PARIS: After billions of years of solitary travel through cold, dark outer space, comet 67P/Churyumov-Gerasimenko has recently yielded many secrets, often surprising ones, to the prodding of Europe’s Rosetta spacecraft.

As the probe drew closer and got a better view, ground teams were amazed to discover their target had a weird rubber-ducky shape, an ultra-dark, rough and carbon-rich surface with boulders and dunes, and gave off the most awful chemical “smell”.

On Wednesday, researchers said they have uncovered yet another of the comet’s long-guarded secrets: it is dotted with deep, cylindrical pits likely created through a process similar to sinkholes on Earth.

“These strange, circular pits are just as deep as they are wide. Rosetta can peer right into them,” said Dennis Bodewits of the University of Maryland, who co-authored a paper published in the journal Nature.

“We propose that they are sinkholes, formed by a surface collapse process very similar to the way sinkholes form here on Earth” — where subsurface erosion creates caverns, the ceilings of which eventually collapse under their own weight.

“We already have a library of information to help us understand how this process works, which allows us to use these pits to study what lies under the comet’s surface,” Bodewits said in a statement. The European Space Agency launched Rosetta in March 2004 on a 10-year journey to meet up with 67P.

After travelling some six billion kilometres (3.8 billion miles), the spacecraft caught its first glimpse of the comet in March 2014, from a distance of about five million km — when it was just a small dot in the sky.

Five months later, Rosetta became the first spacecraft to enter into orbit around a comet, and in November made further history by landing the Philae robot on 67P’s surface.—AFP