Dawn at Ceres Thread

[-Velocity-]

And if there was a man sat inside the probe telling us what he saw through a scope, that'd be relevant. As it is, there's a lot more in this kind of instrument than just a mirror and a couple of lenses.

Which is exactly why the cost of the optics is negligible, at least in this range of aperture.

- - - Updated - - -

You can't compare two measurements which have different units.

He's not. He's comparing the reduction in light intensity at the sensor due to distance from the Sun with the reduction in light intensity at the sensor due to less light being reflected by the object. It's the same unit, power per unit solid angle. In SI, it's watts per steradian. He gave this comparison as distance from the Sun vs. albedo, and assumed it would be obvious to the reader that he was talking about the radiant intensity of reflected light as affected by distance from the Sun vs. albedo.

Edited February 24, 2015 by |Velocity|

[rkman]

It is? I thought it was the opposite- a big, fast telescope, if the objective is single piece, requires A LOT of glass to be removed

I wasn't clear, i suppose i should have said it is optically easier to get a fast telescope with a given magnification if it has a large aperture. It would be hard to have a scope on NH with the same performace as the one it actually has, if its aperture would as small as the scopes on Dawn. Conversely, NH's scope on Dawn would be overkill.

At any rate, i think that given the mission requirements it makes perfect sense that Dawn's telescopes have a considerably smaller aperture than the one on New Horizons.

You can't compare two measurements which have different units.

Both are ratios:

1600 times less received sunlight vs ~7 times less received sunlight (both relative to Earth). (ratio ~230)

and

1/2 reflected sunlight vs 1/10 reflected sunlight (ratio 5)

Edited February 25, 2015 by rkman

[Frida Space]

[Aethon]

Article that goes with the above image.

http://www.nasa.gov/jpl/dawn/bright-spot-on-ceres-has-dimmer-companion/index.html#.VO3rA_nF-Yc

[YNM]

Regarding on-board camera and/or telescope : large apperture and small f/D should be preferred. Other than for the high resolving power (if focus remain fixed), a large apperture provides large FOV (as there (should) only a CCD, a large CCD is also necessary). Also a larger apperture allows more light to be gathered. It means less amount of image capturing and less time required for each image. Equal to this thinking are star survey telescopes - they don't need large magnification, what they need are high resolving power and fast light gathering. Opposite (so high f/D and relatively small apperture) are ground-based planetary telescopes, which needs to reduce the brightness of the planets (in order to resolve more features). Regarding shape and arrangement, it doesn't need to be regular - look up Gaia's optics. That's not a common design at all... Which makes more sense when you have limited space.

[miracmert]

http://2.bp.blogspot.com/-9ukVYNa-HQU/VO3pXnm4GFI/AAAAAAAADgA/Unzayvp4hAk/s1600/pia19183.jpg

Looks like Mun to me

[Frida Space]

Definitely a lot of features to study I'm particularly intrigued by the big crater in the lower hemisphere in the first image. It looks pretty old and eroded, but it has a perfectly circular crater in its exact center which looks a lot younger.

[The_8th_Bit]

Here's another picture from the article, apparently there are actually two white spots.

It will be interesting to see what they are

[Kryten]

It almost looks like there's just ice there, below a shallow rocky crust. Like a gigantic comet.

[nilof]

...Why isn't Dres this cool?

[Mitchz95]

Wow. It's a lot smaller than I thought.

Is that a color picture? I'd hoped Ceres would have a little color to it like Pluto.

[Azimech]

[FishInferno]

Aliens. Its aliens

[Streetwind]

Come on now, the existing thread for this was less than 10 lines down... :s

[Frozen_Heart]

What on Earth (or Ceres in this case) are those white dots. From the original images I just assumed it was a large, more lightly coloured crater but that just looks weird.

Perhaps ice of some sort? Could reflect the sunlight very brightly?

Edited February 25, 2015 by Frozen_Heart

[Brotoro]

I would guess that it's fresh ice.

Dres needs a nice white patch.

[Wjolcz]

Im no expert but to me it looks like an impact uncovered something thats beneath the dust. Its right in the middle of the crater. Ice? Space mirrors? Death rays? Aliens playing with their flashlights?

Dont know how much time it would ttake for it to evaporate if it was water ice. The spot's been there for a while and if Im not mistaken could be observed from the telescopes on earth. Maybe it was Hubble. Not sure, but have seen it a few years ago.

[StrandedonEarth]

Apparently it's something reflective. Ice, metal, glassified regolith, similar to trinitite?

[Bill Phil]

Maybe an out gas occurred? And it's settling down now...

[Kibble]

Dont know how much time it would ttake for it to evaporate if it was water ice.

Ceres has a semi major axis near the lower-end estimates for where the frost line is. In fact detecting a stable patch of exposed volatile ice, water or not, could tell us more precisely where the frost line is, and where to find volatiles in the Asteroids!

[Starwhip]

This is seriously bizarre.

[SpaceExplorer]

Maybe an out gas occurred? And it's settling down now...

Possibly, I guess we will not know for sure until Dawn arrives at Ceres on the 6th of March...

I am really stumped, and super excited to finally find out what this white dot truly is.

[Norpo]

It's space hitchhikers looking for a ride from the Dawn spacecraft, obviously.</sarcasm>

[regex]

...Why isn't Dres this cool?

The best part is once Ceres is properly mapped you can use its height and color maps to make Dres look this cool.

[Vanamonde]

Overlapping threads merged.