Abstract
We observed near-Earth Asteroid (162421) 2000 ET70 using the Arecibo and Goldstone radar systems over a period of 12days during its close approach to the Earth in February 2012. We obtained continuous wave spectra and range-Doppler images with range resolutions as fine as 15m. Inversion of the radar images yields a detailed shape model with an effective spatial resolution of 100m. The asteroid has overall dimensions of 2.6km×2.2km×2.1km (5% uncertainties) and a surface rich with kilometer-scale ridges and concavities. This size, combined with absolute magnitude measurements, implies an extremely low albedo (∼2%). It is a principal axis rotator and spins in a retrograde manner with a sidereal spin period of 8.96±0.01h. In terms of gravitational slopes evaluated at scales of 100m, the surface seems mostly relaxed with over 99% of the surface having slopes less than 30°, but there are some outcrops at the north pole that may have steeper slopes. Our precise measurements of the range and velocity of the asteroid, combined with optical astrometry, enables reliable trajectory predictions for this potentially hazardous asteroid in the interval 460–2813.
Highlights
Radar astronomy is arguably the most powerful Earth-based technique for characterizing the physical properties of near-Earth asteroids (NEAs)
The average radar albedo computed for the opposite circular (OC) continuous wave (CW) spectra shown in Fig. 1 is 0.063 ± 0.017, where the uncertainty is the standard deviation of individual estimates
In images obtained at similar rotational phases, the bandwidth extent of the asteroid increased from February 12 to 20, indicating that our view was more equatorial towards the end of the observing campaign (Fig. 2)
Summary
Radar astronomy is arguably the most powerful Earth-based technique for characterizing the physical properties of near-Earth asteroids (NEAs). Radar observations routinely provide images with decameter spatial resolution These images can be used to obtain accurate astrometry, model shapes, measure near-surface radar scattering properties, and investigate many other physical properties (e.g. sizes, spin states, masses, densities). We present the radar observations and detailed physical characterization of NEA (162421) 2000 ET70 This Aten asteroid (a = 0.947 AU, e = 0.124, i = 22.3°) was discovered on March 8, 2000 by the Lincoln Near-Earth Asteroid Research (LINEAR) program in Socorro, New Mexico. Alvarez et al (2012) obtained a lightcurve of the asteroid during its close approach to the Earth in February 2012 They reported a lightcurve period of 8.947 ± 0.001 h and a lightcurve amplitude of 0.60 ± 0.07. Using spectral observations covering a wavelength range of 0.8–2.5 lm in addition to the visible data, Ellen Howell (personal communication) classified it as Xk in the taxonomic system of Bus-DeMeo (DeMeo et al, 2009)
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