Andrew Yee[_1_]
May 12th 08, 04:48 PM
Observatoire de Paris
Paris, France
Contact:
Benoit Noyelles
Observatoire de Paris, IMCCE
Tel: 33 1 40 51 22 74 Fax: 33 1 40 51 20 58
Alain Vienne
Observatoire de Paris, IMCCE, et Universite de Lille
Tel: 33 3 20 52 44 24 Fax: 33 3 20 58 03 28
6 May 2008
The mystery of Titan's rotation
Usually, the tidal effects applied by the parent planet on their natural
satellites are strong enough to slow down their spin velocities and lock
them in a synchronous rotation. As a consequence, the satellite always shows
the same side to its planet, as it is the case for the Moon. Cassini
spacecraft has recently observed a super-synchronous rotation for Titan, and
several hypotheses are introduced to explain this observation. Some
astronomers of IMCCE (Paris Observatory) are part of a team who suggests
that the spin rate measurements might be altered.
Due to tidal effects, the rotation of the natural satellites is expected to
be synchronous with their revolution, i.e. they perform a whole rotation
during a complete revolution around their parent planet. It corresponds to a
dynamical equilibrium state, that involves that the satellite always shows
the same side to its planet.
Cassini spacecraft has recently observed a slight super-synchronous rotation
of Titan (+0.004%) and the authors interpret it as a signature of an
internal ocean, that would dissociate the rotation of Titan's crust from
this of the core, justified by the fact that the motion of the crust would
be sensitive to the energy exchanges with the atmosphere.
Another explanation is being proposed by researchers of the University of
Namur (Belgium), the University of Lille 1 and Paris Observatory (IMCCE).
Following Benoit Noyelles, Anne Lemaitre and Alain Vienne, there could be a
dynamical forcing of the angle (the wobble) between Titan's rotation and
pole axes, that could false the measurement of Titan's spin rate if these
axes were considered as equal.
Cassini space mission has been extended for at least two years, so more
accurate measurements would allow to confirm or refine these explanations.
References
Lorenz R., Stiles B., Kirk R. et al., 2008, "Titan's Rotation Reveals an
Internal Ocean and Changing Zonal Winds", Science, 319, 1649
Noyelles B., Lemaitre A. & Vienne A., 2008, "Titan's rotation: A
3-dimensional theory", Astron. Astrophys., 478, 959-970
Noyelles B., 2008, "Titan's rotational state: The effects of a forced "free"
resonant wobble", Cel. Mech. Dyn. Astr., in press, arXiv:0709.2293
Paris, France
Contact:
Benoit Noyelles
Observatoire de Paris, IMCCE
Tel: 33 1 40 51 22 74 Fax: 33 1 40 51 20 58
Alain Vienne
Observatoire de Paris, IMCCE, et Universite de Lille
Tel: 33 3 20 52 44 24 Fax: 33 3 20 58 03 28
6 May 2008
The mystery of Titan's rotation
Usually, the tidal effects applied by the parent planet on their natural
satellites are strong enough to slow down their spin velocities and lock
them in a synchronous rotation. As a consequence, the satellite always shows
the same side to its planet, as it is the case for the Moon. Cassini
spacecraft has recently observed a super-synchronous rotation for Titan, and
several hypotheses are introduced to explain this observation. Some
astronomers of IMCCE (Paris Observatory) are part of a team who suggests
that the spin rate measurements might be altered.
Due to tidal effects, the rotation of the natural satellites is expected to
be synchronous with their revolution, i.e. they perform a whole rotation
during a complete revolution around their parent planet. It corresponds to a
dynamical equilibrium state, that involves that the satellite always shows
the same side to its planet.
Cassini spacecraft has recently observed a slight super-synchronous rotation
of Titan (+0.004%) and the authors interpret it as a signature of an
internal ocean, that would dissociate the rotation of Titan's crust from
this of the core, justified by the fact that the motion of the crust would
be sensitive to the energy exchanges with the atmosphere.
Another explanation is being proposed by researchers of the University of
Namur (Belgium), the University of Lille 1 and Paris Observatory (IMCCE).
Following Benoit Noyelles, Anne Lemaitre and Alain Vienne, there could be a
dynamical forcing of the angle (the wobble) between Titan's rotation and
pole axes, that could false the measurement of Titan's spin rate if these
axes were considered as equal.
Cassini space mission has been extended for at least two years, so more
accurate measurements would allow to confirm or refine these explanations.
References
Lorenz R., Stiles B., Kirk R. et al., 2008, "Titan's Rotation Reveals an
Internal Ocean and Changing Zonal Winds", Science, 319, 1649
Noyelles B., Lemaitre A. & Vienne A., 2008, "Titan's rotation: A
3-dimensional theory", Astron. Astrophys., 478, 959-970
Noyelles B., 2008, "Titan's rotational state: The effects of a forced "free"
resonant wobble", Cel. Mech. Dyn. Astr., in press, arXiv:0709.2293