Images taken from the Rosetta spacecraft have revealed a long, deep crack in the fragile neck of comet 67P where the celestial body might one day break in half.

The European Space Agency probe, which dropped its Philae lander onto the comet’s surface in November, has been circling the 4km-wide lump of dust and ice to study the object in detail.

Data beamed back to Earth from the orbiter show that the comet is built up from fluffy layers of dust and ice and has only half the density of water. Its surface is riddled with unusual cylindrical pits that have walls covered in what the scientists refer to as “goosebumps”.

The latest images were released on Thursday among a raft of papers that comprise the first scientific results to be published since Rosetta arrived at the comet. The reports give the first detailed picture of the comet and appear in a special issue of the US journal, Science.

Shaped like an enormous rubber duck, the comet has a large “body” that is joined to a smaller “head” by a narrower neck region. Scientists are unsure whether the comet gained its shape through uneven erosion, or when two bodies fused together to make the comet after an ancient collision in the early solar system.

The large open crack was spotted by Rosetta’s Osiris camera and runs for hundreds of metres around the 1km-wide neck of the comet. In places, the crack is a metre-wide and parts of it are filled with dust.

“We wondered what could create the crack, and we think it’s mechanical stress cause by the comet flexing,” said Holger Sierks, the lead scientist on Osiris. It is unclear how far the crack reaches, but researchers hope to have a better idea in May when the sun illuminates parts of the comet that are currently in shade.

The Rosetta spacecraft will be the first to get a close-up view of a comet as its activity ramps up on its journey around the sun. The comet is losing 11kg of gas and dust a second, but will shed far more as it reaches its closest approach to the sun in August.

A a long, deep crack appears in the neck region of comet 67P/Churyumov-Gerasimenko, as seen here in this latest image from Rosetta spacecraft. Photograph: European Space Agency

The crack across the comet’s neck region could either close up or grow larger, depending on how the stresses in the comet change over time. “It could close up again, but there’s certainly a crack, it’s deep and wide, and it could break apart along the neck,” said Sierks. “It wouldn’t be the first comet that has fractured.”

Measurements from Rosetta’s suite of instruments put the comet’s mass at 10bn tonnes, but its density is half that of water. The body of the comet is unusually fluffy, with a porosity of between 70 to 80%. “The surface layer is dusty and it is very easy to build up fluffy layers, because the gravity is 100,000 times weaker than on Earth, so it doesn’t get compacted,” Sierks said.

Most of the water vapour and dust spewing from the surface of the comet comes from the neck area where scientists spotted the big crack. The gravity is weakest in that region, so dust particles that are dislodged from the comet can drift out to space instead of falling back to the surface. The main body of the comet is less active, because it is covered with a thin layer of dust that acts like an insulating blanket.

Further images from Osiris reveal unusual cylindrical pits on the comet’s surface. Many of the pits are about 200m across and have internal walls covered with features that look like giant goosebumps. The pits may have formed when gas bubbles under the surface expanded and blasted through the thin overlying material. But another theory is that they are holes left by impacts from micrometeorites.

After rendezvous with the comet, the Rosetta probe swung into an orbit that brought the spacecraft within 10km of the comet. Sensors on the spacecraft picked up a range of molecules coming off the surface, including water, carbon monoxide and carbon dioxide. Surrounding the comet is a cloud of dust that includes 100,000 grains larger than 5cm.

A close-up of the crack in the neck region of comet 67P. Photograph: Esa

The water onboard the comet is unlike that found on Earth, casting doubt on the popular theory that comets brought the majority of water to our home planet and so made it hospitable for life. Kathrin Altwegg from the University of Bern found that water on the comet contained a higher proportion of deuterium, a heavier form of hydrogen than that on Earth.

Rosetta will follow the comet through its closest approach to the sun in August and beyond as it heads back out towards Jupiter. When the comet reaches its most active, scientists will fly the probe through the intense jets of dust and gas billowing from the surface to analyse their make-up.

“This is a wonderful time for exploring the building blocks of our solar system,” said Sierks. “It is the first time ever that we can see how a comet really works.”