Paris (AFP) - A page of original comic strip drawings from one of the best Tintin adventures, "Explorers on the Moon", is expected to sell for up to $1 million when it goes under the hammer later this month.
The page, entitled "We walk on the moon", has the boy reporter, his dog Snowy and blundering sidekick Captain Haddock making their first moon walk from their red and white rocket.
With the 1954 book regarded as one of the artist Herge's very best, the Paris auction house Artcurial said it could make up to 900,000 euros.
The late Belgium artist already holds the world record price for a comic strip.
A double-page ink drawing that served as the inside cover of all the Tintin adventures published between 1937 and 1958, sold for $3.7 million to an American fan two years ago.
Rival auction house Christie's said Monday that it was putting another rare Herge strip up for sale -- also in Paris -- on the same day, November 19.
It said the page from the unfinished story "Tintin and the Thermozero" -- estimated at 250,000 euros -- is the first ever to come to market.
Why the artist never finished the tale of espionage and a terrifying secret weapon set against the backdrop of the Cold War, is one of the great mysteries for Tintin-ologists.
Herge wrestled with it for years, "starting it at the end of the 1950s", said Christie's, but never got further than eight pages.
- 'Comic history' -
Artcurial's comics expert Eric Leroy described the "Explorers on the Moon" as "a key moment in the history of comic book art... it has become mythic for many lovers and collectors of comic strips.
"It is one of the most important from Herge's postwar period, on the same level as 'Tintin in Tibet' and 'The Castafiore Emerald'," he added.
The story completes the lunar adventure started in "Destination Moon" (1953) and features several hilarious episodes including Haddock getting drunk on whisky and floating off into space to briefly become a satellite of the asteroid Adonis.
It turns on Tintin foiling a plot by a mysterious foreign power to hijack the rocket by the evil stowaway spy Colonel Jorgen.
Leroy said Herge strips from this period "very rarely come to market".
The moon drawings are being sold alongside 20 ink sketches he created for a series of New Year's greeting cards known as his "snow cards".
The cards are expected to go from between 60,000 and 120,000 euros each, Artcurial estimate.
- 'Tintinmania' -
But all eyes will be watching to see if the price rockets on the moon strip when it goes under the gavel, as has happened at other recent Tintin auctions.
Christie's said another Herge original drawing for a puzzle to go with "Explorers on the Moon" could make 120,000 euros at its sale.
Prices for cartoon art have multiplied tenfold in the last decade, according to gallery owner Daniel Maghen, who also works with comic art.
Herge's British biographer Harry Thompson has called "Explorers on the Moon" a "technical masterpiece" widely regarded as Herge's "greatest artistic achievement".
Drawn more than a decade before the first moon landings, Thompson said it was "uncannily accurate" in its depiction of the moon's surface.
Its cover with Tintin, Snowy and Captain Haddock in their space suits and their ship in the background has become iconic, with reproductions of the chequered red and white rocket among the bestselling selling Tintin figurines.
The sale comes as Tintinmania again grips the French capital, with Herge currently the subject of a huge retrospective exhibition at the Grand Palais.