Large size and slow rotation of the trans-Neptunian object (225088) 2007 OR10 discovered from Herschel and K2 observations (1603.03090v1)

Abstract: We present the first comprehensive thermal and rotational analysis of the second most distant trans-Neptunian object (225088) 2007 OR10. We combined optical light curves provided by the Kepler space telescope -- K2 extended mission and thermal infrared data provided by the Herschel Space Observatory. We found that (225088) 2007 OR10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d=1535^{+75}_{-225} km which places (225088) 2007 OR10 in the biggest top three trans-Neptunian objects. The corresponding visual geometric albedo is p_V=0.089^{+0.031}_{-0.009}. The light curve analysis revealed a slow rotation rate of P_rot=44.81+/-0.37 h, superseded by a very few objects only. The most likely light-curve solution is double-peaked with a slight asymmetry, however, we cannot safely rule out the possibility of having a rotation period of P_rot=22.40+/-0.18 h which corresponds to a single-peaked solution. Due to the size and slow rotation, the shape of the object should be a MacLaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. Its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles -- CH_4, CO and N_2 -- on the surface.

• The paper reveals that trans-Neptunian object 2007 OR10 is significantly larger (diameter ~1535 km) and rotates slower (period ~44.81 hours) than expected based on Herschel and K2 data.
• By combining K2 optical light curves and Herschel thermal infrared data, the study precisely estimates the object's diameter at 1535 km and visual geometric albedo at 0.089.
• The object's large size suggests high surface gravity favorable for retaining volatiles like methane, making it a key comparison for other dwarf planets like Pluto and Eris.

Insights into the Large Size and Slow Rotation of a Trans-Neptunian Object Discovered from Herschel and K2 Observations

This paper presents a comprehensive paper of a distant trans-Neptunian object (TNO) using data from both the Kepler/K2 mission and the Herschel Space Observatory. Notably, the object in question, designated as _{10, is characterized by an unexpectedly large size and slow rotation. The paper employs advanced thermal and rotational analyses, providing new insights into its physical properties and potential implications for the retention of volatile compounds.

Methodology and Key Findings

The authors utilize optical light curves from the K2 mission and thermal infrared data from Herschel. The combined dataset allows for an accurate assessment of the object's diameter and albedo as well as its rotational period. The primary results of the paper include the following:

1. Size and Albedo Estimations: The analysis yields a diameter of $1535^{+75}_{-225}$ km, indicating that _{10 ranks among the top three largest TNOs. The visual geometric albedo is determined to be $0.089^{+0.031}_{-0.009}$. These findings suggest that the object is larger and darker than previously thought.
2. Rotational Dynamics: The light curve reveals a slow rotation period of $44.81\pm0.37$ hours, with a potential alternative of a single-peaked period of $22.40\pm0.18$ hours. Such slow rotation periods are uncommon among TNOs, raising questions about possible tidal interactions and rotational states.
3. Surface and Composition Inferences: The object's size implies significant surface gravity, favoring the retention of volatile compounds such as methane, carbon monoxide, and nitrogen. Additionally, observed surface color differences may result from heterogeneous distributions of these volatiles.

Theoretical and Practical Implications

The findings carry several implications for our understanding of TNOs and the outer Solar System dynamics:

• Comparative Analysis with Other Dwarf Planets: _{10's dimensions and slow rotation position it as a key subject for comparison with other large TNOs and dwarf planets, such as Eris and Pluto. Insights into its surface composition further enrich our understanding of volatile retention and distribution in these distant bodies.
• Constraints on Internal and Surface Features: The paper's implications extend to the internal structure and potential geological history of _{10. The retention of volatiles could hint at complex evolutionary dynamics, including potential cryovolcanism or tectonic activity.
• Implications for Future Observational Campaigns: The paper highlights the utility of multi-instrument datasets in characterizing distant objects. As future missions, both ground-based and space-based, continue to explore the Kuiper Belt, methodologies from this paper could serve as a reference framework for the characterization of other TNOs.

Future Directions

The paper sets the stage for further investigations into TNOs, suggesting several avenues for ongoing and future work:

• Refinement of Rotational Models: Additional observations, possibly from future space missions or larger ground-based telescopes, may further constrain _{10's rotation period and axis orientation.
• Chemical Composition Studies: Spectroscopic studies could elucidate surface composition more accurately, shedding light on the presence and spatial variation of suspected volatiles.
• Comparative Studies in a Broader Context: Expanding the analysis presented in this paper to a broader array of distant objects may yield new patterns and correlations, thereby enhancing our understanding of the Kuiper Belt's role within solar system evolution.

In conclusion, the paper provides a significant advancement in trans-Neptunian research, particularly concerning the physical characterization of large and distant objects. Its methodical approach and integration of diverse data sources serve as a robust model for ongoing studies of the outer reaches of our Solar System.