High Ecliptic Latitude Survey for Small Main-Belt Asteroids

Main-belt asteroids have been continuously colliding with one another since they were formed. Its size distribution is primarily determined by the size dependence of asteroid strength against catastrophic impacts. The strength scaling law as a function of body size could depend on collision velocity, but the relationship remains unknown especially under hypervelocity collisions comparable to 10 km/sec. We present a wide-field imaging survey at ecliptic latitude of around 25 deg for investigating the size distribution of small main-belt asteroids which have highly inclined orbits. The analysis technique allowing for efficient asteroid detections and high-accuracy photometric measurements provide sufficient sample data to estimate the size distribution of sub-km asteroids with inclinations larger than 14 deg. The best-fit power-law slopes of the cumulative size distribution is 1.25 +/- 0.03 in the diameter range of 0.6-1.0 km and 1.84 +/- 0.27 in 1.0-3.0 km. We provide a simple size distribution model that takes into consideration the oscillations of the power-law slope due to the transition from the gravity-scaled regime to the strength-scaled regime. We find that the high-inclination population has a shallow slope of the primary components of the size distribution compared to the low-inclination populations. The asteroid population exposed to hypervelocity impacts undergoes collisional processes that large bodies have a higher disruptive strength and longer life-span relative to tiny bodies than the ecliptic asteroids.