1611.05625
Hayabusa-2 missing target asteroid 162173 Ryugu (1999 JU3): searching for the Object's spin-axis orientation
Müller, et al
The JAXA Hayabusa-2 mission was approved in 2010 and launched on Dec 3 2014. The spacecraft will arrive at the near-Earth asteroid 162173 Ryugu in 2018 where it will perform a survey, land and obtain surface material, then depart in Dec 2019 and return to Earth in Dec 2020. Observed Ryugu with the Herschel Space Observatory in Apr 2012 at far-IR thermal wavelengths, supported by several ground-based observations to obtain optical light curves. Re-analysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer-IRS data set. In addition, used a large set of Spitzer-IRAC observations obtained in the period Jan to May, 2013. The data set includes 2 complete rotational light curves and a series of ten "point-and-shoot" observations. The almost spherical shape of the target together with the insufficient light curve quality forced a combination of radiometric and light curve inversion techniques in different ways to find the object's key physical and thermal parameters. Find that the solution which best matches the data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (lambda=310-340 deg; beta=040±15 deg) in ecliptic coordinates, an effective diameter (of an equal-voume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 Jm-2s-0.5K-1. Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 WK-1m-1, calculate that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a 'design reference model', which is currently used for various planning, operational and modelling purposes by the Hayabusa2 team.
No comments:
Post a Comment