Board Thread:Warhammer 40k General Discussion/@comment-153.107.33.155-20130718023916/@comment-99.160.190.145-20150729010745

Cyclonic torpedoes is one form of exterminatus, along with virus bombs, they would destroy all surface life and  industry/ cities on the planets they were fired upon. They would sanitize the planet but not Destroy it...

however to quote the article

"Two-Stage Cyclonic Torpedoes
Two-Stage Cyclonic Torpedoes, which are a more exotic form of the standard Cyclonic Torpedoes, are the most common of a special class of rare Exterminatus weapons, designed for use against atmosphere-less or biologically-void worlds (Necron Tomb Worlds being the main example). These torpedoes possess two-stage warheads: The first stage is an unusually powerful Melta Charge that bores straight through a planet's surface all the way down to its core. The second stage is a modified Cyclonic Charge that destabilizes it, in most cases physically destroying the planet from the inside out."

Their use is EXTREMELY limited and not to mention requires the highest authority to enact.

so yes they could..