Perihelion Distance Research Articles

Isolating the mechanisms for asteroid surface refreshing

Evidence is seen for young, fresh surfaces among Near-Earth and Main-Belt asteroids even though space-weathering timescales are shorter than the age of the surfaces. A number of mechanisms have been proposed to refresh asteroid surfaces on short timescales, such as planetary encounters, YORP spinup, thermal degradation, and collisions. Additionally, other factors such as grain size effects have been proposed to explain the existence of these “fresh-looking” spectra. To investigate the role each of these mechanisms may play, we collected a sample of visible and near-infrared spectra of 477 near-Earth and Mars Crosser asteroids with similar sizes and compositions — all with absolute magnitude H > 16 and within the S-complex and having olivine to pyroxene (ol/(ol+opx)) ratios >0.65. We taxonomically classify these objects in the Q (fresh) and S (weathered) classes. We find four trends in the Q/S ratio: (1) previous work demonstrated the Q/S ratio increases at smaller sizes down to H ≲16, but we find a sharp increase near H∼19 after which the ratio decreases monotonically. (2) in agreement with many previous studies, the Q/S ratio increases with decreasing perihelion distance, and we find it is non-zero for larger perihelia >1.2AU, (3) as a new finding our work reveals the Q/S ratio has a sharp, significant peak near ∼5° orbital inclination, and (4) we confirm previous findings that the Q/S ratio is higher for objects that have the possibility of encounter with Earth and Venus versus those that do not, however this finding cannot be distinguished from the perihelion trend. No single resurfacing mechanism can explain all of these trends, so multiple mechanisms are required. YORP spin-up scales with size, thermal degradation is dependent on perihelion, planetary encounters trend with inclination, perihelion and MOID, noting that asteroid–asteroid collisions are also dependent on inclination. It is likely that a combination of all four resurfacing mechanisms are needed to account for all observational trends.

Influence of the Yarkovsky Effect on Mean Motion Resonances of Asteroids with Small Perihelion Distances

Influence of the Yarkovsky Effect on Mean Motion Resonances of Asteroids with Small Perihelion Distances

Evidence of surface heterogeneity on active asteroid (3200) Phaethon

Thermal infrared emission and thermophysical modeling techniques are powerful tools in deciphering the surface properties of asteroids. The near-Earth asteroid (3200) Phaethon is an active asteroid with a very small perihelion distance and is likely the source of the Geminid meteor shower. Using a thermophysical model with a non-convex shape of Phaethon we interpret thermal infrared observations that span ten distinct sightings. The results yield an effective diameter of 5.4±0.1km and independent thermal inertia estimates for each sighting. We find that the thermal inertia varies across each of these sightings in a way that is stronger than the theoretical temperature-dependent expectation from radiative heat transfer within the regolith. Thus, we test whether the variation in thermal inertia can be explained by the presence of a regolith layer over bedrock, or by a spatially heterogeneous scenario. We find that a model in which Phaethon’s hemispheres have distinctly different thermophysical properties can sufficiently explain the thermal inertias determined herein. In particular, we find that a boundary is located between latitudes −30∘ and +10∘ that separates two regions: a fine-grained southern latitudes and a northern hemisphere that is dominated by coarse-grained regolith and/or a high coverage of porous boulders. We discuss the implications related to Phaethon’s activity, potential association with 2005 UD, and the upcoming DESTINY+ mission.

Surface Properties of Near-Sun Asteroids

Near-Earth asteroids (NEAs) with small perihelion distances reach subsolar temperatures of ≥1000 K. They are hypothesized to undergo “supercatastrophic” disruption, potentially caused by near-Sun processes such as thermal cracking, spin-up, meteoroid impacts, and subsurface volatile release, all of which are likely to cause surface alteration, which may change the spectral slope of the surface. We attempted to observe 35 of the 53 known near-Sun asteroids with q ≤ 0.15 au from 2017 January to 2020 March to search for trends related to near-Sun processes. We report the optical colors and spectral slopes of 22 objects that we successfully observed and the measured rotation periods for three objects. We find the distribution of colors to be overall bluer than the color distribution of NEAs, though there is a large overlap. We attribute the large scatter to unknown dynamical histories and compositions for individual objects, as well as competing surface altering processes. We also investigated potential correlations between colors and other properties (e.g., perihelion distance, Tisserand parameter, rotation period) and searched for evidence of activity. Finally, we have compiled all known physical and dynamical properties of these objects, including probabilistic source regions and dwell times with q ≤ 0.15 au.

SHINeS: Space and High-Irradiance Near-Sun Simulator

We present SHINeS, a space simulator which can be used to replicate the thermal environment in the immediate neighborhood of the Sun down to a heliocentric distance r~0.06 au. The system consists of three main parts: the solar simulator which was designed and constructed in-house, a vacuum chamber, and the probing and recording equipment needed to monitor the experimental procedures. Our motivation for building this experimental system was to study the effect of intense solar radiation on the surfaces of asteroids when their perihelion distances become smaller than the semi-major axis of the orbit of Mercury. Comparisons between observational data and recent orbit and size-frequency models of the population of near-Earth asteroids suggest that asteroids are super-catastrophically destroyed when they approach the Sun. Whereas the current models are agnostic about the disruption mechanism, SHINeS was developed to study the mechanism or mechanisms responsible. The system can, however, be used for other applications that need to study the effects of high solar radiation on other natural or artificial objects.

The Closest Past Flyby of a Known Star to the Solar System: HD 7977, UCAC4 237-008148 or WISE J072003.20-084651.2?

It is argued that the closest past flyby of a known star to the solar system was that of Scholz’s star (WISE J072003.20-084651.2). Here, we show that the distribution of distances of closest approach of this star has a median value of 0.330 pc with a 90% probability of coming within 0.317–0.345 pc of the Sun; the associated time of perihelion passage is determined to be between 78.6–81.1 kyr ago with 90% confidence, with a most likely value of 79.9 kyr. Using Gaia DR3 data and the latest planetary ephemerides, we found that UCAC4 237-008148 (RUWE = 0.927) approached even closer with a median perihelion distance of 0.259 pc and a 90% confidence interval of 0.249–0.269 pc, 1.158 Myr ago. HD 7977 might have passed 0.15 pc from the Sun 2.77 Myr ago, but it has RUWE = 2.015.

About the Nonlinearity of the Problem of Estimating the Parameters of Asteroids with Small Perihelion Distances

About the Nonlinearity of the Problem of Estimating the Parameters of Asteroids with Small Perihelion Distances

Dynamical evolution of a self-gravitating planetesimal disk in the distant trans-Neptunian region

Aims. We study the dynamical evolution of a system consisting of the giant planets and a massive planetesimal disk over the age of the Solar System. The main question addressed in this study is whether distant trans-Neptunian objects could have come about as a result of the combined action of planetary perturbations and the self-gravity of the disk. Methods. We carried out a series of full N-body numerical simulations of gravitational interactions between the giant planets and a massive outer disk of planetesimals. Results. Our simulations show that the collective gravity of the giant planets and massive planetesimals produces distant trans-Neptunian objects across a wide range of the initial disk mass. The majority of objects that survive up through the age of the Solar System have perihelion distances of q > 40 au. In this region, there is a tendency toward a slow decrease in eccentricities and an increase in perihelion distances for objects with semimajor axes a > 150 au. Secular resonances between distant planetesimals play a major role in increasing their perihelion distances. This explains the origin of Sedna-type objects. In our integrations for the age of the Solar System, we registered times with both high and low clustering of longitudes of perihelion and arguments of perihelion for objects with q > 40 au, a > 150 au. The resulting distribution of inclinations in our model and the observed distribution of inclinations for distant trans-Neptunian objects have similar average values of around 20°. Conclusions. Distant trans-Neptunian objects are a natural consequence in the models that include migrating giant planets and a self-gravitating planetesimal disk.

Approach of the Hyades star cluster to the Solar system

ABSTRACT We present the results of calculations of the motion of the Hyades open cluster in the gravitational field of the Galaxy in the recent past. Our calculations show that the recent close passage of Hyades by the Solar system could cause a noticeable shift of the perihelion distances q of comets. The shift is negligible from q = 3 au to 2.6 au for the semimajor axes a = 14 210 au, but for a = 40 000 au, the perihelion could change from q = 35 au to 34 au, and much more for distant orbits. This could result in the detection of new comets, and drive the migration of comets from the outer region of the Solar system towards the orbit of Neptune. The effect can be enhanced by the simultaneous passage of several stars. For example, if several stars approached the Sun simultaneously in the time interval from −1.5 to −1.0 Myr, the effect may be amplified up to ten times.

Hydrogen emission from meteors and meteorites: mapping traces of H2O molecules and organic compounds in small Solar system bodies

ABSTRACT The hydrogen emission from meteors is assumed to originate mainly from the meteoroid composition, making it a potential tracer of H2O molecules and organic compounds. H α line was previously detected in individual fireballs, but its variation in a larger meteor data set and dependence on the dynamical origin and physical properties have not yet been studied. Here, we investigate the relative intensity of H α within 304 meteor spectra observed by the AMOS (All-sky Meteor Orbit System) network. We demonstrate that H α emission is favoured in faster meteors (vi > > 30 km s−1) which form the high-temperature spectral component. H α was found to be a characteristic spectral feature of cometary meteoroids with ∼92 per cent of all meteoroids with detected H α originating from Halley-type and long-period orbits. Our results suggest that hydrogen is being depleted from meteoroids with lower perihelion distances (q < 0.4 au). No asteroidal meteoroids with detected H emission were found. However, using spectral data from simulated ablation of different meteorite types, we show that H emission from asteroidal materials can occur, and apparently correlates with their water and organic matter content. Strongest H emission was detected from carbonaceous chondrites (CM and CV) and achondrites (ureilite and aubrite), while it was lacking in most ordinary chondrites. The detection of H α in asteroidal meteoroids could be used to identify meteoroids of carbonaceous or achondritic composition. Overall, our results suggest that H α emission correlates with the emission of other volatiles (Na and CN) and presents a suitable tracer of water and organic matter in meteoroids.

The meteoroid stream of comet 109P/Swift-Tuttle, Perseids, and further related meteor showers

The meteoroid stream of comet 109P/Swift-Tuttle, the well-known parent body of the Perseids, #7, is studied. The meteoroids released from the comet’s surface more than about 20kyr ago evolved to orbits similar to the mean orbits of 49 Andromedids, #549, and, possibly, also of the o-Aurigids, #696. These showers are similar to the Perseids and can be regarded as Perseid sub-structures. Interestingly, the modeled, as well as the real, o-Aurigids have a smaller perihelion distance. If they are regarded as a sub-structure of the Perseids, then we can speak about the bimodal structure of this major shower. Some meteoroids of the 109P’s stream, which could evolve over a longer period than about 40kyr, moved into the orbits on which they approach the Earth from the southern sky. They constitute a further shower related to 109P, the o-Hydrids, #569. We found an indication that the January β-Craterids, #582, moving in orbits similar to the o-Hydrids, could also be related to the comet. The radiant areas of the Perseids, 49 Andromedids and o-Aurigids are symmetrical to the radiant areas of the o-Hydrids and January β-Craterids in respect to the apex of the Earth’s heliocentric motion.

The Transformation of Centaurs into Jupiter-family Comets

Centaurs are an ephemeral class of objects that can evolve into Jupiter-family comets (or JFCs) due to gravitational perturbations from the giant planets. In this work, we use numerical integration of massless test particles in the six-body problem (the Sun, four giant planets, and a test particle) to study the transformation of Centaurs into JFCs. We find that Centaurs can transform into JFCs via a rapid, continuous drop in perihelion or aphelion distance to a value below 5.2 au or 7 au, respectively, typically within 5 yr from the start of the drop. We call these JFC perihelion drops and JFC aphelion drops, respectively. These drops are correlated with close approaches to Jupiter. For such perihelion and aphelion drops, the maximum possible fractional change in the associated perihelion or aphelion distance increases with decreasing close-approach distance to Jupiter. A perihelion barrier may exist at 6.3 au. If so, then it must be crossed from above in order for a Centaur to transform into a JFC due to a single close approach to Jupiter. Currently, 93 (or 11%) of the known Centaurs have a perihelion distance, q, below 6.3 au. If the inclination of the orbit of the Centaur to the ecliptic plane is above 10.°2, then orbits with q > 6.3 au and 2 < T J < 3 can exist, where T J is the Tisserand parameter with respect to Jupiter. Small bodies in such orbits could be classified as either Centaurs or JFCs.

К вопросу о нелинейности задачи оценивания орбитальных параметров астероидов с малыми перигелийными расстояниями

The paper presents the results of determining the nonlinearity degree of the problem of estimating the initial orbital parameters of asteroids with small perihelion distances. The values of the nonlinearity index χ were obtained for 53 asteroids known as of September 2021. It allowed to evaluate the nonlinearity as weak, medium or strong. The calculation of the parameter is based on the computation and comparison of the objective function values of the least squares problem (LS) at the vertexes of the confidence ellipsoid. The study showed that for most asteroids (46 objects) the nonlinearity is weak, for six it is moderate, and for one object the nonlinearity is defined as strong. If the nonlinearity is moderate or strong, it is recommended to use non-linear methods for constructing the initial region to obtain the most adequate prediction of the asteroids motion. For asteroids with different nonlinearity degrees, the initial probabilistic regions are constructed using the linear method and the method of perturbed observations. For four asteroids, the evolution of the linear and nonlinear initial regions was traced, and a comparative analysis of their behavior with time was carried out.

Влияние эффекта Ярковского на орбитальные резонансы астероидов с малыми перигелийными расстояниями

The paper presents the study results of the Yarkovsky effect influence on the resonant characteristics of asteroids with small perihelion distances. Out of 52 studied objects, 27 asteroids were identified that move in the vicinity of stable and unstable low-order mean motion resonances with major planets. The evolution of the asteroids orbits is constructed with and without the Yarkovsky effect, and the behavior of the resonance characteristics in both cases is analyzed. The effect was taken into account by including the perturbation from the transversal acceleration A2, the values of which for the presented objects were obtained earlier by the authors of this work. It is shown that the Yarkovsky effect influence on stable resonances is insignificant and leads to small changes in the libration amplitude of the resonance characteristics. The stability of the resonance is preserved. With unstable resonant interaction, the number of passages through the exact commensurability changes, and for some asteroids the resonance becomes more stable.

Determination of the Yarkovsky Effect Parameter for Asteroids with Small Perihelion Distances

Determination of the Yarkovsky Effect Parameter for Asteroids with Small Perihelion Distances

The Stability Boundary of the Distant Scattered Disk

Abstract The distant scattered disk is a vast population of trans-Neptunian minor bodies that orbit the Sun on highly elongated, long-period orbits. The orbital stability of scattered-disk objects (SDOs) is primarily controlled by a single parameter—their perihelion distance. While the existence of a perihelion boundary that separates chaotic and regular motion of long-period orbits is well established through numerical experiments, its theoretical basis as well as its semimajor axis dependence remain poorly understood. In this work, we outline an analytical model for the dynamics of distant trans-Neptunian objects and show that the orbital architecture of the scattered disk is shaped by an infinite chain of exterior 2:j resonances with Neptune. The widths of these resonances increase as the perihelion distance approaches Neptune’s semimajor axis, and their overlap drives chaotic motion. Within the context of this theoretical picture, we derive an analytic criterion for instability of long-period orbits, and demonstrate that rapid dynamical chaos ensues when the perihelion drops below a critical value, given by q crit = a N ln ( ( 24 2 / 5 ) ( m N / M ⊙ ) a / a N 5 / 2 ) 1 / 2 . This expression constitutes an analytic boundary between the “detached” and actively “scattering” subpopulations of distant trans-Neptunian minor bodies. Additionally, we find that within the stochastic layer, the Lyapunov time of SDOs approaches the orbital period, and show that the semimajor axis diffusion coefficient is approximated by  a ∼ ( 8 / ( 5 π ) ) ( m N / M ⊙ )  M ⊙ a N exp ​ − q / a N 2 / 2 . We confirm our results with direct N-body simulations and highlight the connections between scattered-disk dynamics and the Chirikov Standard Map. Implications of our results for the long-term evolution of minor bodies in the distant solar system are discussed.

New constraints on the physical properties and dynamical history of Centaur 174P/Echeclus

ABSTRACT Since 2005 December, recurrent outbursts have been observed for Centaur 174/P Echeclus, confirming it is an active object. Thanks to a large number of photometric data obtained between 2001 April and 2019 December, we were able to compute a shape model of this object. We obtain a sidereal rotation period P = 26.785178 ± 10−6 h and six equally probable pole solutions, each with a large obliquity of the rotational axis (50° or more). We also find the object significantly elongated, with a semi-major axial ratio a/b = 1.32 (and b/c ∼ 1.1 but this second ratio is poorly constrained by the photometric data). Additionally, we present a detailed analysis of the dust emission from the 2016 outburst. Different colour maps are presented that reveal a change in dust colour, which becomes bluer with increasing cometocentric distance. A blue ring-like structure around the nucleus clearly visible in the images obtained on October 4 in the V-R spectral interval points out that the innermost near nucleus region is considerably redder than the surrounding coma. Different jets are also apparent, the main one being oriented southward. A detailed dynamical study is done to investigate past and future orbital elements. These elements appear stable in the period ≈1200 CE to ≈2900 CE. For a period of 12 000 yr the main conclusion is that Echeclus’ perihelion distance was greater than about 4 au, preventing it from following a typical cometary activity like a short-period comet. Close encounters with giant planets nevertheless prevent any study of orbital elements on longer timescale.

No Activity among 13 Centaurs Discovered in the Pan-STARRS1 Detection Database

Abstract Centaurs are small bodies orbiting in the giant planet region that were scattered inward from their source populations beyond Neptune. Some members of the population display comet-like activity during their transition through the solar system, the source of which is not well understood. The range of heliocentric distances where the active Centaurs have been observed and their median lifetime in the region suggest that this activity is driven neither by water-ice sublimation nor entirely by supervolatiles. Here we present an observational and thermodynamical study of 13 Centaurs discovered in the Pan-STARRS1 detection database aimed at identifying and characterizing active objects beyond the orbit of Jupiter. We find no evidence of activity associated with any of our targets at the time of their observations with the Gemini North telescope in 2017 and 2018, or in archival data from 2013 to 2019. Upper limits on the possible volatile and dust production rates from our targets are 1–2 orders of magnitude lower than production rates in some known comets and are in agreement with values measured for other inactive Centaurs. Our numerical integrations show that the orbits of six of our targets evolved interior to r ∼ 15 au over the past 100,000 yr, where several possible processes could trigger sublimation and outgassing, but their apparent inactivity indicates that either their dust production is below our detection limit or the objects are dormant. Only one Centaur in our sample—2014 PQ70—experienced a sudden decrease in semimajor axis and perihelion distance attributed to the onset of activity for some previously known inactive Centaurs, and therefore it is the most likely candidate for any future outburst. This object should be a target of high interest for any further observational monitoring.

Disintegration of Long-period Comet C/2019 Y4 (ATLAS). I. Hubble Space Telescope Observations

Abstract The near-Sun comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a three-day Hubble Space Telescope campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B and showed signs of significant mass loss and changes in size distribution throughout the three-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of subsurface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before its disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of q = 0.25 au. We speculate that Comet ATLAS is derived from the ice-rich interior of a nonuniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, nonuniform interiors that can protect ices against intense solar heating.

Minimum perihelion distances and associated dwell times for near-Earth asteroids

ABSTRACT The observed near-Earth asteroid (NEA) population contains very few objects with small perihelion distances, say, $q \lesssim 0.2\, \mathrm{au}$. NEAs that currently have orbits with larger q might be hiding a past evolution during which they have approached closer to the Sun. We present a probabilistic assessment of the minimum q that an asteroid has reached during its orbital history. At the same time, we offer an estimate of the dwell time, that is, the time q has been in a specific range. We have re-analysed orbital integrations of test asteroids from the moment they enter the near-Earth region until they either collide with a major body or are thrown out from the inner Solar system. We considered a total disruption of asteroids at certain q as a function of absolute magnitude (H). We calculated the probability that an asteroid with given orbital elements and H has reached a q smaller than a given threshold value and its respective dwell time in that range. We have constructed a look-up table that can be used to study the past orbital and thermal evolution of asteroids as well as meteorite falls and their possible parent bodies. An application to 25 meteorite falls shows that carbonaceous chondrites typically have short dwell times at small q, whereas for ordinary chondrites it ranges from $10\, 000$ to $500\, 000$ yr. A dearth of meteorite falls with long dwell times and small minimum q supports a supercatastrophic disruption of asteroids at small q.