Thermal properties and an improved shape model for near-Earth asteroid (162421) 2000 ET70

Sean E. Marshall, Ellen S. Howell, Christopher Magri, Ronald J. Vervack, Donald B. Campbell, Yanga R. Fernández, Michael C. Nolan, Jenna L. Crowell, Michael D. Hicks, Kenneth J. Lawrence, Patrick A. Taylor

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


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 h (± 0.009 h) and a north pole direction of ecliptic coordinates (52,−60)±6. 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.

Original languageEnglish (US)
Pages (from-to)22-35
Number of pages14
StatePublished - Aug 1 2017


  • Asteroids
  • Asteroids
  • Infrared observations
  • Radar observations
  • Spectroscopy
  • rotation
  • surfaces

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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