Dawn taking chem makeup data at 385 km

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Re: Variation in Bright Spots

Postby Faradave on March 17th, 2016, 11:18 pm 

This news clip reports daily variation in the bright spots, suggestive of volatility. This is surprising as prior consensus seemed to lean toward salt composition.

"New observations using the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla in Chile have revealed unexpected daily changes on these spots, suggesting that they change under the influence of sunlight as Ceres rotates."

"The team concluded that the observed changes could be due to the presence of volatile substances that evaporate under the action of solar radiation..."

"Ceres is known to be rich in water, but it is unclear whether this is related to the bright spots. The energy source that drives this continual leakage of material from the surface is also unknown."

Wiki: "On 9 December 2015, NASA scientists reported that the bright spots on Ceres may be related to a type of salt, particularly a form of brine containing magnesium sulfate hexahydrite (MgSO4·6H2O); the spots were also found to be associated with ammonia-rich clays."
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Re: Dawn taking chem makeup data at 385 km

Postby Marshall on March 18th, 2016, 6:10 pm 

http://mnrasl.oxfordjournals.org/conten ... asl.slw017

Daily variability of Ceres' Albedo detected by means of radial velocities changes of the reflected sunlight
P. Molaro1, A. F. Lanza2, L. Monaco3, F. Tosi3, G. Lo Curto5, M. Fulle1 and L. Pasquini5,★,†
+ Author Affiliations

1INAF-Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34143 Trieste, Italy
2INAF-Osservatorio Astrofisico di Catania, Via S. Sofia, 78, 95123 Catania, Italy
3Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile
4INAF-IAPS INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
5ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen, Germany
↵★E-mail: molaro@inaf.oats.it (PM)

Bright features have been recently discovered by Dawn on Ceres, which extend previous photometric and Space Telescope observations. These features should produce distortions of the line profiles of the reflected solar spectrum and therefore an apparent radial velocity variation modulated by the rotation of the dwarf planet. Here we report on two sequences of observations of Ceres performed in the nights of 31 July, 26-27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m La Silla ESO telescope. The observations revealed a quite complex behaviour which likely combines a radial velocity modulation due to the rotation with an amplitude of ≈±6 m s−1 and an unexpected diurnal effect. The latter changes imply changes in the albedo of Occator's bright features due to the blaze produced by the exposure to solar radiation. The short-term variability of Ceres’ albedo is on timescales ranging from hours to months and can both be confirmed and followed by means of dedicated radial velocity observations.


Re: Dawn taking chem makeup data at 385 km

Postby Marshall on March 18th, 2016, 6:21 pm 

Here's a FREE version of the MNRAS article. It is much more informative and easier to read than the abstract.
http://www.eso.org/public/archives/rele ... o1609a.pdf
I think it gives a clearer idea of what is going on.
A fog develops under daylight and the fog has a different mix of reflected wavelengths, a different albedo spectrum from the planet as a whole. they can then use Doppler to track the rotation of the fog patches even though (from earth) they cannot resolve or see the fog patches. Is that how you understand it, or am I missing something?
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Haze Phase

Postby Faradave on March 22nd, 2016, 2:30 am 

Thanks for the freebee. I think that's a good reading of it. I get the impression that the bright spots contribute significantly to the total albedo. Sublimation from hydrated salt crystals or frozen water components could change that contribution. It seems that Ceres aspires to be a comet someday.

"That could mean that sunlight plays an important role, for instance by heating up ice just beneath the surface and causing it to blast off some kind of plume or other feature.

Nathues et al. (2015) reported the presence of localized bright areas which are consistent with hydrate magnesium sulfates. They found a bright pit on the floor of crater Occator that shows probable sublimation of water ice, reducing haze clouds inside which appear and disappear with a diurnal rhythm.
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Re: Dawn taking chem makeup data at 385 km

Postby Marshall on March 24th, 2016, 1:19 pm 


Occator central bright spot
http://techcrunch.com/2016/03/23/ceres- ... ed-detail/
Press briefing Ceres at Lunar and Planetary Science conference, the link is one of several listed here:
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