Color and Size Distributions of Small Jupiter Trojans

Abstract We conducted a two-band imaging survey observation using the Subaru Telescope and its wide-field camera, Suprime-Cam, to study the visible colors and size distribution of Jupiter’s Trojan asteroids. The survey covered an area around Jupiter’s L4 Lagrange point totaling 9.2 square degrees. We detected 120 Trojan asteroids in this survey. From these Trojan asteroids, we extracted 44 unbiased samples with absolute magnitudes in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>g</mml:mi> <mml:mo accent="false">′</mml:mo> </mml:math> band ranging from 12.9 to 16.9 mag (corresponding to diameter ranges of approximately ∼3–16 km assuming an albedo of 0.05) and analyzed their <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>g</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mo>−</mml:mo> <mml:mi>i</mml:mi> <mml:mo accent="false">′</mml:mo> </mml:math> color and size distributions. Large Jupiter Trojan asteroids are known to be classified into two color groups, “red” and “less red.” We found that such bimodality in the color distribution is absent for small Jupiter Trojan asteroids, which is consistent with previous studies. Previous studies have also shown that these two groups have different slopes in the magnitude distributions from each other, which was explained by conversion of red objects to less-red fragments through catastrophic disruptions. In contrast, we found that the size frequency distributions of our two sample groups divided by the color of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>g</mml:mi> <mml:mo accent="false">′</mml:mo> <mml:mo>−</mml:mo> <mml:mi>i</mml:mi> <mml:mo accent="false">′</mml:mo> </mml:math> = 0.7 (in AB magnitude) are quite similar. Our results can provide new insights into collisional evolution of color and size distribution of small Jupiter Trojans.