Cassini Observes the Active South Pole of Enceladus
Abstract
Cassini has identified a geologically active province at the south pole of Saturn's moon Enceladus. In images acquired by the Imaging Science Subsystem (ISS), this region is circumscribed by a chain of folded ridges and troughs at ∼55°S latitude. The terrain southward of this boundary is distinguished by its albedo and color contrasts, elevated temperatures, extreme geologic youth, and narrow tectonic rifts that exhibit coarse-grained ice and coincide with the hottest temperatures measured in the region. Jets of fine icy particles that supply Saturn's E ring emanate from this province, carried aloft by water vapor probably venting from subsurface reservoirs of liquid water. The shape of Enceladus suggests a possible intense heating epoch in the past by capture into a 1:4 secondary spin/orbit resonance.
Get full access to this article
View all available purchase options and get full access to this article.
Already a Subscriber?Sign In
Supplementary Material
File (porcocc.som.pdf)
References and Notes
1
A. J. Verbiscer, R. G. French, C. A. McGhee, Icarus173, 66 (2005).
2
D. P. Cruikshank, Icarus41, 246 (1980).
3
K. D. Pang, C. C. Voge, J. W. Rhoads, J. M. Ajello, J. Geophys. Res.89, 9459 (1984).
4
B. A. Smith et al., Science212, 163 (1981).
5
S. W. Squyres, R. T. Reynolds, P. M. Cassen, S. J. Peale, Icarus53, 319 (1983).
6
J. S. Kargel, S. Pozio, Icarus119, 385 (1996).
7
J. Lewis, Icarus15, 174 (1971).
8
S. J. Peale, Annu. Rev. Astron. Astrophys.37, 533 (1999).
9
J. Wisdom, Astron. J.128, 484 (2004).
10
M. K. Dougherty et al., Science311, 1406 (2006).
11
R. H. Brown et al., Science311, 1425 (2006).
12
C. C. Porco et al., Space Sci. Rev.115, 363 (2004).
13
J. R. Spencer et al., Science311, 1401 (2006).
14
ISS and CIRS are acknowledged in the codiscovery of the correlation between the hottest temperatures measured in the SPT and the tiger stripe fractures.
15
F. Spahn et al., Science311, 1416 (2006).
16
J. H. Waite Jr. et al., Science311, 1419 (2006).
17
C. J. Hansen et al., Science311, 1422 (2006).
18
G. H. Jones et al., Science311, 1412 (2006).
19
G. Hansen, personal communication.
20
C. C. Porco et al., Science307, 1237 (2005).
21
G. Neukumet al., Lunar Planet. Sci. Conf. 36, abstract 2034 [CD-ROM] (2005).
22
R. Wagner et al., Bull. Am. Astron. Soc.37, 701 (2005).
23
G. Neukum, thesis, Ludwig-Maximilians-Universität München (1983).
24
G. P. Horedt, G. Neukum, J. Geophys. Res.89, 10405 (1984).
25
G. Neukum, Adv. Space Res.5, 107 (1985).
26
R. Ionasescu, Jet Propulsion Laboratory Interoffice Memorandum IOM 343J-05-017 (2 May 2005).
27
R. Jacobson and the Cassini Project Navigation team, personal communication.
28
S. F. Dermott, Icarus37, 575 (1979).
29
S. F. Dermott, P. C. Thomas, Icarus109, 241 (1994).
30
Brightness values were converted into particle densities with the use of an assumed analytical particle size distribution (42): n(r) = constant r(1–3b)/b exp(–r/ab), where a is the effective radius (1.0 μm, appropriate for particles in the E ring) and b = 0.25. The quantity b is large enough to ensure a fair fraction of the particles are large enough (i.e., >2 μm) for CDA to detect. Horizontal (line-of-sight) column densities, Nlos, were computed from the peak I/F by the relation Nlos = 4(I/F)/[Asca × P(φ)], where Asca is the scattering cross section appropriate for the chosen particle size distribution, and P(φ) is the phase function computed for Mie scatterers at phase angle φ. The scattering cross section used for the assumed particle size distribution and an effective observation wavelength of 569 nm was 3.12 square μm; P(φ = 161.4) = 6.688.
31
A. Juhasz, M. Horanyi, J. Geophys. Res.107, A6 1066 (2002).
32
M. Hedman, personal communication.
33
J. Eluszkiewicz, J.-L. Moncet, Icarus166, 375 (2003).
34
S. W. Kieffer, in The Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, AZ, 1982), pp. 647–723.
35
E. J. Gaidos, F. Nimmo, Nature405, 637 (2000).
36
D. L. Goldsby, D. L. Kohlstedt, J. Geophys. Res.106, 11017 (2001).
37
C. F. Yoder, Nature279, 767 (1979).
38
G. Schubert, T. Spohn, R. T. Reynolds, in Satellites, J. A. Burns, M. S. Matthews, Eds. (Univ. of Arizona Press, Tucson, AZ, 1986), pp. 224–292.
39
M. N. Ross, G. Schubert, Icarus78, 90 (1989).
40
P. Helfenstein, E. M. Parmentier, Icarus53, 415 (1983).
41
H. J. Melosh, Icarus31, 221 (1977).
42
J. E. Hansen, J. Atmos. Sci.28, 1400 (1971).
43
G. Neukum, B. A. Ivanov, W. K. Hartmann, Space Sci. Rev.96, 55 (2001).
44
K. Zahnle, P. Schenk, H. Levison, L. Dones, Icarus163, 263 (2003).
45
We acknowledge the financial support of NASA/JPL, the UK Particle Physics and Astronomy Research Council, the Deutsches Zentrum fur Luftund Raumfahrt (German Aerospace Center), and UniversiteÌ Paris VII Denis Diderot, Commissariat aÌ€ l'Energie Atomique, Astrophysique Interactions Multieschelle, France.
Information & Authors
Information
Published In
Science
Volume 311 • Issue 5766 • 10 March 2006
Pages: 1393 - 1401
History
Received: 25 November 2005
Accepted: 21 February 2006
Copyright
American Association for the Advancement of Science.
