Exclusive photos: Clouds seen on Pluto for first time, New Scientist
"There has been no public mention of the clouds, suggesting that the team isn't sure about the detection. In February emails, the team discussed a paper due to be published in the journal Science entitled "The Atmosphere of Pluto as Observed by New Horizons" which only mentions clouds in passing, as an as yet-unsolved mystery. But an email sent by John Spencer of the Southwest Research Institute in Boulder, Colorado, on 1 March includes a picture (see top of article) of a cloud that seems to stand out from the surface. "In the first image an extremely bright low altitude limb haze above south-east Sputnik on the left, and a discrete fuzzy cloud seen against the sunlit surface above Krun Macula (I think) on the right," he wrote. ... The emails suggest that the top cloud image has only just been downloaded from New Horizons."
Keith's update: According to the NASA New Horizons PAO rep: "To be clear, no New Horizons personnel broke a news embargo on the Pluto "clouds" story. A listserv used to internally email team members was mistakenly left public and was discovered by New Scientist. The website published imagery and email exchanges without NASA or New Horizons' knowledge or coordination, and before the data had been fully analyzed and confirmed. The email listserv is no longer publicly accessible, and the data remain under scientific review."
My response: "You just admitted that someone made information public. Whether deliberate or by mistake they broke their own embargo."
FWIW if the New Horizons team had submitted a paper "The Atmosphere of Pluto as Observed by New Horizons" to Science magazine then you can be certain that the editors of Science will want the authors to hold all information about that paper under an internal embargo - even before anything is provided (under embargo) to news media. But ... if the authors discuss this paper in a public forum - outside of any media embargo - well, the authors broke that internal embargo and made it public. And it is fair game for news media to cover. Kudos to New Scientist for discovering this news!