Constraining the Shape Distribution of Near-Earth Objects from Partial Light Curves

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 light curves. We have used 867 partial light curves obtained by Spitzer to determine a shape distribution for subkilometer NEOs. From this data we find a best-fit average elongation of \tfrac{b}{a}=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 (PS1) and find the Spitzer-obtained elongation to be in excellent agreement with this PS1 value of \tfrac{b}{a}=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 data sets. Using a smaller sample of NEOs in the size range of 1 < D < 5 km from PS1 data, we obtain an average axis ratio of 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 subkilometer populations.