What is Known about 2012 TC4?

Because 2012 TC4 was only observed for seven days in 2012, little was known about its physical properties. With its 2017 recovery and close approach to the Earth, additional properties are being measured and reported here as they are announced.

The rapid rotation and lightcurve amplitude suggest that the 2012 TC4 is an elongated, monolithic body (a rubble pile would have spun itself apart). Non-principal axis rotation suggests that it probably has a complex (non-ellipsoidal) shape.

Physical Properties

Property Value Reference1
Effective Diameter 7-13 m
from H=27.0, albedo 0.25-0.45
Ryan & Ryan, PDC 2017 conference results
15m (+/- factor of 2)
from absolute mag 26.7
Polishook, D. (2013) Minor Plan. Bull. 40, 42.
Axial Ratio (prolate ellipsoid) > 2
from lightcurve amplitude ~1 mag
Ryan & Ryan, PDC 2017 conference results
> 2.3
from lightcurve amplitude ~1 mag
Polishook, D. (2013) Minor Plan. Bull. 40, 42.
Spectral Type 09 Oct
Spectrum is relatively flat, no 1-μm emission band; Likely C or X taxonomic complex
Bobby Bus; Oct 9, from SpeX (0.7-2.5 μm), IRTF
10 Oct
Confirms Bus results above; Likely C-complex with best fit taxonomy of Cb-type.
Moskovitz, Thirouin, Gustafsson & Hayslip; Oct 10, DeVeny Spectrograph (0.45-0.9 μm), DCT
13 Oct
Based on some rough analysis of the visible and NIR data, there seems to be a sense that TC4 is actually an Xc-type.
Bus et al taxonomy, spectra
updated graph
15 Oct
...have cleaned up the combined DCT / IRTF spectrum of 2012TC4. Note that the .txt file for the IRTF contains relative reflectances that have been shifted to match the DCT spectrum over the overlap interval of 0.8 to 0.9 microns.
2012TC4_IRTF_20171009UT.txt, DCT_IRTF_2012TC4spec.pdf
Colors Preliminary
Sloan DSS Filter colors g-r: 0.55 +/- 0.07, r-i: 0.46 +/-0.07, g-i: 1.01+/-0.08
Gerbs Bauer; from Palomar Observations (9/20, 2017)
Rotation Period Analysis of high time resolution lightcurves indicates that the Primary period is 12.3 min, with a Secondary period ~8.5 min. Christina Thomas, SOAR, Oct 6 (Periodicity analysis by Bill Ryan)
New lightcurves seem confirm non-principal axis rotation with variability on scales of minutes. Both appear to exhibit a primary period ~12.25 minutes. Kramer, Bauer, Masiero & Brozovic Palomar 200-inch Observatory results, Sept 2017
and
Brucker, Scotti & McMillan 4M Mayall .
Non-principal axis rotation with variability on scales of minutes and a primary period ~12 minutes, 13 seconds. Ryan & Ryan, PDC 2017 conference results
Radar Properties Elongated object, roughly 10m, high circular polarization ratio that is consistent with results seen from E- and V-class NEAs previously. Benner et al. Oct. 12, 2017
radar movies
2012 Lightcurves Warner, B.D. (2013). Minor Planet Bul. 40, 71-80.
Polishook, D. (2013). Minor Planet Bul. 40, 42-43.
Odden, C.E., Verhaegh, J.C., McCullough, D.G., and Briggs, J.W. (2013). Minor Planet Bul. 40, 176-177.
Carbognani, A. (2014). Minor Planet Bul. 41, 4-8.
Spin Axis Undefined, Non-Principal Axis rotation

1Unpublished references are for informational purposes only. Contact the authors before citing or reporting on the results they contain.

Comments

Lightcurve Observations: The upcoming close approach will allow accurate lightcurve observations from different viewing geometries to evaluate the NPA rotation, if it has a complex shape, and how its spin state evolves with time. The spin state may change during the closest approach, and obtaining an accurate baseline during its approach is a necessity for allowing that change to be quantified.

Support for Radar Observations: Improved astrometry and characterization will be key to the successful radar campaign. Light curve observations will provide shape information and orientation which will facilitate the planning of the radar power and observing cadence that will be necessary to successfully observe the NEA. An accurate period will enable better estimates of the radar SNRs and how much of the signal must be summed before the rotation starts to smear the radar images.

Radar Observations: 2012 TC4 will probably be detectable at Goldstone from about Oct. 9 - 16, but not at closest approach when it will be too far south. Radar is expecting to image this asteroid at 3.75 m and even 1.875 m resolution. The radar will have multi-hours coverage before and after the closest approach, so it will directly show the asteroid's size, elongation, surface features, orientation, scattering properties behave before and after. The lightcurves, however, more readily measure the non-principal axis rotation periods, so the combination of light curve and radar extensive data sets will be the key to figuring out how the spin state evolves as a consequence of the NEA's close Earth approach.