OPTICAL PROPERTIES OF (162173) 1999 JU3: IN PREPARATION FOR THE JAXA HAYABUSA 2 SAMPLE RETURN MISSION

We investigated the magnitude-phase relation of (162173) 1999 JU3, a target asteroid for the JAXA Hayabusa 2 sample return mission. We initially employed the International Astronomical Union's H-G formalism but found that it fits less well using a single set of parameters. To improve the inadequate fit, we employed two photometric functions: the Shevchenko and Hapke functions. With the Shevchenko function, we found that the magnitude-phase relation exhibits linear behavior in a wide phase angle range (alpha = 5 degrees-75 degrees) and shows weak nonlinear opposition brightening at alpha < 5 degrees, providing a more reliable absolute magnitude of H-V = 19.25 +/- 0.03. The phase slope (0.039 +/- 0.001 mag deg(-1)) and opposition effect amplitude (parameterized by the ratio of intensity at alpha = 0 degrees.3 to that at alpha = 5 degrees, I(0 degrees.3)/I(5 degrees) = 1.31 +/- 0.05) are consistent with those of typical C-type asteroids. We also attempted to determine the parameters for the Hapke model, which are applicable for constructing the surface reflectance map with the Hayabusa 2 onboard cameras. Although we could not constrain the full set of Hapke parameters, we obtained possible values, w = 0.041, g = -0.38, B-0 = 1.43, and h = 0.050, assuming a surface roughness parameter <(theta)over bar> = 20 degrees. By combining our photometric study with a thermal model of the asteroid, we obtained a geometric albedo of p(v) = 0.047 +/- 0.003, phase integral q = 0.32 +/- 0.03, and Bond albedo A(B) = 0.014 +/- 0.002, which are commensurate with the values for common C-type asteroids.