Earth-like Orbit Research Articles

HD 28185 revisited: an outer planet, instead of a brown dwarf, on a Saturn-like orbit

ABSTRACT As exoplanet surveys reach ever-higher sensitivities and durations, planets analogous to the Solar system giant planets are increasingly within reach. HD 28185 is a Sun-like star known to host a $m\sin i=6~M_\mathrm{ J}$ planet on an Earth-like orbit; more recently, a brown dwarf with a more distant orbit has been claimed. In this work, we present a comprehensive re-analysis of the HD 28185 system, based on 22 yr of radial velocity (RV) observations and precision Hipparcos–Gaia astrometry. We confirm the previous characterization of HD 28185 b as a temperate giant planet, with its $385.92^{+0.06}_{-0.07}$ d orbital period giving it an Earth-like incident flux. In contrast, we substantially revise the parameters of HD 28185 c; with a new mass of $m=6.0\pm 0.6~M_\mathrm{ J}$, we reclassify this companion as a super-Jovian planet. HD 28185 c has an orbital period of $24.9^{+1.3}_{-1.1}$ yr, a semimajor axis of $8.50^{+0.29}_{-0.26}$ au, and a modest eccentricity of $0.15\pm 0.04$, resulting in one of the most Saturn-like orbits of any known exoplanet. HD 28185 c lies at the current intersection of detection limits for RVs and direct imaging, and highlights how the discovery of giant planets at $\approx$10 au separations is becoming increasingly routine.

Rotation state, colors, and albedo of the mission-accessible tiny near-Earth asteroid 2001 QJ142

Context. Characterizing mission-accessible asteroids using telescopic observations is fundamental for target-selection and planning for spacecraft missions. Near-Earth asteroids on Earth-like orbits are of particular importance for applications such as asteroid mining. Aims. 2001 QJ142 is a tiny (D ≤ 100 m) near-Earth asteroid on an Earth-like orbit with a semimajor axis of 1.06 au, orbital eccentricity of 0.09, and orbital inclination of 3.10°. We aim to characterize 2001 QJ142 using ground-based observations with future spacecraft missions in mind. Methods. We performed visible multicolor photometry of 2001 QJ142 using the TriCCS on the Seimei 3.8 m telescope in February 2024. We also revisited the images taken with the Suprime-Cam on the Subaru 8.2 m telescope in August 2012. Results. Visible color indices of 2001 QJ142 indicate that 2001 QJ142 is a C- or X-complex asteroid. We detect a possible fast rotation with a period of about 10 min, which is consistent with a previous report. The geometric albedo of 2001 QJ142 is derived to be about 0.3 from a slope of its photometric phase curve, which is consistent with an albedo derived from thermal observations with updated physical quantities. A straightforward interpretation is that 2001 QJ142 is either an E- or M-type asteroid, although surface properties of such tiny fast-rotating asteroids are not well understood. Conclusions. We infer that 2001 QJ142 is a fast-rotating mission-accessible E- or M-type near-Earth asteroid. More characterizations of tiny asteroids are particularly important for a deeper understanding of their nature.

When the horseshoe fits: Characterizing 2023 FY3 with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope

Context. The Arjuna asteroid belt is loosely defined as a diverse group of small asteroids that follow dynamically cold, Earth-like orbits. Most of them are not actively engaged in resonant, co-orbital behavior with Earth. Some of them experience temporary but recurrent horseshoe episodes. Objects in horseshoe paths tend to approach Earth at a low velocity, leading to captures as Earth’s temporary satellites or mini-moons. Four such objects have already been identified: 1991 VG, 2006 RH120, 2020 CD3, and 2022 NX1. Here, we focus on 2023 FY3, a recent finding, the trajectory of which might have a co-orbital status and perhaps lead to temporary captures. Aims. We want to determine the physical properties of 2023 FY3 and explore its dynamical evolution. Methods. We carried out an observational study of 2023 FY3 using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias, to derive its spectral class, and time-series photometry obtained with QHY411M cameras and two units of the Two-meter Twin Telescope to investigate its rotational state. N-body simulations were also performed to examine its possible resonant behavior. Results. The visible reflectance spectrum of 2023 FY3 is consistent with that of an S-type asteroid; its light curve gives a rotation period of 9.3±0.6 min, with an amplitude of 0.48±0.13 mag. We confirm that 2023 FY3 roams the edge of Earth’s co-orbital space. Conclusions. Arjuna 2023 FY3, an S-type asteroid and fast rotator, currently exhibits horseshoe-like resonant behavior and in the past experienced mini-moon engagements of the temporarily captured flyby type that may repeat in the future. The spectral type result further confirms that mini-moons are a diverse population in terms of surface composition.

The Near-Earth Object Surveyor Mission

The Near-Earth Object (NEO) Surveyor mission is a NASA Observatory designed to discover and characterize asteroids and comets. The mission’s primary objective is to find the majority of objects large enough to cause severe regional impact damage (>140 m in effective spherical diameter) within its 5 yr baseline survey. Operating at the Sun–Earth L1 Lagrange point, the mission will survey to within 45° of the Sun in an effort to find objects in the most Earth-like orbits. The survey cadence is optimized to provide observational arcs long enough to distinguish near-Earth objects from more distant small bodies that cannot pose an impact hazard reliably. Over the course of its survey, NEO Surveyor will discover ∼200,000–300,000 new NEOs down to sizes as small as ∼10 m and thousands of comets, significantly improving our understanding of the probability of an Earth impact over the next century.

Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rare orbital pathways

Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasi-satellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on centennial timescales, maintaining this dynamics over megayears. The similarity of its reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of particles launched from different locations on the lunar surface with a range of ejection velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s orbit. The most favored conditions are launch velocities slightly above the escape velocity from the trailing lunar hemisphere.

Mini-moons from horseshoes: A physical characterization of 2022 NX1 with OSIRIS at the 10.4 m Gran Telescopio Canarias

Context. The near-Earth orbital space is shared by natural objects and space debris that can be temporarily captured in geocentric orbits. Short-term natural satellites are often called mini-moons. Reflectance spectroscopy can determine the true nature of transient satellites because the spectral signatures of spacecraft materials and near-Earth asteroids (NEAs) are different. The recently discovered object 2022 NX1 follows an Earth-like orbit that turns it into a recurrent but ephemeral Earth companion. It has been suggested that 2022 NX1 could have an artificial origin or be lunar ejecta. Aims. Here, we use reflectance spectroscopy and N-body simulations to determine the nature and actual origin of 2022 NX1. Methods. We carried out an observational study of 2022 NX1, using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias, to derive its spectral class. N-body simulations were also performed to investigate how it reached NEA space. Results. The reflectance spectrum of 2022 NX1 is neither compatible with an artificial origin nor lunar ejecta; it is also different from the V type of the only other mini-moon with available spectroscopy, 2020 CD3. The visible spectrum of 2022 NX1 is consistent with that of a K-type asteroid, although it could also be classified as an Xk type. Considering typical values of the similar albedo of both K-type and Xk-type asteroids and its absolute magnitude, 2022 NX1 may have a size range of 5 to 15 m. We confirm that 2022 NX1 inhabits the rim of Earth’s co-orbital space, the 1:1 mean-motion resonance, and experiences recurrent co-orbital engagements of the horseshoe-type and mini-moon events. Conclusions. The discovery of 2022 NX1 confirms that mini-moons can be larger than a few meters and also that they belong to a heterogeneous population in terms of surface composition.

Low-Energy Transfer Design of Heliocentric Formation Using Lunar Swingby on the Example of LISA

Space-based gravitational wave (GW) detection at low frequencies is of great scientific significance and has received extensive attention in recent years. This work designs and optimizes the low-energy transfer of the heliocentric formation of GW detectors, which starts from a geosynchronous transfer orbit and targets an Earth-like orbit. Based on the example of the Laser Interferometer Space Antenna (LISA), the transfer is first designed in two-body dynamical models and then refined in simplified high-fidelity dynamical models that only consider the major orbital perturbations evaluated here. The main contributions of this work are to present an adaptive model continuation technique and to exploit the lunar swingby technique to reduce the problem-solving difficulty and velocity increment of orbital transfer, respectively. The adaptive model continuation technique fully reveals the effect of perturbations and rapidly iterates the solutions to the simplified models. The simulation results show that the lunar swingby does reduce the energy needed to escape the Earth’s sphere of influence. It is found that the gravitation of the Earth–Moon system has a significant contribution to reducing the velocity increment. The solution of low-energy transfer in the simplified models is that the duration is 360.6615 days and the total velocity increment is 0.8468 km/s.

Neural representation of a time optimal, constant acceleration rendezvous

We train two neural models to represent, respectively, the optimal policy (i.e. the optimal thrust direction) and the value function (i.e. the time of flight) for a time optimal, constant acceleration, low-thrust rendezvous. In both cases we develop and make use of the data augmentation technique we call backward generation of optimal examples. We are thus able to produce and work with large dataset and to fully exploit the benefit of employing a deep learning framework. We achieve, in all cases, accuracies resulting in successful rendezvous (simulated following the learned optimal policy) and time of flight predictions (using the learned value function). We find that residuals as small as a few m/s, thus well within the possibility of a spacecraft navigation ΔV budget, are achievable for the velocity at rendezvous. We also find that, on average, the absolute error to predict the optimal time of flight to rendezvous from any orbit in the asteroid belt to an Earth-like orbit is small (less than 4%) and thus also of interest for practical uses, for example, during preliminary mission design phases.

How to Become a Mini-moon: Some Hints from 2022 NX1

Low-velocity encounters between our planet and any near-Earth object (NEO) in an Earth-like orbit may induce its temporary capture as a mini-moon. Such mini-moon episodes could lead the NEO to complete one or more revolutions around Earth when gravitationally bound, a temporarily-captured orbiter, like in the cases of 2006 RH120 and 2020 CD3; sometimes not even one revolution is completed, a temporarily-captured flyby, like in the case of 1991 VG. Asteroid 2022 NX1 experienced a temporarily-captured flyby in 1981, has had another one in 2022, and will become a temporarily-captured orbiter in 2051. This object occupies the edge of Earth’s co-orbital space and sometimes it approaches us following a horseshoe path.

Radar Observations of Old Centaur Rocket from 1966

Abstract We report the results of radar observations of a near-Earth object discovered on 17 September 2020, with the Pan-STARRS 1 telescope at the Haleakala Observatory in Hawaii. Initially, this object was considered an asteroid and even received the standard provisional designation 2020 SO by the Minor Planet Center. However, its Earth-like orbit and low relative velocity suggested that the object may be of artificial origin, being the Centaur rocket booster from the Surveyor 2 mission that was launched to the Moon on 20 September 1966. In the period from November 2020 to March 2021, this object approached the Earth twice within one lunar distance of the Earth. Radar observations were conducted on 30 November in bistatic mode with the 70-m Goldstone Solar System Radar DSS-14 and 32-m radio telescope RT-32 at the Svetloe Observatory, while the object was in the visibility window of two antennas at about 200 thousand km from the Earth. The main goal of the study was to determine the physical properties of this object using radar astronomy to clarify its origin.

Exploring the dynamical evolution of minimoon 2020 CD3 in a circular restricted three-body problem framework

Asteroid 2020 CD3 was one of the most recently captured natural objects that became Earth’s transient satellite or minimoon. The asteroid is very likely residing in an Earth-like orbit (ELO) with 1:1 mean-motion resonance and occasionally captured by the Earth. In this study, the dynamical evolution of this object is conducted in a framework of Circular Restricted Three-Body Problem (CR3BP). Five thousand test objects are generated by distributing the orbital space with a random uniform scheme around the object’s nominal values comprising ten sigma-uncertainties of the orbital parameters and four Metonic cycles of the epoch. This numerical task has run for 1000 years with the IAS15 integrator known for its adaptive integration and high accuracy for millions of years of simulation. We found that almost all of the test particles are lying in a boundary region, hence follow chaotic and quasi-periodic trajectories and have become minimoon with an average of 15-16 times. The duration of captures of more than a year is very rare. Interestingly, there seems a preferred recapture time at ∼ 30 years. Most of them still stay in the ELO region, although a few have either been hit the Earth or expelled into vast space.

On the orbital evolution of meteoroid 2020 CD3, a temporarily captured orbiter of the Earth–Moon system

ABSTRACT Any near-Earth object (NEO) following an Earth-like orbit may eventually be captured by Earth’s gravity during low-velocity encounters. This theoretical possibility was first attested during the fly-by of 1991 VG in 1991–1992 with the confirmation of a brief capture episode – for about a month in February 1992. Further evidence was obtained when 2006 RH120 was temporarily captured into a geocentric orbit from July 2006 to July 2007. Here, we perform a numerical assessment of the orbital evolution of 2020 CD3, a small NEO found recently that could be the third instance of a meteoroid temporarily captured by Earth’s gravity. We confirm that 2020 CD3 is currently following a geocentric trajectory although it will escape into a heliocentric path by early May 2020. Our calculations indicate that it was captured by the Earth in 2016$_{-4}^{+2}$, median and 16th and 84th percentiles. This episode is longer (4$_{-2}^{+4}$ yr) than that of 2006 RH120. Prior to its capture as a minimoon, 2020 CD3 was probably a NEO of the Aten type, but an Apollo type cannot be excluded; in both cases, the orbit was very Earth-like, with low eccentricity and low inclination, typical of an Arjuna-type meteoroid. A few clone orbits remained geocentric for nearly a century, opening the door to the existence of yet-to-be-detected minimoons that are relatively stable for time-scales comparable to those of unbound quasi-satellites such as (469219) Kamo‘oalewa 2016 HO3. In addition, nearly 10 per cent of the experiments led to brief moon–moon episodes in which the value of the selenocentric energy of 2020 CD3 became negative.

Goldstone Radar Observations of Horseshoe-orbiting Near-Earth Asteroid 2013 BS45, a Potential Mission Target

Abstract We report radar observations of near-Earth asteroid 2013 BS45 obtained during the 2013 apparition. This object is in a resonant, Earth-like orbit, and it is a backup target for NASA’s NEA Scout mission. 2013 BS45 belongs to the Arjuna orbital domain, which currently has ∼20 discovered representatives. These objects tend to be small and difficult to characterize, and 2013 BS45 is only the third Arjuna object observed with radar to date. We observed 2013 BS45 on three days at Goldstone (8560 MHz, 3.5 cm) between 2013 February 10 and 13. The closest approach occurred on February 12 at a distance of 0.0126 au. We obtained relatively weak echo power spectra and ranging data at resolutions up to 0.125 μs (18.75 m px−1). The Doppler broadening of the echo power spectra strongly suggests an upper bound on the rotation period of 1.9 minutes. The radar data, in combination with an assumption that the asteroid’s radar albedo is no higher than that of metallic NEA 1986 DA, constrain the equivalent diameter to 15 m ≤ D ≤ 38 m. The circular polarization ratio is 0.21 ± 0.06, which implies a near-surface that is relatively smooth on decimeter spatial scales. We bounded the OC radar albedo to η OC ≥ 0.09 and the optical albedo remains relatively unconstrained at 0.05 ≤ p V ≤ 0.35. The Yarkovsky acceleration has not been detected but, due to the object’s rapid rotation, would be dominated by a seasonal component whose direction and magnitude depends on the currently unknown pole orientation and thermal inertia.

Availability and delta-v requirements for delivering water extracted from near-Earth objects to cis-lunar space

We have calculated the number of water-bearing near-Earth objects as a function of return-trip delta-v (ΔvRT). First, we combined a model of the near-Earth object's (NEO) orbit and size-frequency distribution with other measurements of their provenance, and the taxonomic distribution of asteroids in the NEO's main belt sources, to calculate the taxonomic distribution of NEOs as a function of their orbital elements and size. Our calculations are in agreement with recent measurements of the ratio of C- and S-complex bodies within the population of small NEOs. Then we developed a simplified mission model to calculate an upper limit on ΔvRT for a mission from an NEO to distant retrograde lunar orbit (DRLO) in cis-lunar space. Combining the first two steps allowed us to develop a synthetic population of low ΔvRT NEOs that includes their taxonomic distribution. Finally, we used measurements of the water-bearing content of the taxonomic classes based on their assumed meteorite associations to calculate the number of water-bearing NEOs as a function of ΔvRT. We find that there are likely thousands of H2O-rich NEOs larger than about 5 m diameter with ΔvRT≲3kms−1 and the number of objects increases as ΔvRT3. The rapid increase in the number of objects with ΔvRT suggests that in-situ resource utilization (ISRU) of asteroid-derived water can expand quickly throughout the solar system. NEOs with ΔvRT≲3kms−1 tend to be on Earth-like orbits with semi-major axes a∼1au, eccentricities e≳0, and inclinations i≳0∘. The small, dark, low ΔvRT NEOs are difficult or impossible to detect with Earth-based telescopes because many orbit the Sun interior to Earth's orbit and others have such long synodic periods that they are rarely visible.

Dynamical evolution of near-Earth asteroid 1991 VG

The discovery of 1991 VG on 1991 November 6 attracted an unprecedented amount of attention as it was the first near-Earth object (NEO) ever found on an Earth-like orbit. At that time, it was considered by some as the first representative of a new dynamical class of asteroids, while others argued that an artificial (terrestrial or extraterrestrial) origin was more likely. Over a quarter of a century later, this peculiar NEO has been recently recovered and the new data may help in confirming or ruling out early theories about its origin. Here, we use the latest data to perform an independent assessment of its current dynamical status and short-term orbital evolution. Extensive N-body simulations show that its orbit is chaotic on time-scales longer than a few decades. We confirm that 1991 VG was briefly captured by Earth's gravity as a minimoon during its previous fly-by in 1991-1992; although it has been a recurrent transient co-orbital of the horseshoe type in the past and it will return as such in the future, it is not a present-day co-orbital companion of the Earth. A realistic NEO orbital model predicts that objects like 1991 VG must exist and, consistently, we have found three other NEOs --2001 GP2, 2008 UA202 and 2014 WA366-- which are dynamically similar to 1991 VG. All this evidence confirms that there is no compelling reason to believe that 1991 VG is not natural.

Planetary Imaging Concept Testbed Using a Recoverable Experiment–Coronagraph (PICTURE C)

An exoplanet mission based on a high-altitude balloon is a next logical step in humanity’s quest to explore Earthlike planets in Earthlike orbits orbiting Sunlike stars. The mission described here is capable of spectrally imaging debris disks and exozodiacal light around a number of stars spanning a range of infrared excesses, stellar types, and ages. The mission is designed to characterize the background near those stars, to study the disks themselves, and to look for planets in those systems. The background light scattered and emitted from the disk is a key uncertainty in the mission design of any exoplanet direct imaging mission, thus, its characterization is critically important for future imaging of exoplanets.

Infrequent visitors of the Kozai kind: the dynamical lives of 2012 FC71, 2014 EK24, 2014 QD364, and 2014 UR

Context. Asteroids with semi-major axes very close to that of a host planet can avoid node crossings when their nodal points are at perihelion and at aphelion. This layout protects the asteroids from close encounters, and eventual collisions, with the host planet. Aims. Here, we study the short-term dynamical evolution of four recently discovered near-Earth asteroids (NEAs) --2012 FC71, 2014 EK24, 2014 QD364, and 2014 UR-- that follow very Earth-like orbits. Methods. Our analysis is based on results of direct N-body calculations that use the most updated ephemerides and include perturbations from the eight major planets, the Moon, the barycentre of the Pluto-Charon system, and the three largest asteroids. Results. These four NEAs exhibit an orbital evolution unlike any other known near-Earth object (NEO). Beyond horseshoe, tadpole, or quasi-satellite trajectories, they follow co-orbital passing orbits relative to the Earth within the Kozai domain. Our calculations show that secular interactions induce librations of their relative argument of perihelion with respect to our planet but also to Venus, Mars, and Jupiter. Secular chaos is also present. The size of this transient population is probably large. Conclusions. Although some of these NEAs can remain orbitally stable for many thousands of years, their secular dynamics are substantially more complicated than commonly thought and cannot be properly described within the framework of the three-body problem alone owing to the overlapping of multiple secular resonances. Objects in this group are amongst the most atypical NEOs regarding favourable visibility windows because these are separated in time by many decades or even several centuries.

Trajectory and physical properties of near-Earth asteroid 2009 BD

AbstractWe analyze the trajectory of near-Earth asteroid 2009~BD, which is a candidate target of the NASA Asteroid Redirect Mission. The small size of 2009 BD and its Earth-like orbit pose challenges to understanding the dynamical properties of 2009 BD. In particular, nongravitational perturbations, such as solar radiation pressure and the Yarkovsky effect, are essential to match observational data and provide reliable predictions. By using Spitzer Space Telescope IRAC observations and our model for the thermophysical properties and the nongravitational forces acting on 2009 BD we obtain probabilistic derivations of the physical properties of this object. We find two physically possible solutions. The first solution shows 2009 BD as a 2.9 ± 0.3 m diameter rocky body with an extremely high albedo that is covered with regolith-like material, causing it to exhibit a low thermal inertia. The second solution suggests 2009 BD to be a 4 ± 1 m diameter asteroid with albedo 0.45 ± 0.35 that consists of a collection of individual bare rock slabs. We are unable to rule out either solution based on physical reasoning. 2009 BD is the smallest asteroid for which physical properties have been constrained, providing unique information on the physical properties of objects in the size range smaller than 10 m.

Properties and evolution of NEO families created by tidal disruption at Earth

We have calculated the coherence and detectable lifetimes of synthetic near-Earth object (NEO) families created by catastrophic disruption of a progenitor as it suffers a very close Earth approach. The closest or slowest approaches yield the most violent ‘s-class’ disruption events where the largest remaining fragment after disruption and reaccumulation retains less than 50% of the parent’s mass. The resulting fragments have a ‘string of pearls’ configuration after their reaccummulation into gravitationally bound components (Richardson, D.C., Bottke, W.F., Love, S.G. [1998]. Icarus 134, 47–76). We found that the average absolute magnitude (H) difference between the parent body and the largest fragment is ΔH∼1.0. The average slope of the absolute magnitude (H) distribution, N(H)∝10(0.55±0.04)H, for the fragments in the s-class families is steeper than the slope of the NEO population (Mainzer, A., et al. [2011]. Astrophys. J. 743, 156) in the same size range. The es remain coherent as statistically significant clusters of orbits within the NEO population for an average of τ¯c=(14.7±0.6)×103yr after disruption. The detectable lifetimes of tidally disrupted families are extremely short compared to the multi-Myr and -Gyr lifetimes of main belt families due to the chaotic dynamical environment in NEO space—they are detectable with the techniques developed by Fu et al. and Schunová et al. (Fu, H., Jedicke, R., Durda, D.D., Fevig, R., Binzel, R.P. [2005]. Icarus 178(2), 434–449 and Schunová, E., Granvik, M., Jedicke, R., Gronchi, G., Wainscoat, R., Abe, S. [2012]. Icarus 220, 1050–1063) for an average duration (τ¯det) ranging from about 2000 to about 12,000years for progenitors in the absolute magnitude (Hp) range from 20 to 13 corresponding to diameters in the range from about 0.5 to 10km respectively. The maximum absolute magnitude of a progenitor capable of producing an observable NEO family (i.e. detectable by our family finding technique) is Hp,max=20 (about 350m diameter). The short detectability lifetime explains why zero NEO families have been discovered to-date. Nonetheless, every tidal disruption event of a progenitor with diameter greater than 0.5km is capable of producing several million fragments in the 1–10m diameter range that can contribute to temporary local density enhancements of small NEOs in Earth’s vicinity. We expect that there are about 1200 objects in the steady state NEO population in this size range due to tidal disruption assuming that one 1km diameter NEO tidally disrupts at Earth every 2500years. These objects may be suitable targets for asteroid retrieval missions due to their Earth-like orbits with corresponding low v∞ which permits low-cost missions. The fragments from the tidal disruptions evolve into orbits that bring them into collision with terrestrial planets or the Sun or they may be ejected from the Solar System on hyperbolic orbits due to deep planetary encounters. The end-state for the fragments from a tidal disruption at Earth have ∼5× the collision probability with Earth compared to the background NEO population.

Trapping and dynamical evolution of interplanetary dust particles in Earth’s quasi-satellite resonance

We used numerical simulations to model the orbital evolution of interplanetary dust particles (IDPs) evolving inward past Earth’s orbit under the influence of radiation pressure, Poynting–Robertson light drag (PR drag), solar wind drag, and gravitational perturbations from the planets. A series of β values (where β is the ratio of the force from radiation pressure to that of central gravity) were used ranging from 0.0025 up to 0.02. Assuming a composition consistent with astronomical silicate and a particle density of 2.5gcm−3 these β values correspond to dust particle diameters ranging from 200μm down to 25μm. As the dust particle orbits decay past 1AU between 4% (for β=0.02, or 25μm) and 40% (for β=0.0025, or 200μm) of the population became trapped in 1:1 co-orbital resonance with Earth. In addition to traditional horseshoe type co-orbitals, we found about a quarter of the co-orbital IDPs became trapped as so-called quasi-satellites. Quasi-satellite IDPs always remain relatively near to Earth (within 0.1–0.3AU, or 10–30Hill radii, RH) and undergo two close-encounters with Earth each year. While resonant perturbations from Earth halt the decay in semi-major axis of quasi-satellite IDPs their orbital eccentricities continue to decrease under the influence of PR drag and solar wind drag, forcing the IDPs onto more Earth-like orbits. This has dramatic consequences for the relative velocity and distance of closest approach between Earth and the quasi-satellite IDPs. After 104–105years in the quasi-satellite resonance dust particles are typically less than 10RH from Earth and consistently coming within about 3RH. In the late stages of evolution, as the dust particles are escaping the 1:1 resonance, quasi-satellite IDPs can have deep close-encounters with Earth significantly below RH. Removing the effects of Earth’s gravitational acceleration reveals that encounter velocities (i.e., velocities “at infinity”) between quasi-satellite IDPs and Earth during these close-encounters are just a few hundred meters per second or slower, well below the average values of 2–4kms−1 for non-resonant Earth-crossing IDPs with similar initial orbits. These low encounter velocities lead to a factor of 10–100 increase in Earth’s gravitationally enhanced impact cross-section (σgrav) for quasi-satellite IDPs compared to similar non-resonant IDPs. The enhancement in σgrav between quasi-satellite IDPs and cometary Earth-crossing IDPs is even more pronounced, favoring accretion of quasi-satellite dust particles by a factor of 100–3000 over the cometary IDPs. This suggests that quasi-satellite dust particles may dominate the flux of large (25–200μm) IDPs entering Earth’s atmosphere. Furthermore, because quasi-satellite trapping is known to be directly correlated with the host planet’s orbital eccentricity the accretion of quasi-satellite dust likely ebbs and flows on 105year time scales synchronized with Earth’s orbital evolution.