Mysterious Radio Waves on Saturn's Moon Titan

The European Space Agency reported that sensors on Cassini-Huygens Atmosphere Structure Instrument detected a mysterious extremely low frequency (ELF) radio wave during the descent. It was oscillating very slowly for a radio wave, just 36 times a second, and increased slightly in frequency as the probe reached lower altitudes.

nIf the PWA team confirms that the signal is a natural phenomenon and not a result of the way the instrument worked, they will have discovered a powerful new way to probe not just the atmosphere of Titan but its subsurface as well.

The only other world on which ELF waves have been detected has been on Earth. They are reflected by both the surface of the Earth and its ionosphere, the rarefied region of the atmosphere where most particles are electrically charged. This turns the atmosphere into a giant ‘sound box’ where certain frequencies of ELF waves resonate and are reinforced, while other fade away.

On Titan, however, the surface is a poor reflector because of its low conductivity and so these waves penetrate the interior. “The wave could have been reflected by the liquid-ice boundary of a subsurface ocean of water and ammonia predicted by theoretical models,” says Fernando Simões, a member of the mission team.

If Simões is right, successful modelling of how ELF waves resonate on Titan could lend support to the ocean’s existence and tell scientists about its depth. “This does not match any previous prediction for Titan,” says Simões. To some extent, it splits Titan’s atmosphere into two resonating chambers.

But perhaps the biggest mystery is what generated the ELF wave in the first place. On Earth, they are initiated by lightning strikes that make electrons in the atmosphere oscillate, releasing the ELF waves.

However, the Huygens mission suggests that there is no lightning, or very little on Titan. “If there is lightning on Titan, it is significantly less than the amount of lightning that Earth experiences,” says Simões.

So what generated Titan’s ELF? No one on the mission team is quite sure yet.

Posted by Casey Kazan.

Source: ESA

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