On 15 February 2013 , the asteroid 367943 Duende ( 2012 DA14 ) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii .
We present here the results of an extensive , multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby .
Our spectral data reveal no changes within the systematic uncertainties of the data .
Post-flyby lightcurve photometry places strong constraints on the rotation state of Duende , showing that it is in non-principal axis rotation with fundamental periods of P _ { 1 } = 8.71 \pm 0.03 and P _ { 2 } = 23.7 \pm 0.2 hours .
Multiple lightcurve analysis techniques , coupled with theoretical considerations and delay-doppler radar imaging , allows us to assign these periods to specific rotational axes of the body .
In particular we suggest that Duende is now in a non-principal , short axis mode rotation state with a precessional period equal to P _ { 1 } and oscillation about the symmetry axis at a rate equal to P _ { 2 } .
Temporal and signal-to-noise limitations inherent to the pre-flyby photometric dataset make it difficult to definitively diagnose whether these periods represent a change imparted due to gravitational torques during the flyby .
However , based on multiple analysis techniques and a number of plausibility arguments , we suggest that Duende experienced a rotational change during the planetary encounter with an increase in its precessional rotation period .
Our preferred interpretation of the available data is that the precession rate increased from 8.4 hours prior to the flyby to 8.7 hours afterwards .
A companion paper by Benson et al .
( 2019 ) provides a more detailed dynamical analysis of this event and compares the data to synthetic lightcurves computed from a simple shape model of Duende .
The interpretation and results presented in these two works are consistent with one another .
The ultimate outcome of this campaign suggests that the analytic tools we employed are sufficient to extract detailed information about solid-body rotation states given data of high enough quality and temporal sampling .
As current and future discovery surveys find more near-Earth asteroids , the opportunities to monitor for physical changes during planetary encounters will increase .