neufer wrote: ↑
Fri Jul 20, 2018 4:04 am
MarkBour wrote: ↑
Thu Jul 19, 2018 10:51 pm
Over the course of the last 4 billion years, for a given body in a stable orbit around the Sun, it is reasonable to believe that the Solar radiation has increased by about 40%. I wonder what such a change does to a body like Ceres. There are many other factors, of course. The internal heat sources of bodies, and in some cases, atmospheres, with their possibilities (none on Ceres). Would one expect Ceres to have steadily cooled over this time, or gone up in temperature?
Solar radiation has increased by about 30% in the last 4.5 billion years.
nothing else has changed then Ceres would have warmed by less than 12K [or 7% = (1.3)0.25
This in itself would be negligible (especially when spread out over 4.5 billion years).
- However, many (harrowing) things have changed ... even over the last 34 million years:
Finally — A Super-Close Look At Ceres’ Brightest Spot
Astrobob, July 20, 2018
<<Based on crater counts, Occator Crater [i.e., 92 km wide crater was named after the Roman god of the harrow
] is estimated to be 34 million years old
, but the bright spots inside are much younger, only about 4 million years old
. Dawn also mapped Ceres’ gravity field and discovered that it has a rocky core and icy mantle. It’s likely that crater-forming asteroid impacts tapped into that mantle, creating the fractures and low spots that later led to the release of trapped liquids from beneath the surface.
RE: The Sun's Luminosity -- I have found a few sources that say "increased by 30%", and a couple that say "was initially 70%" of the present-day value. (Not much of a survey, just looked at about 8 references.) The one I had quoted had said "initially 70%", so I took the reciprocal and said "increased by around 40%". Of course there's no real meaningful final answer of whether we should say 30% or 40%, at least none that matters in my context here.
But thanks for the other formula, it helps me to see that its temperature could be rising, but as you said, this would be "negligible". At some epoch in its past, I would suppose Ceres had been greatly heated in formation, and cooled down by radiating that heat.
The reason I was thinking about it was that it could help decide if one would see cooling effects or warming effects helping shape the dwarf planet's surface features. There's a huge crack on Mars that is suggested to have been caused by a long cooling process. Upwelling brine must be a result of some heating source. Wikipedia's Ceres article says that what we are looking at in this APOD is a mixture of salts that are supposed to have oozed out from the interior to the surface, due to some geological activity.
This NASA Goddard Youtube is interesting: https://www.youtube.com/watch?v=-6nxKqPIUkE
. I wonder if the source of heat might actually be from asteroid impacts. Your quote of Astrobob would indicate that impacts may provide the "paths" for the salts to escape. Is it ridiculous to imagine an impact also providing the heat that warms a section of the subsurface, which further encourages an upwelling cryovolcano for a while? I was always struck by the fact that a crater is right next to Ahuna Mons that looks related to it.