The word thermosphere is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 22
Highest Scoring Words With Friends™ Plays In The Letters thermosphere
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Seven Letter Word Alert: (39 words)
emoters, emperor, heptose, heteros, meeters, meteors, mothers, porters, pothers, premeet, presort, preterm, rehomes, remeets, remorse, remoter, remotes, reports, reposer, reshore, restore, retrees, rhetors, rompers, seether, sheerer, sheeter, shorter, smother, steeper, steerer, stomper, strophe, teemers, tempers, tempore, theorem, thermos, tremors