Nasa has released new images of Pluto's moon Kerberos, taken by the New Horizons probe.

It is considerably smaller than scientists had expected and has a highly-reflective surface, disproving predictions made prior to the Pluto flyby in July.

'Once again, the Pluto system has surprised us,' said New Horizons Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

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Say 'cheese'! The moon (pictured) is smaller than scientists expected and has a highly-reflective surface, disproving predictions made prior to the Pluto flyby in July. It appears to have a double-lobed shape, with the larger lobe approximately 5 miles (8 km) across and the smaller lobe approximately 3 miles (5 km) across

The new data shows that Kerberos appears to have a double-lobed shape, with the larger lobe approximately 5 miles (8 km) across and the smaller lobe approximately 3 miles (5 km) across.

Scientists speculate from its unusual shape that Kerberos may have been formed by the merger of two smaller objects.

The reflectivity of Kerberos' surface is similar to that of Pluto's other small moons - approximately 50 per cent - and strongly suggests Kerberos, like the others, is coated with relatively clean water ice.

Before the New Horizons encounter with Pluto, researchers had used Hubble Space Telescope images to 'weigh' Kerberos by measuring its gravitational influence on its neighbouring moons.

That influence was surprisingly strong, considering how faint Kerberos was.

The reflectivity of Kerberos' surface is similar to that of Pluto's other small moons - approximately 50 per cent - and strongly suggests Kerberos, like the others, is coated with relatively clean water ice

DID KERBEROS GET ITS DUCK-SHAPE LIKE COMET 67P? The new data shows that Kerberos appears to have a double-lobed shape, with the larger lobe approximately 5 miles (8 km) across and the smaller lobe approximately 3 miles (5 km) across. Scientists speculate from its unusual shape that Kerberos may have been formed by the merger of two smaller objects. Last month scientists revealed that the strange shape of comet 67P/Churyumov–Gerasimenkomay have been sculpted by a collision. Analysis of comet 67P/Churyumov–Gerasimenko has revealed its two 'lobes' appear to be two separate smaller comets that have collided together in the past, becoming joined by a thin 'neck'. The researchers looked at the layers of material on the lobes and found they appear to be separate bodies (pictured) By studying high-resolution images sent back by the European Space Agency's Rosetta spacecraft, researchers have discovered the two lobes of the comet have different compositions. Comet 67P has a larger lobe and a smaller lobe separated by a thin 'neck' region, each of which appear to be made up of 'onion-like' layers. Professor Matteo Massironi, a geoscientist at the University of Padova, Italy, and his colleagues have found that the larger lobe is made up a series of layers 2,130 ft (650 metres) thick. However, these are quite different from the layers that appear in the smaller lobe. Combined with data about the comets gravity, the researchers said this suggests 67P is the result of a low-speed impact between two separate bodies sometime in the distant past. They say these 1.2 mile wide (2km) smaller comets appear to have formed through similar processes by gradually accruing matter as they traveled through the solar system. Professor Massironi said: 'It is clear from the images that both lobes have an outer envelope of material organised in distinct layers, and we think these extend for several hundred metres below the surface. 'You can imagine the layering a bit like an onion, except in this case we are considering two separate onions of differing size that have grown independently before fusing together.' The researchers, whose findings are published in the journal Nature, used images taken by the OSIRIS imaging system on the Rosetta spacecraft. Advertisement

This image, taken by Nasa's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. Styx (initially designated P5), is the innermost of the moons found by Hubble over the past seven years. This image was taken with Hubble's Wide Field Camera 3 on 7 July 2012

They had theorised that Kerberos was relatively large, appearing faint only because its surface was covered in dark material.

PLUTO AND ITS MOON KERBEROS Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth. It is about two thirds the size of our moon. With a surface temperature estimated to be -229°C (-380°F), the environment at Pluto is far too cold to allow liquid water on its surface. Pluto's moons are also in the same frigid environment. Kerberos is a small moon - now thought to be eight miles across. Kerberos was discovered by the Pluto Companion Search Team using the Hubble Space Telescope on 28 June 2011. It was the fourth moon of Pluto to be discovered. The convention for naming Plutonian moons is to use names associated with the god in classical mythology. Cerberus is already the name of an asteroid, so the Greek form of the name, Kerberos, was accepted. Advertisement

But the newly revealed small, bright-surfaced Kerberos shows that the idea was incorrect, for reasons that are not yet fully understood.

'Our predictions were nearly spot-on for the other small moons, but not for Kerberos,' said New Horizons co-investigator Mark Showalter, of the Seti Institute in Mountain View, California.

The new results are expected to lead to a better understanding of Pluto's satellite system.

Now that New Horizons has finished its Pluto fly-by, it is hoped that the next leg of its journey will to explore the Kuiper belt.

Nasa selected the potential next destination for the New Horizons mission to visit after its historic July 14 flyby of the Pluto system.

If approved, the probe will become the first spacecraft to visit the icy blocks encircling our solar system in a ring of debris called the Kuiper Belt.

The fridge-sized craft will head to a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits nearly a billion miles beyond Pluto.

As with all Nasa missions that have finished, scientists must write a proposal to the space agency to fund a KBO mission.

That proposal – due in 2016 – will be evaluated by an independent team of experts before Nasa can give the go-ahead.

Early target selection was important; the team needs to direct New Horizons toward the object this year in order to perform any extended mission with healthy fuel margins.

New Horizons will perform a series of four manoeuvres early November to set its course toward 2014 MU69 – nicknamed 'PT1' (for 'Potential Target 1') – which it expects to reach on January 1, 2019.

In July this year New Horizons became the first spacecraft ever to visit Pluto (illustration shown). It was launched on 19 January 2006 at a speed of 36,373 mph (58,536 km/h) - the fastest spacecraft ever to leave Earth orbit, 100 times faster than a jetliner

If a plan is approved, New Horizons will become the first spacecraft to visit the icy blocks encircling our solar system in a ring of debris called the Kuiper Belt. The fridge-sized craft will head to a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits nearly a billion miles beyond Pluto

Any delays from those dates would cost precious fuel and add mission risk.'2014 MU69 is a great choice because it is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey desired us to fly by,' said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI) in Boulder, Colorado.

'Moreover, this KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.'

New Horizons was originally designed to fly beyond the Pluto system and explore additional Kuiper Belt objects.

The spacecraft carries extra hydrazine fuel for a KBO flyby; its communications system is designed to work from far beyond Pluto; its power system is designed to operate for many more years; and its scientific instruments were designed to operate in light levels much lower than it will experience during the 2014 MU69 flyby.'