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Spin and shape of near-Earth asteroid (53319) 1999 JM8 from radar and lightcurve observations in 1999

Presentation #506.04 in the session Asteroids: Near-Earth Objects (Oral Presentation)

Published onOct 23, 2023
Spin and shape of near-Earth asteroid (53319) 1999 JM8 from radar and lightcurve observations in 1999

1999 JM8 has an absolute magnitude of 15.4 and belongs to an optically dark taxonomy (C, P according to Binzel et al., 2019), making it one the largest objects in the near-Earth population. Delay-Doppler images obtained from July 20 to August 9, 1999 at Goldstone (X-band, 8560-MHz, 3.5-cm) and Arecibo (S-band, 2380-MHz, 13-cm) constitute one of the most detailed and extensive radar imaging datasets. Resolutions as fine as 15 m in range revealed a ~7 km diameter object with a wealth of topography: prominent facets, crater-like features that are few tens to more than a thousand meters in diameter, and a triangular feature that sticks out from an overall rounded pole-on silhouette. Pravec et al. (2005) reported lightcurves obtained from July 3 to 21, 1999.

Benner et al. (2002) suggested that 1999 JM8 is non-principal axis rotator (NPA) based on the echo bandwidth changes that could not be explained with a simple change in viewing geometry. Pravec et al. (2005) also reported significant deviations from a simple periodicity. We will discuss ongoing efforts to reconstruct the object’s shape, size, and spin state based on radar and lightcurve data. Our preliminary results suggest that the JM8 shape has approximate dimensions of 4.5x5.2x6.6 km (~15% error) and that it is likely in a short-axis mode of NPA rotation with principal periods of ~7 days and ~32 days.

Acknowledgments: ©2023. California Institute of Technology. Government sponsorship acknowledged.

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