What are those bright spots? As Dawn nears Ceres, mystery remains

What are those bright spots? As Dawn nears Ceres, mystery remains
This artist's concept shows NASA's Dawn spacecraft arriving at the dwarf planet Ceres, the most massive body in the asteroid belt. Dawn is set to enter orbit on March 6. (NASA/JPL-Caltech)

As NASA's Dawn spacecraft gets ready to enter orbit around Ceres -- the first dwarf planet  visited by a satellite -- mission scientists are using new images to try to understand strange and surprising features on its icy surface.

Dawn will enter orbit on March 6 studying the surface of the dwarf planet in detail in a series of orbits scheduled through June 2016. Dawn will offer unprecedented insight into Ceres' evolution, its surface features, its mineralogy and composition -- as well as whether the surface is active today.


At 590 miles across, Ceres is one of five dwarf planets and the largest member of the asteroid belt, which stretches between the orbits of Mars and Jupiter. Like its fellow giant asteroid Vesta (which Dawn visited earlier, from 2011 to 2012), Ceres is a protoplanet -- the kernel of an almost-planet that never quite came together -- thanks to the disruptive influence of Jupiter's gravity. As such, these rocky fragments offer a unique window into what the early solar system looked like.

"They're literally fossils that we can investigate to really understand the processes that were going on at that time," deputy principal investigator Carol Raymond, a geophysicist at Jet Propulsion Laboratory, said in a press briefing.

Dawn has already picked up a number of strange features on the dwarf planet's surface, including a pair of exceedingly bright spots in the middle of a 57-mile-across crater. The scientists are trying to figure out what they are.

"The team is really, really excited about this feature because it is unique in the solar system," Raymond said. "And we will be revealing its true nature as we get closer and closer to the surface. So the mystery will be solved, but it is one that's really got us on the edge of our seats."

These incredibly bright spots might be rich in salts and water ice; it's possible the spots might have some sort of ice-volcano origin, but Raymond said a so-called cryovolcano was not likely, given that there's thus far no sign of a peaked or mounded structure at that spot.

"A cryovolcano or that kind of mechanism is not at the top of the list for that feature," Raymond said.

The bright spots' location does match one of the two zones where water vapor was spotted steaming off of Ceres by the European Space Agency's Herschel Space Observatory, so the two phenomena may be linked, she added.

The researchers are also studying the craters and basins on the surface for insight into the interior of the dwarf planet. For example, the scientists have also noticed a huge, shallow basin roughly 186 miles across with low walls that seem to have been smoothed out. This would make sense for an icy surface, Raymond said -- ice, if it's "warm" enough, tends to flow, allowing structures to relax over time.

"This may indicate a region of distinct geological processes," Raymond said.

Ceres is thought to have hosted a subsurface ocean at some point. As such, it's one of a few icy "water worlds" in our solar system, such as Jupiter's moon Europa and Saturn's moon Enceladus, that have the potential to support microbial life.

Ceres, as mentioned earlier, is actually Dawn's second stop: The first was fellow giant asteroid Vesta. Where Ceres is icy and round, Vesta is lumpy and dry -- and the differences between the two may help scientists better understand the early solar system's evolution.

Although Ceres is set to enter orbit this week, don't expect a deluge of fresh photos -- Dawn is now approaching the spacecraft from the dark side of the dwarf planet, and it will reemerge onto the sunlit side in about a month, officials said.

"The floodgates are really going to open when we get to our first science orbit, in late April," Dawn project manager Robert Mase said.

What do you think Ceres' two bright spots are? Follow @aminawrite for more science news.