Showing papers by "Joseph L. Hora published in 2016"
Max Planck Society1, Charles University in Prague2, Seoul National University3, Korea Astronomy and Space Science Institute4, European Space Agency5, Planetary Science Institute6, Hungarian Academy of Sciences7, university of lille8, Centre national de la recherche scientifique9, University of Tennessee10, Japan Aerospace Exploration Agency11, Harvard University12, Carnegie Learning13, Johns Hopkins University Applied Physics Laboratory14, Northern Arizona University15, Japan Spaceguard Association16, Heidelberg University17
TL;DR: In this paper, the authors combine radiometric and lightcurve inversion techniques in different ways to find the object's key physical and thermal parameters, and find that the solution which best matches their data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (lambda = 310-340 deg; beta = -40+/-15 deg) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a
Abstract: The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 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. We observed Ryugu with the Herschel Space Observatory in Apr 2012 at far-IR thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer-IRS data set. In addition, we used a large set of Spitzer-IRAC observations obtained in the period Jan to May, 2013. The data set includes two complete rotational lightcurves and a series of ten "point-and-shoot" observations. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object's key physical and thermal parameters. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (lambda = 310-340 deg; beta = -40+/-15 deg) in ecliptic coordinates, an effective diameter (of an equal-volume 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, we calculated 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.
72 citations
TL;DR: In this paper, the authors present the first results from this new program: fluxes and derived diameters and albedos for 80 NEs, together with a description of the overall program and approach, including several updates to the thermal model.
Abstract: Near-Earth objects (NEOs) are small solar system bodies whose orbits bring them close to the Earth’s orbit. We are
carrying out a Warm Spitzer Cycle 11 Exploration Science program entitled NEOSurvey—a fast and efficient flux-limited
survey of 597 known NEOs in which we derive a diameter and albedo for each target. The vast majority of our targets are too faint to be observed by NEOWISE, though a small sample has been or will be observed by both
observatories, which allows for a cross-check of our mutual results. Our primary goal is to create a large and uniform catalog of NEO properties. We present here the first results from this new program: fluxes and derived diameters and albedos for 80 NEOs, together with a description of the overall program and approach, including several updates to our thermal model. The largest source of error in our diameter and albedo solutions, which derive from our single-band thermal emission measurements, is uncertainty in η, the beaming parameter used in our
thermal modeling; for albedos, improvements in solar system absolute magnitudes would also help significantly.
All data and derived diameters and albedos from this entire program are being posted on a publicly accessible Web
page at nearearthobjects.nau.edu .
29 citations
TL;DR: The NEOSurvey as mentioned in this paper is a fast and efficient flux-limited survey of 597 known near Earth Objects (NEOs) in which they derive diameter and albedo for each target.
Abstract: Near Earth Objects (NEOs) are small Solar System bodies whose orbits bring them close to the Earth's orbit. We are carrying out a Warm Spitzer Cycle 11 Exploration Science program entitled NEOSurvey --- a fast and efficient flux-limited survey of 597 known NEOs in which we derive diameter and albedo for each target. The vast majority of our targets are too faint to be observed by NEOWISE, though a small sample has been or will be observed by both observatories, which allows for a cross-check of our mutual results. Our primary goal is to create a large and uniform catalog of NEO properties. We present here the first results from this new program: fluxes and derived diameters and albedos for 80 NEOs, together with a description of the overall program and approach, including several updates to our thermal model. The largest source of error in our diameter and albedo solutions, which derive from our single band thermal emission measurements, is uncertainty in eta, the beaming parameter used in our thermal modeling; for albedos, improvements in Solar System absolute magnitudes would also help significantly. All data and derived diameters and albedos from this entire program are being posted on a publicly accessible webpage at this http URL .
6 citations