A mysterious 'pyramid' has been spotted on the surface of a comet that scientists are hoping will unlock the secrets to how Earth formed.
The strange structure was discovered by the Rosetta probe as it orbited comet 67P/Churyumov-Gerasimenko 297 million miles (478 million km) from Earth.
At around 82ft-tall (25 metres), the structure is one of the larger boulders seen on the comet and could help scientists better understand its history.
The 'pyramid' stood out among a group of boulders on the lower side of 67P/C-G's larger lobe – an area that has reminded scientists of the famous pyramids at Giza near Cairo in Egypt.
Esa has now named the structure Cheops, after the largest of those pyramids, the Great Pyramid, which was built as a tomb for the pharaoh Cheops around 2550 BC.
Rosetta has spent 10 years chasing down comet 67P/Churyumov-Gerasimenko and is now in orbit around the 'ice mountain', edging in closer to its surface each day.
For a sense of scale, the comet is about three times the size of Ben Nevis and Rosetta is the size of a car with 105ft (32 metre) wings.
Cheops was seen for the first time in images obtained in early August upon Rosetta's arrival at the comet.
But in the past few weeks, as Rosetta has navigated closer and closer to the comet, it imaged the unique structure again – but this time with a much higher resolution of 50 cm per pixel.
The boulder-like structures that Rosetta has revealed in many places on the surface of 67P/C-G have been described as one of the comet's 'most striking and mysterious' features.
Principal Investigator Holger Sierks, from the Max Planck Institute for Solar System Research (MPS) in Germany, describes the surface of Cheops as 'very craggy and irregular.'
Interspersed between the lighter lumps on the boulder's surface are intriguing small patches of darker material, similar in brightness and texture to the ground upon which the boulder lies.
'It almost looks as if loose dust covering the surface of the comet has settled in the boulder's cracks. But, of course, it is much too early to be sure,' says Dr Sierks.
Apart from their size distribution, which is being measured through careful analysis of the images, almost all other properties of 67P/C-G's boulders are still a mystery to researchers.
VIDEO: Rosetta spacecraft: Story of the comet-chasing probe so far
As Rosetta continues to survey and monitor the comet's surface in the next months, the scientists will be looking for clues to better explain the formation of the comet.
'For example, if the boulders are exposed by cometary activity or are displaced following the comet's gravity field, we should be able to track this down in our images,' says Dr Sierks.
Last month a 2.4 mile-wide (4km) region on the 'head' of comet 67P/Churyumov-Gerasimenko was revealed as the spot for the daring landing of Rosetta's Philae probe.
The high-risk manoeuvre on November 11, if successful, will be the first time in history that a probe has been landed on a comet.
Scientists at mission control in Germany hope the spider-like probe will send back data that could answer questions on the origin of Earth's water and perhaps even life.But they've warned that the landing should be seen as an 'exciting extra' on the Rosetta mission as the mission carries a 'high risk'
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