Physical properties of trans-neptunian binaries (120347) Salacia-Actaea and (42355) Typhon-Echidna

Abstract 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 20  kg. The semi-major axis, period, and eccentricity of the binary orbit are a  = 5619 ± 87 km, P  = 5.49380 ± 0.00016 days, 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 ± 109 km (making it one of the largest known TNOs), and p V = 3.57 - 0.72 + 1.03 % . Thermophysical models for (120347) Salacia suggest that it probably has a thermal inertia ⩽5 J m −2  s −1/2  K −1 , although we cannot rule out values as high as 30 J m −2  s −1/2  K −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 ± 103 km and d 2  = 303 ± 35 km. 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 ± 34 km, and p V = 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 + 0.72 g / cm 3 , consistent with the very low densities of most other TNOs smaller than 500 km 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 400 km diameter all having densities less than 1 g/cm 3 , and those with diameters greater than 800 km all having densities greater than 1 g/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.

[1]  Paul S. Smith,et al.  The Multiband Imaging Photometer for Spitzer (MIPS) , 2004 .

[2]  Physical Properties of Trans-Neptunian Object (20000) Varuna , 2002, astro-ph/0201082.

[3]  J. Ortiz,et al.  Photometric Lightcurves of Transneptunian Objects and Centaurs: Rotations, Shapes, and Densities , 2008 .

[4]  Wm. A. Wheaton,et al.  Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 μm Imaging , 2007, 0704.2196.

[5]  L. Lebofsky,et al.  Systematic biases in radiometric diameter determinations , 1989 .

[6]  Mark Clampin,et al.  Advanced camera for the Hubble Space Telescope , 1996, Astronomical Telescopes and Instrumentation.

[7]  I. A. Steele,et al.  A Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation , 2011, Nature.

[8]  J. Beeman,et al.  Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. III. An Asteroid‐based Calibration of MIPS at 160 μm , 2007, 0707.2103.

[9]  M. Burgdorf,et al.  Fundamental thermal emission parameters of main-belt asteroids derived from ISO , 1999 .

[10]  J. Kavelaars,et al.  COLLISIONAL EVOLUTION OF ULTRA-WIDE TRANS-NEPTUNIAN BINARIES , 2011, 1111.2046.

[11]  Darin Ragozzine,et al.  A collisional family of icy objects in the Kuiper belt , 2007, Nature.

[12]  The Diverse Solar Phase Curves of Distant Icy Bodies. I. Photometric Observations of 18 Trans-Neptunian Objects, 7 Centaurs, and Nereid , 2006, astro-ph/0605745.

[13]  Dale P. Cruikshank,et al.  Thermal properties of Pluto’s and Charon’s surfaces from Spitzer observations , 2011 .

[14]  G. Rieke,et al.  The Albedo, Size, and Density of Binary Kuiper Belt Object (47171) 1999 TC36 , 2006, astro-ph/0602316.

[15]  Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61 , 2007, 0709.0328.

[16]  J. Spencer.  A rough-surface thermophysical model for airless planets , 1990 .

[17]  E. Chiang,et al.  High albedos of low inclination Classical Kuiper belt objects , 2008, 0812.4290.

[18]  Re'em Sari,et al.  Formation of Kuiper-belt binaries by dynamical friction and three-body encounters , 2002, Nature.

[19]  H. N. Russell,et al.  On the Albedo of the Planets and Their Satellites. , 1916, Proceedings of the National Academy of Sciences of the United States of America.

[20]  Steven Soter,et al.  Q in the solar system , 1966 .

[21]  R. Gomes.  The origin of TNO 2004 XR190 as a primordial scattered object , 2011 .

[22]  Scott S. Sheppard,et al.  Light Curves of Dwarf Plutonian Planets and other Large Kuiper Belt Objects: Their Rotations, Phase Functions, and Absolute Magnitudes , 2007, 0704.1636.

[23]  R. Rand,et al.  Synchronous Locking of Tidally Evolving Satellites , 1996 .

[24]  J. R. Spencer,et al.  (42355) Typhon–Echidna: Scheduling observations for binary orbit determination , 2008 .

[25]  M. E. Brown,et al.  THE SIZE, DENSITY, AND FORMATION OF THE ORCUS–VANTH SYSTEM IN THE KUIPER BELT , 2009, 0910.4784.

[26]  Richard P. Binzel,et al.  Keck observations of near-Earth asteroids in the thermal infrared , 2003 .

[27]  Alan W. Harris,et al.  Application of photometric models to asteroids. , 1989 .

[28]  C. Trujillo,et al.  2007 TY430: A COLD CLASSICAL KUIPER BELT TYPE BINARY IN THE PLUTINO POPULATION , 2011, 1112.2708.

[29]  M. W. Buie,et al.  Mutual orbits and masses of six transneptunian binaries , 2009 .

[30]  A. Evans,et al.  The size and albedo of the Kuiper-belt object (20000) Varuna , 2001, Nature.

[31]  G. Rieke,et al.  The High-Albedo Kuiper Belt Object (55565) 2002 AW197 , 2005 .

[32]  F. Bertoldi,et al.  Size estimates of some optically bright KBOs , 2004 .

[33]  T. Owen,et al.  Surface composition and temperature of the TNO Orcus , 2008 .

[34]  E. Schaller,et al.  Detection of Additional Members of the 2003 EL61 Collisional Family via Near-Infrared Spectroscopy , 2008, 0808.0185.

[35]  J. Ortiz,et al.  Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs , 2010, 1004.4841.

[36]  David Trilling,et al.  Physical Properties of Kuiper Belt and Centaur Objects: Constraints from the Spitzer Space Telescope , 2007 .

[37]  E. Chiang,et al.  High albedos of low inclination Classical Kuiper belt objects , 2008, 0812.4290.

[38]  J. R. Spencer,et al.  The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur , 2007, 0704.1523.

[39]  Nicolas Thomas,et al.  ``TNOs are Cool'': A survey of the trans-Neptunian region . III. Thermophysical properties of 90482 Orcus and 136472 Makemake , 2010 .

[40]  M. W. Buie,et al.  The correlated colors of transneptunian binaries , 2009 .

[41]  Jean-Luc Margot,et al.  Binaries in the Kuiper Belt , 2007, astro-ph/0703134.

[42]  A. Youdin,et al.  FORMATION OF KUIPER BELT BINARIES BY GRAVITATIONAL COLLAPSE , 2010, 1007.1465.

[43]  David Jewitt,et al.  The Albedo Distribution of Jovian Trojan Asteroids , 2003 .

[44]  David E. Trilling,et al.  The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population , 2005 .

[45]  J. Brimacombe,et al.  Size and albedo of Kuiper belt object 55636 from a stellar occultation , 2010, Nature.

[46]  D. Ragozzine,et al.  ORBITS AND MASSES OF THE SATELLITES OF THE DWARF PLANET HAUMEA (2003 EL61) , 2009, 0903.4213.

[47]  S. Astakhov,et al.  Production of trans-Neptunian binaries through chaos-assisted capture , 2007, 0705.0475.

[48]  M. E. Brown,et al.  Satellites of the largest Kuiper Belt objects , 2006 .

[49]  A. Doressoundiram,et al.  Color Properties and Trends of the Transneptunian Objects , 2008 .

[50]  C. Trujillo,et al.  A PHOTOMETRIC SYSTEM FOR DETECTION OF WATER AND METHANE ICES ON KUIPER BELT OBJECTS , 2011, 1102.1971.

[51]  Chile,et al.  Characterisation of candidate members of (136108) Haumea's family , 2009, 0912.3171.

[52]  Paul S. Smith,et al.  Reduction Algorithms for the Multiband Imaging Photometer for Spitzer , 2005, astro-ph/0502079.

[53]  J. Krist.  The Tiny Tim User’s Guide , 2004 .

[54]  Stephen C. Tegler,et al.  Color Patterns in the Kuiper Belt: A Possible Primordial Origin , 2003 .

[55]  Joel Parker,et al.  CHARACTERIZATION OF SEVEN ULTRA-WIDE TRANS-NEPTUNIAN BINARIES , 2011, 1108.2505.

[56]  R. Canup,et al.  ON A GIANT IMPACT ORIGIN OF CHARON, NIX, AND HYDRA , 2011 .

[57]  Alan W. Harris,et al.  A Thermal Model for Near-Earth Asteroids , 1998 .

[58]  F. DeMeo,et al.  Visible and near-infrared colors of Transneptunian objects and Centaurs from the second ESO large program , 2009 .

[59]  Dale P. Cruikshank,et al.  The solar system beyond Neptune , 2008 .

[60]  David L. Rabinowitz,et al.  Photometric Observations Constraining the Size, Shape, and Albedo of 2003 EL61, a Rapidly Rotating, Pluto-sized Object in the Kuiper Belt , 2006 .

[61]  David Farrelly,et al.  Capture and escape in the elliptic restricted three‐body problem , 2004 .

[62]  B. G. Marsden,et al.  Nomenclature in the Outer Solar System , 2008 .

[63]  A. Pál,et al.  Sedna, Eris and Quaoar: physical properties of prominent trans-Neptunian objects, based on Herschel observations , 2011 .

[64]  E. Schaller,et al.  The Mass of Dwarf Planet Eris , 2007, Science.

[65]  H. F. Levison,et al.  (47171) 1999 TC36, A transneptunian triple , 2009 .

[66]  R. O. Gray,et al.  ABSOLUTE PHYSICAL CALIBRATION IN THE INFRARED , 2008, 0806.1910.

[67]  M. Barucci,et al.  Rotational properties of Centaurs and Trans-Neptunian Objects - Lightcurves and densities , 2008 .

[68]  Richard J. Rudy,et al.  A refined “standard” thermal model for asteroids based on observations of 1 Ceres and 2 Pallas , 1986 .

[69]  F. Henry,et al.  “TNOs are Cool”: A survey of the trans-Neptunian region , 2010, Astronomy & Astrophysics.

[70]  M. W. Buie,et al.  Five New and Three Improved Mutual Orbits of Transneptunian Binaries , 2011 .

[71]  H. N. Russell.  On the Albedo of the Planets and Their Satellites , 1916 .

[72]  J. Emery,et al.  Composition and Surface Properties of Transneptunian Objects and Centaurs , 2008 .

[73]  Formation of Kuiper-belt binaries through multiple chaotic scattering encounters with low-mass intruders , 2005, astro-ph/0504060.

[74]  S. Weidenschilling.  On the Origin of Binary Transneptunian Objects , 2002 .

[75]  C. F. Yoder.  Tidal rigidity of Phobos , 1982 .

[76]  Douglas M. Summers,et al.  LGS AO at W.M. Keck Observatory: routine operations and remaining challenges , 2006, SPIE Astronomical Telescopes + Instrumentation.

[77]  Maria Vanina Martinez,et al.  Stellar Occultations by TNOs: the January 08, 2011 by (208996) 2003 AZ84 and the May 04, 2011 by (50000) Quaoar , 2011 .

[78]  W. Fraser,et al.  QUAOAR: A ROCK IN THE KUIPER BELT , 2009, 1003.5911.

[79]  Light Curves of 20-100 km Kuiper Belt Objects Using the Hubble Space Telescope* , 2005, astro-ph/0510454.

[80]  J. Ortiz,et al.  A study of short term rotational variability in TNOs and Centaurs from Sierra Nevada Observatory , 2003 .

[81]  A. Doressoundiram,et al.  "TNOs are Cool": A survey of the trans-Neptunian region I. Results from the Herschel science demonstration phase (SDP) , 2010, 1005.2923.

[82]  A. Doressoundiram,et al.  "TNOs are cool": A survey of the trans-Neptunian region II. The thermal lightcurve of (136108) Haumea , 2010 .

[83]  R. Gomes.  The Common Origin of the High Inclination TNO's , 2003 .