It is true that Titan does not have its own magnetic field. It has been confirmed by magnetometer data from a flyby of Titan by the Cassini spacecraft. Although scientist argues that the absence of magnetic field is not a decisive factor whether Titan has a metallic core, they implied that either Titan does not have an iron core or it has a core but doesn't act as an operative dynamo. Saturn's magnetosphere is so huge that it covers all of its satellites including Titan. Almost all of Titan's orbit (95%) is spent inside of Saturn's magnetosphere. With no intrinsic magnetic field to repel the planet, Titan is so much influenced that the either moon gets magnetized and in return sucking away its atmosphere.
Saturn’s magnetosphere acts like a giant vacuum, basically sucking up Titan’s atmosphere. All the gases including hydrogen and nitrogen, are ripped away from moon in the form of plasma. As Titan orbits closer to Saturn, this magnetization gets stronger, wreaking havoc on Titan’s atmosphere and weather. This has been confirmed from the calculation sent from the flybys.
By the time Titan leaves Saturn's magnetosphere, it retains part of Saturn's magnetic field. This has been confirmed when the Cassini spacecraft finally flew through Titan’s upper atmosphere at a time when it had edged out of the influence of Saturn’s magnetic field. The encounter, which took place on 13 June 2007, showed that Titan’s atmosphere actually retains a memory of the magnetic field of the plasma that surrounds Saturn. This memory lasted for 3 hours. Titan’s emergence fully exposes it to the solar winds but since it retained its magnetization temporarily (it looked like a draped sheath of magnetic field lines forming a comet-like tail around the moon), it might have protect it from substantial losses. Scientist have put forward two theories:
- Saturn's magnetic field is almost aligned to the spin axis of Titan thus helping it retain some magnetic fields.
- The possibility of a salty, electrically conducting ocean beneath the surface as suggested by recent measurements of the moon’s spin rate
You can find more details in the reference.
- Edberg, N. J. T., et al. (2015), Effects of Saturn's magnetospheric dynamics on Titan's ionosphere, J. Geophys. Res. Space Physics, 120, 8884– 8898, doi:10.1002/2015JA021373.
- Backes et. al. (2005). Titan's Magnetic Field Signature During the First Cassini Encounter. Science (New York, N.Y.). 308. 992-5. 10.1126/science.1109763.
- Electric field variability and classifications of Titan’s magnetoplasma environment by ARRIDGE ET AL. (PDF)
- Encyclopedia of Geomagnetism and Paleomagnetism by David Gubbins, Emilio Herrero-Bervera, Springer Science & Business Media, 2007
- Titan: Interior, Surface, Atmosphere, and Space Environment,
Ingo Müller-Wodarg, Caitlin A. Griffith, Emmanuel Lellouch, Thomas E. Cravens
Cambridge University Press, 2014
- Titan from Cassini-Huygens, Robert Brown, Jean Pierre Lebreton, Hunter Waite
Springer Science & Business Media, 2009
- How does Titan maintain its atmosphere?