Dawn approaches Ceres, From opnav images to first orbit Options

[Phil Stooke]

On Tuesday (two days from now, for visitors from the future), the first optical navigation image will be taken... hopefully we'll have it in our hands soon after that. So it's time for a new topic. Over the next few months we'll have progressively closer images and full orbit characterization sequences, no doubt including multispectral image sets.

A new world...

This is a bit of reprocessing I have been doing with the Hubble images from a few years ago.




Phil

[MizarKey]

I very excited to see this little world better. Nice processing on those Hubble images though!

[vikingmars]

A new world...
This is a bit of reprocessing I have been doing with the Hubble images from a few years ago.
Phil

WOW, Phil : you are still the best !
Thanks to this VERY NICE processing of yours, I just realize how bright some craters are (very bright indeed)... and why the astronomers community is just drooling over the underlying layer of ice (and a possible ocean) on this small world.
Thanks so much again !

[tedstryk]

Beautiful! I've fooled with this dataset a little and not gotten anything worth showing out of it.

[Phil Stooke]

This is a cylindrical map made from those images. Longitudes start at 0 at the left edge, following the mapping by Li et al. in Icarus in 2006. My registration is not very good, and the dark southern polar region must be an artifact, but it's something to play with as we start to get the early images.

Phil

[DrShank]

Very Nice!
can i post it on my blog later today?

[4th rock from th...]

Great map!
Besides the lighter patches I see one or two interesting dark ones.

[Phil Stooke]

Hi Paul - by all means post it. It's not as nice as you suggest but it's a start! I look forward to its very rapid replacement with something better.

Phil

[DrShank]

I am most intrigued by the apparent 'bluing' near the poles. will be interested to see if that is real.

[Phil Stooke]

In the single images, it's bluer near the limb and terminator, and the composite leaves that blue near the poles but loses it where images overlap near the equator. I expect it's an artifact or a photometric effect, but there is a possibility of higher albedo (looking blue) near the poles as we see at Ganymede.

Phil

[DrShank]

true. but some of the images seem to show stronger 'blue' near the poles. wont know till we get there!

[PDP8E]

Dawn is supposed to take another Ceres image today -- release will most likely be .....? (soonish)

[DrShank]

can't comment on pronunciation as my latin is rusty, but i do have a blog about the approach posted . . .

http://stereomoons.blogspot.com/2015/01/ye...-pluto-get.html

Attached thumbnail(s)

 

[Mithridates]

It's now the evening of the 13th. Is it safe to say that the Dawn team is looking at the 25 pixel image of Ceres as we speak?

[Decepticon]

The image that was taken Dec 1,2014 took 7 or 8 days to release.


We just have to wait.

[Phil Stooke]

"Is it safe to say that the Dawn team is looking at the 25 pixel image of Ceres as we speak?"

You might very well think that. But I couldn't possibly comment.

Phil

[Superstring]

Is every image during approach going to be delayed several days? If so, is there a reason for that? Not to sound too impatient -- I don't recall that being the case for past missions so I'm just curious. And I may or may not have marked Jan 13, Jan 26, Feb 4, etc in my calendar...

[Explorer1]

Pretty sure it was like that for Vesta too; thrusting takes a priority, since it can't point at Ceres and keep on trajectory at the same time. Dawn isn't Voyager, so no scan platform.

[djellison]

I don't recall that being the case for past missions

It was very much the case for Vesta approach. Dawn doesn't operate an image policy like MER, MSL and Cassini.

[Superstring]

Ah, I guess my memory from the Vesta encounter is fuzzy -- thanks for the clarification.

[Mithridates]

During Vesta approach Dawn did the following:

http://dawn.jpl.nasa.gov/mission/journal_05_27_11.asp

To help target the probe for survey orbit, controllers have commanded it to observe Vesta once a week since the beginning of the approach phase on May 3. As we saw that day, the pictures allow navigators to gain a better fix on Dawn's trajectory relative to Vesta. So far, the images reveal little more than the desired important information of where Vesta appears against the background of stars. And yet, in a sense they show much more...

It was this image:

http://3.bp.blogspot.com/-d3pKJNvHCGg/Te2F...Sad%20Vesta.jpg

An image of Vesta from 1.3 or so million km away was taken on May 3 and released a week later. The next one was released on June 18th at a distance of 218,000 km, this one:

http://3.bp.blogspot.com/-XLZukRt5LlY/Tfw4...s1600/Vesta.jpg

Later on (though I don't remember where exactly I read it) the team said they didn't release the images in between because they were small, boring, untouched, etc.

[elakdawalla]

Because of the severe limitations imposed on the mission by the loss of the use of the reaction wheels, Dawn will be taking fewer approach images of Ceres than it did of Vesta -- I think there are only 8 opnav sessions planned before arrival (compared to 24 for Vesta), so it's far from every day. These limitations also mean fewer comm sessions. On the other hand, op nav images are by definition important for navigation, so I expect they are planned in such a way that they can be returned to Earth very soon after being taken. But it took them forever to release approach images for Vesta, and I don't expect Ceres to be any different.

[DrShank]

Pretty sure it was like that for Vesta too; thrusting takes a priority, since it can't point at Ceres and keep on trajectory at the same time. Dawn isn't Voyager, so no scan platform.

Thats correct. The cadence of observations is that a set is taken for a hour or so on approach every 1 to 2 weeks, depending on the distance. >95% of mission time is spent ion thrusting and it can't point at ceres. There are a variety of exposures and filters and such during each sequence and it takes a few days to select the optimal exposure, remove camera artifacts, etc to release to the public. No worries, the team is eager to show the world what the target looks like! Once they settle into mapping phase, there will likely be a photo of the day release just as there was for Vesta.

[Mithridates]

Because of the severe limitations imposed on the mission by the loss of the use of the reaction wheels, Dawn will be taking fewer approach images of Ceres than it did of Vesta -- I think there are only 8 opnav sessions planned before arrival (compared to 24 for Vesta), so it's far from every day. These limitations also mean fewer comm sessions. On the other hand, op nav images are by definition important for navigation, so I expect they are planned in such a way that they can be returned to Earth very soon after being taken. But it took them forever to release approach images for Vesta, and I don't expect Ceres to be any different.

I wonder. Because on the other hand Ceres is already at a distance where it has a similar resolution to the second Vesta photo, the one where the team thought it had become interesting enough to release.

[djellison]

I wonder.

I wouldn't. Images will show up when they show up. There's really very little point in try to guess when it'll happen.

[Explorer1]

Wonder no more: I have a strange sense that an image will be released on the 20th.

https://twitter.com/NASA_Dawn/status/555511503369940992

It pays to check the most obvious source sometimes...

[Mithridates]

Nice! I was looking at that Twitter feed earlier in the day before they wrote that, glad to see they've given us a date.

[DrShank]

Nice! I was looking at that Twitter feed earlier in the day before they wrote that, glad to see they've given us a date.

nice to see these dates are being posted!

[TheAnt]

Once they settle into mapping phase, there will likely be a photo of the day release just as there was for Vesta.

Close but not quite, due to the flywheel problem Dawn will have to use thruster power to reorient to send back to Earth.
To conserve fuel Dawn will be spending longer time taking images and do measurements, therefore we will be getting new images every second day at best.

[DrShank]

Close but not quite, due to the flywheel problem Dawn will have to use thruster power to reorient to send back to Earth.
To conserve fuel Dawn will be spending longer time taking images and do measurements, therefore we will be getting new images every second day at best.

yes, but by then there will be lots more archived to chose from to post on the Pic-o-the-Day site. Each orbit returns dozens of frames. The number will vary depending on altitude and which mapping phase we are in, of course, but I don't have those numbers.

[TheAnt]

yes, but by then there will be lots more archived to chose from to post on the Pic-o-the-Day site. Each orbit returns dozens of frames. The number will vary depending on altitude and which mapping phase we are in, of course, but I don't have those numbers.

Oh yes you're absolutely right, and I don't believe anyone have the definite numbers of images but its obvious that there should be some who sits and make plans for the imagining campaign at Ceres now already. =)

I checked on the facts and this blog entry mentioned that I had in the back of my head when I posted:
"So over the course of 14 complete circuits around Ceres in 11 days, the spacecraft will turn only six or eight times. Ever the responsible conservationists, the team developed all the details of this plan to acquire as much data as possible with the minimum expenditure of hydrazine." Source

[elakdawalla]

Moved a bunch of pronunciation posts to the Junk Drawer topic. Let's keep the signal-to-noise ratio high, folks.

[DrShank]

Oh yes you're absolutely right, and I don't believe anyone have the definite numbers of images but its obvious that there should be some who sits and make plans for the imagining campaign at Ceres now already. =)

I checked on the facts and this blog entry mentioned that I had in the back of my head when I posted:
"So over the course of 14 complete circuits around Ceres in 11 days, the spacecraft will turn only six or eight times. Ever the responsible conservationists, the team developed all the details of this plan to acquire as much data as possible with the minimum expenditure of hydrazine." Source

Yes indeed. the team has done a fantastic job to make the adjustment to the hybrid form of orbital mapping and still meet the main objectives. It was also a very prudent decision to have a significant supply of hydrazine on board. without that it would be a bit more difficult to do the mapping of ceres without the wheels. Ceres has a lot more area to map as well (the ratio can be easily calculated of course from the radii), and also much darker than vesta. this will require longer exposures, but also a longer mapping phase to get the same coverage for stereo mapping. I'm impressed . . .

[TheAnt]

.... Ceres has a lot more area to map as well (the ratio can be easily calculated of course from the radii), and also much darker than vesta. this will require longer exposures, but also a longer mapping phase to get the same coverage for stereo mapping. I'm impressed . . .

'Prudent' is nearly one understatement, considering the fact that space mission planning usually involves the task of hunting down every unnecessary gramme with even more diligence than a builder of a supercar. =)

And yes, Ceres is quite dark and comes with one albedo of 0,09 compared to the bright Vesta: albedo 0,423. This means there will most likely be a lot of dust that have been captured after various collisions of C type asteroids in the neighbourhood. I guess this asteroid 'pollution' might make it somewhat harder to determine some parts of the history of the asteroid, though I do rather think the idea of seeing Ceres as one surviving planetesimal in the end will be strengthened.

[DrShank]

'Prudent' is nearly one understatement, considering the fact that space mission planning usually involves the task of hunting down every unnecessary gramme with even more diligence than a builder of a supercar. =)

And yes, Ceres is quite dark and comes with one albedo of 0,09 compared to the bright Vesta: albedo 0,423. This means there will most likely be a lot of dust that have been captured after various collisions of C type asteroids in the neighbourhood. I guess this asteroid 'pollution' might make it somewhat harder to determine some parts of the history of the asteroid, though I do rather think the idea of seeing Ceres as one surviving planetesimal in the end will be strengthened.

projectile contamination is also a question for ganymede and callisto. we have several members interested in that problem, and ill let them think about that when we get some spectra to work with. my main focus will be impact craters and what we can learn about the interior and icy shell.

[nprev]

Paul, you may know this right off the bat: Where does Ceres rate on the PPP scale? Is it on par with Mars, Europa & Titan, rated somewhat lower, or not even on the radar at this time?

Not directly applicable to Dawn, of course, save that it might be a factor in EOM planning.

[Phil Stooke]

http://www.jpl.nasa.gov/news/news.php?feature=4449


First pics - very nice.

Phil

[nprev]

Oh, boy; here we go!!!

Looks like the most obvious confirmed feature (since it's also in the Hubble imagery) is that big white spot in the northern hemisphere. Almost certainly a fresh impact crater, of course, but it'll be interesting to see if that high contrast persists at higher resolutions.

I see hints of 'wrinkles' or ridges on the rest of the surface as well as some older big craters. Might just be eroded crater rims from even older & bigger impacts.

[Explorer1]

Yeah, that spot seems like a crater; I can almost make out a dark edge at the top (shadows?).
Very nice!

Also VIRS first light (not in the link provided, strangely enough):

https://twitter.com/NASA_Dawn/status/557214894269800449

[Habukaz]

My layman-self is a bit confused.

This picture has several very obvious crater candidates (including the big one near the middle that makes Ceres look like Mimas looking like the Death Star), but the shiny contrast feature is nowhere to be seen; so how does it fit with the animation?

This picture, on the other hand, has no obvious crater candidates (except from the shiny feature, which is pretty unique), and it also has a big wavy low-albedo feature in the lower hemisphere (looks a bit like to massive craters on a leash).

So, to my untrained eyes, the first picture makes Ceres look a body with a very old surface, while the latter one makes Ceres look a place with a potentially youthful surface (although the image processing looks kind of different between the two images, so maybe that's a clue).

[Hungry4info]

Comparing the new Dawn images to an HST image, I think it's clear that several surface features are visible in both.

Attached thumbnail(s)

 

[Phil Stooke]

replying to Habukaz - At this resolution you can't be making interpretations like that. It is not yet possible to tell the difference between albedo markings and topography, or noise and topography. The next set we get might make those things possible, or maybe the one after that.

Phil

[Habukaz]

replying to Habukaz - At this resolution you can't be making interpretations like that. It is not yet possible to tell the difference between albedo markings and topography, or noise and topography. The next set we get might make those things possible, or maybe the one after that.

Phil

Well, the lead investigator for the framing camera thinks we might be seing craters:

“Already, the [latest] images hint at first surface structures such as craters," said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research, Gottingen, Germany.

[Holder of the Tw...]

But I think the operative word there is "hint".

[Habukaz]

But I think the operative word there is "hint".

Yes, and that's why I labelled them as candidates. It will be interesting to see what's what as we get closer; I just felt like scribbling down what came to mind when I saw the pictures.

My main point was though that I don't get how the "cratery" picture without the bright spot fits the animation; is it included somewhere within it?

[elakdawalla]

Chitchatting with other people here at the New Horizons science team meeting, I think it's true to say that many here would be surprised if some of the features we're looking at did not turn out to be craters. However, there are also a lot of spots that look weird that everybody's on the fence about whether they are craters or albedo markings, and we'll just have to wait and see. Jan 26 images will have resolution twice as good.

[MarkG]

Spectacular pictures! Wild cheering from the bleachers...!

[Bjorn Jonsson]

It's interesting that even though the resolution of these images is a bit lower than HST's, the higher phase angle apparently partially 'compensates' for that by making topography easier to see near the terminator thanks to what are probably shadows/topographic shading. I see hints of probable big craters. Also elongated features but I'm not sure whether they are ridges, depressions, albedo features or some combination of these. It will be very interesting to see the January 26 images; they should provide some answers.

[elakdawalla]

Bjorn, what you said is pretty much what the New Horizons geology and geophysics team said about these images

[dvandorn]

These images, and especially the animation made from them, do give the impression of a cratered body. In much the same way that the early Mariner 10 images gave the impression of a cratered Mercury -- very suggestive, but not enough to say for sure.

Of course, we would most definitely expect Ceres to be cratered -- with no tidal "pumping" I can't conceive of a heat source (internal or external) that would result in ongoing re-surfacing, and every other airless body that lacks an internal heat source (i.e., pretty much all of them except Io, and to a lesser extent Europa and Enceladus) that we've looked at in our solar system has been heavily cratered. Even Enceladus has some heavily cratered terrain far away from its active plumes. It would be the scientific discovery of the decade were Ceres not heavily cratered.

The one nice thing we can say is that we don't have very long to wait, in the overall scheme of things, to get a much better look at this dwarf planet. The Hubble suggestions of an almost Mars-colored world have had me intrigued for quite some time. Now we are very near to knowing, if not the whole truth of the matter, then at least enough data to raise questions we don't even know enough to start asking yet.

-the other Doug

[Guest_alex_k_*]

An attempt to process raw image, x8, details are exaggerated:


For comparision processed version from NASA in the same size:

[Fran Ontanaya]

Very crude attempt at overlaying HST and Dawn

[Habukaz]

Of course, we would most definitely expect Ceres to be cratered -- with no tidal "pumping" I can't conceive of a heat source (internal or external) that would result in ongoing re-surfacing, and every other airless body that lacks an internal heat source (i.e., pretty much all of them except Io, and to a lesser extent Europa and Enceladus) that we've looked at in our solar system has been heavily cratered. Even Enceladus has some heavily cratered terrain far away from its active plumes. It would be the scientific discovery of the decade were Ceres not heavily cratered.

Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

[Phil Stooke]

There was so much mixing going on that the difference in location might not make much difference, regarding distribution of isotopes. However, dvandorn's point about cratering overlooks relaxation as a way of removing craters. Ceres is warmer than Callisto and its ice might have relaxed more. Recent studies have been suggesting that craters would be found near the colder poles, but would be flattened - maybe resembling palimpsests on Ganymede if not lost completely - at lower latitudes.

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1798.pdf

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1655.pdf

http://levee.wustl.edu/~mbland/pubs/Bland_13.pdf


Here is a rough reprojection of the new Ceres images. VERY rough. The registration is not very good. Proper maps will be produced by the Dawn team. This is just to start to show what a map might look like. So positions can't be counted on for high accuracy. I compare it with the HST map (EDIT - replaced map with a properly aligned one - also improved the registration of the HST map).

Phil

[TheAnt]

The Hubble suggestions of an almost Mars-colored world have had me intrigued for quite some time. Now we are very near to knowing, if not the whole truth of the matter, then at least enough data to raise questions we don't even know enough to start asking yet.

The orange material on the surface that is of huge interest to some of us, though it might have been somewhat changed by sunlight and radiation, it might be quite more pristine than the material we have gotten a glimpse of at Titan, which is heavily reprocessed.

Habukaz:
Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

It is the current thinking that a world like Ceres indeed formed on its own, the question is how it is related to the other large asteroids.
Were those once more similar to Ceres in the past? And lost their surface layers by collisions, which Ceres simply were lucky to escape.
Or is Ceres one interloper, that somehow have gotten the orbit circularized in the asteroid belt. I consider the latter less likely, but mentioned for completeness since it has been suggested.

Internal heating by radioactive decay is of course possible, but remember this is a miniature world, and after aeons after formation the activity would be very low with correspondingly rather little heat. There have been some suggestion that serpentinization of minerals might be a heat source that could keep water liquid close to the core. I am personally pessimistic, but for DrShank's and his colleagues sake I hope to be proven wrong, it could make his work more interesting. =)

And thank you all who posted images of the first glimpse of one intriguing little world. =)

[elakdawalla]

I assumed that the flickering of the animation was due to filter wheels, but it turns out they're all clear-filter images, and the flickering is due to lack of calibration. So don't be tempted (as I was) to try to turn them into color pictures!

[Astroboy]

Can we call the faint smudge the Little White Spot, in the tradition of Jupiter and Neptune?

[Phil Stooke]

I edited my map comparison, just above, to correct the positioning of the Dawn images. I replaced the image, but I thought an additional post might be a good idea to draw attention to the change in case anyone downloaded the bad version.

Phil

[Gladstoner]

So far it reminds me of Umbriel.

[dvandorn]

Could not Ceres having formed "alone" compared to the icy satellites of the gas planets who formed right next to giants have an impact on, say, local distribution of radioactive isotopes (and heavier elements in general)?

AIUI, planet formation theory would have it that metals get less and less common in the original protoplanetary disk as you moved away from the Sun, reflected in the relative abundances of metals in the planets as you move outwards.

I have also heard theories that Jupiter once orbited much closer to the Sun, approximately where the asteroid belt is now located, while Saturn was created approximately where Jupiter is now located. As we have seen happen in other solar systems, Jupiter began to migrate closer to the Sun and supposedly began to draw off materials that ought to have contributed to the overall mass of Mars (resulting in Mars ending up smaller and less massive than would otherwise have been expected), but that before Jupiter could move far enough in to begin to disrupt the formation of Earth or any of the other inner planets an orbital resonance with Saturn began pulling it back away from the Sun, in the process tossing Saturn much farther out and likely tossing Neptune out past Uranus.

This all could have affected the formation of Ceres by disrupting its formation at a critical time, such that Ceres had a much larger amount of mass taken away from it by Jupiter. The square-dancing swing-arounds that reorganized the outer planets could also well have been responsible for tossing Ceres into its current, somewhat-skewed orbit -- meaning it could have been a planetesimal that had been forming closer to the Sun than its current location, and thus more enriched in metals than the moons of the outer planets. But it was far enough away from the Sun by the end of its creation that it accumulated a lot of snowballs near the end, accounting for its (potential) resemblance to the icy moons of Jupiter and Saturn.

However, in terms of radioactive heating, most of the planetary formation theories I've read point at Aluminum-26 as the major heat producer in the cores of the inner planets during their early histories. AL-26, however, has a relatively short half-life after it is created in a supernova, so the heating would have contributed only to the initial melting of the rocky planets' cores. None of the other radioactive heat-producing elements that survive to modern times could be contained in great enough quantity in such a small body as Ceres to create a hot core that would have persisted to modern times.

-the other Doug

[Astro0]

Can't wait for the next image to come in



What features will be revealed?

[Explorer1]

Well, here's one idea:

http://xkcd.com/1476/

[Habukaz]

Those replies about Ceres' formation is something to chew on; thanks.

From looking at the more carefully processed Dawn image in this MPS entry, it appears that PIA19167 has actually been rotated 90 degrees relative to the animation for some reason (the bright spot is also darker relative to the rest of the terrain, but is still very much there), so that's what threw me off. Confused no more.

[DrShank]

hey ho!
was busy at a New Horizons meeting all week. fun to watch the speculations. I was making my own, only to decide i couldn't make out anything for sure. some dark markings looked like craters but the animation makes some things look like arcuate structures. grrrr! frustratingly tantalizing.

as far as ppp goes, i can't say, but I'm sure that will change once we find out what the venting is related to. could bump it up high on the list.

[Sherbert]

The comparisons with Pluto and Charon will be interesting. With the musical chairs mentioned above I suppose its not beyond the bounds of possibility Ceres may have originated in the Kuiper belt. Another exciting adventure to a new world begins. Can't wait!

[Tom Tamlyn]

* * * Where does Ceres rate on the PPP scale? Is it on par with Mars, Europa & Titan, rated somewhat lower, or not even on the radar at this time?

Not directly applicable to Dawn, of course, save that it might be a factor in EOM planning.

Once google helped me to remember what PPP stood for , a couple of interesting items turned up with a quick additional search. A summary of planetary protection categories is here.

Io and asteroids of the "[u]ndifferentiated, metamorphosed kind" are in Category I, the category of least concern. Other asteroids are in Category II, along with the Earth's Moon, Jupiter, and a host of other bodies.

Titan is in Category II* (an intermediate category for icy satellites) for all types of missions. Mars and Europa are in Category III for flybys and orbiters, Category IV for landers and probes.

A NASA planetary protection powerpoint from November 2014 lists Dawn at Ceres as Category II (a body of “significant interest * * * where there is only a remote chance that contamination carried by a spacecraft could compromise future investigations”), based on a determination that "Dawn will not impact Ceres due to orbital mechanics constraints." The 2009 flyby of Mars, by contrast is listed as Category III.

A powerpoint specific to the Dawn Mission from January 2013 is a little confusing to the lay reader; a specific category isn't assigned with respect to Ceres. On a page that characterizes the Mars flyby as a Category III mission, it notes that the mission was required to demonstrate “Orbital lifetime around Ceres of greater than 20 years post-orbital insertion."

This restriction is subject to change, based on assessment of... let's just call it conditions on Ceres as discovered by the mission. Based on what the mission finds, it could apply for a release from the 20 year orbit requirement. On the other hand, the mission might (the presentation specifically mentions observations of recent melting as relevant here) instead be required to demonstrate (i) a stable orbital lifetime for an additional 20 year period, (ii) a "long-term stable orbit around Ceres" ["long term" undefined] or (iii) a plan to "leave Ceres orbit."

So the answer to your question seems to be "Category II," subject to change.

In the course of researching this post, I found the November 2013 minutes of the planetary protection subcommittee of the NASA Advisory Council. I'm confused by the highlighted words in the following sentence at p.7: "If the Dawn mission successfully enters orbit around Ceres, it will be going so fast that impact avoidance is assured." I can't figure out what "so fast" has to do with Dawn's method of gradually slipping into a stable orbit.

Can anyone interpret that, or is it just a (perfectly understandable) instance of an over-worked minute taker writing something down that's a little confused?

Edited for a typo, to fix a quote, and to avoid potential issue with forum guidelines.

This post has been edited by Tom Tamlyn: Jan 22 2015, 07:36 AM

[Explorer1]

I believe that what they mean by 'so fast' is that the initial orbit will be very high above Ceres.

This is mostly academic, at any rate; space itself does a plenty fine job sterilizing everything we send up sooner or later. The distances and times spent in those environments mean Dawn has nothing to worry about (unlike the onboard labs of Curiosity or Viking).

[Tom Tamlyn]

I believe that what they mean by 'so fast' is that the initial orbit will be very high above Ceres.

Yabut, even my admittedly shaky understanding of orbital mechanics tells me that the higher the orbit the slower the orbital speed. (Kepler's Third Law). So I still don't grok "so fast."

The orbital speed will increase as the whispering ion drive wafts the craft to closer orbits, but these orbits will continue to be stable -- and thus pose no measurable risk of impact -- so long as they keep their shape and stay outside of the influence of any vestigial "atmosphere" of Ceres and of the gravitational influence of surface and subsurface features. (I think that we can skip perturbation theory for the mission's likely length, especially since the ion drive is available to keep the orbits in trim.)

To me, "so fast" might make some sense if the maneuver in question involved a conventional rocket firing to adjust a flyby or set up an orbital insertion, where the analysis might be that the delta-V available to the vehicle was inadequate to lead to impact even if the desired result (whether flyby or insertion) were to fail.*

It's not a matter of great interest, particularly if (as I think) the confusing phrase was the result of the minute taker's misunderstanding of something said in passing by Dr. Conley. (And I doubt that it's important enough for me to impose on her by writing for an explanation.) But for me it's a rare pleasure to be able to summon up anything at all about Kepler's Laws, and I'm grateful to any members who will humor me.

* The phrase could refer to the fact that Dawn is catching up to Ceres, rather than achieving a position on front of Ceres that would let Ceres catch up to the vehicle, the latter case creating, I suppose, the possibility of impact if Dawn suddenly ceased to be commandable. Hmmm. In any event, I don't have the chops to analyze that kind of situation.

[vikingmars]

.../... What features will be revealed?

...and here is the view from DeviantArt...

[belleraphon1]

This ESA press release on HERSCHEL discovery of Ceres water vapor release has a map of the regions where the water emanates from.

http://www.esa.int/Our_Activities/Space_Sc...rf_planet_Ceres


Phil or anyone, are either of these areas (Piazzi or Region A) covered in this Ceres image release? My eye cannot find a good match.

Is the bright spot in Piazzi?

Craig

[Phil Stooke]

My longitudes look like they are a bit off. I'll look into that later.

Phil

[belleraphon1]

Thanks Phil...

If Region A contains the bright spot, my guess is we are seeing a fairly fresh impact with watery ejecta blanket sublimating away. Perhaps adding to the vapor emissions spotted by HERSCHEL?

From the news release “We estimate that approximately 6 kg of water vapour is being produced per second, requiring only a tiny fraction of Ceres to be covered by water ice, which links nicely to the two localised surface features we have observed."

6 kg seems an awful lot to come from just an ejecta blanket and crater interior so would suspect this is just a contributor.

In about a month we will know if impact crater... cool

[Habukaz]

...and here is the view from DeviantArt...

Nice! There is something about it that makes it very believable.

Meanwhile, I tried to get an answer on when the next image(s) are released, and here's the reply:

hoping by the end of the month

so if we are lucky, maybe by the end of next week? (Sunday next week is 1 February)

[climber]

...and here is the view from DeviantArt...

Olivier, I remember the picture you show us on Philae landing day about what we "may be" were going to see once on the ground...
So, well, yes, we may see what you are showing here... may be not
La critique est facile mais l'Art est... très beau ici
(I love the view you're showing here...thanks so much.)

[vikingmars]

.../... (I love the view you're showing here...thanks so much.)

Thanks so much Climber !

[hendric]

Just for my own curiosity, I looked at if Dawn could soft-land on Ceres, and I don't think it can. g at Ceres surface is .28 m/s^2, which is way more than the Ion thrusters can provide. Dawn also has RCS thrusters, but they likely can't thrust that hard either, or have enough fuel to reduce the speed from orbit before impact. A circular orbit at 2 R_ceres is about 250m/s, skimming the surface is about 350 m/s. Chances for a moon are probably slim with such a well studied object, but maybe Dawn will find a small 10m moonlet to land on.

[djellison]

Each of Dawn's 12 RCS thrusters are I believe 0.9N - 4 of which could be used if one were trying to 'land' it - but they lack both the thrust and the delta V, by probably an order of magnitude. The 747kg dry mass of Dawn would require >200 newtons - not <4.

Not to mention planetary protection.

[DrShank]

thats right. no soft landing. no way to slow down. i don't recall how long the end-of-mission orbit will last (i think 50 years but don't quote me), but we wont be going to really low altitude. the orbits become less stable, and fuel use becomes excessive, are among the reasons.

[algorimancer]

Wasn't there discussion of Dawn possibly going on to visit one or more other targets following mission completion at Ceres? Is the plan to remain in Ceres orbit fully committed now?

[Phil Stooke]

I don't know if that was discussed as a vague possibility, but it's not been a realistic plan for a long time, if ever. Ceres is big - 4 times the surface area of Vesta, so needing 4 times the number of images to cover it at any given resolution. Any extended mission which might be possible with the current limitations of the spacecraft will be most productively used adding data for Ceres, not starting off on a long cruise to some other destination.

Phil

[DrShank]

I don't know if that was discussed as a vague possibility, but it's not been a realistic plan for a long time, if ever. Ceres is big - 4 times the surface area of Vesta, so needing 4 times the number of images to cover it at any given resolution. Any extended mission which might be possible with the current limitations of the spacecraft will be most productively used adding data for Ceres, not starting off on a long cruise to some other destination.

Phil

That is quite right. more area requires more time. also the shift to using hydrazine removes any margin that we might have had for a hypothetical transfer to another object, if it ever was seriously an option (which i don't know). the other factor is that the GRAND gamma ray instrument requires really long integration times to accumulate enough signal to confidently detect elements on the surface. the final orbit is not as low as they would like so getting extra time to fully map out Ceres composition would be a logical and compelling justification for extending the mission. any exciting discoveries like volcanoes or well, who knows, would also be a compelling reason.

[K-P]

Wasn't there discussion of Dawn possibly going on to visit one or more other targets following mission completion at Ceres? Is the plan to remain in Ceres orbit fully committed now?

Pallas was considered as a potential target initially, but I don't know how seriously. Anyway, the delays in launch and also problems with ion thrusters after Vesta departure propably rendered that option impossible to achieve?

It would have been a flyby anyway, and made possible only by orbital mechanics of certain date when Pallas and Ceres were close to each other during their orbits (Pallas has different inclination).
Correct me if I'm wrong.

But yes, would have been a huge bonus for this mission, especially since Pallas is the third (or second) big one out there.

I'm more than overjoyed by the fact that Dawn got even this far. Ceres is a place to see, definitely.

[TheAnt]

also the shift to using hydrazine removes any margin that we might have had for a hypothetical transfer to another object, if it ever was seriously an option (which i don't know).

Yes a colleague of yours stated in a blog that any transfer to any third object was now no longer even considered due to the flywheel problem. Getting good data from GRAND is better science than just a snapshot from a quick flyby.

So the third lowest orbit is out of the question now then? I tried to find any information about that, since I figured that would indeed be more costly on hydrazine?

So as for algorimancer's question I know Pallas have been mentioned, but have no idea if that was ever on any extended planning or just ideas that were tossed around. [I toss 14 ideas or more around daily, something that have taken years for some people to getting used to not to take too seriously.] =)

One ancient ice volcano would be really cool, and could provide some information about both history and perhaps even the interior of Ceres. But only if it have survived large impacts since the early days of Ceres. That artwork vikingmars posted is actually very close to my hopes for a best case scenario, even a polar cap, of what Ceres would provide for us. Hmm arcuate structures, like Miranda? Temporary melting after one impact, who knows.....

[Habukaz]

So the third lowest orbit is out of the question now then? I tried to find any information about that, since I figured that would indeed be more costly on hydrazine?

I guess the information you are looking for can be found in this blog entry from last year (which also mentions why a landing is impossible, cf. debate above):

What fate awaits our stalwart adventurer following the completion of its primary assignment? There are several possibilities, but they all conclude the same way. If hydrazine remains at the end, and if the spacecraft is still healthy, NASA will decide whether to invest further in Dawn. NASA has many exciting and important activities to choose among — after all, there’s a vast universe to explore! If it provides further funds, Dawn will perform further investigations in LAMO, making GRaND’s gamma ray and neutron pictures even sharper, refining the gravitational measurements, collecting still more photos of the expansive surface, and acquiring even more spectra with VIR.

There is no intention to fly to a lower orbit. Even if the two remaining reaction wheels operate, hydrazine will be running very low, so time will be short. Following another spiral to a different altitude would not be wise. There will be no below-LAMO (BLAMO) or super low altitude mapping orbit (SLAMO) phase of the mission.

[TheAnt]

I guess the information you are looking for can be found in this blog entry from last year (which also mentions why a landing is impossible, cf. debate above):

Thank you Habukaz, what I thought, it would have been one tempting idea if all gyros had been ok since the low gravity field of Ceres might have allowed the spacecraft to orbit really close without being to fast to take really high resolution images and better data from GRAND as well.
Now DrShank mentioned 'very long' integration time I guess they hope to get equal results anyhow from a higher orbit.

[algorimancer]

It sounds pretty settled. Leaving Dawn in a stable orbit around Ceres seems like a nice end to the mission. Someday perhaps we can look forward to a subsequent probe coming along and snapping a picture of it -- which would be really cool.

[DrShank]

GRAND basically observes the whole planet at one time, so to improve resolution you have to observe, observe, observe, with multiple overlapping orbits. Its simply the more the better. Its all mysterious to me, but it works. which reminds me that to get the highest resolution gravity map and best constraints on interior structure (does it have a core, how large . . . ?) is also improved significantly by getting as many orbits as possible. of course both are improved by going as low as possible, but we are constrained.

the blogs by Marc Rayman on the Dawn website are excellent for describing the Ceres mapping mission and why things are done as they are. google should get u there. excellent posts throughout 2014.
p

[elakdawalla]

Continuing operations as long as possible in the lowest orbit will also likely mean more thorough high-res imaging coverage. They won't waste hydrazine slewing to point at gaps; instead, they'll exert patience, just waiting until an orbit happens to pass over a gap.

A lot of these questions are also answered in my Sky & Tel article on Dawn at Ceres, coming out in the April issue but I think I will also try to go through and prepare a blog with a Cliff's Notes version of Marc's posts on the Ceres mission, when I can find the time!

[Mithridates]

It sounds pretty settled. Leaving Dawn in a stable orbit around Ceres seems like a nice end to the mission. Someday perhaps we can look forward to a subsequent probe coming along and snapping a picture of it -- which would be really cool.

In one of the most recent Dawn journals describing the moment of capture they used the term "and they will be together forevermore" or something along those lines so yes, it sounds pretty settled.

[DrShank]

it sounds pretty settled.

very much so. Our final orbit is also determined, though I would not mind getting even lower. But as we will be covering the majority of the surface in our final orbit altitude at ~35 meter resolution I can't and won't complain! (That is almost three times as good as our effective global resolution of approximately 100 meters over most of Enceladus, our best mapped icy world at present.)

[fredk]

When you view an animated gif of the released set your brain can pull real structure out of the noise, and you end up seeing more structure than in any single frame. This makes me wonder about producing a super-res from this set. It would be a lot of work. You'd have to create a rotation model and transform each image into some fixed projection, before doing the stacking with each frame aligned in longitude. Of course you'd get maximal improvement near the central region of the central frame, and less improvement towards the edges. Still, it would be interesting to see what could be done.

Or you could wait for the next release...

[MarsInMyLifetime]

If only for a spare hole in the filter wheel that a parfocal 3x teleconverter could have been slipped into. ;-) But I suppose it would have been beyond budget and requirements.

[Bjorn Jonsson]

...This makes me wonder about producing a super-res from this set. It would be a lot of work. You'd have to create a rotation model and transform each image into some fixed projection...

I originally wasn't going to spend any time doing this since there isn't a long time until the next images arrive but I found that I simply couldn't resist checking if more details could be revealed, also this was an interesting image processing experiment. I used the last 9 images from the set, reprojected them to simple cylindrical projection and then aligned and stacked the maps. This was followed by rendering an ellipsoid using the map as a texture map. I was rather disappointed with the result and I'm not sure which 'new' details are real, maybe some but maybe none.

Below are two versions, the left one sharpened with an unsharp mask and the right one processed with a high pass filter followed by a contrast stretch:



I'm more happy with the version at left. The most interesting feature is the one below center that stretches from the left limb and more than half the way to the right limb. This looks like a possible 'depression' (reminds me a bit of Tethys' Ithaca Chasma!?) but an albedo feature (or something else) can't be ruled out. One important caveat is that the images in the rotation movie have been processed and enlarged - I'd me more confident in these results if I was using the original, raw images.

It should be mentioned that the original 20 images were obtained over a period of ~1 hour at a range of 383,000 km and the subspacecraft latitude is 28.2 degrees south.

[dvandorn]

Great work, Bjorn!

It seems obvious that the "head" of the dark horizontal feature you mention is surrounded by a brighter annulus -- at least, several brighter points appear in arcs around the place where the dark steak spreads out into a "handle" shape, the arcs defining what looks like a large encircling crater or basin. It certainly gives the impression of a large crater or small basin in the animation, though of course it's no more than an impression, at these resolutions.

However, if the center of the "handle" were some kind of eruptive feature, the bright annulus could be extent of the outer eruption ring. (Think in terms of Ionian volcanoes.)

It's quite exciting to know that we will have much better views within weeks!

-the other Doug

[fredk]

Very cool to see this, Bjorn. As important as any new features we can see this way are the fake features, due to noise, that go away. Nine frames should naively give us a 3-fold increase in S/N. This is probably the best image we have yet of Ceres.

[Bjorn Jonsson]

Looking at the movie and other versions of the image, I get the impression that the eastern end of the horizontal feature might be a big crater with a central peak and there might more craters and/or an elongated depresson to its west (probably both).

It will be very interesting to see the next set of images. It might have sufficient resolution to show what this feature is (and it will give me information on how well this image processing method works).

[Sherbert]

Very nicely done Bjorn.

I think there could be two deep craters to the North East of the elongated dark feature, similar but not as deep as the big white crater top left. One thing is for sure, to see features at this distance, the elevation changes could be quite dramatic on the surface, whatever their nature. We await with eager anticipation to see what the images planned for this week reveal.

[machi]

...The most interesting feature is the one below center that stretches from the left limb and more than half the way to the right limb. This looks like a possible 'depression' (reminds me a bit of Tethys' Ithaca Chasma!?) but an albedo feature (or something else) can't be ruled out...

Nice reprocessed images Bjorn!
I had similar thoughts about possible canyon on the Ceres after I've watched published animation.
My bet is that Ceres will be similar to the one of the middle size icy satellite of Saturn or Uranus.
Question is which one (Umbriel? Tethys?...).

[DrShank]

All very interesting speculations. I've wondered about that arcuate feature that looks like a possible depression, as well. But Im prepared for anything. Ive also been discussing Saturnian satellite analogs with colleagues, and thats a good starting point, but there are of course key differences, in composition, heat source, etc. be assured that the Saturnian moon maps will got some use when we start trying to figure Ceres out. Im posting a blog about it later tonite.
cheers
p

[Habukaz]

The first new Ceres images are coming down, and they 'look very impressive'. They may be released tomorrow already; although time will tell, I guess.