The Cartoon Network has provided clips from the May 12th episode of Green Lantern: The Animated Series, Flight Club" which features the appearance of Thanagarians. Here's the description for the new episode and a preview clip:
The Green Lanterns travel to a prison asteroid to find a legendary code that holds the key to crossing an impenetrable asteroid barrier called “The Maelstrom” before Atrocitus and his Red Lantern armada can do so. Unfortunately, a Thanagarian prisoner named Byth Rok is the only one that knows the code.
Green Lantern: The Animated Series airs on the Cartoon Network Saturday mornings at 10am and is available for digital download from Amazon on Demand, iTunes, PSN and the Zune Marketplace on the Xbox 360.