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Thermal mapping of large KBO systems: putting the equal albedo assumption to the test

Presentation #203.06 in the session “Centaurs and Kuiper Belt Objects: Physical Characterization”.

Published onOct 26, 2020
Thermal mapping of large KBO systems: putting the equal albedo assumption to the test

High-resolution optical imaging of Kuiper-Belt objects has revealed that a surprisingly high fraction of objects are in binary or multiple systems, up to 70% in some dynamical populations. Several system formation mechanisms may be at play, such as capture, disruption, co-formation and collision, which are in turn indicative of the dynamical history of the region at large. Detailed studies of a systems’ orbital properties as well as measurements of member sizes’ ratios can help to distinguish across such formation mechanisms. Unfortunately with optical imaging alone, size ratios can only be determined under the unverified assumption of equal albedo across the system.

The specific contribution of thermal mapping for a KBO system lies in the possibility to determine geometric albedos for each detected system’s member, by using the radiometric method, hence allowing one to break the albedo/size degeneracy. This technique can possibly reveal a different picture of a system’s physical properties than what can be determined from optical imaging alone.

The Atacama Large Millimeter Array is the only instrument operating in the thermal regime offering sufficient spatial resolution and point source sensitivity to be able to detect and separate Kuiper-Belt multiple systems other than Pluto/Charon. We present the first spatially resolved thermal ALMA observations of three well known Kuiper Belt systems: Varda/Ilmare, Salacia/Actea and Lempo/Hiisi, which belong to different dynamical populations. Our results indicate that in two of these systems, the assumption of equal albedo across the system does not hold, resulting in a significant reassessment of size ratios.

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