TY - JOUR
T1 - Physical properties of trans-neptunian binaries (120347) Salacia-Actaea and (42355) Typhon-Echidna
AU - Stansberry, J. A.
AU - Grundy, W. M.
AU - Mueller, M.
AU - Benecchi, S. D.
AU - Rieke, G. H.
AU - Noll, K. S.
AU - Buie, M. W.
AU - Levison, H. F.
AU - Porter, S. B.
AU - Roe, H. G.
N1 - Funding Information:
Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding Information:
This work is based in part on NASA/ESA Hubble Space Telescope observations from Cycle 14 program 10514 and Cycle 16 program 11178. Support for these programs was provided by NASA through grants from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. We are especially grateful to Tony Roman at STScI for his quick action in scheduling HST follow-up observations in program 11178. This work is also based in part on Spitzer Space Telescope programs 30081 and 40016. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA through an award issued by JPL/Caltech.
Funding Information:
W.M.G., S.B.P., and H.G.R. gratefully acknowledge partial support from NSF Planetary Astronomy Grant AST-1109872 .
PY - 2012/6
Y1 - 2012/6
N2 - We report new Hubble Space Telescope and Spitzer Space Telescope results concerning the physical properties of the trans-neptunian object (TNO) binaries (120347) Salacia-Actaea (formerly 2004 SB 60), and (42355) Typhon-Echidna (formerly 2002 CR 46). The mass of the (120347) Salacia-Actaea system is 4.66±0.22×10 20kg. The semi-major axis, period, and eccentricity of the binary orbit are a=5619±87km, P=5.49380±0.00016days, and e=0.0084±0.0076, respectively. In terms of the ratio of the semimajor axis to the radius of the Hill sphere, a/r H, (120347) Salacia-Actaea is the tightest TNO binary system with a known orbit. Based on hybrid Standard Thermal Model (hybrid-STM) fits to the data, the effective diameter and V-band geometric albedo of the system are D=954±109km (making it one of the largest known TNOs), and pV=3.57-0.72+1.03%. Thermophysical models for (120347) Salacia suggest that it probably has a thermal inertia ≤5Jm -2s -1/2K -1, although we cannot rule out values as high as 30Jm -2s -1/2K -1. Based on the magnitude difference between Salacia and Actaea, δ=2.37±0.06, we estimate their individual diameters to be d 1=905±103km and d 2=303±35km. The mass density of the components is ρ=1.16-0.36+0.59 g/cm 3. Hybrid-STM fits to new Spitzer data for Typhon-Echidna give an effective diameter and V-band geometric albedo for the system of D=157±34km, and pV=6.00-2.08+4.10%. Thermophysical models for (42355) Typhon suggest somewhat lower albedos (probably no higher than about 8.2%, as compared to the hybrid-STM upper limit of 10.1%). Taken together with the previously reported mass, this diameter indicates a density of ρ=0.60-0.29+0.72g/cm3, consistent with the very low densities of most other TNOs smaller than 500km diameter. Both objects must have significant amounts of void space in their interiors, particularly if they contain silicates as well as water-ice (as is expected). The ensemble of binary-TNO densities suggests a trend of increasing density with size, with objects smaller than 400km diameter all having densities less than 1g/cm 3, and those with diameters greater than 800km all having densities greater than 1g/cm 3. If the eccentricity of the binary orbit of (42355) Typhon-Echidna is not due to recent perturbations, considerations of tidal evolution suggest that (42355) Typhon-Echidna must have a rigidity close to that of solid water ice, otherwise the orbital eccentricity of the system would have been damped by now.
AB - We report new Hubble Space Telescope and Spitzer Space Telescope results concerning the physical properties of the trans-neptunian object (TNO) binaries (120347) Salacia-Actaea (formerly 2004 SB 60), and (42355) Typhon-Echidna (formerly 2002 CR 46). The mass of the (120347) Salacia-Actaea system is 4.66±0.22×10 20kg. The semi-major axis, period, and eccentricity of the binary orbit are a=5619±87km, P=5.49380±0.00016days, and e=0.0084±0.0076, respectively. In terms of the ratio of the semimajor axis to the radius of the Hill sphere, a/r H, (120347) Salacia-Actaea is the tightest TNO binary system with a known orbit. Based on hybrid Standard Thermal Model (hybrid-STM) fits to the data, the effective diameter and V-band geometric albedo of the system are D=954±109km (making it one of the largest known TNOs), and pV=3.57-0.72+1.03%. Thermophysical models for (120347) Salacia suggest that it probably has a thermal inertia ≤5Jm -2s -1/2K -1, although we cannot rule out values as high as 30Jm -2s -1/2K -1. Based on the magnitude difference between Salacia and Actaea, δ=2.37±0.06, we estimate their individual diameters to be d 1=905±103km and d 2=303±35km. The mass density of the components is ρ=1.16-0.36+0.59 g/cm 3. Hybrid-STM fits to new Spitzer data for Typhon-Echidna give an effective diameter and V-band geometric albedo for the system of D=157±34km, and pV=6.00-2.08+4.10%. Thermophysical models for (42355) Typhon suggest somewhat lower albedos (probably no higher than about 8.2%, as compared to the hybrid-STM upper limit of 10.1%). Taken together with the previously reported mass, this diameter indicates a density of ρ=0.60-0.29+0.72g/cm3, consistent with the very low densities of most other TNOs smaller than 500km diameter. Both objects must have significant amounts of void space in their interiors, particularly if they contain silicates as well as water-ice (as is expected). The ensemble of binary-TNO densities suggests a trend of increasing density with size, with objects smaller than 400km diameter all having densities less than 1g/cm 3, and those with diameters greater than 800km all having densities greater than 1g/cm 3. If the eccentricity of the binary orbit of (42355) Typhon-Echidna is not due to recent perturbations, considerations of tidal evolution suggest that (42355) Typhon-Echidna must have a rigidity close to that of solid water ice, otherwise the orbital eccentricity of the system would have been damped by now.
KW - Centaurs
KW - Kuiper belt
KW - Trans-neptunian objects
UR - http://www.scopus.com/inward/record.url?scp=84860378439&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84860378439&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2012.03.029
DO - 10.1016/j.icarus.2012.03.029
M3 - Article
AN - SCOPUS:84860378439
SN - 0019-1035
VL - 219
SP - 676
EP - 688
JO - Icarus
JF - Icarus
IS - 2
ER -