PhD thesis
Most asteroids are found to be in principal axis rotation states. There is, however, a group of asteroids, called tumblers, which are in an excited state of rotation, i.e., freely precessing. This is indicated by their complex, two-periodic, lightcurves and also by radar measurements of the first confirmed and also the best described tumbler, 4179 Toutatis.
A damping of the excited rotation is rather fast in most asteroids which explains why we observe most of them in a basic rotation state. A question arises on how were the asteroids excited. There are two major mechanisms to explain this, collisions and a torque related to Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect.
In the thesis we describe an analytical model we constructed to verify the plausibility of the collisional mechanism of the excitation of asteroid rotation. The main features of the model are the scaling laws used for calculation of the impact crater dimensions and the angular momentum transfer efficiency based on laboratory impact experiments. After the collision, a rotational lightcurve is generated for the simulated asteroid and we judge if the tumbling is detectable by the standard photometric analysis.
We found that large subcatastrophic collisions are a plausible mechanism to excite rotations of small slowly rotating asteroids. The rotational axis misalignment is used as a measure of tumbling magnitude. Tumbling begins to be detectable for the misalignment angle larger than ~15° with high accuracy data.
We also found that the result of a collision can be simply described by the ratio of the orbital angular momentum (mainly carried by the projectile) and the rotational angular momentum of the target. We derived a relation between this ratio and the rotational axis misalignment.
In addition, we compared the specific impact energy of the collision to the threshold energy which would already cause a serious damage to the asteroid. We found that asteroids as small as ~100 m can have excited rotation by collision without being damaged. Finally, we discuss our results and describe further work to be done to understand the processes that excite asteroid rotations.
- excitation of asteroid rotations through impacts[pdf, 1.7 MB]
CD8 workshop presentation
The contributed talk given at the 8th Workshop on Catastrophic Disruption in the Solar System (CD8) on Hawai'i, USA.
- Asteroid rotation excitation by subcatastrophic impacts, 26 June 2013[pdf, 358 KB]
MNRAS article
The article contains main ideas of our recent research on collisional excitation of asteroid rotations. It is described more thoroughly in the thesis above.
- Henych, T. and Pravec, P. 2013. Asteroid rotation excitation by subcatastrophic impacts. MNRAS~432, 10.1093/mnras/stt581, arXiv.org reprint
GA CR project seminars
Our research was partly supported by joint GA CR grant 'Physics of Sun, stars, and stellar systems' of AsU AV CR, PrF MU and AU MFF UK. Doctoral meetings with presentations of the ongoing work were part of the output.
- Excited rotation of asteroids, 22 January 2009[pdf, 134 KB]
- What's it like to be excited?, 27 October 2009[pdf, 873 KB]
- Collision model and scaling laws, 16 November 2010[pdf, 765 KB]