Iapetus' geophysics: Rotation rate, shape, and equatorial ridge

被引:100
作者
Castillo-Rogez, J. C.
Matson, D. L.
Sotin, C.
Johnson, T. V.
Lunine, J. I.
Thomas, P. C.
机构
[1] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA
[2] Lab Planetol & Geodynam Nantes, CNRS UMR 6112, F-44322 Nantes 3, France
[3] Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA
[4] Cornell Univ, Dept Astron, Ithaca, NY 14853 USA
基金
美国国家航空航天局;
关键词
Iapetus; interiors; geophysics; satellites; shapes; dynamics;
D O I
10.1016/j.icarus.2007.02.018
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Iapetus has preserved evidence that constrains the modeling of its geophysical history from the time of its accretion until now. The evidence is (a) its present 79.33-day rotation or spin rate, (b) its shape that corresponds to the equilibrium figure for a hydrostatic body rotating with a period of similar to 16 h, and (c) its high, equatorial ridge, which is unique in the Solar System. This paper reports the results of an investigation into the coupling between Iapetus' thermal and orbital evolution for a wide range of conditions including the spatial distributions with time of composition, porosity. short-lived radioactive isotopes (SLRI), and temperature. The thermal model uses conductive heat transfer with temperature-dependent conductivity. Only models with a thick lithosphere and an interior viscosity in the range of about the water ice melting point can explain the observed shape. Short-lived radioactive isotopes provide the heat needed to decrease porosity in Iapetus' early history. This increases thermal conductivity and allows the development of the strong lithosphere that is required to preserve the 16-h rotational shape and the high vertical relief of the topography. Long-lived radioactive isotopes and SLRI raise internal temperatures high enough that significant tidal dissipation can start, and despin Iapetus to synchronous rotation. This Occurred several hundred million years after Iapetus formed. The models also constrain the time when Iapetus formed because the successful models are critically dependent upon having just the right amount of heat added by SLRI decay in this early period. The amount of heat available from short-lived radioactivity is not a free parameter but is fixed by the time when Iapetus accreted, by the canonical concentration of (26)A], and, to a lesser extent, by the concentration of Fe-60. The needed amount of heat is available only if Iapetus accreted between 2.5 and 5.0 Myr after the formation of the calcium aluminum inclusions as found in meteorites. Models with these features allow us to explain lapetus' present synchronous rotation, its fossil 16-h shape, and the context within which the equatorial ridge arose. (c) 2007 Elsevier Inc. All rights reserved.
引用
收藏
页码:179 / 202
页数:24
相关论文
共 101 条
[71]   HEATING AND MELTING OF SMALL ICY SATELLITES BY THE DECAY OF AL-26 [J].
PRIALNIK, D ;
BARNUN, A .
ASTROPHYSICAL JOURNAL, 1990, 355 (01) :281-286
[72]  
Pritchard M.E., 2000, Origin of the Earth and Moon, P179, DOI [10.2307/j.ctv1v7zdrp.16, DOI 10.2307/J.CTV1V7ZDRP.16]
[73]   Tidal bending of glaciers: a linear viscoelastic approach [J].
Reeh, N ;
Christensen, EL ;
Mayer, C ;
Olesen, OB .
ANNALS OF GLACIOLOGY, VOL 37, 2003, 37 :83-89
[74]  
Ross RG, 1998, ASTROPHYS SPACE SC L, V227, P33, DOI 10.1007/978-94-011-5252-5_2
[75]  
SAFRONOV VS, 1972, S OR SOL SYST 3 7 AP
[76]   Coupled orbital and thermal evolution of Ganymede [J].
Showman, AP ;
Stevenson, DJ ;
Malhotra, R .
ICARUS, 1997, 129 (02) :367-383
[77]   Toward an astrophysical theory of chondrites [J].
Shu, FH ;
Shang, H ;
Lee, T .
SCIENCE, 1996, 271 (5255) :1545-1552
[78]   Onset of convection in fluids with strongly temperature-dependent, power-law viscosity [J].
Solomatov, VS ;
Barr, AC .
PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 2006, 155 (1-2) :140-145
[79]   Europa: Tidal heating of upwelling thermal plumes and the origin of lenticulae and chaos melting [J].
Sotin, C ;
Head, JW ;
Tobie, G .
GEOPHYSICAL RESEARCH LETTERS, 2002, 29 (08) :74-1
[80]  
SOTIN C, 2006, EGU06A08124