Scientists say they are hugely excited to learn the origin of two bright spots on the surface of Ceres.
The US space agency’s Dawn probe is bearing down on the dwarf planet and on Friday will be captured by its gravity.
That will allow the satellite to spiral down in altitude in the coming months, to take ever sharper images of the spots, which sit inside a wide crater.
The striking features could be where an impact has dug out surface deposits and exposed the dwarf’s interior layers.
But deputy project scientist Dr Carol Raymond cautioned that the resolution of Dawn’s imagery was not good enough at the moment to make any definitive statements.
“These spots were extremely surprising and they have been puzzling to everyone who has seen them,” the Nasa Jet Propulsion Laboratory researcher told reporters.
“They show up in a 92km-wide crater that’s about 19 degrees North latitude. The spot in the centre is about twice as bright as the spot on the side of the crater, and as yet it has not been resolved, meaning it is smaller than the 4km pixel size [of the images].
“But its apparent brightness is already off-scale; it’s consistent with high reflective materials.”
Intriguingly, the European Space Agency’s Herschel telescope reported last year seeing water vapour coming from two sectors on Ceres. One of these sectors includes the location of the spots. That could be very significant, Dr Raymond said.
“The association with the impact crater may indicate that impact heating resulted in exposure of underlying ice [and] its vaporisation; and perhaps we’re seeing a deposit left behind which is rich in material like salts.”
Dawn will spend 14 months studying the 950km-diameter dwarf planet, which is the largest object in the asteroid belt between Mars and Jupiter.
The satellite has turned up at Ceres having previously visited the asteroid Vesta. This 530km-wide rock had the look of a punctured football, the result of a colossal collision sometime in its past that ripped a big chunk out of its southern polar region.
Ceres, on the other hand, is big enough for gravity to have pulled it into a more spherical shape.
Scientists think both bodies are fledglings that never quite made it to the planetary big time.
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SOURCE: BBC, Jonathan Amos