With a key federal tax incentive about to expire, the U.S. installed a 5.5 gigawatts of wind power in December to cap off a year that saw a record 13.2 gigawatts of wind energy come online, according to a report released Friday by research firm Bloomberg New Energy Finance.

FORBES: U.S. Installed Record 13.2 Gigawatts Of Wind Energy In 2012

Impact craters surrounding the cap appear to be filled with ice and dust that was either deposited by wind or condensation, or perhaps further remains from an earlier larger ice cap.

BBC: By BBC News Online Science Editor Dr David Whitehouse

When wind started whipping up, Francis took off his skull cap, letting the breeze tussle his hair.

NPR: Francis Honors John Paul II Before Installation

If your cap rate is 8% you could, of course, wind up with a real return well below that-if a tenant trashes the place or if the house is near a city with a weak economy.

FORBES: I, Landlord

"There is no cap and no limit on it but we want to pursue onshore wind in a sensible way, " he said.

BBC: Ed Davey

The structure's cone-like shape was designed to reduce wind turbulence, yet there is only one piece of curved glass on the building: a lens-shaped cap at the very top.

FORBES: Magazine Article