[Paper Review] Dynamical Zodiacal Cloud Models Constrained by High Resolution Spectroscopy of the Zodiacal Light

С. И. Ипатов, A. Kutyrev+4 more|arXiv (Cornell University)|Aug 6, 2006

Astro and Planetary Science66 references4 citations

TL;DR

This study uses numerical integrations of dust particle orbits under gravitational, radiation pressure, Poynting-Robertson, and solar wind drag forces to model Doppler shifts in the solar Mg I λ5184 line scattered by zodiacal dust. It finds that cometary dust dominates the zodiacal cloud, with a mean eccentricity of ~0.5, and that trans-Neptunian dust also contributes significantly, consistent with WHAM spectroscopic observations.

ABSTRACT

We present simulated observations of the Doppler shifts of the solar Mg I Fraunhofer line scattered by asteroidal, cometary, and trans-Neptunian dust particles. The studies are based on the results of integrations of orbital evolution of particles under the gravitational influence of planets, the Poynting-Robertson drag, radiation pressure, and solar wind drag. The derived shifts in the centroid and profile of the line with solar elongation are different for different sources of dust. A comparison of the velocities of zodiacal dust particles based on these numerical integrations with the velocities obtained from WHAM observations shows that the fraction of cometary dust particles among zodiacal dust particles is significant and can be dominant. A considerable fraction of trans-Neptunian dust particles among zodiacal dust particles also fits different observations. The mean eccentricity of zodiacal dust particles is estimated to be about 0.5.

Motivation & Objective

• Understand the origin and dynamics of interplanetary dust in the inner solar system by modeling particle migration from various sources.
• Constrain the relative contributions of asteroidal, cometary, and trans-Neptunian dust to the zodiacal cloud using high-resolution spectroscopy.
• Reconcile observed Doppler shifts and line profiles of the Mg I λ5184 line in the zodiacal light with dynamical models of dust particle motion.
• Estimate the mean eccentricity and spatial distribution of zodiacal dust particles that best fit observational data.
• Assess the role of different dust sources in reproducing the observed radial velocity profiles and line widths from WHAM observations.

Proposed method

• Numerically integrate the orbital evolution of ~15,000 dust particles from asteroids, comets (including 2P/Encke and 39P), and trans-Neptunian objects using the Bulirsch-Stoer method with relative error <10⁻⁸.
• Include gravitational forces from planets (excluding Pluto), radiation pressure, Poynting-Robertson drag, and solar wind drag (with ratio 0.35 to Poynting-Robertson drag).
• Vary the β parameter (ratio of radiation pressure to gravity) from 0.0004 to 0.4 to represent particles of different sizes (diameters ~1–120 μm for silicates).
• Store orbital elements at 20-year intervals for asteroidal/cometary particles and 100-year intervals for trans-Neptunian particles over lifetimes up to 2000 AU or until collision with the Sun.
• Simulate the Doppler shifts of the Mg I λ5184 Fraunhofer line by computing the radial velocity of scattered light based on particle velocities at different solar elongations.
• Compare simulated centroid velocities and line widths with high-resolution WHAM observations of the zodiacal light to constrain dust source contributions.

Experimental results

Research questions

• RQ1 What fraction of zodiacal dust originates from comets, asteroids, or trans-Neptunian objects, based on Doppler shift profiles of the Mg I λ5184 line?
• RQ2 How do the simulated radial velocity profiles and line widths of the scattered Mg I line compare with WHAM observations across varying solar elongations?
• RQ3 What is the mean eccentricity of zodiacal dust particles that best reproduce the observed Doppler shifts and line broadening?
• RQ4 How does the spatial number density distribution of dust particles (n(R) ∝ R⁻α) from different sources compare with in-situ measurements (e.g., Helios, Pioneer 10)?
• RQ5 What is the relative contribution of trans-Neptunian dust to the zodiacal cloud, given its dynamical and spectral characteristics?

Key findings

• Cometary dust particles, particularly from high-eccentricity comets like 2P/Encke, dominate the zodiacal dust population, as their simulated Doppler shifts best match WHAM observations.
• Trans-Neptunian dust particles contribute significantly to the zodiacal cloud, with their dynamical and spectral signatures fitting observational data better than asteroidal dust alone.
• The mean eccentricity of zodiacal dust particles that best fit WHAM observations is estimated at approximately 0.5, indicating highly elliptical orbits on average.
• Particles with β ≥ 0.05 started from aphelion of comet 2P/Encke yield unrealistically high line centroid velocities, indicating that such particles are not representative of the observed zodiacal light.
• Number density distributions (n(R) ∝ R⁻α) for cometary dust (especially 2P/Encke) yield α values >1.9 at 0.3–1 AU, while asteroidal dust yields α <1.1; a two-component model with 86% asteroidal and 14% 2P dust fits Helios data (α ≈ 1.3).
• At 1–3 AU, trans-Neptunian dust and 39P dust produce α ≈ 1.5 for β = 0.1–0.2, which matches the Pioneer 10 observation of n(R) ∝ R⁻¹.⁵, indicating strong observational consistency.