Press releases on scientific discoveries are sometimes "embargoed," meaning that the press is given materials in advance, but only on the condition that the findings not be released before a given date (often the date of a press conference or publication of a magazine). Nature, one of the most prestigious scientific journals, is extraordinarily strict; at one point, they requested that scientists not publish their work as "pre-prints" (copies of articles distributed in advance of official publication, primarily to other scientists in the same field). That borders on being scientifically unethical, as science thrives only on the free flow of information. Thankfully Nature backed down on that request.
Anyway, I'm on a NASA email list with advanced notice of press releases. I'm not sure how I got on the list, but I get notices anyway (I may have requested membership somewhere at some point, but I don't remember). Typically the news is embargoed for a day or two.
Yesterday, I got an announcement about a press release that will be made tomorrow, and strict notice of the media embargo was given. Looking at the release, I had to laugh at how silly the embargo is. The topic is science close to what I work on, and the results have been freely available on our preprint server for six months! The results are also quite intriguing, so I've been chatting about it with colleagues, and I even spoke about it with the science teachers at the workshop I helped lead a couple of weeks ago. So the idea of an embargo is, frankly, silly.
Now, I won't spoil the fun and talk about NASA's release early (there are some cool pictures); I'll talk about it tomorrow. But I'd urge media outlets to re-think the purpose of an embargo. If you are going to make a press release, is there a good reason for embargoing the news? If you just want everyone to get the data at the same time, why not release everything at the time of the press conference (if there is one)?