We present thermal properties and an improved shape model for potentially hazardous asteroid ( 162421 ) 2000 ET70 .
In addition to the radar data from 2000 ET70 ’ s apparition in 2012 , our model incorporates optical lightcurves and infrared spectra that were not included in the analysis of Naidu et al .
( 2013 , Icarus 226 , 323-335 ) .
We confirm the general “ clenched fist ” appearance of the Naidu et al .
model , but compared to their model , our best-fit model is about 10 % longer along its long principal axis , nearly identical along the intermediate axis , and about 25 % shorter along the short axis .
We find the asteroid ’ s dimensions to be 2.9 km × 2.2 km × 1.5 km ( with relative uncertainties of about 10 % , 15 % , and 25 % , respectively ) .
With the available data , 2000 ET70 ’ s period and pole position are degenerate with each other .
The radar and lightcurve data together constrain the pole direction to fall along an arc that is about twenty-three degrees long and eight degrees wide .
Infrared spectra from the NASA InfraRed Telescope Facility ( IRTF ) provide an additional constraint on the pole .
Thermophysical modeling , using our SHERMAN software , shows that only a subset of the pole directions , about twelve degrees of that arc , are compatible with the infrared data .
Using all of the available data , we find that 2000 ET70 has a sidereal rotation period of 8.944 hours ( ± 0.009 h ) and a north pole direction of ecliptic coordinates ( 52 ^ { \circ } , -60 ^ { \circ } ) \pm 6 ^ { \circ } .
The infrared data , acquired over several dates , require that the thermal properties ( albedo , thermal inertia , surface roughness ) must change across the asteroid ’ s surface .
By incorporating the detailed shape model and spin state into our thermal modeling , the multiple ground-based observations at different viewing geometries have allowed us to constrain the levels of the variations in the surface properties of this asteroid .