APOD: An Unusual Mountain on Asteroid Ceres (2015 Jun 30)

[APOD Robot]

An Unusual Mountain on Asteroid Ceres

Explanation: What created this large mountain on asteroid Ceres? No one is yet sure. As if in anticipation of today being Asteroid Day on Earth, the robotic spacecraft Dawn in orbit around Ceres took the best yet image of an unusually tall mountain on the Asteroid Belt's largest asteroid. Visible at the top of the featured image, the exceptional mountain rises about five kilometers up from an area that otherwise appears pretty level. The image was taken about two weeks ago from about 4,400 kilometers away. Although origin hypotheses for the mountain include volcanism, impacts, and plate tectonics, clear evidence backing any of these is currently lacking. Also visible across Ceres' surface are some enigmatic light areas: bright spots whose origin and composition that also remain an active topic of investigation. Even though Dawn is expected to continue to orbit Ceres, officially dubbed a dwarf planet, for millions of years, the hydrazine fuel used to point Dawn's communications antenna toward Earth is expected to run out sometime next year.

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[pdtx]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

[Gemini Astronaut]

What does the equation look like, so to speak, that surmises Dawn will orbit Ceres for millions of years? Is that accurate and realistic to arrive at that determination? Just wondering...

[Nitpicker]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

The reason Ceres appears to have some hexagonal craters, is because they appear to be six sided.

I dunno. I suppose nature isn't perfect, and when a crater fails to form in a perfect circle, it must sometimes form an imperfect hexagon. I'd say that a crater only needs a couple of straight-ish edges before it starts looking somewhat polygonal, especially when viewed obliquely.

[bmesser]

Couldn't the antenna be positioned mechanically with electric motors powered by solar panels?

Or is it maybe that the whole satellite's attitude needs adjusting to point back to blighty because the dish is rigidly fixed to it?

[Markus Schwarz]

What does the equation look like, so to speak, that surmises Dawn will orbit Ceres for millions of years? Is that accurate and realistic to arrive at that determination? Just wondering...

Newton's equation of motion and his law of gravitation. Given proper initial conditions (position and velocity) an object like Dawn can orbit a central mass like Ceres on a stable orbit. Just like Earth orbits the Sun for billions of years. Also, Ceres does not have an atmosphere, which would lead to friction. AFAIK, it is Earth's atmosphere which causes the ISS's and Hubble's orbit to decrease slowly.

[cheggers]

the Lonely Mountain... a massive iceberg?

[Dad is watching]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

The reason Ceres appears to have some hexagonal craters, is because they appear to be six sided.

I dunno. I suppose nature isn't perfect, and when a crater fails to form in a perfect circle, it must sometimes form an imperfect hexagon. I'd say that a crater only needs a couple of straight-ish edges before it starts looking somewhat polygonal, especially when viewed obliquely.

We were thinking about the hexagonal shapes as well. The thoughts included a honey-comb like structure, but the craters are not really packed that tightly together to make it likely. Then it occurred to us that snowflakes have 6 points too; making them hexagonal type structures. Are we looking at some sort of post impact freezing of some sort of water based structure at or close to the surface? Could that account for the apparent symmetry? After all, nature doesn't really like straight lines (mostly).

[Chris Peterson]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

Craters are round when they are created (outside of some special cases like extremely oblique impacts). The most likely reason for non-round craters is subsequent slumping of the crater walls. We see that when there is some sort of structure in the material where the crater lies- faulting, patterning, or other non-continuities. The squared-off shape of Meteor Crater in Arizona is a good example, caused in that case by faulted rock.

[Chris Peterson]

Couldn't the antenna be positioned mechanically with electric motors powered by solar panels?

The probe needs to orient itself to properly manage the solar panels, cameras, and antenna (all of which are partly or completely fixed). By design, this is accomplished with electric reaction wheels. Unfortunately, two of those wheels have failed, so orientation is now accomplished using the remaining wheel along with hydrazine thrusters. Once the fuel is gone, the ability to orient the craft will be lost as well.

[Chris Peterson]

What does the equation look like, so to speak, that surmises Dawn will orbit Ceres for millions of years? Is that accurate and realistic to arrive at that determination? Just wondering...

Newton's equation of motion and his law of gravitation. Given proper initial conditions (position and velocity) an object like Dawn can orbit a central mass like Ceres on a stable orbit. Just like Earth orbits the Sun for billions of years. Also, Ceres does not have an atmosphere, which would lead to friction. AFAIK, it is Earth's atmosphere which causes the ISS's and Hubble's orbit to decrease slowly.

Also, I assume the stable orbit is related to the gravitational uniformity of Ceres and the distance from the body that Dawn is orbiting. It isn't possible to maintain a stable orbit around the Moon because of mass concentrations in the lunar crust and perturbations from Earth. Ceres is apparently a more gravitationally friendly environment.

[Ron-Astro Pharmacist]

And we thought our traffic on Earth was congested. Apparently someone is trying to direct traffic in the asteroid belt without much success. Don't you hate equipment failure?

Alien Drone.jpg (11.3 KiB) Viewed 3694 times

Maybe the bright spot is what's left of a stop light? Dwarf planets must need roundabouts.

Roundabouts.jpg (11.05 KiB) Viewed 3694 times

Need one. They live in one.

[montylc2001]

Not sure about the mountain, could be a water volcano. However I did seem to notice that there seems to be flow aprons emanating from the large group of bright spots in the one large crater. Could some of the larger craters actually be volcanic water calderas?

[Boomer12k]

Thought on Six Side Craters.... Maybe ANGLE of descent and strike?

As for the Mountain? ...very interesting...

Sorry....Large Asteroid...not Dwarf Planet....my opinion...which means nothing of course...

http://www.arcadiastreet.com/cgvistas/ceres_1050.htm

Need to drop a Rover on it...

:---[===] *

[Chris Peterson]

Thought on Six Side Craters.... Maybe ANGLE of descent and strike?

No, crater shape doesn't depend on angle of impact, except for extreme cases.

Sorry....Large Asteroid...not Dwarf Planet....my opinion...which means nothing of course...

The definitions and categorizations currently used for planets inside the Solar System are so vague and detached from origin that you can consider the terminology largely arbitrary. There's really no difference between an asteroid and a dwarf planet when we're talking about bodies in the asteroid belt.

[dlw]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

As an engineer, I'm reminded of the famous Devil's Postpile basalt columns that appear roughly hexagonal in cross-section. This is due to a "least energy solution" to differential cooling of the top versus the interior.

Suppose Ceres were to have developed a source of heat deep in the interior, e.g., from radioactive decay. The entire sphere might expand slightly and then eventually, as the heat source dissipated, shrink back. Craters that existed at the time might have become distorted into roughly hexagonal shapes as a result. Craters formed later would be "normal" looking.

This theoretical heat event might also have caused an ash "volcano" ...

Just a thought.

Devil's Postpile column tops

DEPO_DYK_ColumnTops.jpg (5.44 KiB) Viewed 3641 times

[hoohaw]

It isn't possible to maintain a stable orbit around the Moon because of mass concentrations in the lunar crust and perturbations from Earth.

In fact I am really amazed that we were able to land men, six times, successfully on the Moon, and also to retrieve them. A technological and computational tour de force!

[hoohaw]

" There's really no difference between an asteroid and a dwarf planet when we're talking about bodies in the asteroid belt."
And, if you cut an asteroid in two, you get ... two half-asteroids?

[Nitpicker]

Tall mountains are interesting but what is the explanation for the hexagonal craters?

Craters are round when they are created (outside of some special cases like extremely oblique impacts). The most likely reason for non-round craters is subsequent slumping of the crater walls. We see that when there is some sort of structure in the material where the crater lies- faulting, patterning, or other non-continuities. The squared-off shape of Meteor Crater in Arizona is a good example, caused in that case by faulted rock.

The article available from this link:
https://journals.uair.arizona.edu/index ... view/15304

... suggests that (at least for the 829 straight rims of the 269 polygonal Martian craters studied in the Argyre region) the "polygonality is not caused by degradation, but originates from the cratering process itself". The statistical distribution of the strikes (the geological term for the bearings) of all these straight rims, indicates an underlying and preexisting geometry in the geological structure.

[Interociter Operator]

Never mind the mountain!!!
What does spectroscopic-analysis show those BRIGHT SPOTS to be made from!?!?!??!?!

Also - Even if the ship can't be pointed back at Earth directly, what is the math behind how many times it will accidentally be pointed at earth as it slowly tumbles around the planet. If even a broken clock tells the correct time twice a day, how frequently, and when, will the ship be pointed in the right direction without our assistance?

[DavidLeodis]

It's a very interesting object. Viewed in the 'upside down' orientation that the image was released it looks like something forming from a drip. Perhaps it's a giant stalagmite! .

[Joe New]

I'll remedy the overlooking of one vital step, indispensable to history, by our scientific community: I hereby declare the Ceresian summit "Mount Marmaduke."

[ta152h0]

Is this object interesting enough to conduct an EROS style landing before the fuel runs out ? Near or on the bright spots ?

[neufer]

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Is this object interesting enough to conduct an EROS style landing before the fuel runs out ? Near or on the bright spots ?

Ceres's surface escape velocity is 0.51 km/s
and it's "surface" orbital velocity is 0.36 km/s [= 0.51/sqrt(2)].

Dawn's weak ion propulsion is only capable of slowly spiraling down to a ~0.36 km/s collision with the mountain.

[ta152h0]

that collision would be more interesting than a million year journey around Ceres. Like messenger on Mercury. The locals are etting off fireworks here