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Determining thermal inertia of eclipsing binary asteroids: the role of shape

Weijgaert, M. van de (2017) Determining thermal inertia of eclipsing binary asteroids: the role of shape. Master's Thesis / Essay, Astronomy.

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The physical and dynamical properties of asteroids are windows into the complex history of the solar system. Of particular interest is the thermal inertia of asteroids, a very sensitive indicator for the looseness of surface material: mature, fine-grained regolith has a much lower thermal inertia than compact material. Knowledge of thermal inertia aids the planning of spacecraft operations near or on asteroid surfaces. Through the Yarkovsky effect, thermal inertia can measurably influence asteroid orbits and plays a crucial role in the prediction and prevention of asteroid impacts on Earth. The topic of this work is to study the role of component shape in the analysis of the thermal emission of eclipsing binary asteroids. This method was pioneered by Mueller et al. (2010) with Spitzer IRS observations of eclipses in the binary Trojan asteroid system (617) Patroclus-Menoetius. Their analysis yielded the first direct measurement of asteroid thermal inertia and the first determination of this property for a Trojan asteroid. Based on the evidence available at the time, Mueller et al. (2010) assumed spherical component shapes. However, Buie et al. (2015) derived a significantly ellipsoidal shape through occultation observations. We reanalyze the Spitzer observations of Patroclus using that shape as an input parameter. We also employed other shape models, interpolating between the sphere and the Buie et al. shape model as well as extrapolating beyond it, in order to study the influence of component shape. We find component shape to have a dramatic impact on the thermal emission of eclipsing binary asteroids. As a consequence, we find thermal-inertia values that are reduced by factors of several J s^-1/2 K^-1 m^-2. For one eclipse event (’event 1’), we find 0.23 ± 0.17 J s^-1/2 K^-1 m^-2 while Mueller et al. found 21 ± 14 J s^-1/2 K^-1 m^-2. For the other eclipse event (’event 2’), we find 1.00 ± 0.45 J s^-1/2 K^-1 m^-2 while Mueller et al. found 6.4 ± 1.6 J s^-1/2 K^-1 m^-2. Our thermal-inertia result is at the low edge of the plausible range and indicates extreme looseness in the topmost surface layer. The two events are representative of the thermal inertia of the two separate components of the Patroclus system. If the two components are formed from the same material, one would expect them to display identical thermal inertia. The comparison between the thermal inertia for events 1 and 2 does not support nor reject this possibility. These results will support further studies into the thermal properties, composition and structure of asteroids. Patroclus, our target asteroid, is also among the targets of the Lucy mission, currently under study at NASA. If approved, Lucy will fly by Patroclus in 2033, providing highly resolved data.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Astronomy
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:27
Last Modified: 15 Feb 2018 08:27

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