Dynamical Evolution and Thermal History of Asteroids (3200) Phaethon and (155140) 2005 UD

TL;DR

This study models the thermal and dynamical history of asteroids Phaethon and 2005 UD, revealing insights into their origins, surface processes, and the effects of their close perihelion passages.

Contribution

It combines thermophysical modeling with orbital integrations to trace the past thermal evolution and orbital history of these NEOs, challenging previous parent body assumptions.

Findings

Pallas is unlikely the parent body for Phaethon and 2005 UD.

Orbital histories show cyclic perihelion shifts between current values and 0.3 au.

Subsurface temperatures are too high for stable water ice over the timescale.

Abstract

The near-Earth objects (NEOs) (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, which results in them having perihelion temperatures of or exceeding 1000 K. The current activity from Phaethon is relevant to the destruction of NEOs close to the Sun, which most likely has produced meteor streams linked to asteroids in the past. We model the past thermal characteristics of Phaethon and 2005 UD using a combination of a thermophysical model (TPM) and orbital integrations of each object. 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. Next, 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 then combined with the temperature characteristics to model the past evolution of thermal characteristics such as maximum (and minimum) surface temperature and thermal gradient. We find that dwarf planet (2) Pallas is unlikely to be the parent body for Phaethon and 2005 UD, and it is more likely that the source is in the inner part of the asteroid belt. The orbital histories of Phaethon and 2005 UD are characterized by cyclic changes in, resulting in perihelia values periodically shifting between present-day values and 0.3 au. We find that the subsurface temperatures are too large over this timescale for water ice to be stable unless actively supplied somehow. The near-surface thermal gradients strongly suggest that thermal fracturing may be very effective at breaking down surface regolith.