Tag Archives: Occator Crater

Ceres’s brightest spot

Brightest Spot in Occator Crater on Ceres

Cool image time: While I was in Washington the Dawn science team released a very nice close-up image of the bright spots inside Occator Crater on Ceres. On the right is a cropped version which focuses solely on the central brightest spot. The spot appears to overlie a central dome with a depression in the middle. Other data says the spot is the low area in the crater, and the linear cracks that radiate away as well as in concentric rings around the spot suggest that this central area has subsided, causing those cracks.

Make sure you look at the full image, as it includes the other smaller spots that are also inside Occator.

New close-up of Occator Crater’s spots

Occator Crater central spot

The Dawn science team have released new images taken from the spacecraft’s low orbit observations, including a close-up of the central white spot at Occator Crater, the brightest spot on Ceres.

The image on the right is a cropped though full resolution version of the full image. I have reduced it only slightly. As they note,

Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, contains the brightest area on Ceres, the dwarf planet that Dawn has explored since early 2015. The latest images, taken from 240 miles (385 kilometers) above the surface of Ceres, reveal a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. Prominent fractures also surround the dome and run through smaller, bright regions found within the crater.

Changes in Ceres’s white spots

The uncertainty of science: Ground-based observations of Ceres now suggest that the white spots imaged by Dawn undergo subtle unexpected variations

As Ceres rotates every 9 hours, HARPS is so sensitive that it can detect the very slight Doppler shift in spectrum frequency as the bright spots rotate toward and away Earth, but during observations for 2 nights in July and August 2015, more changes not related to Ceres’ spin were detected. “The result was a surprise,” said co-author Antonino Lanza, also from the INAF–Catania Astrophysical Observatory. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.”

And it appears that these changes are consistent with some kind of volatile (ice) being exposed to sunlight and venting vapor into space, causing an increase in reflectivity. It seems that when Occator experiences solar heating, plumes are produced and then evaporate, creating a complex spectroscopic signal that evolves during that hemisphere’s daytime. This finding appears to be consistent with earlier observations made by Dawn showing a mysterious haze over Occator.

The problem with this theory is that it assumes the white spots are comprised of water ice. However, data from Dawn has instead suggested that the white spots are not water but salt deposits.

It could be that the white spots are salt left behind when water vented from inside Ceres evaporates away, but so far the data from Dawn has not found any evidence of water at the spots. If it was venting there, Dawn should have seen it.

Oblique view of Ceres’s bright spots

Occator Crater on Ceres

Cool image time! The image above is a newly released image of Occator Crater on Ceres, the location of the dwarf planet’s double bright spots, taken by Dawn in October.

I have cropped the image to focus on the crater and the bright spots. Unlike most previous images, this one is taken from an angle to bring out the topography, which also confirms what other data had shown, that the bright spots are not on top of any peaks. If anything, they appear to be located at low spots in the crater, as that previous data had suggested.

Though the spots are not really very bright, they are very bright relative to the dark surface of Ceres. This is why it is difficult to get a good image of them. Either you have to over-expose the spots to see the surface details around them, or under-expose the surface around them to see some detail in the spots. This image tries to find a middle ground.

Eventually they will move Dawn in very close to try to get higher resolution images of the spots alone. At that time we might finally be able to get a better understanding of what causes them.