Wen-Han Zhou

Wen-Han Zhou

PhD student in planetary science

Solar system small bodies

My research includes:

Binary Yarkovsky effect on binary asteroids (Zhou et al. 2024a; Zhou, submitted)

We discovered how the Yarkovsky effect affects the binary asteroids.

(1) The eclipse-induced thermal perturbation produces a net thermal force that moves the component towards the synchronous orbit where the spin period equals the orbital period.

(2) The radiation from the other component produces a net thermal force moves the component towards the opposite direction of the synchronous orbit.

For nearly co-planar binaries, for which the mutual orbit aligns with the heliocentric orbit, the (1) always dominates over (2). We propose this effect could account for the synchronization process of small binary asteroids in main belt asteroids and near Earth asteroids.

This is the caption for the image
Schematics of binary Yarkovsky effect.

With this newly discovered effect, more discoveries on binary asteroid dynamics to come soon…

Crater-induced YORP (CYORP) effect on main belt asteroids (Zhou et al. 2022; Zhou & Michel 2024)

We developed a semi-analytical method to calculate the temperature distribution of a crater and the produced thermal torque, namely the CYORP torque. We found that roughly speaking, a crater with the size 1/3 of the asteroid could produce a CYORP torque comparable to the YORP torque. Based on this tool, we can estimate the YORP torque change brought by a sub-catastrophic impact, and study the asteroid rotational evolution under collisions and YORP.

Image 1
Temperature of Bennu's surface over a day (numerical).
Image 2
Temperature of a crater over a day (analytical).
This is the caption for the image
Evolution of the spin rate (left panel) and the obliquity (right panel) of a 10 km synthetic asteroid. In the presence of the static YORP torque (blue line), the asteroid gradually decelerates until it reaches a quasi-non-rotational state. Subsequently, we impose a new rotational state on the asteroid by assigning random values of rotational speed and obliquity. Conversely, when incorporating the CYORP torque (red line), the asteroid follows a different path, exhibiting random fluctuations in its spin rate due to the occurrence of impacts, creating new craters that lead to changes in the CYORP torque. As a result, the asteroid experiences intermittent transitions between spin up and spin down.

With CYORP, it’s time to estimate the stochastic YORP and Yarkovsky effect…

Rotational evolution of main belt asteroids (Zhou et al. accepted by Nature Astronomy)

This is the caption for the image
Period-diameter distribution of main belt asteroids from Gaia (Durech & Hanus, 2023).

Durech & Hanus (2023) discovered slowly rotating asteroids are seperated from fast ones by a gap.

I have discovered a truly marvelous explanation of this gap, which this space is too narrow to contain.