"TNOs are Cool": A survey of the trans-Neptunian region -- VII. Size and surface characteristics of (90377) Sedna and 2010 EK139

TL;DR

This study uses Herschel Space Observatory data to estimate the size and surface reflectivity of Sedna and 2010 EK139, revealing larger albedos and smaller sizes than previously thought, implying icy surfaces.

Contribution

First thermophysical modeling estimates of Sedna and 2010 EK139's sizes and albedos based on Herschel observations, improving understanding of their surface compositions.

Findings

Sedna diameter ~995 km with high albedo (~0.32)

2010 EK139 diameter ~470 km with moderate albedo (~0.25)

Surfaces likely covered by ices in larger fractions than previously assumed

Abstract

We present estimates of the basic physical properties (size and albedo) of (90377) Sedna, a prominent member of the detached trans-Neptunian object population and the recently discovered scattered disk object 2010 EK139, based on the recent observations acquired with the Herschel Space Observatory, within the "TNOs are Cool!" key programme. Our modeling of the thermal measurements shows that both objects have larger albedos and smaller sizes than the previous expectations, thus their surfaces might be covered by ices in a significantly larger fraction. The derived diameter of Sedna and 2010 EK139 are 995 +/- 80 km and 470 +35/-10 km, while the respective geometric albedos are pV 0.32 +/- 0.06 and 0.25 +0.02/-0.05. These estimates are based on thermophysical model techniques.