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The Thermal and Dynamical History of Phaethon and 2005 UD

Presentation #214.05 in the session “Asteroid Dynamics”.

Published onOct 26, 2020
The Thermal and Dynamical History of Phaethon and 2005 UD

The near-Earth asteroids (NEAs) (3200) Phaethon and (155140) 2005 UD are thought to share a common origin, with the former exhibiting dust activity at perihelion that is thought to directly supply the Geminid meteor stream. Both of these objects currently have very small perihelion distances (0.140 and 0.163 au for Phaethon and 2005 UD, respectively), which results in them having perihelion temperatures of or exceeding 1000 K. NEA population models compared to observation may suggest that low-perihelion objects are destroyed over time by a temperature-dependent mechanism that becomes relevant at heliocentric distances %gt% 0.3 au. Thus, the current activity from Phaethon is relevant to the destruction of NEAs close to the Sun, which most likely has produced meteor streams linked to asteroids in the past.

In this work, we model the past thermal characteristics of Phaethon and 2005 UD using a detailed thermophysical model (TPM) and orbital integrations of each object. Our aim is to investigate and inform a temperature-dependent mechanism responsible for Phaethon’s dust activity and the destruction of NEAs at small heliocentric distances. We consider volatile sublimation and thermal fracturing as potential candidate processes. First, dynamical integrations of orbital clones of Phaethon and 2005 UD are used to estimate the past orbital elements of each object. These dynamical results are later combined with the temperature characteristics to model the past evolution of thermal characteristics. We also consider escape-route probabilities of Phaethon and UD and find the most likely source-region to be the inner Main-Belt (nu6 resonance), rather than the Pallas region. The inner-belt Svea family contains a significant fraction of B-types, thus making it a potential source candidate.

We use a TPM in order to calculate temperatures (surface and subsurface) along an entire orbit for a spherical object, given its semimajor axis and eccentricity (a and e). Temperature characteristics such as maximum daily temperature, maximum thermal gradient, and temperature at varying depths are extracted from the model, which is run for a predefined set of a and e. The thermal history of the maximum surface temperatures, for example, thus follows a pattern of extreme heating (up to 1000 K) every 20 kyr. We find that even temperatures at-depth are too large over these timescales for water ice to be stable-unless actively supplied somehow and that thermal fracturing may be extremely effective at breaking down surface regolith.

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