DARMSTADT, GERMANY—The comet 67P/Churyumov-Gerasimenko, which the Rosetta spacecraft is now orbiting, is by all accounts a fascinating chunk of dust and ice. This week, scientists using the spacecraft’s high-resolution camera presented some staggering images of the duck-shaped comet at a planetary science conference in Tucson, Arizona. They showed the first color images of the comet. They showed dust grains being ejected from the surface, arcs that could be traced back, presumably, to geysers of sublimating ice. And they showed brightness variations less than 10 centimeters apart—which could indicate that they have found sparkling bits of ice peeking through a black crust of dust.

But Rosetta’s operator, the European Space Agency (ESA), has released none of these images to the public. Nor have any of these images been presented in Darmstadt, Germany, where scientists at ESA’s mission control are preparing to drop the Philae lander to the comet surface on Wednesday. Project scientist Matt Taylor was reduced to learning about the new results at the Arizona conference by thumbing through Twitter feeds on his phone.

For the Rosetta mission, there is an explicit tension between satisfying the public with new discoveries and allowing scientists first crack at publishing papers based on their own hard-won data. “There is a tightrope there,” says Taylor, who’s based at ESA’s European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands. But some ESA officials are worried that the principal investigators for the spacecraft’s 11 instruments are not releasing enough information. In particular, the camera team, led by principal investigator Holger Sierks, has come under special criticism for what some say is a stingy release policy. “It’s a family that’s fighting, and Holger is in the middle of it, because he holds the crown jewels,” says Mark McCaughrean, an ESA senior science adviser at ESTEC.

Allowing scientists to withhold data for some period is not uncommon in planetary science. At NASA, a 6-month period is typical for principal investigator–led spacecraft, such as the MESSENGER mission to Mercury, says James Green, the director of NASA’s planetary science division in Washington, D.C. However, Green says, NASA headquarters can insist that the principal investigator release data for key media events. For larger strategic, or “flagship,” missions, NASA has tried to release data even faster. The Mars rovers, such as Curiosity, have put out images almost as immediately as they are gathered.

ESA has a different structure from NASA’s. It relies much more on contributions from member-states, whereas NASA pays for most instrument development directly. On Rosetta, for example, ESA hasn’t paid for very much of the €100 million camera, called OSIRIS, and therefore has less control over how its data is disseminated. “It’s easier for [NASA] to negotiate [data release] because we’re paying the bills,” Green says, whereas ESA has to do it “by influence.”

Prior to Rosetta’s launch in 2004, an embargo of 6 months was set for all the instrument teams. McCaughrean points out that mission documents also stipulate that instrument teams provide “adequate support” to ESA management in its communication efforts—but that term has been debated by the camera team. “I believe that [the OSIRIS camera team’s support] has by no means been adequate, and they believe it has,” McCaughrean says. “But they hold the images, and it’s a completely asymmetric relationship.”

So far, OSIRIS has not released any images from its closest orbits at 10 kilometers above the comet. The vast majority of publicly released images have come from navigation cameras, engineering instruments that ESA management has more control over. OSIRIS has about five times better resolution than the navigation cameras.

Sierks, of the Max Planck Institute for Solar System Research in Göttingen, Germany, feels that the OSIRIS team has already been providing a fair amount of data to the public—about one image every week. Each image his team puts out is better than anything that has ever been seen before in comet research, he says. Furthermore, he says other researchers, unaffiliated with the Rosetta team, have submitted papers based on these released images, while his team has been consumed with the daily task of planning the mission. After working on OSIRIS since 1997, Sierks feels that his team should get the first shot at using the data.

“Let’s give us a chance of a half a year or so,” he says. He also feels that his team has been pressured to release more data than other instruments. “Of course there is more of a focus on our instrument,” which he calls “the eyes of the mission.”

Another reason why Rosetta instrument teams have been slow to release information is that some of them have submitted papers to Science, which, upon acceptance, carries an embargo that forbids public discussion of specific results in the papers. But some ESA officials think that team members have become too fearful about disclosing everyday discoveries. Because of concerns over embargoes, the team has only reluctantly disclosed the dimensions and volume of the comet, for instance, and it has yet to publicly describe the comet’s albedo, or reflectivity.

At a press briefing on Tuesday in Darmstadt, a reporter asked Fred Jansen, the project manager, if the Wednesday landing event would include any new images from Sierks’s OSIRIS camera. “We definitely intend to squeeze these out of him,” Jansen said. “There is an agreement that we’ll get pictures tomorrow.”

To read more Rosetta coverage, visit our Rosetta collection page.