Jets of gas caused by melting ice are slowing down the spinning rotation of Comet 67P Chryumov/Gerasimenko, said European scientists based on data from the orbiting Rosetta spacecraft.

Scientists said the four kilometer wide comet takes 12.4 hours to complete one rotation but have noticed this is being lengthened by about a second every day.

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"The gas jets coming out of the comet -- they are acting like thrusters and are slowing down the comet," said European Space Agency flight director Andrea Accomazzo.

Mission controllers in September 2014 determined the comet's rotation period was extending by 33 milliseconds every day. Now, with the comet moving closer to the Sun and ejecting out much larger volumes of gas and dust, this spin-down is approaching one second a day.

"OK, it's not going to slow down completely but this gives you an order of magnitude for the accuracy we're now achieving with the navigation of the spacecraft around the comet," said Accomazzo.

Unfortunately, the increased amount of gas and dust being ejected by the comet will prevent Rosetta from approaching any closer.

"The aerodynamic effects are now more and more important. The jets are getting stronger and stronger," he told BBCNews.

Previously, it was possible to fly Rosetta around Comet 67P with remarkable precision. To achieve this, mission controllers used a system of landmarks on the comet to understand how it's rotating and moving through space. This information is fed into a model that helps plan a trajectory for Rosetta.

Because of the huge amount of gas now being vented by the 18 billion tonne comet, controllers discovered these landmarks weren't turning up in the right place at the expected time.

Accomazzo said these gases are moving at 800 meters per second, fast enough to endanger Rosetta.

"We definitely have to take this into account. We are a big spacecraft with 64 square metres of solar panels. We're like a big sail," he pointed out.

Comet 67P is also emitting more dust as it approaches the Sun. Accomazzo said the dust in the environment around the comet has confused the star trackers Rosetta uses to work out its orientation. The trackers now see the dust particles as stars.

Mission controllers have also kept up the search for the missing Philae lander. Accomazzo said controllers are now using Rosetta to make radio "shout outs" to Philae and hope enough sunshine will soon fall on the lander's solar panels to reboot it.