The Yarkovsky and YORP Effects

Abstract

The Yarkovsky effect describes a small but significant force that affects the orbital motion of meteoroids and asteroids smaller than $30-40$ kilometers in diameter. It is caused by sunlight; when these bodies heat up in the Sun, they eventually re-radiate the energy away in the thermal waveband, which in turn creates a tiny thrust. This recoil acceleration is much weaker than solar and planetary gravitational forces, but it can produce measurable orbital changes over decades and substantial orbital effects over millions to billions of years. The same physical phenomenon also creates a thermal torque that, complemented by a torque produced by scattered sunlight, can modify the rotation rates and obliquities of small bodies as well. This rotational variant has been coined the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. During the past decade or so, the Yarkovsky and YORP effects have been used to explore and potentially resolve a number of unsolved mysteries in planetary science dealing with small bodies. Here we review the main results to date, and preview the goals for future work.Comment: Chapter to appear in the Space Science Series Book: Asteroids I

Near-Earth asteroid (3200) Phaethon: Characterization of its orbit, spin state, and thermophysical parameters

“…Vokrouhlický et al (2015) obtained a similar result, but their uncertainty was larger than that of Chernetenko (2010), such that the signal-to-noise ratio was only about 1.4, and for this reason the value was not listed in their Table 1 (we do not know the reason for the difference). We have made use of our pole solutions from Sect.…”

“…While certainly more photometric and thermal observations will be taken late in 2017, it would be interesting to collect the current knowledge about Phaethon's physical parameters relevant for determining the Yarkovsky effect (such as the size, albedo, thermal inertia, spin axis direction, macroscopic shape, and surface roughness). If a sufficiently rich dataset is available, the Yarkovsky effect allows determining the asteroid bulk density: see Vokrouhlický et al (2015) for general overview, and Chesley et al (2014), Emery et al (2014), Rozitis et al (2013, Rozitis & Green (2014) for specific cases. We note that knowing the bulk density of asteroids is fundamental to shed light on their internal structure (such as monolithic vs rubble pile).…”

The young Datura asteroid family

“…12. As to the last term, we note that sub-kilometer size observed Datura members may haveȧ prop 5 × 10 −4 au Myr −1 (e.g., Bottke et al 2006;Vokrouhlický et al 2015) or smaller, which implies the third term in Eq. (1) may be approximately 0.7 • , about an order of magnitude smaller than the second term, but already larger than the first term.…”

“…Either the degree of internal dissipation in (89309) 2001 VN36 is unusually large or, more likely, the body was formed by a gentle-enough process that did not excite the rotational wobble. A more exotic, third possibility would be assume that these elongated bodies are in fact re-collapsed binary systems by the binary YORP effect (e.g., Vokrouhlický et al 2015). In this case, tides in the two components could possibly damp tumbling.…”

“…For this particular goal we would like to have available a snapshot of the family emerging right from the formation event. This is because as time passes, several dynamical processes influence the overall configuration of asteroids in the family, their surface properties and their rotation states (e.g., Nesvorný et al 2015;Vokrouhlický et al 2015). Our ability to determine, or at least constrain, ages of asteroid families, could be therefore highlighted as one of the important achievements of the past decade or so.…”