The dynamics and evolution of simulated near-Earth asteroid families and interplanetary dust

We present a study into the dynamics and evolution of small Solar System bodies. This is the culmination of a PhD which focused on the application of N-body simulations of near-Earth asteroid and interplanetary dust clusters.

This work is split into three projects, which applied N-body simulations of 100 – 1000 particle clusters with a spread up to a maximum velocity. These represented the outcome of an asteroid breakup, with the mechanism represented by the magnitude of the initial spread of the cluster. For the parts of the work which simulated dust, Poynting-Robertson drag (PR drag) was added as an additional force, where each particle was assigned a size and corresponding drag strength.

The first project studied the evolution of synthetic NEA families. As we approach first light of the Vera C. Rubin telescope’s Legacy Survey of Space and Time, with maybe 100,000 new near-Earth asteroids (NEAs) to be discovered [1], it is important to prepare for new searches for NEA families. This project is intended as a guide, so that families and pairs can be searched for where they’re likely to stay closer together for longer. If found, these families can tell us a great deal about the dynamics, composition, and formation of asteroids [2][3]. 

A grid of clusters were integrated with different initial orbital elements and conditions. Areas of focus included initial inclination, breakup mechanism, Kozai-Lidov oscillations, and mean-motion resonances (MMRs). A power-law relationship was found in the increase in orbital dispersion of the semi-major axis, allowing an easier comparison between different initial conditions. This further led us to find the importance of eccentricity and inclination, and how it has an effect on the oscillations caused by the Kozai-Lidov effect.

The second project looked at the hypothetical breakup of an Earth co-orbital – an object in the 1:1 MMR with the Earth. The zodiacal light, or zodiacal dust, is a band of light visible at dusk or dawn when observed close to the plane of the ecliptic [4]. It is caused by the presence of interplanetary dust which scatters the light from the Sun. The zodiacal light has different components identified by spacecraft such as IRAS and COBE [5], including a broad, cometary band, and background interstellar dust. Two strong narrow asteroidal features have also been identified at 士1.4^॰ and 士10.2^॰ ecliptic latitude, as well as a broader band centred at 士10^॰[6]. There have been a number of suggestions as to the exact origin of the asteroid dust bands, most often the scattering of main-belt asteroid families falling into Jupiter resonances [7]. One major factor affecting the evolution of the dust is PR drag, which causes it to spiral into the Sun, requiring the dust to either be regularly replenished, or temporary [8].

We integrated synthetic clusters in the horseshoe, trojan, and quasi-satellite co-orbital configurations, as well as clusters at the position of real Earth co-orbitals. We studied the different factors which affect the infall time and how long dust remains within a co-orbital, along with the appearance of the dust from the Earth, based on how much light is scattered. While no features matching the zodiacal dust bands have been found, we present a quasi-satellite region which is stable for longer periods of time than expected. We also show that while a lot of dust will fall unimpeded into the Sun due to PR drag, some will get trapped in MMRs of terrestrial planets, slowing their infall rate.

The third project looks at the evolution of dust from a hypothetical impact on the Martian trojan (5261) Eureka. A large amount of dust, both interplanetary in the orbital plane of Mars and high up in the Martian atmosphere has been detected by the Juno and MAVEN (The Mars Atmosphere and Volatile Evolution) spacecraft [9][10]. Its properties and quantity cannot be explained by dust storms on Mars, as it is too high in the atmosphere, and is too spread in inclination to originate from the moons Phobos and Deimos.

The dynamics of this dust under the effects of the co-orbital resonance, PR drag, and the gravitational influence of the terrestrial planets has been studied. The minimum orbital intersection distance between the dust and Mars has been calculated, and the orbital dynamics and infall time of the dust studied. The dust seems to stay within the resonance for long periods of time, though PR drag acts quickly on the smaller objects. We again see evidence of terrestrial planet MMRs impeding the infall of the dust.  

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