J. D. Giorgini, Jet Propulsion Laboratory (JPL); E. S. Howell, P. A. Taylor, J. E. Richardson, L. A. Ford, L. F. Zambrano-Marin, and M. C. Nolan, Arecibo Observatory, National Astronomy and Ionosphere Center; and M. Brozovic and L. A. M. Benner, JPL, report that a strongly-detected (though small) non-gravitational acceleration, consistent with Yarkovsky thermal re-radiation, has been observed influencing the motion of minor planet (2340) Hathor. Arecibo (2380-MHz, 12.6-cm) and Goldstone (8560-MHz, 3.5-cm) round-trip delay measurements of (2340) Hathor on Oct. 20-22 detected offsets of 2498.6 (+/- 0.3) x 10**-6 seconds and 2499.2 (+/- 3.0) 10**-6 seconds relative to the ballistic trajectory predicted from initial plane-of-sky angular measurements spanning 1976-2012 (JPL orbit solution no. 48, dated 2014 June 9; most recent orbits for minor planets are posted at website URL http://ssd.jpl.nasa.gov/dat/ELEMENTS.NUMBR). This 22-sigma delay offset, along with a 4.6-sigma Doppler frequency shift offset relative to the pre-radar prediction, are dynamically consistent with a heliocentric transverse non-gravitational acceleration (approximating Yarkovsky thermal acceleration over the time span) of -6.1 +/- 0.3 x 10**-13 m/s**2, estimated in JPL orbit solution no. 60 (from 2014 Oct. 24) using a combined astrometric dataset of 182 optical measurements (1976-2014) with four radar delay and three Doppler measurements. Radar imaging with 15-m resolution suggests a diameter of 210 +/- 30 m and a generally spheroidal shape with little or only moderate elongation.
International Astronomical Union Circular
- Pub Date:
- October 2014