{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

This preview shows pages 1–6. Sign up to view the full content.

Radiometry of Asteroids and Comets October 13, 2009

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
OUTLINE I. Introduction: Thermal Emission and Reflected Light II. Standard Thermal Model (STM) III. Deviations from the STM: Fast-rotating (ILM) Thermophysical Model NEATM Non-sphericity I. A Few Examples: 1 Ceres NEAs Comets Centaur 2060 Chiron I. Future Observations
In addition to being diagnostic of the mineralogy of asteroids, infrared observations can also be used to derive their sizes and albedos. The observed thermal flux from any atmosphereless solar system object, in combination with a measurement of the reflected sunlight, can be used to derive the size and albedo of the object. The first application of thermal radiometry to derive the radii of asteroids was done in 1970. Several asteroids, including 4 Vesta, were found to be larger and darker than expected. I. INTRODUCTION

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
II. Standard Thermal Model Basic Principles The principle is simple, the visible brightness of an asteroid is a function of the geometric albedo (p) and its cross section: Bv = π R 2 pSd -2 The total thermal emission is proportional to the total insolation, times (1-A), where A is the Bond albedo*, and the cross section B th ~ π R 2 (1-A)S d -2 “R” is the asteroid’s radius, “d” is the heliocentric distance of the asteroid in astronomical units, and S is the solar constant**. *This is close but not the same as the geometric albedo, more on this later ** If you do not know what the S is the solar constant, look it up and come see me .
II. Standard Thermal Model Basic Principles (cont) - For a surface in equilibrium with the radiation field, the reflected and emitted radiation must add to the total solar radiation intercepted. Hence, simultaneous measurements of the reflected and emitted components are sufficient to determine both the size and albedo of the asteroid. -

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}