Titan's Magnetic Field Signature During the First Cassini Encounter
Abstract
The magnetic field signature obtained by Cassini during its first close encounter with Titan on 26 October 2004 is presented and explained in terms of an advanced model. Titan was inside the saturnian magnetosphere. A magnetic field minimum before closest approach marked Cassini's entry into the magnetic ionopause layer. Cassini then left the northern and entered the southern magnetic tail lobe. The magnetic field before and after the encounter was approximately constant for ∼20 Titan radii, but the field orientation changed exactly at the location of Titan's orbit. No evidence of an internal magnetic field at Titan was detected.
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 (backes.som.pdf)
References and Notes
1
A. W. Schardt et al., Saturn, T. Gehrels, M. S. Matthews, Eds. (Univ. of Ariz. Press, Tucson, AZ, 1984), pp. 417-459.
2
This velocity was measured by Voyager 1 (3). Ideal corotation would imply a velocity of 200 km/s in Titan's restframe.
3
F. M. Neubauer, D. A. Gurnett, J. D. Scudder, R. E. Hartle, Saturn, T. Gehrels, M. S. Matthews, Eds. (Univ. of Ariz. Press, Tucson, AZ, 1984), pp. 760-787.
4
Plasma-β: ratio of thermal and magnetic pressure.
5
M. K. Dougherty, Space Sci. Rev., 114, 331 (2004).
6
Space Craft Event Time (SCET) in the universal time frame (UTC). All times given here are in this time frame.
7
M. K. Dougherty et al., Science307, 1266 (2005).
8
The coordinate system used is the Titan interaction system (TIIS) defined in Fig. 1.
9
H. Alfvén, Tellus9, 92 (1957).
10
N. F. Ness, M. H. Acuña, K. W. Behannon, F. M. Neubauer, J. Geophys. Res.87, 1369 (1982).
11
H. Backes, thesis, Institut für Geophysik und Meteorologie, University of Cologne, Germany (2004).
12
13
C. N. Keller, T. E. Cravens, L. Gan, J. Geophys. Res.97, 12117 (1992).
14
P. G. Richards, J. A. Fennelly, D. G. Torr, J. Geophys. Res.99, 8981 (1994).
15
Materials and methods are available as supporting material on Science Online.
16
Conditions at TA: CA time, 26 October 2004, 15:30:05 UTC; CA altitude, 1174 km; SLT = 10.6; solar declination, -23.23°; angle between ideal corotation direction and Sun-Titan line, 109.2°; flyby through northern tail.
17
R. E. Hartle et al., J. Geophys. Res.87, 1383 (1982).
18
M. G. Kivelson, C. T. Russel, J. Geophys. Res.88, 49 (1983).
19
J.-E. Wahlund et al., Science308, 986 (2005).
20
W.-H. Ip, Astrophys. J.362, 354 (1990).
21
C. N. Keller, T. E. Cravens, L. Gan, J. Geophys. Res.99, 6511 (1994).
22
The layer between the northern and the southern lobe can have two configurations: In the first, the magnetic field is at a minimum. In this case, it is called a “neutral sheet.” In the second, the magnetic field rotates continuously from the field direction in the northern lobe to the field direction in the southern lobe, while the field magnitude is constant. In this case, the expression “neutral sheet” is not appropriate and we call it “polarity reversal layer” instead.
23
T. E. Cravens, C. J. Lindgren, S. A. Ledvina, Planet. Space Sci.46, 1193 (1998).
24
S. A. Ledvina, T. E. Cravens, Planet. Space Sci.46, 1175 (1998).
25
K. Kabin, T. I. Gombosi, D. L. D. Zeeuw, K. G. Powell, P. L. Israelevich, J. Geophys. Res.104, 2451 (1999).
26
S. H. Brecht, J. G. Luhmann, D. J. Larson, J. Geophys. Res.105, 13119 (2000).
27
A. F. Nagy et al., J. Geophys. Res.106, 6151 (2001).
28
We acknowledge the superb work done by the technical and data processing staff of the MAG team. H.B., F.M.N., and A.W. are supported by the DLR (Germany). M.K.D., C.B., C.S.A., and N. Achilleos are supported by PPARC (UK). N. André is supported by CNES (France). This research was performed while G.H.J. held a National Research Council Research Associateship at the Jet Propulsion Laboratory (JPL). The research at the University of California, Los Angeles, was supported by NASA under a grant administered by JPL.
Information & Authors
Information
Published In
Science
Volume 308 • Issue 5724 • 13 May 2005
Pages: 992 - 995
History
Received: 13 January 2005
Accepted: 10 March 2005
Copyright
American Association for the Advancement of Science.
