1. Spin State of Returning Fly-by Near Earth Asteroid 2012 TC4
William H. Ryan & Eileen V. Ryan
(New Mexico Tech/MRO)
DPS 2017

2. 2012 TC4 October 2012 Discovery Apparition:
Passed within 0.25 LD of Earth
Observed as part of Magdalena Ridge Observatory NEO Target-of-Opportunity program – the objective was to identify spin rate.
Observations acquired before close approach
October 2017 Return:
First observing opportunity since previous 2012 fly-by
Is there any evidence of this close approach in the current rotation state?
DPS 2017

3. 2012 TC4 Rotational Period DPS 2017
Large amplitude (~0.9 mag) 12.2 minute period composite lightcurves generated by multiple observers.
=> Highly elongated (a/b>2.3) object of non-negligible strength.
Warner, B.D. (2013). Minor Planet Bul. 40,
Polishook, D. (2013). Minor Planet Bul. 40,
Odden, C.E., Verhaegh, J.C., McCullough, D.G., and Briggs, J.W. (2013). Minor Planet Bul. 40,
Carbognani, A. (2014). Minor Planet Bul. 41, 4-8.
Pollock, J. unpublished
Ryan and Ryan, 2017
DPS 2017

4. Sequential Lightcurves Indicate: NPA Rotation
P1 = h ± (~12.2 min)
P2 = h ± (~8.50 min)
DPS 2017

5. Photometric Calibrations: (Landolt-based)
V-R = 0.41±0.02 => Q, X, V-ish?? (Dandy et al. 2003)
Phase Curve derived from mean magnitudes on two nights. G
Slope 25-30°
(mag/°) C
0.09
0.031 S
0.23
0.027
E, V
0.4
0.024
Harris, 1989
DPS 2017

6. October 2017 Apparition DPS 2017 Early Apparition Lightcurves:
Kramer, Bauer, Masiero, and Brozovic
(17 and 20 Sept - Palomar 5m)
McMillian, Scotti, and Brucker
(13 and 14 Sept - Mayall 4m)
Large amplitude, 12.2 min period identified; noise indicative of additional periodicity.
Thomas (6 Oct – SOAR 4m) – second period
clearly identified.
P1 = h ± (~12.2 min)
P2 = h ± (~8.50 min)
Ryan and Ryan (9, 11, and 12 Oct – MRO 2.4m)
DPS 2017

7. October 2017 (~3 hours before closest approach)
2 sec exposures – 1 sec readout
Airmass ~
V ~
P1 = ± h
P2 = ± h
Ryan and Ryan (12 Oct – MRO 2.4-meter)
DPS 2017

8. Photometric Calibrations: 2017
2017 (left) and combined 2012 and 2017 data (right). G
Slope 31-70°
(mag/°) C
0.09
0.030 S
0.23
0.028
E, V
0.4
0.026
DPS 2017

9. Summary
Within currently analyzed precision, periods appear unchanged since 2012 apparition.
H ~27.0±0.1 G ~0.38± (MPC H ~26.7)
Albedo: ~0.35±0.1 => Diameter: ~7-13 meters
To do: 1) Further analyze rotation states to greater precision.
2) Assess whether higher precision data and/or synthesis with radar results
can lead to interpretation of the physical meaning of observed periods.
2012 TC4 is a highly elongated, ~10 meter diameter, tumbling object of non-negligible strength.
DPS 2017