NEW HAVEN, Conn. (AP) – As art restorers in London inspected a 230-year-old painting by master landscape artist Thomas Hodges, they noticed the canvas was thicker in some areas than others. Using an X-ray machine, they peered behind the lush greens of New Zealand and discovered the oldest-known painting of Antarctica.

The X-ray revealed two icebergs, painted during Captain James Cook’s historic expedition below the Antarctic circle. Until the National Maritime Museum in London made the discovery last year, historians believed that only sketches of the frozen continent had been produced.

“In the history of art, there’s nothing comparable,” said Angus Trumble, curator at the Yale Center for British Art, where the Hodges painting and the accompanying X-ray are on temporary display for their only United States appearance.

The discovery ignited a discussion over why Hodges endured frigid temperatures, fog and wind to capture the first image of the frozen continent, only to paint over it months later.

Cook had set out in 1772 to discover “Terra Australis Incognita,” the mythical southern continent. Hodges was aboard the HMS Resolution to document the voyage, on which Cook spent nearly four months circumnavigating Antarctica.

“It put the final nail in the coffin that there wasn’t a big land mass there suitable for commercial exploitation,” said Brian Sandford, head of the U.S. chapter of the Captain Cook Society.

Painting the polar landscape would have made sense, experts agree, as it had never been seen before. And forensic analysis showed that Hodges took the time to complete the work.

Yet when the Resolution left Antarctica and made its first stop in New Zealand, Hodges immediately turned on his iceberg canvas and painted his “View in Pickersgill Harbour, Dusky Bay Sound, New Zealand.”

One theory is that the brutal weather destroyed some of Hodges’ supplies, forcing him to reuse a canvas. Others suggest the bleak polar landscape didn’t fit the popular style.

Or maybe four months in Antarctic waters were enough to make Hodges want to erase the artistic record of such a a perilous voyage.