New images reveal that the deep-space comet on which mankind plans to land a probe later this year, has an "extraordinarily irregular", duck-like shape, the European Space Agency (ESA) said Thursday.

The icy body dubbed Comet 67P/Churyumov-Gerasimenko is composed of two parts: one flat and long, the other bulbous, according to a blog on the ESA website.

A photo of the comet was taken from the agency's Rosetta spacecraft, designed to team up with "67P" in August and follow the ice ball on its journey around the Sun.

"This week's images of comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape," said the agency, adding: "This is no ordinary comet."

Some have likened the shape to a duck, it said, "with a distinct body and head."

Rosetta mission manger Fred Jansen said much more analysis and modelling will have to be done to determine how best to fly around the weirdly-shaped rock, and how to place a lander on it.

"We currently see images that suggest a rather complex cometary shape, but there is still a lot that we need to learn before jumping to conclusions," he said.

Rosetta took a highly pixellated image of the rock from a distance of 12,000 kilometres (7,500 miles) on July 14, which was then processed for a smoother image.

It also released a movie composed of a sequence of 36 interpolated images separated by 20 minutes.

Dual objects like this, known as "contact binaries", are not uncommon yet it was not clear how they are formed, ESA said.

"The scientific rewards of studying such a comet would be high, as a number of possibilities exist as to how they form."

One theory is two comets melded together in a low-velocity collision during the Solar System's formation billions of years ago, another that a single comet was tugged into a strange shape by the strong gravitational pull of a large object like a planet or the Sun.

A third theory is that "67P" may have once been round but became asymmetric due to ice evaporation as it first entered the Solar System from deep, cold outer Space, or on subsequent orbits around the Sun.

"One could also speculate that the striking dichotomy of the comet's morphology is the result of a near catastrophic impact event that ripped out one side of the comet," said the blog.

"Similarly, it is not unreasonable to think that a large outburst event may have weakened one side of the comet so much that it simply gave away, crumbling into space."

In November, Rosetta will send down a 100-kilogramme (220-pound) refrigerator-sized lander, Philae, which will hook itself to the comet's surface and carry out scientific experiments.

The blog with images can be viewed at: http://blogs.esa.int/rosetta/2014/07/17/the-dual-personality-of-comet-67pc-g/