Moon photo mystery solved
Posted: Tuesday, December 04, 2007 5:30 PM by Alan Boyle
CNSA via Reuters / Xinhua |
A detail from China's Chang'e lunar orbiter
shows cratered terrain on the moon. A yellow
circle has been added to highlight craters that
show evidence of botched photo retouching.
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Some dogged sleuthing by a fellow space blogger has tracked down the truth behind the controversial first photo from China's moon orbiter.
In the week since the picture was released amid much fanfare in Beijing, there have been widespread rumors that the photo was a fake, copied from an old picture collected by a U.S. space probe.
The good news for the Chinese is that Planetary Society blogger Emily Lakdawalla's clears them of outright fakery. The bad news is, she found evidence that the photo was badly retouched for public release.
Lakdawalla's explanation would be embarrassing for Beijing, but it makes the most sense as the solution to this week's moon photo mystery.
Lakdawalla began her investigation by plowing through databases of lunar imagery and dredging up a U.S.-produced picture for comparison. It's not a NASA picture, as reported by the rumor mill. Instead, it's one of the tens of thousands of pictures taken by the Pentagon's Clementine lunar mapping orbiter back in 1994.
The photo from China's Chang'e 1 orbiter is clearly a higher-resolution view, with sunlight streaming from the northwest rather than the north.
"So the notion that China faked their lunar photo can be put to rest. (What is it about the moon and conspiracy theories, anyway?)," Lakdawalla wrote. "At least it certainly isn't a copy of the Clementine image; and it's certainly not a Lunar Orbiter image, either."
Case closed? Not quite.
Lakdawalla found that a mistake was apparently made in stitching together the 19 strips of imagery to produce the finished picture - and that Chinese officials unknowingly pointed out that mistake as they defended the photo's veracity.
NASA / DOD / CAST |
The Planetary Society's Emily
Lakdawalla compared
Clementine imagery of the
crater, at left, with Chang'e imagery at right.
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The mission's chief scientist, Ouyang Ziyuan, told the Beijing News that a new crater had been spotted on the Chang'e imagery - a crater that didn't appear on the U.S. imagery. Lakdawalla determined that crater in question it wasn't exactly new - instead, it appeared to be a crater that had been moved from one spot on the picture to another spot slightly south.
Lakdawalla, who knows her way around spacecraft photo databases as well as photo-retouching tools, hit upon the likeliest explanation for the gaffe. Often, surface features that show up on two strips of data have to be manually corrected to produce the finished image, due to subtle changes in perspective.
"You know that there should have been seams in that image, and I just did not look for them carefully at the time," Lakdawalla told me today.
She said the Chinese must have blended together the seams between the strips - misplacing the crater. The picture may be pretty, but it's pretty much useless as a scientific product, Lakdawalla said.
The detective work came in for kudos from other space mythbusters. "Go check out her really amazing sleuthing," said Bad Astronomy blogger Phil Plait. "This is how it's done, folks. Case closed!"
NBC News space analyst James Oberg, who has had his own experience with moon-hoax controversies, also saluted Lakdawalla's efforts. Even though the Chinese insist that the first picture from Chang'e is scientifically accurate, Oberg said he expected the Chinese to "be forced to backtrack a bit" once they see the full evidence.
"This isn't the first time that photo problems have created illusory 'moon features,'" Oberg wrote in an e-mail. "The very first Soviet moon photo probe, Luna 3 in 1959, sent back images of the back side that included a view of what Moscow grandiosely called 'the Soviet Mountains,' stretching for hundreds of miles. It turned out to be an emulsion smear on the negative."
"For a 'dead world,' the moon sure continues to offer surprises to explorers," Oberg said, "even if many of the 'surprises' are self-induced flaws in the exploration process!"
