Despite their rarity, massive stars dominate the ecology of galaxies via their strong, radiatively-driven winds throughout their lives and as supernovae in their deaths. However, their evolution and subsequent impact on their environment can be significantly affected by the presence of a magnetic field. While recent studies indicate that about 7% of OB stars in the Milky Way host strong, stable, organised (fossil) magnetic fields at their surfaces, little is known about the fields of very massive stars, nor the magnetic properties of stars outside our Galaxy. We aim to continue searching for strong magnetic fields in a diverse set of massive and very massive stars (VMS) in the Large and Small Magellanic Clouds (LMC/SMC), and we evaluate the overall capability of FORS2 to usefully search for and detect stellar magnetic fields in extra-galactic environments. We have obtained FORS2 spectropolarimetry of a sample of 41 stars, which principally consist of spectral types B, O, Of/WN, WNh, and classical WR stars in the LMC and SMC. Four of our targets are Of?p stars; one of them was just recently discovered. Each spectrum was analysed to infer the longitudinal magnetic field. No magnetic fields were formally detected in our study, although Bayesian statistical considerations suggest that the Of?p star SMC 159-2 is magnetic with a dipolar field of the order of 2.4–4.4 kG. In addition, our first constraints of magnetic fields in VMS provide interesting insights into the formation of the most massive stars in the Universe.

Using orbital integrations of particles ejected from Comet Halley's passages between 1404 BC and 240 BC, the authors investigate possible outbursts of the Orionids (twin shower of the Eta Aquariids) that may have been observed in the western hemisphere. In an earlier orbital integration study the authors determined there was a high probability linking probable outbursts of the Eta Aquariid meteor shower with certain events recorded in inscriptions during the Maya Classic Period, AD 250-900. This prior examination was the first scientific inquiry of its kind into ancient meteor outbursts possibly recorded in the western hemisphere where previously no pre-Columbian observations had existed. In the current paper the aim is to describe orbital dynamics of rare but probable Orionid outbursts that would have occurred on or near applicable dates recorded in the Classic Maya inscriptions. Specifically, significant probable outbursts are found in AD 417 and 585 out of 30 possible target years. The driving mechanisms for outbursts in those two years are Jovian 1:6 and 1:7 mean motion resonances acting to maintain compact structures within the Orionid stream for over 1 kyr. Furthermore, an Orionid outburst in AD 585 recorded by China is confirmed.

We describe the digest2 software package, a fast, short-arc orbit classifier for small solar system bodies. The digest2 algorithm has been serving the community for more than 13 yr. The code provides a score, D-2, which represents a pseudo-probability that a tracklet belongs to a given solar system orbit type. digest2 is primarily used as a classifier for Near-Earth Object (NEO) candidates, to identify those to be prioritized for follow-up observation. We describe the historical development of digest2 and demonstrate its use on real and synthetic data. We find that digest2 can accurately and precisely distinguish NEOs from non-NEOs. At the time of detection, 14% of NEO tracklets and 98.5% of non-NEOs tracklets have D2 below the critical value of D-2 = 65.94% of our simulated NEOs achieved the maximum D-2 = 100% and 99.6% of NEOs achieved D-2 >= 65 at least once during the simulated 10-year timeframe. We demonstrate that D-2 varies as a function of time, rate of motion, magnitude and sky-plane location, and show that NEOs tend to have lower D-2 at low Solar elongations close to the ecliptic. We use our findings to recommend future development directions for the digest2 code.

We can only speculate how long ago a human first consciously noticed a shooting star in the sky. Writings go back thousands of years. The Egyptian hieratic papyrus of the Hermitage museum in St. Petersburg (archive number 1115) dates from between the twentieth and seventeenth centuries BC and mentions a falling star in the “Tale of the Shipwrecked Sailor” (Astapovich, 1958). Aristotle hypothesised on the nature of meteors, though the correct scientific basis and the connection with meteorites had to wait until Ernst Chladni’s work two hundred years ago: see Beech (1995), and chapter 3 of Littmann (1998). For a long time there had been civilisations around the world that kept careful and extensive records that we can now recognise relate to meteor outbursts, meteor showers or fireballs. Notable among such ancient records are those from China, Japan and Korea (Imoto and Hasegawa, 1958; Zhuang, 1977; Ahn, 2005). Many records include exact dates, of immense value in modern studies to test our ideas of how processes in space have operated over millennia. More about the history of meteor observations and meteor work can be found in Williams and Murad (2002), chapter 1 of Jenniskens (2006) and references therein. Humans have seen meteors for millennia; since Chladni it has been known that underlying the meteor phenomenon is the existence of solid objects in space, which we call meteoroids. The fundamental scientific study is concerned with meteoroids; meteors are the light, ionisation, sound and other phenomena produced when meteoroids collide with a planetary atmosphere. Recently, the International Astronomical Union updated the definitions of meteor and meteoroid, motivated by the blurring of the line between asteroids and meteoroids. When the previous definitions were put in place in 1961, a meteoroid was defined as “a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule” (Millman, 1961). This worked well until improvements in asteroid searches began to find many objects smaller than 100 m, some as small as a few metres (Beech and Steel, 1995). The Chelyabinsk impact was caused by an object 19 m in diameter; according to the old definitions it could not be called an asteroid because it was not observed in interstellar space, while the smaller, ≈3 m 2008 TC3, which struck the Earth one day after it was discovered (Jenniskens et al., 2009), was an asteroid. In order to resolve this, Commission F1 of the IAU proposed to establish a size threshold to divide asteroids from meteoroids (Borovička, 2016). There is no natural size limit, as the population is continuous from small to large objects, so an arbitrary limit of 1 metre was chosen; objects larger than this are asteroids (or comets, if they show activity). At the smaller end, a division was introduced between meteoroids and interplanetary dust; in this case, the natural division is the size at which a particle is too small to produce light and ionisation when it strikes a planetary atmosphere. This limit depends on the speed of the object, but an arbitrary limit of 30 μm was chosen as being characteristic. Remarks to the definitions include some elasticity, so that any object that causesmeteor phenomenamay be called ameteoroid; the Chelyabinsk impactor was both an asteroid and a meteoroid. Also, any natural object observed in space, even if below the 1-metre threshold, may be called an asteroid. Although the science is of meteoroids, with meteors a manifestation thereof, the term ‘meteor science’ is often used to encompass the study of meteoroids. Meteor science continues to be studied for scientific and practical reasons. The practical includes the development of the ability to mitigate effects of impacting meteoroids when potentially harmful: the hazard on Earth and to spacecraft must be understood over a wide size range of impactors. Scientifically, the motivation is to understand ongoing processes in nature: how comets and asteroids evolve, or what happens to their debris, in space and in planetary atmospheres. As in other sciences, observation or experiment combine with theory to elucidate what processes really occur. Models fits data if given processes operate. Theory suggests that various forces in principle could act on particles moving in the Solar System (e.g., radiative, electrostatic, relativistic). If the forces are not directly observable, a model should predict an observable consequence. For example, if the radiative Poynting–Robertson effect influences the dynamical evolution of small grains (meteoroids) in space, this can help to explain observations at the Earth relating to theGeminid stream (Jakubík and Neslušan, 2015) or at Mercury relating to the Taurids (Christou et al., 2015). Despite the fact that cometary dust trails have been observed, the dust particle concentrations in space cannot be detected by modern instruments, as a rule. Therefore studies of the dynamics and structure of meteoroid streams, and particularly the orbital resonances that operate, are important (Soja et al., 2011;Kortenkamp, 2013). A goodmodel of the composition and structure of the meteoroids themselves can predict how they will interact with the atmosphere, including the early release of volatiles like sodium (Vojáček et al., 2019). The interaction strongly depends on fragmentation, which affects both the meteor light and the dynamics of the meteoroid (Ceplecha and Revelle, 2005; Borovička et al., 2007). The twenty-first century brings great opportunities to advance meteor science. Modern astronomy has been characterised by each new generation of telescopes seeing fainter and with better resolution, allowing discoveries that drive the theoretical

Recent work by MacDonald et al. has highlighted the valuable work carried out by sky watchers and auroral enthusiasts in obtaining high-quality digital images of rare and unusual auroral structures. A feature of particular interest, which has been nicknamed Steve, typically takes the form of a short-lived arch, beam, or narrow band of light in the sky. MacDonald et al. have established that the phenomenon is characterised by a range of optically visible low magnetic latitude structures associated with a strong subauroral ion drift. Respecting its nickname, they have dubbed the phenomenon STEVE, an acronym for Strong Thermal Emission Velocity Enhancement. Here, we draw attention to earlier observations of similar structures, showing that some previously unidentified atmospheric, meteoric or auroral anomalies can now be recognized as examples of Steve, and therefore as part of a broad spectrum of occasional auroral features that may appear well below the region of magnetic latitudes represented by the traditional auroral oval. This highlights the contributions of citizen scientists dating back hundreds of years, and the importance of reassessing historical reports of rare auroral luminosities for a full understanding of the range of solar activity over millennia.

Both General Relativistic (GR) precession and the Lidov-Kozai mechanism, separately, are known to play an important role in the orbital evolution of solar system bodies. Previous works have studied these two mechanisms independently in great detail. However, both these phenomena occurring at the same time in real solar system bodies have rarely been explored. In this work, we find a continuum connecting the GR precession dominant and Lidov-Kozai like mechanism dominant regimes, i.e. an intermediate regime where the competing effects of GR precession and Lidov-Kozai like oscillations co-exist simultaneously. We find some real examples in the solar system in this intermediate regime. Moreover we identify a rare example amongst them, comet 96P/Machholz 1, which shows significant changes in the rates of GR precession (an order of magnitude higher than Mercury's GR precession rate) due to sungrazing and sun colliding phases induced by Lidov-Kozai like oscillations. This comet's combination of orbital elements and initial conditions (at the present epoch) favour this measurable rapid change in GR precession (at some points peaking up to 60 times Mercury's GR precession rate) along with prograde-retrograde inclination flip (due to Lidov-Kozai like oscillations). Similar tests are performed for hundreds of bodies lying in the moderately low perihelion distance and moderately low semi-major axis phase space in the solar system, the present lowest perihelion distance asteroid 322P/SOHO 1, and further examples connected with 96P/Machholz 1 namely, the Marsden and Kracht families of sungrazing comets plus low perihelion meteoroid streams like Daytime Arietids (ARI) and Southern Delta Aquariids (SDA).

As part of the EURONEAR project, almost 70,000 mosaic Suprime-Cam images taken between 1999 and 2013 were data mined for about 9,800 near Earth asteroids (NEAs) known by 2013 May. Using our PRECOVERY server and the "Find Subaru CCD" tool, we scrutinized 4,186 candidate CCD images possibly holding 518 NEAs. We found 113 NEAs as faint as V<25 magnitude, their positions being measured in 589 images using Astrometrica, then reported to the Minor Planet Center. Among them, 18 objects represent encounters of previously single opposition NEAs, their orbital arcs being extended by up to 10 years. In the second part of this work we searched for unknown NEAs in 78 sequences (780 CCD fields) of 4-5 mosaic images selected from the same Suprime-Cam archive and totaling 16.6 sq.deg, with the aim to assess the faint NEA distribution observable with an 8-m class survey. A total of 2,018 moving objects were measured, from which we identified 18 better NEA candidates. Using the R_c filter in good weather conditions, mostly dark time and sky directions slightly biased towards the ecliptic, at least one NEA could be discovered in every 1 sq.deg surveyed.

No firm evidence has existed that the ancient Maya civilization recorded specific occurrences of meteor showers or outbursts in the corpus of Maya hieroglyphic inscriptions. In fact, there has been no evidence of any pre-Hispanic civilization in the Western Hemisphere recording any observations of any meteor showers on any specific dates.The authors numerically integrated meteoroid-sized particles released by Comet Halley as early as 1404 BC to identify years within the Maya Classic Period, AD 250-909, when Eta Aquariid outbursts might have occurred. Outbursts determined by computer model were then compared to specific events in the Maya record to see if any correlation existed between the date of the event and the date of the outburst. The model was validated by successfully explaining several outbursts around the same epoch in the Chinese record. Some outbursts observed by the Maya were due to recent revolutions of Comet Halley, within a few centuries, and some to resonant behavior in older Halley trails, of the order of a thousand years. Examples were found of several different Jovian mean motion resonances as well as the 1:3 Saturnian resonance that have controlled the dynamical evolution of meteoroids in apparently observed outbursts.

A. Sekhar (1, 2), D. J. Asher (2), J. Vaubaillon (3), M. Hajduková (4), J. Tóth (5), R. Rudawska (6), R. Soja (7) (1) Centre for Earth Evolution and Dynamics, University of Oslo, Norway (aswin.sekhar@geo.uio.no), (2) Armagh Observatory, United Kingdom (3) IMCCE, Paris Observatory, France (4) Astronomical Institute, Slovak Academy of Sciences, Slovakia (5) Comenius University, Slovakia (6) ESA/ESTEC, Netherlands (7) University of Stuttgart, Germany

A. Sekhar (1, 2), S. C. Werner (1), D. J. Asher (2), J. Vaubaillon (3), M. Hajduková (4), G. Li (5), (1) Centre for Earth Evolution and Dynamics, University of Oslo, Norway (aswin.sekhar@geo.uio.no), (2) Armagh Observatory, United Kingdom (3) IMCCE, Observatory of Paris, France (4) Astronomical Institute, Slovak Academy of Sciences, Slovakia (5) Harvard-Smithsonian Center for Astrophysics, United States of America

Mean-motion resonances play an important role in the evolution of various meteoroid streams. Previous works have studied the effects of two-body resonances in different comets and streams. These already established two-body resonances were mainly induced either by Jovian or Saturnian effects but not both at the same time. Some of these resonances have led to spectacular meteor outbursts and storms in the past. In this work, we find a new resonance mechanism involving three bodies - i.e. meteoroid particle, Jupiter and Saturn, in the Perseid meteoroid stream. Long-term three-body resonances are not very common in real small bodies in our Solar system although they can mathematically exist at many resonant sweet spots in an abstract sense in any dynamical system. This particular resonance combination in the Perseid stream is such that it is close to the ratio of 1:4:10 if the orbital periods of Perseid particle, Saturn and Jupiter are considered, respectively. These resonant Perseid meteoroids stay resonant for typically about 2 kyr. Highly compact dust trails due to this unique resonance phenomenon are present in our simulations. Some past and future years are presented where three-body resonant meteoroids of different sizes (or subject to different radiation pressures) are computed to come near the Earth. This is the first theoretical example of an active and stable three-body resonance mechanism in the realm of meteoroid streams.

Assessments of the risk posed by near-Earth objects ignore the possibility of a giant comet entering the inner solar system. Bill Napier, David Asher, Mark Bailey and Duncan Steel examine the likelihood and potential consequences of the appearance of such a centaur.

Sungrazing comets have always captured a lot of interest and curiosity among the general public as well as scientists since ancient times. The perihelion passage of comet C/2012 S1 (ISON) at the end of this year (on 2013 November 28) is an eagerly awaited event. In this work, we do a mathematical study to check whether meteoroids ejected from this comet during its journey around the Sun can produce spectacular meteor phenomena on Earth. Our calculations show that although the orbital elements of this comet are much more favourable than for most sungrazers to have its descending node near the Earth's orbit, even ejection velocities as high as 1 km s(-1) do not induce sufficient nodal dispersion to bring meteoroids to Earth intersection during present times. A similar result applies to Newton's comet C/1680 V1 which has surprisingly similar orbital elements, although it is known to be a distinct comet from C/2012 S1. Our analysis also shows that for meteoroids ejected from all known sungrazing groups during recent epochs, only the Marsden family (with required ejection velocities of some hundreds of m s(-1)) can produce meteor phenomena during present times. In a broader sense, we indicate why we do not observe visually brilliant meteor showers from frequently observed sungrazers.

Comet 1P/Halley has the unique distinction of having a very comprehensive set of observational records for almost every perihelion passage from 240 B.C. This has helped to constrain theoretical models pertaining to its orbital evolution. Many previous works have shown the active role of mean motion resonances (MMR) in the evolution of various meteoroid streams. Here, we look at how various resonances, especially the 1:6 and 2:13 MMR with Jupiter, affect comet 1P/Halley and thereby enhance the chances of meteoroid particles getting trapped in resonance, leading to meteor outbursts in some particular years. Comet Halley itself librated in the 2:13 resonance from 240 B.C. to 1700 A.D. and in the 1:6 resonance from 1404 B.C. to 690 B.C., while stream particles can survive for time scales of the order of 10,000 yr and 1,000 yr in the 1:6 and 2:13 resonances, respectively. This determines the long‐term dynamical evolution and stream structure, influencing the occurrence of Orionid outbursts. Specifically, we are able to correlate the occurrence of enhanced meteor phenomena seen between 1436–1440, 1933–1938, and 2006–2010 with the 1:6 resonance and meteor outbursts in 1916 and 1993 with the 2:13 resonance. Ancient as well as modern observational records agree with these theoretical simulations to a very good degree.

Context. The quasi-Hilda comets (QHCs), being in unstable 3:2 Jovian mean motion resonance, are considered a major cause of temporary satellite capture (TSC) by Jupiter. Though the QHCs may be escaped Hilda asteroids, their origin and nature have not yet been studied in suffi cient detail. Of particular interest are long TSCs/orbiters. Orbiters - in which at least one full revolution about the planet is completed - are rare astronomical events; only four have been known to occur in the last several decades. Every case has been associated with a QHC: 82P/Gehrels 3; 111P/Helin-Roman-Crockett; P/1996 R2 (Lagerkvist); and the possibly QHC-derived D/1993 F2 (Shoemaker-Levy 9, SL9). Aims. We focus on long TSC/orbiter events involving QHCs and Jupiter. Thus we survey the known QHCs, searching for further long TSCs/orbiters over the past century. Methods. First, we confirmed the long TSC/orbiter events of 82P, 111P, and 1996 R2 in order to test our method against previous work, applying a general N-body Newtonian code. We then used the same procedure to survey the remaining known QHCs and search for long TSC/orbiter events.

Many previous works have shown the relevance and dynamics of Jovian mean motion resonances (MMR) in various meteoroid streams. These resonant swarms are known to have produced spectacular meteor displays in the past. In this work, we investigate whether any MMR due to Saturn are feasible, and subsequently check whether such effects are strong enough to trap meteoroids so as to cause enhanced meteor phenomena on Earth. Extensive numerical simulations are done on two major meteoroid streams, which are known to exhibit exterior Jovian resonances. The roles of the 1:6 and 5:14 Jovian MMR have already been studied in the Orionids and Leonids, respectively. Now we find strong evidence of 1:3 and 8:9 Saturnian MMR in Orionids and Leonids, respectively. The presence of compact dust trails in real space due to these two Saturnian resonances is confirmed from our calculations.

We report follow-up observations of 477 program Near-Earth Asteroids (NEAs) using nine telescopes of the EURONEAR network having apertures between 0.3 and 4.2 m. Adding these NEAs to our previous results we now count 739 program NEAs followed-up by the EURONEAR network since 2006. The targets were selected using EURONEAR planning tools focusing on high priority objects. Analyzing the resulting orbital improvements suggests astrometric follow-up is most important days to weeks after discovery, with recovery at a new opposition also valuable. Additionally we observed 40 survey fields spanning three nights covering 11 sq. degrees near opposition, using the Wide Field Camera on the 2.5m Isaac Newton Telescope (INT), resulting in 104 discovered main belt asteroids (MBAs) and another 626 unknown one-night objects. These fields, plus program NEA fields from the INT and from the wide field MOSAIC II camera on the Blanco 4m telescope, generated around 12,000 observations of 2,000 minor planets (mostly MBAs) observed in 34 square degrees. We identify Near Earth Object (NEO) candidates among the unknown (single night) objects using three selection criteria. Testing these criteria on the (known) program NEAs shows the best selection methods are our epsilon-miu model which checks solar elongation and sky motion and the MPC's NEO rating tool. Our new data show that on average 0.5 NEO candidates per square degree should be observable in a 2m-class survey (in agreement with past results), while an average of 2.7 NEO candidates per square degree should be observable in a 4m-class survey (although our Blanco statistics were affected by clouds). At opposition just over 100 MBAs (1.6 unknown to every 1 known) per square degree are detectable to R=22 in a 2m survey based on the INT data, while our two best ecliptic Blanco fields away from opposition lead to 135 MBAs (2 unknown to every 1 known) to R=23.

A numerical simulation of the Oort cloud is used to explain the observed orbital distributions and numbers of Jupiter-family (JF) and Halley-type (HT) short-period (SP) comets. Comets are given initial orbits with perihelion distances between 5 and 36 au, and evolve under planetary, stellar and Galactic perturbations for 4.5 Gyr. This process leads to the formation of an Oort cloud (which we define as the region of semimajor axes a > 1,000 au), and to a flux of cometary bodies from the Oort cloud returning to the planetary region at the present epoch. The results are consistent with the dynamical characteristics of SP comets and other observed cometary populations: the near-parabolic flux, Centaurs, and high-eccentricity trans-Neptunian objects. To achieve this consistency with observations, the model requires that the number of comets versus initial perihelion distance is concentrated towards the outer planetary region. Moreover, the mean physical lifetime of observable comets in the inner planetary region ( q < 2.5 au) at the present epoch should be an increasing function of the comets’ initial perihelion distances. Virtually all observed HT comets and nearly half of observed JF comets come from the Oort cloud, and initially (4.5 Gyr ago) from orbits concentrated near the outer planetary region. Comets that have been in the Oort cloud also return to the Centaur (5 < q < 28 au, a < 1,000 au) and near-Neptune high-eccentricity regions. Such objects with perihelia near Neptune are hard to discover, but Centaurs with characteristics predicted by the model (e.g. large semimajor axes, above 60 au, or high inclinations, above 40°) are increasingly being found by observers. The model provides a unified picture for the origin of JF and HT comets. It predicts that the mean physical lifetime of all comets in the region q < 1.5 au is less than ∼200 revolutions.