APOD: Cerealia Facula (2018 Jul 19)

[APOD Robot]

Cerealia Facula

Explanation: Cerealia Facula, also known as the brightest spot on Ceres, is shown in this stunning mosaic close-up view. The high-resolution image data was recorded by the Dawn spacecraft, in a looping orbit, from altitudes as low as 34 kilometers (21 miles) above the dwarf planet's surface. Cerealia Facula is about 15 kilometers wide, found in the center of 90 kilometer diameter Occator crater. Like the other bright spots (faculae) scattered around Ceres, Cerealia Facula is not ice, but an exposed salty residue with a reflectivity like dirty snow. The residue is thought to be mostly sodium carbonate and ammonium chloride from a slushy brine within or below the dwarf planet's crust. Driven by advanced ion propulsion on an 11-year mission, Dawn explored main-belt asteriod Vesta before traveling on to Ceres. But sometime between this August and October, the interplanetary spacecraft is expected to finally run out of fuel for its hydrazine thrusters, with the subsequent loss of control of its orientation, losing power and the ability to communicate with Earth. Meanwhile Dawn will continue to explore Ceres in unprecedented detail, and ultimately retire in its orbit around the small world.

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[bystander]

viewtopic.php?p=284174#p284174

[daniel.reardon]

The residue is thought to be mostly sodium carbonate and ammonium chloride from a slushy brine within or below the dwarf planet's crust.

The term "slushy brine" suggests the presence of liquid water. Is that right, or am I misunderstanding this? I'd have assumed that Ceres would be too cold to hold liquid water.

[starsurfer]

It says "asteriod" instead of asteroid.

[Chris Peterson]

The residue is thought to be mostly sodium carbonate and ammonium chloride from a slushy brine within or below the dwarf planet's crust.

The term "slushy brine" suggests the presence of liquid water. Is that right, or am I misunderstanding this? I'd have assumed that Ceres would be too cold to hold liquid water.

Depending upon the salts dissolved in the water, the freezing point can be far lower than that of pure water. Also, the interior of Ceres may still be somewhat warm from radioactive decay, allowing brine to remain unfrozen.

[Yup]

The residue is thought to be mostly sodium carbonate and ammonium chloride from a slushy brine within or below the dwarf planet's crust.

The term "slushy brine" suggests the presence of liquid water. Is that right, or am I misunderstanding this? I'd have assumed that Ceres would be too cold to hold liquid water.

It is too cold for liquid water but large impacts could heat the ice and aid it in mixing with the mineral salts which would then deposit as residues as the water ablates.

[neufer]

The residue is thought to be mostly sodium carbonate and ammonium chloride from a slushy brine within or below the dwarf planet's crust.

The term "slushy brine" suggests the presence of liquid water. Is that right, or am I misunderstanding this? I'd have assumed that Ceres would be too cold to hold liquid water.

Depending upon the salts dissolved in the water, the freezing point can be far lower than that of pure water. Also, the interior of Ceres may still be somewhat warm from radioactive decay, allowing brine to remain unfrozen.

https://en.wikipedia.org/wiki/Geology_of_Ceres

<<Ceres's surface has an albedo of 0.09 [vs. Vesta albedo = 0.42, Pallas albedo = 0.16], which is quite dark compared to the moons in the outer Solar System. This might be a result of the relatively high temperature of Ceres's surface, the maximum temperature with the Sun overhead was estimated from measurements to be 235 K (−38 °C; −37 °F) on 5 May 1991. In a vacuum, ice is unstable at this temperature.>>

[Chris Peterson]

The term "slushy brine" suggests the presence of liquid water. Is that right, or am I misunderstanding this? I'd have assumed that Ceres would be too cold to hold liquid water.

Depending upon the salts dissolved in the water, the freezing point can be far lower than that of pure water. Also, the interior of Ceres may still be somewhat warm from radioactive decay, allowing brine to remain unfrozen.

https://en.wikipedia.org/wiki/Geology_of_Ceres

<<Ceres's surface has an albedo of 0.09 [vs. Vesta albedo = 0.42, Pallas albedo = 0.16], which is quite dark compared to the moons in the outer Solar System. This might be a result of the relatively high temperature of Ceres's surface, the maximum temperature with the Sun overhead was estimated from measurements to be 235 K (−38 °C; −37 °F) on 5 May 1991. In a vacuum, ice is unstable at this temperature.>>

Interesting. Makes sense. Ceres is less than 3 AU from the Sun. Nothing like outer moons.

[MarkBour]

Cerealia Cornflakeula :

http://www.dailymail.co.uk/femail/food/ ... LAKES.html

Artist wins a place in the prestigious Royal Academy exhibition for her framed collection of CORNFLAKES (but she prefers toast for breakfast)
Anne Griffiths, 54, of Wantage, Oxford

[De58te]

Ok I can understand that these bright spots formed at the bottom of a crater most likely from the collision itself. But what are the extremely dark spots made out of? They are adjacent to the bright spots, one noticeable one at the 8 and 9 o'clock position. These are much darker than the regular gray surface, because I turned my brightness control way up and still it remained darker than the surroundings. Excepting the bright spots of course.

[dlw]

I can't seem to grok this formation.

Is it elevated with respect to the black material or did it form and displace the black material or . . . ?

Just curious.

[neufer]

This mosaic of a prominent mound located on the western side of Cerealia Facula was obtained by NASA's Dawn spacecraft on June 22, 2018 from an altitude of about 21 miles (34 kilometers). Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

---

Ok I can understand that these bright spots formed at the bottom of a crater most likely from the collision itself. But what are the extremely dark spots made out of? They are adjacent to the bright spots, one noticeable one at the 8 and 9 o'clock position. These are much darker than the regular gray surface, because I turned my brightness control way up and still it remained darker than the surroundings. Excepting the bright spots of course.

Shadows?

[dlw]

Mystery solved! Thanks.

[Astronymus]

There seem fault lines nearby. I wonder if this salty mass might have been pushed out like outcrops on earth. Like exposed salt domes. Such mass doesn't need to be wet with water to flow. Maybe shrinking of the asteroids crust and shape due to an cooling core caused it.

[MarkBour]

Just 34 km in altitude ! These are beautiful pics. This looks very much like a mountain of salt. I see lots of craters, too.

There seem fault lines nearby. I wonder if this salty mass might have been pushed out like outcrops on earth. Like exposed salt domes. Such mass doesn't need to be wet with water to flow. Maybe shrinking of the asteroids crust and shape due to an cooling core caused it.

I find this very plausible, @Astronymus.

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?

[Boomer12k]

So if and when we go there we can make GLASS....

:---[===] *

[neufer]

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.
https://en.wikipedia.org/wiki/Sun#Main_sequence

IF nothing else has changed then Ceres would have warmed by less than 12K [or 7% = (1.3)^0.25- 1.0].

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.>>

[bporter]

Where is the scale bar? Come on, I know they don't come preprinted on the terrain, but we don't have any idea of the scale here.

I add my voice to the cacophony pointing out that this is an ongoing problem in APOD images.

[Chris Peterson]

Where is the scale bar? Come on, I know they don't come preprinted on the terrain, but we don't have any idea of the scale here.

I add my voice to the cacophony pointing out that this is an ongoing problem in APOD images.

APOD selects images, it doesn't create them. An awful lot of excellent images (such as this one) would go unseen if we demanded scale bars.

In this case, if you don't have any idea of the scale, it's only because you didn't bother to read the caption. It couldn't be much clearer.

[MarkBour]

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.
https://en.wikipedia.org/wiki/Sun#Main_sequence

IF nothing else has changed then Ceres would have warmed by less than 12K [or 7% = (1.3)^0.25- 1.0].

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.

[CNewman]

I have a tangentially related question. This stunning photograph seduced me into perusing JPL's Dawn web site, and at https://www.jpl.nasa.gov/missions/dawn/ is a "Key Discoveries" about Dawn's visit to Vesta, which states that "Vesta has a crater more than 300 miles in diameter. In the center is a mountain more than twice the height of Mount Everest."
My question, then, is what reference is used for the height of features on non-terrestrial bodies? In such discussions about mountain heights on Earth, the reference is typically sea level, unless otherwise specified.
If the reference for that mountain on Vesta is the mountain's base, would it be better to compare it to Mauna Kea, whose height from base to peak is over 10,000 meters, according to https://en.wikipedia.org/wiki/Mauna_Kea?

[Chris Peterson]

I have a tangentially related question. This stunning photograph seduced me into perusing JPL's Dawn web site, and at https://www.jpl.nasa.gov/missions/dawn/ is a "Key Discoveries" about Dawn's visit to Vesta, which states that "Vesta has a crater more than 300 miles in diameter. In the center is a mountain more than twice the height of Mount Everest."
My question, then, is what reference is used for the height of features on non-terrestrial bodies? In such discussions about mountain heights on Earth, the reference is typically sea level, unless otherwise specified.
If the reference for that mountain on Vesta is the mountain's base, would it be better to compare it to Mauna Kea, whose height from base to peak is over 10,000 meters, according to https://en.wikipedia.org/wiki/Mauna_Kea?

Well, I don't know that there's an accepted global altitude reference for Vesta. At least in the case of the crater you're talking about, the measurement is from the lowest point in the crater to the highest point of the central peak.

Different bodies have different reference systems. For instance, Mars has a mathematically defined reference surface calculated from high accuracy laser altimetry data (equipotential for gravity and rotation). Before we had the altimetry data, the altitude reference for Mars was based on atmospheric pressure, with zero altitude set to the water triple point pressure. So basically, where there's a need for an absolute altitude reference, some practical, but perhaps arbitrary system is adopted.

[neufer]

JPL's Dawn web site, and at https://www.jpl.nasa.gov/missions/dawn/ is a "Key Discoveries" about Dawn's visit to Vesta, which states that "Vesta has a crater more than 300 miles in diameter. In the center is a mountain more than twice the height of Mount Everest."
My question, then, is what reference is used for the height of features on non-terrestrial bodies? In such discussions about mountain heights on Earth, the reference is typically sea level, unless otherwise specified.

If the reference for that mountain on Vesta is the mountain's base, would it be better to compare it to Mauna Kea, whose height from base to peak is over 10,000 meters, according to https://en.wikipedia.org/wiki/Mauna_Kea?

---

Indubitably...more than twice the height of Mount Kea:

Code: Select all

Vesta 	   Rheasilvia central peak 	22 km
Mars 	   Olympus Mons 	        21.9 km
Iapetus    equatorial ridge 	        20 km
Io 	   Boösaule Montes "South" 	17.5 to 18.2 km
Oberon 	   unnamed ("limb mountain") 	11 km
Earth 	   Mauna Kea and Mauna Loa 	10.2 km
Mimas 	   Herschel central peak 	 7 km
Venus 	   Skadi Mons 	                 6.4 km
Pluto 	   Tenzing Montes, peak "T2" 	~6.2 km
Moon 	   Mons Huygens 	         5.5 km

Rheasilvia, the largest impact basin on Vesta, is 500 kilometers in diameter. Scientists estimate that it formed 1 billion years ago by counting its smaller craters. The other basin, Veneneia, is 400 kilometers across and lies partially beneath Rheasilvia. Veneneia is at least 2 billion years old.

[SeedsofEarth]

Maybe I missed it somewhere in this thread, but can someone tell me why some segments of this photo are out of focus?

[Chris Peterson]

Maybe I missed it somewhere in this thread, but can someone tell me why some segments of this photo are out of focus?

I don't think it's an issue of focus. The image is a mosaic of many individual images, and some parts of it were collected from farther away, which means lower resolution.