The Dawn space probe will enter orbit of the dwarf planet Ceres this Friday. Once in orbit it will be at a separation distance of 40,000km. Years ago, Hubble photos revealed a curious bright patch on Ceres. The Dawn probe has been capturing increasingly clearer images as it approaches Ceres and the spots remain mysterious. Rather than a large lighter patch, the resulting photos reveal multiple spots, smaller and brighter than expected.
From a recent BBC article:
"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].
By December it will have reached a final orbit of just 380km, from that distance the images it captures will resolve much finer detail, and hopefully will reveal more about these odd reflective areas.
According to a Scientific American article, "No one knows what the bright spots are but guesses abound: Perhaps they are scars from recent impacts or minerals deposited by active geysers or water ice erupted by “cryovolcanoes”—or something even wilder."
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The Dawn mission arrived at Ceres last Spring and has been slowly spiraling in to its final mapping orbit, which it will reach around December 18.
The asteroid Vesta and the recently categorized dwarf planet Ceres have been selected because, while both speak to conditions and processes early in the formation of the solar system, they developed into two different kinds of bodies. Vesta is a dry, differentiated object with a surface that shows signs of resurfacing. It resembles the rocky bodies of the inner solar system, including Earth. Ceres, by contrast, has a primitive surface containing water-bearing minerals, and may possess a weak atmosphere. It appears to have many similarities to the large icy moons of the outer solar system.
By studying both these two distinct bodies with the same complement of instruments on the same spacecraft, the Dawn mission hopes to compare the different evolutionary path each took as well as create a picture of the early solar system overall. Data returned from the Dawn spacecraft could provide opportunities for significant breakthroughs in our knowledge of how the solar system formed.
To carry out its scientific mission, the Dawn spacecraft will carry three science instruments whose data will be used in combination to characterize these bodies. These instruments consist of a visible camera, a visible and infrared mapping spectrometer, and a gamma ray and neutron spectrometer. In addition to these instruments, radiometric and optical navigation data will provide data relating to the gravity field and thus bulk properties and internal structure of the two bodies.
Initial results from the data recorded during its approach and high orbit phases has been published in two papers. The first paper argues that the mysterious bright spots on its surface are salt deposits, but it isn't obvious why the salt is there. The second paper confirms the presence of ammonia bound up in clay materials. Ammonia is typically found out beyond the orbit of Neptune where it condenses more readily, so it is an interesting question why we'd find ammoniated material bound up in the soil so close to the Sun.
Bright Areas on Ceres Suggest Geologic Activity
Since Dawn arrived in orbit at Ceres in March 2015, scientists have located more than 300 bright areas on Ceres. A new study in the journal Icarus, led by Nathan Stein, a doctoral researcher at Caltech in Pasadena, California, divides Ceres' features into four categories.
The first group of bright spots contains the most reflective material on Ceres, which is found on crater floors. The most iconic examples are in Occator Crater, which hosts two prominent bright areas. Cerealia Facula, in the center of the crater, consists of bright material covering a 6-mile-wide (10-kilometer-wide) pit, within which sits a small dome. East of the center is a collection of slightly less reflective and more diffuse features called Vinalia Faculae. All the bright material in Occator Crater is made of salt-rich material, which was likely once mixed in water. Although Cerealia Facula is the brightest area on all of Ceres, it would resemble dirty snow to the human eye.
More commonly, in the second category, bright material is found on the rims of craters, streaking down toward the floors. Impacting bodies likely exposed bright material that was already in the subsurface or had formed in a previous impact event.
Separately, in the third category, bright material can be found in the material ejected when craters were formed.
The mountain Ahuna Mons gets its own fourth category -- the one instance on Ceres where bright material is unaffiliated with any impact crater. This likely cryovolcano, a volcano formed by the gradual accumulation of thick, slowly flowing icy materials, has prominent bright streaks on its flanks.
Ceres and cryovolcanos.
The formation and evolution of bright spots on Ceres (open, DOI: 10.1016/j.icarus.2017.10.014) (DX)
Previously: A Closer Look At Mystery Spots On Dwarf Planet Ceres
NASA's Dawn Orbiter Finds a Mountain on Ceres
Ceres's Cryovolcanoes Viscously Relax Into Nothingness
Organic Molecules Found on Ceres
Dawn Mission Extended at Ceres
Ceres May Have Had a Global Surface Ocean in the Past
(Score: 3, Interesting) by frojack on Tuesday March 03 2015, @06:12PM
I suspect they could just be frozen water or other hydrocarbons heated and precipitated from impact events.
No, you are mistaken. I've always had this sig.
(Score: 3, Interesting) by dx3bydt3 on Tuesday March 03 2015, @06:32PM
It probably is ice, but the photos so far show something very bright considering that explanation.
The reflectivity of Ceres is even less than that of our moon, one figure I saw was roughly 9%. If the bright patches are ice whether it be from impacts exposing interior ice, or from cryovolcanoes, the reflectivity of those areas would be perhaps 90%. Assuming that the ice and the rest of the surface are diffusely reflecting, then the ratio of brightness should only be ~10:1 The brightness differences shown in the recent photos suggest a greater discrepancy, given that they have yet to resolve to the scale of the bright patches. They can't be much smaller than the ~4km scale that the current photos resolve. If they're smaller, they would have to be brighter, and to be much brighter relative to the rest of the surface there would have to be a specular reflection like a sun glint, the fact the bright spots have shown up in numerous images with different angles of illumination make that unlikely though, so I'm guessing that it's areas of exposed ice at least 4km across.
(Score: 2) by frojack on Tuesday March 03 2015, @06:51PM
TFS also mentions geysers.
Isn't Ceres just too small (590 miles) to generate enough internal pressure and heat to maintain any kind of geysers?
No, you are mistaken. I've always had this sig.
(Score: 3, Interesting) by c0lo on Tuesday March 03 2015, @08:27PM
Keep into account that the Ceres' surface gravity is 0.029g: you won't need much of a pressure to create geysers.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 1) by takyon on Tuesday March 03 2015, @10:03PM
Just frozen water? Sounds good to me!
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(Score: 2) by Adamsjas on Tuesday March 03 2015, @10:51PM
Maybe we should land it on mars somehow?
(Score: 3, Interesting) by takyon on Tuesday March 03 2015, @11:14PM
The great "crash Ceres into Mars" plan. Increase Mars's gravity, increase surface water, induce magnetic field, all in one big bang.
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(Score: 2, Funny) by Anonymous Coward on Tuesday March 03 2015, @06:40PM
But, you know, aliens.
(Score: 2) by Nobuddy on Tuesday March 03 2015, @07:47PM
It would be quite a boost to the NASA budget if it was some sort of alien artifact. Satellite, relay dish, or what have you. I bet the US would start really pouring money in to a mission to investigate and bring it back before anyone else could. most likely a manned mission.
(Score: 3, Funny) by bucc5062 on Tuesday March 03 2015, @08:40PM
See, I'm going with this explanation. All of these other hypotheses are too complicated. Geysers? Need heat/water and where did it all come from and why only at that one spot. Impact material? Only in that spot and remaining visible for years and is there enough ice around to create the effect?
It's an alien artifact. The pisser is that the moment NASA gets clear enough resolution they will start to deny it is artificial, they will doctor photos to "prove" it is just a natural formation and secretly ensure no more probes can study the mini planet. Manned mission, bah! The last thing they want
/wink
The more things change, the more they look the same
(Score: 0) by Anonymous Coward on Tuesday March 03 2015, @09:10PM
For the doubters. [xkcd.com]
-- gewg_
(Score: 0) by Anonymous Coward on Wednesday March 04 2015, @02:43AM
It's huge diamonds that are remnants from the core of the planet that blew up creating the asteroid belt.
(Score: 2) by Covalent on Tuesday March 03 2015, @07:47PM
From the article:
“Bright” is a relative term—all the bright spots are actually quite dark but still far brighter than the rest of Ceres, which is blacker than coal.
I wish they had indicated exactly how much brighter "far brighter" is, but they are not particularly clear. At one point the article mentions that the bright spot is "4 times brighter" than the spot on side of the crater, but that doesn't really say much in terms of absolute brightness.
That said, my guess is that it's just ejecta from an impact. The surface of 67P is also exceptionally dark, as are most asteroids. So perhaps large bodies like Ceres get formed from rock and ice and the like, then get covered with dust from comets and asteroids. The original body is slightly lighter than the dust covering, so when the body gets hit, the impact looks lighter. Old impacts get covered with a fresh layer of dust, so they look dark again.
The interesting thing to me is that there are a few of these bright spots. If they are caused by impacts, then perhaps impacts on Ceres are reasonably common?
You can't rationally argue somebody out of a position they didn't rationally get into.
(Score: 2) by takyon on Tuesday March 03 2015, @11:19PM
Well you can already see the cratered surface of Ceres, and it is in an asteroid belt.
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