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Marc Rayman

Dawn Journal: Descent to HAMO

Posted by Marc Rayman

30-07-2015 9:45 CDT

Topics: mission status, asteroids, Dawn, asteroid 1 Ceres

Dear Descendawnts,

Flying on a blue-green ray of xenon ions, Dawn is gracefully descending toward dwarf planet Ceres. Even as Dawn prepares for a sumptuous new feast in its next mapping orbit, scientists are continuing to delight in the delicacies Ceres has already served. With a wonderfully rich bounty of pictures and other observations already secured, the explorer is now on its way to an even better vantage point.

Ceres from Dawn's Survey Orbit

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Ceres from Dawn's second mapping orbit

Dawn was in its second mapping orbit at an altitude of 2,700 miles (4,400 kilometers) when it took this picture of Ceres. This area shows relatively few craters, suggesting it is younger than some other areas on Ceres. Some bright spots are visible, although they are not as prominent as the most famous bright spots. Scientists do not yet have a clear explanation for them, but you can register your vote here. Click on the picture for a better view of some interesting narrow, straight features in the lower left.

Dawn takes great advantage of its unique ion propulsion system to maneuver extensively in orbit, optimizing its views of the alien world that beckoned for more than two centuries before a terrestrial ambassador arrived in March. Dawn has been in powered flight for most of its time in space, gently thrusting with its ion engine for 69 percent of the time since it embarked on its bold interplanetary adventure in 2007. Such a flight profile is entirely different from the great majority of space missions. Most spacecraft coast most of the time (just as planets do), making only brief maneuvers that may add up to just a few hours or even less over the course of a mission of many years. But most spacecraft could not accomplish Dawn’s ambitious mission. Indeed, no other spacecraft could. The only ship ever to orbit two extraterrestrial destinations, Dawn accomplishes what would be impossible with conventional technology. With the extraordinary capability of ion propulsion, it is truly an interplanetary spaceship.

In addition to using its ion engine to travel to Vesta, enter into orbit around the protoplanet in 2011, break out of orbit in 2012, travel to Ceres and enter into orbit there this year, Dawn relies on the same system to fly to different orbits around these worlds it unveils, executing complex and graceful spirals around its gravitational master. After conducting wonderfully successful observation campaigns in its preantepenultimate Ceres orbit 8,400 miles (13,600 kilometers) high in April and May and its antepenultimate orbit at 2,700 miles (4,400 kilometers) in June, Dawn commenced its spiral descent to the penultimate orbit at 915 miles (1,470 kilometers) on June 30. (We will discuss this orbital altitude in more detail below.) A glitch interrupted the maneuvering almost as soon as it began, when protective software detected a discrepancy in the probe’s orientation. But thanks to the exceptional flexibility built into the plans, the mission could easily accommodate the change in schedule that followed. It will have no effect on the outcome of the exploration of Ceres. Let’s see what happened.

Descent to HAMO

NASA / JPL-Caltech

Descent to HAMO
Dawn’s spiral descent from its second mapping orbit (survey) to its third (HAMO). The two mapping orbits are shown in green. The color of Dawn’s trajectory progresses through the spectrum from blue, when it began ion-thrusting in survey orbit, to red, when it arrives in HAMO. The red dashed sections show where Dawn is coasting for telecommunications. Compare this to the previous spiral.

Control of Dawn’s orientation in the weightless conditions of spaceflight is the responsibility of the attitude control system. (To maintain a mystique about their work, engineers use the term “attitude” instead of “orientation.” This system also happens to have a very positive attitude about its work.) Dawn (and all other objects in three-dimensional space) can turn about three mutually perpendicular axes. The axes may be called pitch, roll and yaw; left/right, front/back and up/down; x, y and z; rock, paper and scissors; chocolate, vanilla and strawberry; Peter, Paul and Mary; etc., but whatever their names, attitude control has several different means to turn or to stabilize each axis. Earlier in its journey, the spacecraft depended on devices known as reaction wheels. As we have discussed in many Dawn Journals, that method is now used only rarely, because two of the four units have failed. The remaining two are being saved for the ultimate orbit at about 230 miles (375 kilometers), which Dawn will attain at the end of this year. Instead of reaction wheels, Dawn has been using its reaction control system, shooting puffs of hydrazine, a conventional rocket propellant, through small jets. (This is entirely different from the ion propulsion system, which expels high velocity xenon ions to change and control Dawn’s path through space. The reaction control system is used only to change and control attitude.)

Whenever Dawn is firing one of its three ion engines, its attitude control system uses still another method. The ship only operates one engine at a time, and attitude control swivels the mechanical gimbal system that holds that engine, thus imparting a small torque to the spacecraft, providing the means to control two axes (pitch and yaw, for example, or chocolate and strawberry). For the third axis (roll or vanilla), it still uses the hydrazine jets of the reaction control system.

On June 30, engine #3 came to life on schedule at 10:32:19 p.m. PDT to begin nearly five weeks of maneuvers. Attitude control deftly switched from using the reaction control system for all three axes to only one, and controlling the other two axes by tipping and tilting the engine with gimbal #3. But the control was not as effective as it should have been. Software monitoring the attitude recognized the condition but wisely avoided reacting too soon, instead giving attitude control time to try to rectify it. Nevertheless, the situation did not improve. Gradually the attitude deviated more and more from what it should have been, despite attitude control’s efforts. Seventeen minutes after thrusting started, the error had grown to 10 degrees. That’s comparable to how far the hour hand of a clock moves in 20 minutes, so Dawn was rotating only a little faster than an hour hand. But even that was more than the sophisticated probe could allow, so at 10:49:27 p.m., the main computer declared one of the “safe modes,” special configurations designed to protect the ship and the mission in uncertain, unexpected or difficult circumstances.

The spacecraft smoothly entered safe mode by turning off the ion engine, reconfiguring other systems, broadcasting a continuous radio signal through one of its antennas and then patiently awaiting further instructions. The radio transmission was received on a distant planet the next day. (It may yet be received on some other planets in the future, but we shall focus here on the response by Earthlings.) One of NASA’s Deep Space Network stations in Australia picked up the signal on July 1, and the mission control team at JPL began investigating immediately.

Engineers assessed the health of the spacecraft and soon started returning it to its normal configuration. By analyzing the myriad diagnostic details reported by the robot over the next few days, they determined that the gimbal mechanism had not operated correctly, so when attitude control tried to change the angle of the ion engine, it did not achieve the desired result.

Because Dawn had already accomplished more than 96 percent of the planned ion-thrusting for the entire mission (nearly 5.5 years so far), the remaining thrusting could easily be accomplished with only one of the ion engines. (Note that the 96 percent here is different from the 69 percent of the total time since launch mentioned above, simply because Dawn has been scheduled not to thrust some of the time, including when it takes data at Vesta and Ceres.) Similarly, of the ion propulsion system’s two computer controllers, two power units and two sets of valves and other plumbing for the xenon, the mission could be completed with only one of each. So although engineers likely could restore gimbal #3’s performance, they chose to switch to another gimbal (and thus another engine) and move on. Dawn’s goal is to explore a mysterious, fascinating world that used to be known as a planet, not to perform complex (and unnecessary) interplanetary gimbal repairs.

Ceres from Dawn Survey's Orbit

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Haulani crater from Dawn's second mapping orbit

This view of Ceres from the second mapping orbit shows some bright material that is not confined to “spots.” The crater on the right with bright material is Haulani, visible on the left side of the topographical map below.

One of the benefits of being in orbit (besides it being an incredibly cool place to be) is that Dawn can linger at Ceres, studying it in great detail rather than being constrained by a fast flight and a quick glimpse. By the same principle, there was no urgency in resuming the spiral descent. The second mapping orbit was a perfectly fine place for the spacecraft, and it could circle Ceres there every 3.1 days as long as necessary. (Dawn consumed its hydrazine propellant at a very, very low rate while in that orbit, so the extra time there had a negligible cost, even as measured by the most precious resource.)

The operations team took the time to be cautious and to ensure that they understood the nature of the faulty gimbal well enough to be confident that the ship could continue its smooth sailing. They devised a test to confirm Dawn’s readiness to resume its spiral maneuvers. After swapping to gimbal #2 (and ipso facto engine #2), Dawn thrust from July 14 to 16 and demonstrated the excellent performance the operations team has seen so often from the veteran space traveler. Having passed its test with flying colors (or perhaps even with orbiting colors), Dawn is now well on its way to its third mapping orbit.

Dawn in survey orbit at Ceres

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Dawn in survey orbit at Ceres

Artist’s concept of Dawn thrusting with ion engine #2. The spacecraft captured the view of Ceres in June, and the intriguing cone described last month is visible on the limb at lower left.

The gradual descent from the second mapping orbit to the third will require 25 revolutions. The maneuvers will conclude in about two weeks. (As always, you can follow the progress with your correspondent’s frequent and succinct updates here.) As in each mapping orbit, following arrival, a few days will be required in order to prepare for a new round of intensive observations. That third observing campaign will begin on August 17 and last more than two months.

Although this is the second lowest of the mapping orbits, it is also known as the high altitude mapping orbit (HAMO) for mysterious historical reasons. We presented an overview of the HAMO plans last year. Next month, we will describe how the flight team has built on a number of successes since then to make the plans even better.

The view of the landscapes on this distant and exotic dwarf planet from the third mapping orbit will be fantastic. How can we be so sure? The view in the second mapping orbit was fantastic, and it will be three times sharper in the upcoming orbit. Quod erat demonstrandum! To see the sights at Ceres, go there or go here.

Part of the flexibility built into the plans was to measure Ceres’ gravity field as accurately as possible in each mapping orbit and use that knowledge to refine the design for the subsequent orbital phase. Thanks to the extensive gravity measurements in the second mapping orbit in June, navigators were able not only to plot a spiral course but also to calculate the parameters for the next orbit to provide the views needed for the complex mapping activities.

Topographic map of Ceres with crater names

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Topography of Ceres

This map of Ceres depicts the topography ranging from 4.7 miles (7.5 kilometers) low in indigo to 4.7 miles (7.5 kilometers) high in white. (As a technical detail, the topography is shown relative to an ellipsoid of dimensions very close to those in the paragraph below.) The names of features have been approved by the International Astronomical Union following the system described in December.

We have discussed some of the difficulty in describing the orbital altitude, including variations in the elevation of the terrain, just as a plane flying over mountains and valleys does not maintain a fixed altitude. As you might expect on a world battered by more than four billion years in the main asteroid belt and with its own internal geological forces, Ceres has its ups and downs. (The topographical map above displays them, and you can see a cool animation of Ceres showing off its topography here.) In addition to local topographical features, its overall shape is not perfectly spherical, as we discussed in May. Ongoing refinements based on Dawn’s measurements now indicate the average diameter is 584 miles (940 kilometers), but the equatorial diameter is 599 miles (964 kilometers), whereas the polar diameter is 556 miles (894 kilometers). Moreover, the orbits themselves are not perfect circles, and irregularities in the gravitational field, caused by regions of lower and higher density inside the dwarf planet, tug less or more on the craft, making it move up and down somewhat. (By using that same principle, scientists learn about the interior structure of Ceres and Vesta with very accurate measurements of the subtleties in the spacecraft’s orbital motions.) Although Dawn’s average altitude will be 915 miles (1,470 kilometers), its actual distance above the ground will vary over a range of about 25 miles (40 kilometers).

In March we summarized the four Ceres mapping orbits along with a guarantee that the dates would change. In addition to delivering exciting interplanetary adventures to thrill anyone who has ever gazed at the night sky in wonder, Dawn delivers on its promises. Therefore, we present the updated table here. With such a long and complex mission taking place in orbit around the largest previously uncharted world in the inner solar system, further changes are highly likely. (Nevertheless, we would consider the probability to be low that changes will occur for the phases in the past.)

Mapping
Orbit
Dawn code
name
Tentative dates (further changes are likely)Altitude
in miles
(kilometers)
Resolution in
feet (meters)
per pixel
Resolution compared to HubbleOrbit
period
Equivalent
distance of
a soccer ball
1 RC3 April 23 –
May 9
8,400
(13,600)
4,200
(1,300)
24 15
days
10 feet
(3.0 meters)
Survey June 6-30 2,700
(4,400)
1,400
(410)
73 3.1
days
3.3 feet
(1.0 meters)
HAMO Aug 17 –
Oct 23
915
(1,470)
450
(140)
217 19
hours
13 inches
(33 cm)
LAMO Dec 15 –
end of mission
230
(375)
120
(35)
850 5.5
hours
3.3 inches
(8.5 cm)

Click on the name of each orbit for a more detailed description. As a reminder, the last column illustrates how large Ceres appears to be from Dawn’s perspective by comparing it with a view of a soccer ball. (Note that Ceres is not only 4.4 million times the diameter of a soccer ball but it is a lot more fun to play with.)

Resolute and resilient, Dawn patiently continues its graceful spirals, propelled not only by its ion engine but also by the passions of everyone who yearns for new knowledge and noble adventures. Humankind’s robotic emissary is well on its way to providing more fascinating insights for everyone who longs to know the cosmos.

Dawn is 1,500 miles (2,400 kilometers) from Ceres. It is also 1.95 AU (181 million miles, or 291 million kilometers) from Earth, or 785 times as far as the moon and 1.92 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 32 minutes to make the round trip.

Dr. Marc D. Rayman
8:00 p.m. PDT July 29, 2015

 
See other posts from July 2015

 

Or read more blog entries about: mission status, asteroids, Dawn, asteroid 1 Ceres

Comments:

Bob Ware: 07/30/2015 08:21 CDT

Wow! Spedawncular images! Thanks! Comparing these to Pluto one can see what appears to be a great and vibrant youthful body just like Pluto or Pluto is just like Ceres. All of that "white stuff" reminds me of another bloggers suggestion in part, that Ceres' 'crust' may not be all that thick. One day ...

ScienceNotFiction: 07/31/2015 12:51 CDT

I had closely examined those tiny "white heads" that scattered all over Ceres. Assuming large presence of hydrated magnesium silicate on Ceres, the mantle must be saturated with this substance as well. Since Mg silicate can suspend in salt water without settlement (appears as murky white), the visible white heads may in fact be the remaining open exposures. As more and more hydrated Mg silicate accumulated at these openings, the chance of this liquid being frozen before aggregating into new crust is highly possible. Freezing occurs faster in small openings. Many of the white heads are at the tips of bulges and ridges while some are near crater edges. These whitish caps has a high concentration of Mg silicate which make them brighter than the surrounding when light is reflected off their surface at any angle. This can explain why IR imaging cannot show any temperature variation with their surrounding. The harden crust can prevent heat from escaping to the surface (asbestos effect). If all assumptions are true, then we can summarize the following observation of Ceres: 1. Ceres has a liquid mantle with salt water and high concentration of Mg silicate and salts. 2. The core can reach at least 2000 C and the mantle's surface temp. is near freezing point of salt water. 3. The crust is mainly composed of magnesium silicate, magnesium amalgams, and mineral salts. 4. The crust is relatively thin and soft near the equatorial regions while the poles are harder. 5. Thermo-circulation within the liquid layer is much more active than Earth. 6. In some cases, liquid may be splashed from high velocity impact events resulting white marks around the craters. 7. Large crust debris from impacts will resurface and speed up the crater-resealing process. 8. Ceres has an unique tectonic behavior. Some of the impact crust debris may resurface underneath the softer crust areas pushing upward to form mountains. 9. The core is heated by ongoing magnesium salt water reaction.

sepiae: 07/31/2015 03:39 CDT

Wonderful article, thanks! Wonderfully humorous as well :) My admiration for the engineering increases daily. Also thanks to ScienceNotFiction above for the summary.

ScienceNotFiction: 07/31/2015 04:45 CDT

What causes the periodic haze over the Occator crater? Under my suggested Mg-silicate theory, there will be gas byproducts (oxygen & hydrogen) build up underneath the crust over time. I believe that the high elevation areas may actually be pockets of gases sandwiched between the crust and the liquid mantle. Because liquid cannot touch the bottom side of the elevated crust, these surfaces should be much harder and cooler because their bottom has been dried for an extended period. As for those deep basins (4.7mi depth), the bottom is very close to the liquid mantle, touching the crust during high tide period, thus continuing its re-sealing process. The murky salt water mantle also disperses and dims the light coming from the core's huge Mg chemical reaction (the Occator's light spots). It is like a high voltage LED light shining from behind a piece of sanded-glass. Trapped gases from Occator's nearby air pockets may consolidate periodically (due to tidal effect) and find their way to escape from these tiny openings. If we can verify these gases as oxygen and hydrogen, we would have solved all the mysteries of Ceres.

ScienceNotFiction: 07/31/2015 04:48 CDT

We really need to figure out how Ceres produces its heat and light energy at its core. If we can harness this knowledge, we can build spacecrafts for deep space exploration as well as space colonies anywhere in the universe. Building such giant fuel cell in space can supply us unlimited amount of energy and give us all of the essential elements for human survival without the need of a solar source. (ie. hydrogen, oxygen, Mg, minerals, salt and water)

Piotr: 07/31/2015 11:20 CDT

Marc, I just thought I'd say how much I love the sense of humour in your posts. Not there to do interplanetary gimbal repairs, indeed!

dougforworldsexplr: 08/01/2015 09:29 CDT

To Marc Rayman or anyone else concerned with Dawn; One thing I read before in some of my astronomy books and my research on the internet that I thought would be of special interest to most members of The Planetary Society is that Ceres is not only the largest asteroid but also the largest Carbonaceous Chondrite asteroid in the asteroid belt. I also read that unlike Vesta before the Dawn mission there were no meteorites on Earth associated with Ceres although there are a good number of Carbonaceous Chondrite meteorites on Earth. Of course as the name suggests Carbonaceous Chondrite meterorites have carbon which is at least partly in the form of organic chemicals. My main question is why hasn't there been more mention about or focus on learning about the carbonaceous possible surface material on Ceres? I read in one of your articles about Ceres, Dr. Rayman, that there have been some problems with the Visible and Infrared Mapping Spectrometer instrument that can be used to determine the composition I think the chemical or mineralogical makeup of material on Ceres. Is this instrument working now and if not what can be done to get it working soon while the Dawn Mission is still ongoing? Correct me if I am wrong but I think this is the instrument that would determine whether surface or in the LAMO phase immediate subsurface material is organic and possibly what organic chemicals or other material. One of the articles also mentioned I think that Dawn might be moving to LAMO in August. Was the Dawn mission able to gain any information in the HAMO or earlier phases that supports the view that Ceres is a carbonaceous chondrite asteroid and has this material on its surface. Also will the Dawn spacecraft in LAMO be able to get chemical composition data on the top of the surface and the immediate subsurface of Ceres. Also will the gamma ray and neutron detector detect the isotope ratios including of organics so these can be compared to carbonaceous chondrite meteorites on Earth

Marc Rayman: 08/01/2015 03:09 CDT

dougforworldsexplr: Although Ceres displays some similarities to carbonaceous chondrites, it is different. The visible and infrared mapping spectrometer is working well and has acquired a wealth of spectra. (It had a couple of minor glitches in June, as I described in my previous Dawn Journal, and they should prove inconsequential in the overall exploration of Ceres.) In any case, specific organic molecules are notoriously difficult to identify, but Dawn will reveal much about the mineralogy of Ceres. The science team is still analyzing the data. When they are properly reviewed, results will be released. The approximate schedule for Dawn's orbits is in the table above. The gamma ray and neutron spectrometers, which get their best results in the final mapping orbit, will reveal the elemental composition but not isotope ratios. Piotr and sepiae, thank you for your nice comments. Your speculations are interesting, ScienceNotFiction. There's a lot of exciting science still to be done!

Jonathan Chone: 08/02/2015 07:35 CDT

"Bright Spot 5" in Occator Crater, "Bright Spot 1" in Haulani Crater, how about the 2, 3 and 4, where are their location?

Anonymous: 08/03/2015 01:21 CDT

Dr. Rayman: Thanks for your interest in my scientific speculation. I hope you and your team can examine Ceres from this new perspective. Based on my speculative theory, I have also answered another mystery of the Occator's light spots. Since the first public photo of the Occator Crater in May, I have been searching for a logical reason why the lights are evenly glowed. If you zoom in on the latest photo, you may discover that the white lights has some precipitants within (not JPEG artifacts). Now I can safely assumed that the liquid mantle should have properties similar to a Liquid Light Guide - liquid that conducts light (like in liquid fiber optic cable). The impurity of the liquid mantle should be the culprit of these precipitants. A follow up future mission to Ceres should include a way to collect a sample of this mantle liquid. It will be a huge scientific breakthrough for mankind. In my view, NASA should focus on a follow up mission to CERES instead of landing human on Mars.

ScienceNotFiction: 08/03/2015 03:47 CDT

Besides magnesium silicates, the other active ingredient of Cere's liquid mantle will most likely be calcium chloride. Its solubility in water increases with temperature. It can prevent water from freezing down to -52C and prevent water from boiling below 1935C. It is hygroscopic, ability to absorb moisture such as water vapor. Its light conductive property fits the case for Ceres' mantle liquid. To me, another big puzzle of the white light emitted from the Occator spots is the lack of visible red/orange spectrum. As it turns out, the weakness of using calcium chloride solution as light conductive liquid is the poor conductivity of the red spectrum. If we add up all of my speculative hypotheses, we are not too far from exposing the inner workings of Ceres. Planetary science has never been so exciting since Titan's visit by Cassini. This DAWN mission should go down in NASA's history book as the most influential scientific find of the millennium. This cheap renewable energy model is the new beginning of our future. A new chapter of industrial revolution will take place very soon. This is the "NEXT BIG THING" for human.

ScienceNotFiction: 08/03/2015 08:08 CDT

The structures surrounding the Occator spots are 'splash stalactites' formed on the bottom side of the crust. There may be a variety of compositions on these stalactites. Some are rich in iron and carbon while a majority of them are rich in calcium deposit. There may even be an abundance of serpentine stalactites underneath many areas of Ceres. Based on the topographic map of Ceres, we can see the Occator crater is located on an evenly elevated region of Ceres. A recent asteroid impact has created the Occator crater. Before this impact, this region has already existed a large patch of sandwiched gas pockets. Networks of ancient stalactites had been formed there. If we closely examine the edge structures surrounded the largest light spot, we can see irregular stalactites pointing toward the interior core of Ceres. This discovery confirms that the splashy internal ocean undergoes tidal period which can touch the different subsurface regions of the planet. Based on DAWN's observed data, this gas layer of Occator may be in between 100m to 1000m. The tidal period changes during its 4.6 years of solar orbit in relation to its surrounding planets. Another four factors may influence greatly on Ceres' tidal range - the depth of its mantle ocean, the concentration of precipitants, the weak gravity and the high speed of rotation. Combining all these factors, I would not be surprised that the tidal range can reach 1 mile high (or even greater in some area). If we can determine the varying distance from the open spot to the surface of the exposed liquid mantle during Cere's rotation period, we may be able to estimate the depth of Ceres' ocean more precisely using simulation tools.

ScienceNotFiction: 08/03/2015 08:10 CDT

Seems to me, a landing mission on Ceres would bring us incalculable benefit in comparing to another rover landing on Mars. Based on all of the observable evidences on Ceres, I believe that strange sound can be heard on the surface of Ceres, especially near the Occator region. Gases rushing toward the small openings may generate whistle like howls. The intricate stalacite cavities may form all kinds of resonance frequencies, plus the echoes of the splashy mantle. A symphony of sounds is waiting for us to discover. Don't forget to bring a microphone on the next landing mission on Ceres :-)

ScienceNotFiction: 08/03/2015 09:57 CDT

Ceres is the next stop in our search of extraterrestrial life forms, not Mars. Given the unique condition of an active liquid mantle on Ceres, I think the chance of discovering life underneath the crust is almost 100%. There should have no shortage of microbes, fungi, snottites and bacteria inside of Ceres. With internal light source, there may even be multi-cellular organisms living on the stalactite "rocky sky" as well as the surface depth region (temp. between 30C to -2C) of the internal sea. Imagine a self-sustaining subterranean planetary ecosystem is less than 2 AU away from us. If we had focused all of our attention on Ceres 40 years ago, our world will be different today. We can build small bases on the dark side of the moon and pay human visits to other moons of the solar system. The moon will become our launching station for all sort of space missions.

Mike: 08/03/2015 11:46 CDT

"ScienceNotFiction", you should try to fit your theories to the observations, not the other way around. Given the orbit of Ceres is outside the "snow line" and the abundance of H and O in the universe, I still think ice is the most likely candidate for the spots. (Which would be super exciting!) Marc, I think I vaguely remember it from one of your blog entries, but what is the "geostationary" orbit altitude for Ceres? and is/was that one of the planned orbiting altitudes? (or is Dawn in a retrograde orbit?). Even now as I ask the question I think GEO is probably only useful for communication satellites, but I wonder if there might not be some science that might be done by moving Dawn to a fixed relative position (say, over the spots) at the end of LAMO?

Marc Rayman: 08/05/2015 10:47 CDT

Jonathan: The numbers are from 11 vague features that could be discerned with Hubble Space Telescope observations made in Dec. 2003 and Jan. 2004. Very roughly, 2 is near Dantu; 3 is near Toharu; and 4 is in the general area of Nawish. Now that we have detailed imagery and some official names, the numbers are becoming less common. Mike: The "geostationary" altitude is 450 miles (720 kilometers). So Dawn's final orbital altitude will be about half that. Dawn always uses polar orbits (at Vesta as well as Ceres), because that yields the best views of the entire surface. (I explained this in more detail in my Feb. 2014 Dawn Journal.) I am highly doubtful that Occator, or any other region, would display enough variability to warrant limiting Dawn's view to a small portion of the large surface. There is too much worthwhile science to be done on Ceres to restrict us to a fixed location.

Jonathan Chone: 08/09/2015 09:03 CDT

Oh I see, I learn new things again, thank you for your kindly reply

ScienceNotFiction: 08/14/2015 03:50 CDT

The "Pyramid" feature may have formed over a billion years ago when this region of Ceres was "muddy soft" (the soapy clay crust). A piece of icy porous asteroid impacted a nearby surface at high velocity. As it penetrated through the muddy crust toward the dense liquid mantle, this light weight asteroid floated back up and push up a portion of itself on the soft muddy surface. Dipped inside the liquid mantle, this resurfacing asteroid was coated with the dense liquid, and continued to push upward reaching 4 mile high until the surrounding crust was fully harden. Keep in mind that the mantle liquid does not freeze easily (freezing temperature may be -52C). The streak marks were the evidence of frozen and dried up magnesium silicate compound. This mountain creation process was an extremely rare event to occur on Ceres.

ScienceNotFiction: 08/14/2015 04:08 CDT

Based on my speculative theory, here presents a possible history of CERES: 1. Ceres' planetary formation started out as a protoplanet with olivine/serpentine/lime molten core encased with liquid salt water. 2. As Ceres gathered more asteroids, it grew in size as well as sustained an equilibrium state on its magnesium core reaction with the salt water. 3. The formation of sepiolite and many other mineral byproducts helped Ceres to form a thin layer of soapy crust (Early Muddy Crust Period). 4. This muddy crust underwent billions of years of the hardening process which had helped to rebuild the surface of Ceres from countless asteroid impacts. By comparing the same size craters, one will notice that there existed a range of depth variance. 5. The Pyramid was the only mountain created during the time of Semi Muddy Crust Period. 6. During the evolution of Ceres, stalactites of various kinds were formed underneath the surface crust. Intricate interconnecting chambers and gas pockets were formed which pushed up certain regions of the surface, thus forming the higher elevation regions. 7. The Occator Crater may have been formed many millennium years ago by a large asteroid (First Occator Crater Impact). It had punched a hole on this higher elevation area, and ever since the liquid mantle had been sealing this crater. Another tiny asteroid impact event (last year) had punctured this newly formed thin crust area again, leaving a cluster of holes on the surface. 8. The collapsed stalactite roof exposed the bright liquid mantle, and the resealing process repeats again. 9. Because there are only so much mineral deposit to form inside Ceres, This time the liquid mantle may no longer be able to fill the holes as the internal sea level may have lowered drastically due to the rapid evaporation of water from the giant impact of the first asteroid. If this is true, the light spots may stay open for a very long time.

Jonathan Chone: 08/15/2015 05:00 CDT

Now we have seen many global maps of Ceres, including a exaggerated-color photographic map released in April, black and white photographic map and hemispheric topographic maps release in July. Any global maps in thermal infrared or true color?

ScienceNotFiction: 08/17/2015 12:37 CDT

Besides the Occator Crater, there are many more tiny light exposures appeared on DAWN's June/July survey photos. Take a look at Survey Orbit #28, the bright dot was in fact another opening similar to Occator. If you take a closer look at Haulani Crater, it too has been covered with openings showing the interior light of Ceres. On Photo #19593, one clearly sees a crescent-shape trench opening exposing the interior. Evidences are clear, the crust of Ceres is very "CRUNCHY", it can easily be "broken" or "punctured" due to the loosely connected splash stalactite ceiling composed of sepiolite. I use "broken" and "punctured" to describe the phenomenon because the formation of these exposures are diverse and unique. Let us examine these formation processes: 1. A space rock from the asteroid belt flew in and punctured a thin crust region forming a tiny opening. The underneath crust ceiling are filled with networks of splash stalactites, in between them are connecting areas which forms the thin crust regions, very similar to Earth's stalactite caves. 2. Over an extended period, large stalactite columns breaks off from the ceiling due to overweight and fell into the splashy mantle. This may be the prevailing method of forming these light exposures. (analogous to Earth's sink holes) 3. An incomplete re-sealing process by the liquid mantle over an impact crater eventually left a cluster of openings (with or without a thin layer of transparent ice sheet.) 4. Planetary expansion and contraction may cause high crust stress, thus causing a collapse of heavier stalactites underneath. 5. Large floating debris on the mantle sea may collide to the stalactites ceiling during super high tide period, thus knocking down some of the stalactite columns. Assuming there are large floating debris in the mantle, this would mean there are floating islands inside Ceres. In addition, stalactites that had grown toward the ocean will connect the ceiling to the liquid, thus forming mineral crystals.

ScienceNotFiction: 08/18/2015 02:00 CDT

Triple Thermo Insulation Effect on Ceres Ceres has many unique ways to maintain its liquid sea. To study the water cycle of Ceres would require a subterranean science mission. However, based on the Mg-reaction theory, we can hypothesize the mechanisms behind the water cycle on Ceres during its 4.5B years of evolution. Earth's ocean floor has been shown to be around 200 million yrs old. As we descend deeper into the lithosphere, we may be deceived by the fact that the lava mantle is actively rebuilding the lithosphere from inside out. Similarly on Ceres, the core is constantly generating precipitants that circulate the ocean. Thermo circulation coupled with extreme tidal wave effect will keep the liquid inside Ceres in constant motion. The heavy presence of calcium chloride and magnesium silicates will alter the density of the sea as well as the basic property of water. Calcium chloride will prevent water from boiling at extreme high temperature (>1,900C). This will keep the core to maintain its chemical reaction equalibrium without converting H2O to steam. Thus the internal atmospheric pressure of Ceres remains within a fixed range. The lowering of freezing point of water aids Ceres to seal its surface openings with a mixture of materials. Without this viscous mantle, Ceres would have dried up long time ago. The hydrated magnesium silicates particles help Ceres to stablize the ocean's surface temperature. The exterior crust of Ceres may be around -10C to -50C, but the surface temperature of the sea may be well above 10C. Similar to asbestos, magnesium silicates (crust) acts as a global blanket that keep the subterranean sea warm over time, similar to the global warming of Earth by CO2. ....continues below...

ScienceNotFiction: 08/18/2015 02:10 CDT

As new H2O formed near the Mg reaction core, warm H2O molecules will surface to the top layer of the sea and will cool off. Some of the water molecules will escape toward the ceiling and freeze underneath the crust (the ceiling temp. is -5C to -10C depending on surface solar absorption rate). This process will seal openings with ice initially. A secondary deposit process would come from the direct contact of the mantle liquid with the ceiling in high tide. Sepiolite, calcium deposits and metal silicates will deposit upside down on the newly formed frozen H2O caps. Eventually the surface icy rinks will sublimate into space exposing the ever growing crystallized silicates layer. Internal pressure may push upward on these soft mineral seals creating bulges. This forms the CRUNCHY CRUST. As the viscous liquid dripped from the ceiling over billions of years, complex stalactite network grow in length and may break off easily under various conditions. The sea level may be lowered due to prolong exposure of the internal sea to space from excessive asteroid impacts over time. Ceres self-sealing mechanism is weakening.Based on my speculative theory, Ceres has three layers of thermo insulation - the liquid ocean, the gas gap layer and the ceiling crust.

ScienceNotFiction: 08/18/2015 04:09 CDT

WHAT KIIND OF ORGANISMS CAN LIVE ON CERES ? The unique setup of Ceres will increase the likelihood of finding organisms living inside Ceres. The gas layer have enough O, H, CO2 to sustain an ecosystem. On the ceiling crust, we may have viny plants that grow on the stalactite columns. They absorb mineral nutrients, water vapor and ocean light to grow. In the top ocean layer, we may find photosynthetic jellyfish species, algae and plankton. Predatory marine species with high body buoyancy may live in the deeper region of the sea where their buoyancy ratio cancels out the effect of density and gravity. They can just rest on this layer like an invisible sea floor. They may resemble octopus or cuttlefish. They swim with liquid jet propulsion and breath through the skin. Conventional fish-style swimming will consume too much energy in dense liquid, but there may still exist some body inflatable fish species. The weak gravity may evolve certain aquatic species into flying insects. They dwell in the stalactite forest above and feed on the stalactite columns that are rich in calcium and magnesium salt, plus plants. Their body can resist cold temperature due to the prolong absorption of calcium chloride. They may appear greenish. All mentioned creatures would have developed sensor organs to detect light and temperature. Some varieties of the flying insect may have radar vision similar to bats which can help them prey on other species. Eye sight would be useless under brightly lit environment but the sense of smell and hearing may be more important. Dead organisms may sink near the core and get incinerated by the high temperature. It will be difficult to find fossilized samples of species except the sepiolite precipitant. It may contain organic or DNA molecules. A robotic submersible mission will be needed to explore all possibilities. A manned-mission to Ceres is a must for the next 20 years before it is too late for "us" (borned in the 60's and 70s) to see.

ScienceNotFiction: 08/18/2015 09:32 CDT

Detail Analysis of the Second Occator Impact Event at Occator Crater Based on my detail observation of the Occator Crater openings, a fuller understanding of how these holes were formed has emerged. Here are my detail findings. The largest light hole was first created by a single asteroid of the same diameter size. It struck through the middle of the ancient Occator basin with high velocity. This impact had generated an abrupt seismic shock wave to its surrounding shaking off a number of large stalactite columns. Because this region was originally on a higher elevation where the gas layer stretched at least over 100 meter high, there was no apparent surface spilling of the mantle liquid from this large hole. However the seismic shock-wave had shaken down a connected pair of stalactite columns to the right, and several stalactites of much smaller diameters. These fallen holes are much rounder and smoother which coincides to the round root nature of natural stalactites. Due to the weak gravity of Ceres, Ceres' stalactites will tend to be wider at the root and more cylindrical toward the tip. The different orientation of splashy stalactites helps to build interconnecting networks, they can also merge with surrounding stalactites to form a larger cluster. For example, the crescent shape exposure was probably caused by a fallen cluster of stalactite which was first formed along a section of the rim of a sunken crater. This area tends to be lower toward the mantle where stalactite can form more easily over time. Based on my theoretical analysis, light holes can appear on many terrains of Ceres as long as there are stalactite columns formed directly below.

ScienceNotFiction: 08/19/2015 10:10 CDT

DETAIL EXPLANATION OF THE MYSTERIOUS TINY BLACK HOLES ON CERES: There are many tiny black holes on the surface of Ceres as shown on almost every close-up photos taken by DAWN. Building upon my stalactite ceiling theory, these black holes can be easily explained here. For those of you familiar to stalactite formation, one particular form is called the straw stalactite. When a smaller diameter stalactite breaks off from the ceiling, the water vapor will first seal the new opening with ice formation. During the secondary deposit process, a new column of stalactite will form and grow underneath the icy cap, and eventually sealing the light hole at the bottom completely for thousands of years. The exposed icy cap would have been completely sublimated to space at much earlier period leaving a small deep hole on the surface of Ceres. This process occurs everywhere on Ceres. This continuing geological phenomenon also explains why we continue to see new "White Heads" and "Straw Holes" forming on Ceres. They represent the stages of the same geological process. Now, my "speculative" theory brings us much closer to the scientific fact. I think I had pretty much resolved every observable mysteries of Ceres from DAWN's photos. The next step is to explore what lives in the mysterious subterranean sea of Ceres. This will be equally exciting in comparison to the complex geology of Ceres. Without sending a probe through the Occator Light Hole, we may never know the truth.

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