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Dawn at Ceres Thread


Frida Space
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Better than nothing :) Besides, if Ceres retains even a bit of activity, and will start noticeable venting at perihelion it would be a huge find. Anyways, when Dawn finally loses ability to maneuver - how stable her orbit will be? Will she stay as an artificial satellite of Ceres for any extended period of time?

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  • 3 weeks later...

So yea, the Dawn team asked NASA to depart from Ceres orbit in October this year and flyby asteroid Adeona in May 2019; NASA, however, didn't approve this scenario and simply extended Dawn's stay at Ceres. Dawn is in a stable orbit and therefore will remain at Ceres "indefinitely" (a.k.a. centuries at least, if not millenia).

Recently in the news, Dawn identified several spots in Ceres' northern hemisphere which haven't been reached by sunlight in perhaps a billion years or more. Temperatures in these regions can reach -151 °C. They cover 1800 square kilometers, or 0.13% of the hemisphere. This is similar to Mercury; however, being Ceres much further away from the Sun, it's likely that these regions on Ceres represent cold traps (spots were water ice is stable) even at relatively low latitudes, whereas such regions on Mercury exist only in the very close proximity of the poles.

Scientists estimate that, throughout a Ceres year (1682 Earth days), around 14 water molecules out of 10 thousand get trapped in these regons. At this rate, a macroscopic ice deposit would take about a hundred thousand years to accumulate.

ceres.jpg

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Apparently, Ceres severely lacks big impact basins. Scientists suspect these have all been wiped out. This erosion process might have been made easier by the abundance of ice in the subsurface layers and/or by cryovulcanic activities. Also, the three planitiae spotted by Dawn could be the remnants of these huge and ancient impact basins.

www.nasa.gov/feature/jpl/the-case-of-the-missing-ceres-craters

cerere.PNG

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On 7/27/2016 at 2:58 AM, Frida Space said:

Apparently, Ceres severely lacks big impact basins. Scientists suspect these have all been wiped out. This erosion process might have been made easier by the abundance of ice in the subsurface layers and/or by cryovulcanic activities. Also, the three planitiae spotted by Dawn could be the remnants of these huge and ancient impact basins.

www.nasa.gov/feature/jpl/the-case-of-the-missing-ceres-craters

cerere.PNG

Or Ceres did not become gravitationally rounded until after Earth's late bombardment phase. At which point the gravitational forces heated the surface up smoothing it and the later activities spotted. 

In answer to the ice plot, the rotation away from the poles over 100,000 year period might be expected because the planet is relatively small compared to nearby objects it could interact with, its rotation is very slow, and so it does not have much angular momentum, and it could rather easily shift poles with small perturbations.

 

Edited by PB666
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New data from Dawn on Ceres' internal structure. Dawn provided the first measurements of the moment of inertia and the first confirmation that the dwarf planet is in hydrostatical equilibrium - two conditions that allow scientists to simulate its internal structure. The results are that Ceres is differentiated (although the boundaries between layers are not so clear as on Earth), with a rocky core (the temperatures were never high enough for the silicates to melt) surrounded by a volatile-rich shell. The density, as predicted, is quite low (lower than Vesta). The lighter materials, such as water ice, probably separated from the rock and migrated towards the surface early on in Ceres' history. Furthermore, there isn't a big difference in the gravitational field intensity between mountains and depressions, which suggests that mountains are able to move away the mass in the mantle underneath them, thus evening out the gravitational field, a bit like a boat floating because of the water moved.

www.nasa.gov/feature/jpl/what-s-inside-ceres-new-findings-from-gravity-data

pia20867.jpg

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  • 4 weeks later...

In two days' time, Dawn will move to a new orbit at 1460 km (910 miles) from Ceres. Apparently, it is some sort of hydrazine-saving effort, as moving further out means less orbital control is needed. From what I understand, there will also be a change in Dawn's orbital inclination, allowing it to view Ceres from a slightly different perspective.

http://www.nasa.gov/feature/jpl/dawn-sets-course-for-higher-orbit

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F1.large+%25281%2529.jpg

Lots of news out of Ceres. I read the five papers published just now on Science magazine and here are my highlights:

  • Ahuna Mons, the 4 km tall, 17 km wide mountain, is probably a cryovulcano. This would explain the troughs and the crests at its feet and the landslides on its sides. It would have been formed by extrusion of a viscous, molten material, which would have been present along with some hydrated salts with low eutectic temperatures and low thermal conductivity. Ahuna Mons is surprisingly crater-free; this suggests its last activity took place as recently as 180-240 million years ago.
  • Ceres's low density (2162 kg per cube metre) implies an abundance of water; this could be proven by the detection of hydroxyl (OH) and hydrated (H2O) minerals, like clays, carbonates and various salts. Indeed, Dawn has found hydroxyls; however, the news (not really new actually) is that it has seen all three absorption bands (1.28, 1.65 and 2.0 micrometres) typical of water in Oxo Crater, which is 10 km wide. Its high latitude, 44°, means it is in the shadow for most of the day, which is good for stabilising water. Several water transport and formation mechanisms have been proposed. From the most likely to the least: excavation of underground water (either through impacts or landslides or both), sublimation, extra-Cerean contamination and interaction with the solar wind.
  • A six day-long acceleration in the solar wind's electrons could be explained by a transient atmosphere. I couldn't find an actual paper on this, but the NASA press release mentioned it, so here it is.
  • Phillosilicates are very abundant. Their composition is the same all over Ceres; however, their abundance varies a bit. Low density regions, such as Yalode crater, are both smooth and rugged; high density regions, such as Kerwan, on the other hand, are only smooth.
  • The depth-diameter ratio of several floor-fractured craters (FFCs) reveals that they are anomalously shallow; hence, scientists propose the terrain was uplifted following cryomagmatic intrusion.
  • The crater morphology allowed scientists to study the relaxation of the surface, which appears to be impact-driven rather than internal/endogenic. The scientists conclude that Ceres's crust is nor pure ice nor pure rock, but rather a mix of the two which allows limited relaxation.
  • Overall, all the studies imply acqueous alteration has been one of the main mechanisms that shaped Ceres.

Interesting stuff!

Edited by Frida Space
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