The Dawn team maneuvered the spacecraft into an orbit that dives 22 miles (35 km) above the dwarf planet’s surface and viewed Occator crater, home to a cluster of strange bright spots.

With a diameter of 57 miles (92 km), Occator is larger than Tycho crater on the Moon. Its steep walls stand tall at over 1.4 miles (2 km), higher than the North face of the Eiger in the Bernese Alps.

The eye-catching dome-like deposit at the heart of the crater is called Cerealia Facula, while the slightly less reflective patches to the east are known as Vinalia Faculae.

In more than three years of orbiting Ceres, Dawn’s lowest altitude before this month was 240 miles (385 km), so the data from the current orbit bring the dwarf planet into much sharper focus.

These low orbits have revealed unprecedented details of the relationships between bright and dark materials in Vinalia Faculae.

Dawn’s visible and infrared mapping spectrometer had previously found the bright deposits to be made of sodium carbonate, a material commonly found in evaporite deposits on Earth.

Last week the spacecraft fired its ion engine to fly nearer Cerealia Facula.

“The first views of Ceres obtained by Dawn beckoned us with a single, blinding bright spot,” said Dawn’s principal investigator Dr. Carol Raymond, from NASA’s Jet Propulsion Laboratory.

“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.”

“Acquiring these spectacular pictures has been one of the greatest challenges in Dawn’s extraordinary extraterrestrial expedition, and the results are better than we had ever hoped,” said Dawn chief engineer and project manager Dr. Marc Rayman, also from NASA’s Jet Propulsion Laboratory.

“Dawn is like a master artist, adding rich details to the otherworldly beauty in its intimate portrait of Ceres.”

The wealth of information contained in these images, and more that are planned in the coming weeks, will help address key, open questions about the origin of the faculae, the largest deposits of carbonates observed thus far outside Earth, and possibly Mars.

In particular, scientists have been wondering how that material was exposed, either from a shallow, sub-surface reservoir of mineral-laden water, or from a deeper source of brines (liquid water enriched in salts) percolating upward through fractures.

And the low-altitude observations obtained with Dawn’s other instruments, a gamma ray and neutron detector and a visible and infrared mapping spectrometer, will reveal the composition of Ceres at finer scale, shedding new light on the origin of the materials found across the dwarf planet’s surface. New gravity measurements also may reveal details of the subsurface.

Source : sci-news.com

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