Here’s a quick list of some crazy things that the Ceres bright dots could (or could not) be.
- A Biological Alien City
Unlikely. Current measurements of reflectivity of the spots says “they’re as reflective as water ice” or, in other terms “white as snow”. Now, that’s not to say that there couldn’t be a race of aliens who have constructed a completely white city (complete with nearby suburbs!) but it seems quite unlikely.
For biological life, there needs to be lots of other things present, likely water, source of food energy, like other plants and/or animals, or some kind of “Food farm”. We could be looking at the top of a “biodome” type structure, enclosing a habitation environment, though. (As below, likely coated in something like Titanium Dioxide to reduce heat & radiation exposure)
- A Mechanical Alien City
By “Mechanical Alien” I mean “Machine Intelligence” or more simply: “robots from outer space”. This seems more likely than any form of biological alien. If the spots are created by aliens, then why would they choose Ceres over all the other nearby planets? One simple choice would be the presence of unique or rare elements in Ceres’ crust or core. Mechanical life could be attracted by an abundance of rare elements like Gallium or Titanium or even Helium (or tons of other options).
We could be looking at a drilling or mining station and outpost, or even a single large mechanical life-form that’s working, stranded or crashed in that location. Remember that when you think about mechanical life, all assumptions about size & scale can be thrown out the window. This could be a colony of trillions of small machines, or one single big one, or something in between.
This even (somewhat) could explain the “white as ice” nature of the spots. If you were to make machines capable of interstellar travel, what color would you make the ships? Probably very, very white — this would give you maximum visibility in space, but also maximum reflectivity (or control thereof) to minimize the heating from nearby sun(s). There are several common elements that would lead to the white nature — Something like a thin coating of Titanium Oxide on the surface of a building or machine. The interesting point about this is that it also explains the Infrared readings showing that some of the spots were not cooler than their surroundings, and I believe that white titanium dioxide would almost exactly match this behavior, since it’s highly reflective to Infrared radiation.
- A Mechanical Alien City
- Some kind of “Beacon”
Something left behind by a biological or mechanical intelligence. Also seems unlikely — if this were truly meant as a beacon of some sort, then why just reflective and not emissive?
- Water or Carbon Dioxide Ice
The weird thing about this is that on a planet with little to no atmosphere, the common belief is that over several millenia, anything on the surface gets coated by dust from the impact ejecta from the constant bombardment of meteors.
So, for there to be surface-exposed ice in such a large volume (many km across) and for it to not be covered in ice, it either needs to be a very recent feature (recent impact exposing sub-surface ice) or an active geological feature. Because this is at the center of a crater that doesn’t appear to be recent, we then assume that this is an active geological feature, erupting out sub-surface ice in a somewhat constant manner.
But, science measurements from Dawn’s onboard Infrared cameras have shown that this region (Spot 5) is *not* cooler than its surroundings, so that sort of negates the possibility of some sort of ice.