Characterization and Temporal Evolution of the Ejecta Created by the DART Impact on Dimorphos

The goal of this project is to provide constraints to the momentum transfer coefficient to support the
DART mission goal, and to understand the ejecta development and evolution of asteroid impact. We
have four observational objectives are to:
1. Characterize the ejecta morphology, including the shape, spatial distribution, and orientation;
2. Measure the velocity and velocity distribution, and determine the temporal evolution of the
ejecta;
3. Estimate the total ejecta mass from the brightness of ejecta; and
4. Constrain the particle size and size distribution of ejecta material.

We will use 19 orbits to observe the DART impact ejecta with WFC3/UVIS for a total duration of three
weeks to characterize the ejecta brightness, morphology, and temporal evolution. Our objectives are to
constrain the mass, velocity and velocity distributions, particle size and size frequency distributions of
the ejecta. The observations will result in about 300 images total through a single filter, F350LP, at
multiple exposure levels. We will measure aperture photometry from all images to constrain the total
mass of ejecta through particle photometric modeling. We will extract the radial and azimuthal
brightness profiles from all images to constrain the brightness distribution of the ejecta and evolution, to
derive the velocity distribution, and to measure the orientation of the ejecta. The ejecta velocity will
also be determined from differential images throughout the whole duration of observations. We will
model the ejecta evolution based on the observed brightness distribution and brightness evolution of the
ejecta. We will also model the solar radiation pressure effects from the ejecta morphology and evolution
to constrain particle size distribution of the ejecta. Search for large eject blocks will be performed using
about 10 deep exposures of 100 – 200 s exposure time. The results will be interpreted in the context of
the local surface topography and geology near the impact site as provided by the DART observations
prior to the impact. Our observations will also be put into the context of the LICIAcube observations of
the inner ~50 km of the ejecta in the initial few tens of minutes after the impact and the large scale,
ground-based observations of the ejecta, to construct a full picture of the ejecta development and
evolution. We will estimate the momentum transfer coefficient for the impact based on our results to
serve for the goal of the DART mission.