Koronis Family Asteroids Rotation Lightcurve Observing Program

Introduction

I've been studying the spin properties of members of the Koronis family of asteroids, which are thought to be shattered remains of a single body that was catastrophically disrupted by a collision. The Koronis family is part of the main belt of asteroids between Mars and Jupiter, and family member (243) Ida was visited by the Galileo spacecraft in 1993.

These objects are small (diameters less than about 45 km) and too far away to appear as anything but star-like unresolved blots of light in a telescope. However, we can tell that they're irregularly shaped because each object's observed brightness varies as it rotates on its axis, alternately presenting side-on and end-on views. A series of brightness measurements of an asteroid as it rotates is called a rotation lightcurve; most of the Koronis member lightcurve periods known so far are between about 3.5 hours and 20 hours. With enough lightcurve data it's possible to determine not only the object's rotation period but also its spin axis orientation, the direction of spin about the axis, and a first-order estimate of the object's shape.

Analysis of rotation lightcurves has revealed that spin vectors in the Koronis family are markedly nonrandom, which led to the suggestion of “YORP” thermal effects (more information below). New observations of lightcurves are needed to increase the sample of well-determined spin vectors. Materials and information at this site have been assembled in support of this ongoing observing program.

More Information (reverse chronological)