mos prize crossword

[marjessica]

Sorry I need help with the following:
10a Pass the Greeks failed to hold against the Persians in 480BC? (11)
26A Orbiting body with a frozen nucleus and luminous tail? (5)
25d Computer operating system developed by AT&T?(4)
35D Mafia code of silence?(6)
37d Jagged Spanish mountain range?(6)

[Littlegem]

Thermopylae
Comet
UNIX
Omerta
Sierra