In the absence of dense photometry for a large population of Near Earth Objects (NEOs), the best method of obtaining a shape distribution comes from sparse photometry and partial lightcurves. We have used 867 partial lightcurves obtained by Spitzer to determine a shape distribution for sub-kilometre NEOs. From this data we find a best fit average elongation ab=0.72±0.08. We compare this result with a shape distribution obtained from 1869 NEOs in the same size range observed by Pan-STARRS 1 and find the Spitzer-obtained elongation to be in excellent agreement with this PS1 value of ab=0.70±0.10. These values are also in agreement with literature values for 1<D<10 km objects in the main asteroid belt, however, there is a size discrepancy between the two datasets. Using a smaller sample of NEOs in the size range 1<D<5 km from PS1 data, we obtain an average axis ratio b/a=0.70±0.12. This is more elongated than the shape distribution for main belt objects in the same size regime, although the current uncertainties are sizeable and this should be verified using a larger data set. As future large surveys come online it will be possible to observe smaller main belt asteroids to allow for better comparisons of different sub-kilometre populations.
@article{arxiv.1903.03159,
title = {Constraining the Shape Distribution of Near Earth Objects from Partial Lightcurves},
author = {Andrew McNeill and Joseph L. Hora and Annika Gustafsson and David E. Trilling and Michael Mommert},
journal= {arXiv preprint arXiv:1903.03159},
year = {2019}
}