05-06 05:54:27, independently analyzed events Sariçiçek (2015-09-02 20:10:30) (Un- salan et al., 2019), Ozerki (2018-06-21 01:16:20) (Maksimova et al., appear to be somehow clusterized. The geocentric radiants of these 4 2020; Kartashova et al., 2020), Viñales (2019-02-01 18:17:10) (Zu- fireballs are suspiciously distributed around the Gemini constellation luaga et al., 2019), 2019 MO (2019-06-22 21:25:48) (JPL Horizons, with an average radiant distance to the constellation center point of 2023), Flensburg (2019-09-12 12:49:48) (Borovička et al., 2021), Novo 34.2◦ . We check the likelihood that 4 out of 6 randomly selected Mesto (2020-02-28 09:30:34) (Vida et al., 2021), Ådalen (2020-11- events from the CNEOS database (the 255 fireballs analyzed in Peña- 07 21:27:04) (Kyrylenko et al., 2023), and 2022 EB5 (2022-03-11 Asensio et al. (2022)) have a lower mean distance value to Gemini 21:22:46) (JPL Horizons, 2023). (10,000 draws). We find that these 4 hyperbolic events represent 1.7𝜎 From the comparison of independently analyzed events presented in with respect to the mean, which denotes a probability of 6.9% having Table 4, it is found that the CNEOS radiants have a mean deviation of occurred by chance (see Fig. 6). From a completely isotropic radiant 21.3 ± 43.2◦ in right ascension and 4.8 ± 6.8◦ in declination, and a mean distribution, the probability of having obtained a smaller distance entry velocity deviation of 11.1 ± 15.6%. It can be deduced from the for 4/6 events is 4.3%. However, this does not strictly imply they standard deviations that the errors do not follow a normal distribution, are associated with each other as the anisotropic radiant distribution as these distributions strongly depend on the relative geometry of the could be explained as well by both observational bias and solar system sensor and the fireball. induced dynamics. 7 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Fig. 6. Result of randomly selecting 6 CNEOS events and computing the mean minimum distance to the Gemini constellation center of 4 of them. The calculation is repeated 10,000 times. In cyan color are shown the draws with equal or smaller distances than the 6 CNEOS hyperbolic events. The fit to a Gaussian distribution is shown in red. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 4.2. The massive objects fly-by hypothesis anisotropies on the geocentric radiant distribution with a statistically significant overdensity of high-speed radiants towards the constellation Not all gravitationally unbound objects from our solar system are of Gemini, which appears to be consistent in terms of time and location necessarily interstellar interlopers. There are different mechanisms ca- with the Scholz fly-by. Precisely the geocentric radiant of FH1 falls in pable of accelerating objects native to our solar nebula into hyperbolic this constellation, as well as 4 of the 6 hyperbolic fireballs from the orbits. Some of them are the secular perturbations induced by the CNEOS database that are close to Gemini or the recent Scholz motion Galactic disk or fly-by impulsive interaction of massive extra-solar direction. bodies (Fouchard et al., 2011; Królikowska and Dybczyński, 2017). We test the compatibility of this hypothesis by integrating backward Furthermore, close encounters with the Sun or giant planets may result in time the FH1 grazer and the 6 CNEOS interstellar candidates for in an inbound excess velocity, although these are not frequent enough 109,000 years to account for the estimated upper time limit of the to explain the observed hyperbolic meteor orbits (Hajduková et al., Scholz close encounter (85,000 years). To this end, we use an orbital 2014, 2019). Mercury has also been identified as a possible efficient integrator based on a leapfrog scheme with different time steps to producer of hyperbolic projectiles to Earth (Wiegert, 2014). Other properly resolve the Earth-induced zenith attraction prior to the im- exotic hypotheses suggest unseen stellar companions to the Sun (Davis pact (Socas-Navarro, 2019). We account for the gravitational influence et al., 1984) or unknown planets (Socas-Navarro, 2023) as a source of of the Sun, Earth, Moon, Mars, Jupiter, Saturn, Uranus, and Neptune by hyperbolic Earth impactors. querying ephemerids to JPL HORIZONS system. Fig. 7 shows the appar- When the idea of the Oort cloud was introduced, i.e. a very distant ent motion of the objects starting from their geocentric radiants for the region with long-period comets, it was also pointed out the existence considered time. None of the events experienced a close encounter with of a mechanism to shorten their perihelia, for example, inbound hyper- planets, only 2021-05-06 05:54:27 fireball passed ∼5 years ago at ∼3 bolic injection produced by passing stars (Oort, 1950). Indeed, recent times Hill radius from Uranus. studies suggest that stellar close encounters send accelerated bodies into the planetary zone (Dybczyński and Królikowska, 2022). Higuchi New results definitively dismiss the possibility that Scholz may have and Kokubo (2020) showed that celestial bodies of sub-stellar mass penetrated the dynamically active inner Oort cloud region (<20 kAU), (down to approximately 0.2 Jupiter masses) possess the ability to divert but support the notion that it would have passed through the outer Oort Oort cloud comets into hyperbolic trajectories characterized by small cloud where objects can have stable orbits (Dupuy et al., 2019; de la eccentricity but large perihelion distance. Other stellar systems may Fuente Marcos and de la Fuente Marcos, 2022). Given the apparently have also their own Oort-like clouds which could induce an influx of better constrained time (∼80 kya) and distance (∼68 kau) for the Scholz extra-solar objects through the planetary region when approaching the close encounter, and its current separation from the Sun (6.80 pc), Sun (Stern, 1987). The most recent stellar fly-by to our solar system it can be computed a linear velocity with respect to the solar system was the low-mass binary star WISE J072003.20–084651.2, also known barycenter of 𝑣∗ = 82.4 ± 0.3 km s−1 , which is a valid approximation for as Scholz’s star (hereafter Scholz), which crossed the outer layers of the 100 kya within 2.5% accuracy (Mamajek et al., 2015). Considering the Oort cloud at 52+23 −14 kau about 70+15 −10 kya ago (Scholz, 2014; Burgasser fly-by occurring at high velocity and the low mass of the Scholz system et al., 2015; Mamajek et al., 2015). (𝑀∗ = 165 ± 7 𝑀𝐽 𝑢𝑝 ), it appears plausible that small bodies may have de la Fuente Marcos et al. (2018) analyzed hyperbolic small bodies been injected towards the Earth. of the data provided by JPL’s solar system Dynamics Group Small- The meteoroid FH1 was 36 ± 18 kya ago at ∼67 kau, and the IM2 Body and the Minor Planets Center (MPC) databases. They found strong object reached the same distance 14 ± 2 kya ago. The closest encounter 8 E. Peña-Asensio et al. Icarus 408 (2024) 115844 Fig. 7. Apparent motion of the objects starting from their geocentric radiants during the backward orbital integration. Scholz, FH1 grazer event, 1I/’Oumuamua (Meech et al., 2017), and 2I/Borisov (de León et al., 2020) are shown. The 6 dated events correspond to the hyperbolic fireballs in the CNEOS database and include the new mean deviation found for the 17 fireballs compared. All CNEOS non-hyperbolic events are also depicted, together with a center point of the Gemini constellation. Markers represent the radiant position at impact or at the current time in the case of Scholz. The ecliptic plane is plotted in yellow. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) found in the simulation of FH1 with the Scholz trajectory was at 39 kau, system and the Sun, which occurs at 68.7 kau. According to Eq. (6), the while IM2 passed at 131 kau. In spite of almost intersecting trajectories, interaction with the Scholz could impart a maximum velocity change of the excess velocity of IM2 at impact (−8 km s−1 ) causes it not to be approximately 0.136 m s−1 . In the defined encounter geometry within compatible in time with the Scholz passage. Looking at Table 4, it can the Oort Cloud, the object would need to achieve a velocity of 0.982 be seen that ∼18% of the events have velocity errors around 30% or m s−1 to attain a perihelion distance of 1 au. The velocity impulse more of the nominal value. If the IM2 measurement had an uncertainty generated by the Scholz star would represent approximately 14% of the of 22% it would be perfectly compatible in time with the Scholz fly-by. object’s perigee velocity. Therefore, such a perturbation has the capac- Velocities proximal to the parabolic limit for FH1 are consistent, both ity to significantly modify the orbital parameters of a distantly located temporally and directionally, with the passage of Scholz. This consis- object, resulting in a highly eccentric inbound trajectory towards Earth. tency necessitates only a 1% reduction in Scholz’s nominal velocity, a Detection of exocomets and warm and cold debris belts around stars value well within the estimated range of uncertainty. Fig. 8 presents suggests the existence of Oort-like outer clouds material in other stellar the geometric configuration of the encounter involving FH1, IM2, and systems (Marois et al., 2010; Kiefer et al., 2014). Highly eccentric Scholz. evaporating comets are compatible with the metallic absorption lines Long-period objects can acquire excess velocity from relatively low observed in debris disk spectra, which may be evidence of exocomet gravitational perturbations with no need for very close encounters if clouds (Beust et al., 1990; Hanse et al., 2018). Hanse et al. (2018) they are oriented in the appropriate direction at the appropriate time. found that 25% to 65% of the mass lost from the Oort cloud is due to Moreover, the perturbation may not necessarily have occurred during objects being either injected into the planetary region or ejected into the time of the maximum approach of Scholz, which took ∼21.5 kya to interstellar space mainly because of stellar encounters. A hypothetical traverse the Oort cloud. Considering that an object is fixed in reference Oort-like Scholz cloud should have the outer edge less distant from its to the solar system barycenter, it is possible to estimate the time- center than the Sun due to its smaller mass. Assuming that both stellar integrated impulse exerted by a passing star from classical impulse systems have undergone similar processes, we can establish that the approximation (Rickman et al., 2005): binding energies of their outer clouds of material are roughly the same ( ) 2𝐺𝑀∗ 𝑏̂ 𝑜 𝑏̂ ∗ and, therefore, their gravitational potential energies as well: 𝛥𝑣 = − , (6) 𝑣∗ 𝑏𝑜 𝑏∗ 𝐺𝑀⊙ 𝑚𝑜 𝐺𝑀∗ 𝑚𝑜 − =− , (7) 𝑅⊙ 𝑅∗ where 𝐺 is the gravitational constant, 𝑏𝑜 is the vector from the Oort cloud object to the Scholz closest approach, and 𝑏∗ is the vector from where 𝑅 is the distance from the objects to the star, 𝑚𝑜 is the mass of the Sun to the Scholz closest approach. the surrounding objects, ⊙ subscript refers to the Sun, and ∗ to another To elucidate, consider a notional object situated at a radial distance star. Accordingly, the outer edge of the Scholz outer cloud should be of 39 kau beyond the point of closest approach between the Scholz star scaled down as 𝑅∗ = 0.16𝑅⊙ . 9 E. Peña-Asensio et al. Icarus 408 (2024) 115844 With successive data releases from Gaia, the space observatory of the European Space Agency, the identification of new stellar close encounters has been increasing. For example, in the first Gaia data release (GDR1) 2 stars (out of 300,000) were found to come within 1 pc of the Sun (Bailer-Jones, 2018), while in GDR2 were 26 stars (out of 7.2 million) passing within the same distance (Bailer-Jones et al., 2018) and 61 stars (out of 33 million) in GDR3 (Bailer-Jones, 2022). Bailer- Jones et al. (2018) inferred the present rate of stellar encounters to be 19.7 ± 2.2 per Myr within 1 pc. This implies that the Oort cloud is expected to have experienced ∼2 interloper visits in the last 80 kya. However, only one has been identified during this period of time. We stress that as uncertainties of CNEOS data are unavailable, no definite conclusions can be established regarding IM2. Nevertheless, considering that there may be complex gravitational interactions, we claim that both FH1 and IM2 are consistent with being gravitationally accelerated impactors originating from the Oort Cloud, likely injected during Scholz’s recent fly-by. Additionally, IM2 could plausibly be an object ejected from the outer cloud of the Scholz binary system. The other CNEOS hyperbolic events (if they are not outliers) possibly have experienced close encounters with massive objects (such as stars, free- floating brown dwarfs, rogue planets, sub-stellar or sub-Jovian mass perturbers, rogue planets, primordial black holes...) when traversing the Oort cloud less time ago than the Scholz passage, which in the case of a star could be supported by the current rate of stellar encounters. 5. Conclusions We have analyzed an unusual grazing meteor (FH1) recorded in October 2022 by the Finnish Fireball Network. The cm-sized meteoroid exhibited an inbound likely hyperbolic orbit and an (at least) asteroidal consistency. Considering that its orbital plane coincides with the eclip- tic and is close to the parabolic velocity limit, it seems more likely to be a perturbed Oort cloud object rather than an interstellar interloper. Within the estimated uncertainties, FH1 could be associated with the known most recent stellar encounter with our solar system, i.e., the Scholz system. 4 of the 6 hyperbolic CNEOS fireballs exhibit a statistical oddity Fig. 8. Integration of clones for FH1, IM2, and Scholz. The diagram illustrates in the geocentric radiant distribution around the Gemini constellation, the heliocentric cartesian coordinates evolution during the encounter, including the an area with an overdensity of hyperbolic radiants and identified as respective outer clouds of material associated with both the Sun and Scholz. The compatible in time with the Scholz fly-by. We show statistical evidence arrow at the bottom right shows the direction to the point of the vernal equinox. (For that these events cannot really pertain to a randomly incoming inter- interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) stellar population as the likelihood of their low orbital inclinations is extremely improbable compared to the expected one (with a probability of having occurred by chance of 0.00007%). Therefore, these impactors most likely belonged to our solar nebula and have been perturbed by Given that the classical outer edge of the Oort cloud is 200 kau massive objects lying on or intersecting the plane of the ecliptic. These (Dones et al., 2004), it is expected that the Scholz system has an outer cloud edge of 32 kau, close enough to the Sun for any object massive objects could also form part of the Oort cloud, although this to be disturbed towards the planetary region during the fly-by, even would limit the excess velocity of the projectiles. more so when Scholz Hill sphere at the closest approach was 26 kau. Given the new mean uncertainties estimated in this work for CNEOS In fact, IM2 clone trajectory traversed the path of the Scholz cloud detections by benchmarking with 17 independent ground-based obser- and a considerable percentage of the clones intersected its Hill sphere vations, the 2017-03-09 04:16:37 (IM2) fireball appears to be consistent path, while some FH1 clones passed at 2 Scholz Hill sphere radius. with the Scholz close encounter if the velocity was overestimated by These possible injections could be facilitated by the joined effect of 22%, which is within the error range for ∼18% of events compared. In the Galactic disk, other passing stars interactions, and the presence addition, IM2 showed a peak power in its light curve that corresponded of massive objects on the outskirts of the Scholz system or of our to a dynamic pressure (i.e. aerodynamic strength) typical of iron mete- solar system. For example, the Scholz motion region passes through orites, about ∼75 MPa, and most likely produced a recoverable metallic the zone of high probability for the putative planet 9 and multiple meteorite (Peña-Asensio et al., 2022; Siraj and Loeb, 2022b). This hyperbolic CNEOS fireballs fall around it (Batygin and Brown, 2016; would inaugurate a window of opportunity for stellar archaeology Brown and Batygin, 2021; Socas-Navarro, 2023). Note that although sample collection with known trajectory beyond the tiny presolar grains the maximum velocity change in a fly-by is double the relative velocity embedded in meteorites. of the encounter, a very massive nearly static object could redirect If these hyperbolic impactors were interstellar visitors, it would another with a zero net velocity change into a hyperbolic orbit due have significant implications both for the incoming flux of extra-solar to the new geometry of the motion with respect to the central body. objects and for the characterization of their physical properties, which However, this situation would lead to slow unbound orbits, which would be biased towards high-strength compositions and low incli- might explain the modest impact velocity excess for many hyperbolic nations. If they were Oort cloud objects, FH1 would be the second solar objects. cm-sized asteroid-like observed object after Vida et al. (2023) and 10 E. Peña-Asensio et al. Icarus 408 (2024) 115844 IM2 the first detected iron-like body from the outermost part of our Appendix solar or another stellar system. This would provide further evidence for the massive proto-asteroid belt and Jupiter’s ‘‘Grand Tack’’ dynamical instability scenario (Shannon et al., 2019). It would imply that the Oort cloud could currently be populated not only by weak cometary objects See Tables 5–7 for observational data of FH1. but also by ice-free rocky material scattered by giant planets’s round trip to inner orbits. The absence of interstellar meteorites and the low orbital inclina- tions of the hyperbolic projectiles studied indicate that the population of massive objects forming and crossing the Oort cloud may be larger than previously thought, injecting large meteoroids to the planetary Table 5 regions. Our results reinforce the idea that passing stars or other Position vectors of the initial and final points of FH1’s luminous path in the Earth-centered Earth-fixed coordinate system, as recorded by each of the four massive objects represent a source of hyperbolic Earth impactors that stations. must be examined in detail on a case-by-case basis before claiming the Nyrola Vaala Tampere Sastamala interstellar origin of any object with excess velocity. X𝑏𝑒𝑔 (m) 2,684,184 ± 6 2,637,480 ± 4 2,743,469 ± 4 2,701,116 ± 3 Y𝑏𝑒𝑔 (m) 1,161,276 ± 14 1,188,673 ± 56 1,126,497 ± 7 1,151,343 ± 11 CRediT authorship contribution statement Z𝑏𝑒𝑔 (m) 5,787,091 ± 29 5,806,802 ± 26 5,762,070 ± 20 5,779,945 ± 31 X𝑒𝑛𝑑 (m) 2,969,352 ± 17 2,891,289 ± 15 2,838,781 ± 2 2,800,918 ± 3 Y𝑒𝑛𝑑 (m) 993,989 ± 114 1,039,782 ± 122 1,070,585 ± 21 1,092,797 ± 10 Eloy Peña-Asensio: Performed the analysis of FH1, The statistical Z𝑒𝑛𝑑 (m) 5,666,739 ± 24 5,699,684 ± 6 5,721,845 ± 21 5,737,825 ± 19 study of CNEOS hyperbolic events, The investigation of the massive object close encounters hypothesis, Wrote the manuscript. Jaakko Visuri: Coordinated the Finnish Fireball Network efforts and supported the astrometry and atmospheric trajectory calculation of FH1. Josep M. Trigo-Rodríguez: Oversaw the research activity and provided scientific Table 6 Detected positions of FH1 in a horizontal coordinate system for each frame from insights. Hector Socas-Navarro: Performed the N-body simulations Nyrola. The table presents the azimuth and elevation coordinates along with their and suggested the possible association of FH1 with Scholz’s star. Maria corresponding frame numbers. The mean residuals from astrometry are 0.0139◦ for Gritsevich: Clarified the issues with the dynamic model fit and con- azimuth and 0.0121◦ for elevation. tributed to the estimation of the terminal velocity. Markku Siljama: # Azi. (◦ ) Elev. (◦ ) # Azi. (◦ ) Elev. (◦ ) # Azi. (◦ ) Elev. (◦ ) First identified FH1 as an interstellar candidate. Albert Rimola: Ac- 11 317.3931 37.8781 51 281.3995 29.5673 91 263.1464 20.2415 quired financial support for the project leading to this publication, 12 316.2749 37.8103 52 280.7005 29.2648 92 262.8051 20.0648 Supervised the work. 13 315.3540 37.7320 53 280.0772 28.9837 93 262.5361 19.8995 14 314.1403 37.6221 54 279.4517 28.7645 94 262.2554 19.7190 15 313.1072 37.5227 55 278.8840 28.4955 95 261.9023 19.5021 Declaration of competing interest 16 311.9602 37.4195 56 278.2156 28.2280 96 261.6241 19.3508 17 310.8714 37.2770 57 277.6835 27.9869 97 261.3567 19.1678 18 309.8847 37.1485 58 277.0828 27.6925 98 261.1147 19.0138 The authors declare that they have no known competing finan- 19 308.7614 36.9825 59 276.4748 27.4461 99 260.8124 18.8077 cial interests or personal relationships that could have appeared to 20 307.8117 36.8475 60 276.0162 27.2016 100 260.5358 18.6459 influence the work reported in this paper. 21 306.6819 36.6881 61 275.4985 26.9515 101 260.2954 18.4980 22 305.7508 36.5257 62 274.9191 26.6835 102 260.0438 18.3728 23 304.6602 36.3582 63 274.3874 26.4317 103 259.7673 18.1635 Data availability 24 303.5926 36.1520 64 273.8917 26.1857 104 259.4929 18.0146 25 302.6033 35.9439 65 273.3587 25.9597 105 259.2896 17.8871 26 301.5501 35.7376 66 272.8778 25.6810 106 259.0386 17.7289 Data will be made available on request. 27 300.6744 35.5661 67 272.3491 25.4399 107 258.8114 17.5625 28 299.6912 35.3705 68 271.8988 25.2108 108 258.5265 17.3885 29 298.7177 35.1155 69 271.4487 24.9688 109 258.3008 17.2594 Acknowledgments 30 297.7942 34.9211 70 271.0233 24.7566 110 258.0748 17.0994 31 296.9946 34.6887 71 270.5782 24.5114 111 257.8603 16.9311 This project has received funding from the European Research 32 295.9840 34.4713 72 270.0966 24.2465 112 257.6202 16.7871 33 295.1154 34.1997 73 269.6739 23.9963 113 257.3981 16.6365 Council (ERC) under the European Union’s Horizon 2020 research and 34 294.3219 34.0078 74 269.2575 23.7892 114 257.1762 16.4860 innovation programme (grant agreement No. 865657) for the project 35 293.4068 33.7414 75 268.8598 23.5792 115 256.9630 16.3234 ‘‘Quantum Chemistry on Interstellar Grains’’ (QUANTUMGRAIN). JMT- 36 292.5561 33.4805 76 268.4249 23.3262 116 256.7421 16.2062 R and EP-A. acknowledge financial support from the project PID2021- 37 291.7253 33.2369 77 268.0482 23.1121 117 256.5569 16.0777 38 290.9343 33.0065 78 267.6577 22.9201 118 256.3266 15.9198 128062NB-I00 funded by MCIN/AEI/10.13039/501100011033, as well 39 290.0894 32.7342 79 267.2421 22.6909 119 256.1412 15.8074 as the Unidad de Excelencia María de Maeztu CEX2020-001058-M. AR 40 289.3101 32.4818 80 266.8870 22.4885 120 255.9655 15.7245 acknowledges financial support from the FEDER/Ministerio de Ciencia 41 288.5378 32.2250 81 266.4824 22.2579 121 255.7539 15.5943 e Innovación – Agencia Estatal de Investigación (PID2021-126427NB- 42 287.7816 31.9863 82 266.1553 22.0821 122 255.5601 15.4522 I00, PI: AR). MG acknowledges the Academy of Finland project no. 43 287.0466 31.7155 83 265.7647 21.8330 123 255.3926 15.2929 44 286.1926 31.4039 84 265.4642 21.6612 124 255.2166 15.1914 325806 (PlanetS). HS-N acknowledges support from the Agencia Estatal 45 285.4432 31.1795 85 265.1273 21.4680 125 255.0321 15.0947 de Investigación del Ministerio de Ciencia e Innovación (AEI-MCINN) 46 284.7507 30.8916 86 264.7417 21.2385 126 254.8746 14.9874 under grant Hydrated Minerals and Organic Compounds in Primitive 47 284.0495 30.6277 87 264.4171 21.0196 127 254.7251 14.8853 Asteroids with reference PID2020-120464GB-I100. We thank all FFN 48 283.3727 30.3440 88 264.1204 20.8522 128 254.5671 14.7714 49 282.7171 30.1159 89 263.7876 20.6626 129 254.4091 14.6573 station operators and photographers whose continuous dedication has 50 281.9793 29.8009 90 263.4555 20.4567 130 254.2257 14.5249 allowed to record this grazing meteor: Jarmo Moilanen, Harri Kiiski- nen, Markku Lintinen, Jari Luomanen, and Kari Haila. We also thank Marc Corretgé-Gilart for his support in astrometric calibrations. All authors read, edited, and approved the manuscript. 11 E. Peña-Asensio et al. 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