Asteroid and comets are distinct by their formation region and by their orbital properties. Cometary nuclei formed comparatively far from the sun and were stored beyond the orbit of Neptune where many volatiles, including water, are frozen. They enter the warm inner solar system only occasionally and temporarily due to gravitational interactions with the outer planets or neighbouring stars. While passing close to the sun they display their well-known activity that is driven by volatile sublimation. By contrast, asteroids likely formed much closer to the sun and have spent most of the time since then on stable orbits between those of Mars and Jupiter, where surface volatiles are not stable. However, over the past two decades, evidence of occasional dust emission from asteroids has increased. Possible causes include collisions and rotational disintegration, but also transient sublimation of sub-surface volatiles uncovered by one of these processes.
We study the distribution of dust ejected from active asteroids and how it evolves under the influence of solar gravity and radiation pressure, from which we can infer the dust emission velocity and production rate as functions of time and particle size. These quantities allow us to constrain the process driving the dust emission, e.g. whether in was instantaneous (like an impact), or continuous and dependent on the distance to the Sun (like sublimation-driven activity). To this purpose we compare images obtained by state-of-the-art astronomical telescopes to numerical simulations of the dust motion, whose parameters are then optimised to match the observations.
Using telescope images obtained during inactive phases, we also study the properties of the objects themselves, such as their sizes and rotation periods. Such information is required to e.g. understand if fast rotation played a role in uncovering ice, ejecting dust, or even entirely disintegrating an object.
