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Ceres' bright spot
A mosaic of images from NASA’s Dawn spacecraft shows a prominent mound of bright material on the western side of Cerealia Facula on dwarf planet Ceres. (NASA / JPL-Caltech / UCLA / MPS / DLR / IDA Photo)

The once-mysterious bright spots shining on the surface of the dwarf planet Ceres are getting their closest close-ups from NASA’s Dawn spacecraft, adding to the strangest sights of the solar system.

This week, NASA released a mosaic of images captured on June 22 from a height of 22 miles, showing mounds of the white stuff at the center of Occator Crater. Dawn’s current close-up orbit will serve as the last act of a scientific saga that began with its launch more than a decade ago and featured visits to Ceres and Vesta, the two biggest objects in the main asteroid belt.

Ceres’ white spots shone brightly with reflected sunlight in the pictures that Dawn took from millions of miles away, leading some to dub them “alien headlights.” For a time, Dawn’s scientists puzzled over what they were made of. But the probe’s spectral readings confirmed that the material in the bright spots consisted primarily of sodium carbonate.

The close-up pictures should help Dawn’s team answer follow-up questions relating to the origins of the bright spots. “In particular, scientists have been wondering how that material was exposed, either from a shallow, subsurface reservoir of mineral-laden water, or from a deeper source of brines (liquid water enriched in salts) percolating upward through fractures,” NASA said in this week’s image advisory.

Occator Crater
A June 24 image from NASA’s Dawn spacecraft shows the Vinalia Faculae region inside Occator Crater on dwarf planet Ceres, as seen from an altitude of 24 miles. The complex structure of the dark background is reminiscent of lava flows on Earth. On Ceres, however, the process appears to have involved flowing ice rather than flowing lava. (NASA / JPL-Caltech / UCLA / MPS / DLR / IDA Photo)

Carol Raymond, a planetary scientist at NASA’s Jet Propulsion Laboratory who serves as the Dawn mission’s principal investigator, said the latest spotting brings the probe’s adventure at Ceres full circle.

“The first views of Ceres obtained by Dawn beckoned us with a single, blinding bright spot,” she said. “Unraveling the nature and history of this fascinating dwarf planet during the course of Dawn’s extended stay at Ceres has been thrilling, and it is especially fitting that Dawn’s last act will provide rich new data sets to test those theories.”

Dawn’s scientific sunset is expected to occur later this year when its thruster fuel runs out, but even then, the probe will continue to circle Ceres in a stable orbit — to preserve the dwarf planet’s surface in pristine condition for any life-detection probes that may follow.

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