A Further Investigation of Apparent Periodicities and the Rotational State of Comet 103p/Hartley 2 From Combined Coma Morphology and Light Curve Data Sets

Abstract

We present an analysis of Kitt Peak National Observatory and Lowell Observatory observations of comet 103P/ Hartley 2 obtained from 2010 August through December. The results are then compared with contemporaneous observations made by the EPOXI spacecraft. Each ground-based data set has previously been investigated individually; the combined data set has complementary coverage that reduces the time between observing runs and allows us to determine additional apparent periods at intermediate times. We compare CN coma morphology between ground-based data sets, making nine new measurements of apparent periods. The first five are consistent with the roughly linearly increasing apparent period during the apparition found by previous authors. The final four suggest that the change in apparent period slowed or stopped by late November. We also measure an inner coma light curve in both CN and R-band ground-based images, finding a single-peaked light curve which repeats in phase with the coma morphology. The apparent period from the light curve had significantly larger uncertainties than from the coma morphology, but varied over the apparition in a similar manner. Our ground-based light curve aligns with the published EPOXI light curve, indicating that the light curve represents changing activity rather than viewing geometry of structures in the coma. The EPOXI light curve can best be phased by a triple-peaked period near 54-55 hr that increases from October to November. This phasing reveals that the spacing between maxima is not constant, and that the overall light curve shape evolves from one triple-peaked cycle to the next. These behaviors suggest that much of the scatter in apparent periods derived from ground-based data sets acquired at similar epochs are likely due to limited sampling of the data.

Rotationally induced surface slope-instabilities and the activation of CO2 activity on comet 103P/Hartley 2

“…Other ground-based observations are consistent with these rapid changes in the rotation state of the nucleus (Knight & Schleicher, 2011;Meech et al 2011;Samarasinha et al 2011;Knight et al 2015).…”

“…Other ground-based observations are consistent with these rapid changes in the rotation state of the nucleus (Knight & Schleicher, 2011;Meech et al 2011;Samarasinha et al 2011;Knight et al 2015). This suggests that Hartley 2 was likely spinning much faster about its principal axis in the recent past.…”

“…Although the principal rotation period of Hartley 2's nucleus was increasing by ~1 minute/day during the DIXI encounter (Drahus et al 2011), this rate is not maintained during an entire orbit (Knight et al 2015). Drahus et al (2013) estimated the orbitally averaged decrease in the principal axis rotation frequency to be ~0.012 hr -1 per orbit.…”

Rotation of cometary nuclei: new light curves and an update of the ensemble properties of Jupiter-family comets

“…The rotation period of 103P was studied in detail using the EPOXI data as well as the extensive support observations from ground. It was established that the nucleus is slowing down during the perihelion passage and that it is in a non-principal axis rotation (A'Hearn et al 2011;Belton et al 2013;Drahus et al 2011;Harmon et al 2011;Jehin et al 2010;Knight et al 2011Knight et al , 2015Meech et al 2011b;Samarasinha et al 2010Samarasinha et al , 2011Samarasinha et al , 2012. The EPOXI lightcurve suggested several periodicities ranging from 17 to 90 hours (A'Hearn et al 2011;Belton et al 2013), which were used to understand the complex rotation of the nucleus (A'Hearn et al 2011;Belton et al 2013;Samarasinha et al 2012).…”

Systematics and Consequences of Comet Nucleus Outgassing Torques

“…In most comets, the period drifts slowly, and the reported period changes are noticed only when comparing determinations made in different orbits. In comets 41P/Tuttle-Giacobini-Kresak, 46P/Wirtanen and 103P/Hartley, the rotational period varies so quickly that the rate of change, dP/dt, can be measured within a single orbit (Drahus et al 2011, Knight et al 2015, Bodewits et al 2018, Moulane et al 2018, Schleicher et al 2019, Farnham et al 2021. Note that, while ∆P can be positive or negative, and a given nucleus can be either spinning up or spinning down, we are interested only in the magnitude of the change, |∆P |.…”