Dawn Arrives at Ceres: Coverage

We should be seeing some new images of Ceres on about April 16th. Dawn is currently approaching the planet with the Sun in nearly the same direction. If they tried to take pictures, they might damage the camera with excessively bright Sunlight. This was in the plan all along. It has nothing to do with anything that has been discovered.

I help out at Zooniverse It's very gratifying! When I began we were helping classify the galaxies!
reply to: AgentSmith

Here's a good article from Phil Plait about why we aren't seeing pictures from Dawn: www.slate.com...

Dawn doesn’t use conventional chemical rocket thrusters. While these can provide a lot of oomph, the fuel is heavy, which means you need to carry more fuel to carry that fuel, and so on. You can change directions quickly, but the cost is dedicating more of your precious payload mass to fuel instead of scientific equipment.

Instead, Dawn uses ion thrusters, which uses complex electric fields to fling ionized atoms out the back end at high speed. The thrust is a lot lower, but you use fuel so efficiently you can literally keep your engines on for months at a time. In the end, you get the same ability to change the direction and speed of your spacecraft; it’s just a lot more gentle and takes a lot longer.

So instead of blasting toward Ceres and blasting into orbit, it’s more like Dawn is sliding into orbit, catching up with the asteroid slowly and easing its way closer. To do that it flew past Ceres a bit, and is now on the side of Ceres away from the Sun. From its vantage point it’s looking down on the dark side of the asteroid. It’s also on a trajectory that took it farther away from Ceres, and is now falling down closer to it (like tossing a rock in the air, and having it fall back down into your hand).

originally posted by: wildespace
Here's a good article from Phil Plait about why we aren't seeing pictures from Dawn: www.slate.com...

Dawn doesn’t use conventional chemical rocket thrusters. While these can provide a lot of oomph, the fuel is heavy, which means you need to carry more fuel to carry that fuel, and so on. You can change directions quickly, but the cost is dedicating more of your precious payload mass to fuel instead of scientific equipment.

Instead, Dawn uses ion thrusters, which uses complex electric fields to fling ionized atoms out the back end at high speed. The thrust is a lot lower, but you use fuel so efficiently you can literally keep your engines on for months at a time. In the end, you get the same ability to change the direction and speed of your spacecraft; it’s just a lot more gentle and takes a lot longer.

So instead of blasting toward Ceres and blasting into orbit, it’s more like Dawn is sliding into orbit, catching up with the asteroid slowly and easing its way closer. To do that it flew past Ceres a bit, and is now on the side of Ceres away from the Sun. From its vantage point it’s looking down on the dark side of the asteroid. It’s also on a trajectory that took it farther away from Ceres, and is now falling down closer to it (like tossing a rock in the air, and having it fall back down into your hand).

The maths involved in making that work are mind-bottling.

a reply to: wildespace

From its vantage point it’s looking down on the dark side of the asteroid.

Yes, fantastic science has put a camera near Ceres. Dawn was taking pictures while it neared Ceres. It was doing 2 things at once.

Now, it cant chew bubble gum and walk at the same time, because its on the dark side???

originally posted by: wildespace
Here's a good article from Phil Plait about why we aren't seeing pictures from Dawn: www.slate.com...

Thanks for this, wildespace. The graphic in the article tells us why it is not in position yet to begin a full image analysis, which I further annotated below showing the date of orbital insertion, and where the spacecraft is today (March 23).
My additions to the graphic are shown in Teal.

Original Caption: The orbital insertion path for Dawn is not an easy one. The new trajectory is in green, and the tick marks are Dawn's positions one day apart. Note the long, looping path designed to save fuel over the old trajectory (red). Right now, Dawn is at the apex of the long loop.

Also, according the Wikipedia entry on Dawn, it is explained that the failure of the reaction wheels (which was what prompted the odd orbital insertion maneuver as shown above) also has limited the photo opportunities on approach. Another issue is that the Sun is dangerously in the field of view at the moment, which could damage Dawn's cameras if images are taken:

Because of the failure of two reaction wheels, Dawn made fewer camera observations of Ceres during its approach phase than it did during its Vesta approach. Camera observations required turning the spacecraft, which consumed precious hydrazine fuel. Seven optical navigation photo sessions (OpNav 1–7, on January 13 and 25, February 3 and 25, March 1, and April 10 and 15) and two full rotation observation sessions (RC1–2, on February 12 and 19) are planned before full observation begins with orbital capture. The gap in March and early April is due to a period when Ceres appears too close to the Sun from Dawn '​s vantage point to take pictures safely.

en.wikipedia.org...

To add to the information above about when to expect additional images from Dawn, the next "OpNav" (Optical Navigation) opportunity will be "OpNav 6", which happens April 10. At that time, Ceres will be an 18% lit crescent. "OpNav 7" will occur on April 14, and will allow them to see 50% of the disk, similar to a half-lit Moon. After that, Ceres will achieve its regular orbit, and will allow Dawn to begin to take its full gamut of images and data gathering.

However, until OpNav 6 on April 10, Dawn is not in a good position for images, and in fact its view of Ceres includes a view directly the Sun, which could damage the imaging equipment if pictures are taken:

OpNav images of a narrow crescent won’t contain enough information to warrant the expenditure of hydrazine in all that turning. Moreover, the camera’s precision optics and sensitive detector, designed for revealing the landscapes of Vesta and Ceres, cannot tolerate looking too close to the sun, even as far from the brilliant star as it is now. Therefore, no pictures will be taken in March and early April when Dawn is far on the opposite side of Ceres from the sun. By the end of April, the probe will have descended to its first observational orbit (RC3), where it will begin its intensive observations.

Source:
Dawn Journal | January 29


Here is a video showing an animation of Dawn's approach to Ceres and its orbital insertion:

Cmooooonnnn....

*Please be aliens, please be aliens*

originally posted by: raikata
Cmooooonnnn....

*Please be aliens, please be aliens*

Well, I'm not sure what you mean by "Aliens" ,
but researchers working on the Dawn Ceres mission feel it's possible for Ceres to have (or have had) life.

Dwarf planet Ceres might have right stuff for life

The fact that Ceres is believed to have a subsurface layer of water -- maybe even liquid water (perhaps warmed to liquid state due to radioactive decay of it's core materials)

Ceres is a dwarf planet with giant potential. As NASA's Dawn spacecraft gears up for the first in-depth look at this tiny world, speculation is rife. Could Ceres be an overgrown comet? Host an ocean made of mud? Or even possess icy volcanoes that make it an unexpected host for life in the asteroid belt?...

...Remote observations using the Herschel space telescope show Ceres spitting water from somewhere on its surface, probably towards the equator. We think other icy bodies in the solar system, like Jupiter's moon Europa and Saturn's moon Enceladus, spew water in spectacular plumes from subsurface oceans (see diagram). If Ceres also has a buried sea, that could boost its chances of playing host to life – so astronomers are keen to track the plumes to their source.

Dawn is not able to look for life, but it can certainly analyze the conditions of Ceres and the material that make the Dwarf planet -- and maybe even do some rudimentary analysis on the potential plumes of material (water?) that may emanate from Ceres, and it may be able to discern whether or not Ceres is a place that could potentially harbor life as we know it.

The icy plumes on Ceres are very thin and erratic. Their appearance seems to be tied to Ceres' proximity to the Sun. They are probably more like sublimation of ice from the surface of a comet, than geysers forced up from a subsurface liquid ocean.
The presence of such an ocean in Ceres is highly questionable. There is no significant tidal friction to provide heat to keep water liquid. It is such heat that is believed to drive the icy plumes on certain moons of Jupiter and Saturn.

Even if liquid water could exist beneath Ceres' surface, a new analysis suggests that there would be inadequate energy to force it to the surface.

originally posted by: Ross 54
The icy plumes on Ceres are very thin and erratic. Their appearance seems to be tied to Ceres' proximity to the Sun. They are probably more like sublimation of ice from the surface of a comet, than geysers forced up from a subsurface liquid ocean.
The presence of such an ocean in Ceres is highly questionable. There is no significant tidal friction to provide heat to keep water liquid. It is such heat that is believed to drive the icy plumes on certain moons of Jupiter and Saturn.

Even if liquid water could exist beneath Ceres' surface, a new analysis suggests that there would be inadequate energy to force it to the surface.

There still may water that is warm enough to be liquid due to the decay of the radioactive material that may make up the core of Ceres. Maybe, maybe not. There is not enough information either way to decisive say either way if there is subsurface liquid water.

An excerpt from the link in my post above:

There is more than one way to make a cryovolcano, though. Some models suggest the core of Ceres may be heated by radioactive isotopes left over from the dwarf planet's formation. These could provide enough energy for punchier volcanism, perhaps producing larger plumes – and heat would be beneficial for any bacteria lurking below the surface.

Some other hypotheses state that even though there way not be enough pressure for the subsurface liquid water or mud (if there is liquid water or mud) to reach the surface, perhaps there is enough pressure for the subsurface water or mud to reach as far as the bottom of deep crater floors, as described in this except from the link in my post above [color emphasis provided by me]

What about cryovolcanism? In this scenario, ice and water are ejected from the surface by processes similar to those that drive magma volcanoes on Earth. Ceres doesn't have enough muscle to drive these eruptions, according to a second model presented at the LPSC by David O'Brien of the Planetary Science Institute in Tucson, Arizona.

Let's suppose that Ceres has a subsurface ocean covered by an icy shell. As the bottom of the shell freezes, it expands, putting pressure on the ocean and the shell itself. To create a cryovolcano, says O'Brien, the water pressure has to build up enough to shoot up through the shell before the ice cracks and relieves the pressure.

Since we don't know exactly how deep the ice is on Ceres, O'Brien modelled a range of plausible depths. None recreated the conditions for spewing cryovolcanoes – the ice always cracked before enough pressure accumulated. In the best-case scenario, water reached about 90 per cent of the way to the surface.

Intriguingly, that might mean water could reach the surface from a deep crater, where there would be less ice to negotiate – perhaps even from a crater like the one where Dawn saw the bright spot. "Everybody wants to know what's going on there," says O'Brien. A cryovolcano could be producing enough of a plume to replenish the ice on the surface. So Ceres could be producing comet-like emissions, driven by a weak cryovolcano. "It's sort of a midpoint between comets and cryovolcanic icy worlds," says Titus.

So the plumes may just be from offgassing (or not), or maybe they are more geyser-like phenomenon driven by some sort of hydrogeology/cryovulcanism going on (or not). There is still too much that needs to be learned about Ceres before anyone can say for sure.

The number of contingencies that must each go a certain way for there to be cryovolcanoes or geysers, or the like, on Ceres seems to argue against their existence.
First, there must be sufficient radioactive materials to keep the subsurface water liquid.
Then, there must be enough pressure to force the water to near the surface.
Then, there must be a crater deep enough to reach the water.
Then, there must be only one crater on all of Ceres that is allowing this to happen.
Of course, this may be exactly what's happening, but the odds seem to be against it.

Phil Plait made a correction to his article, pointing out that the unplanned course correction was actually due to a cosmic ray striking the ion engine machinery and disabling it: www.slate.com...

In September, a cosmic ray particle hit a part of Dawn's machinery that controls the ion propulsion, shutting it down. The spacecraft cruised for 95 hours when it was supposed to have been under thrust, forcing the need to change the incoming trajectory once the problem was fixed.

a reply to: Ross 54

There is more than just one possibilities for how icy material (or a mixed bag of different materials) could be expelling itself at the surface of Ceres.

According to the article I posted above, it seemed that they think if Ceres was somehow warmer than expected (as in due to the decay of radioactive material, as we both mentioned) then there may be enough pressure to power the cryovolcanoes through to the surface.

There is more than one way to make a cryovolcano, though. Some models suggest the core of Ceres may be heated by radioactive isotopes left over from the dwarf planet's formation. These could provide enough energy for punchier volcanism, perhaps producing larger plumes

Source:
Bright spots on Ceres could be water volcanoes

And it may not even be just water and traditional cryovolcanism. Scientists are saying there could be other materials besides water expelling itself at the surface to form these spots.

Other possibilities say that it is surface ice being excited by the sun and offgassing -- much like a comet

Another scientist cast doubt that the plumes are caused by cryovolcanism — ice volcanoes. David O'Brien, of the Planetary Science Institute in Tucson, said Ceres lacks the internal forces to create such eruptions.

Others theorized that the vapor blasts might be similar to emissions from comets.

"Could the bright spot be an icy plume caused by the vaporization of Ceres' surface as it turns towards the sun's heat, and then dropping away as night falls?" wrote Monica Grady, a professor of planetary and space sciences at the Open University. "Corridor talk at the conference speculates that Ceres might be closer to a comet than the asteroid it is usually regarded as."

Source:
Ceres' bright spots: Icy volcanoes?

However, it is also pointed out by others that the models show that outgassing like this on Ceres should on occur at thigh latutdes, not so close to the equator:

Timothy Titus of the US Geological Survey in Flagstaff, Arizona, presented a thermal model that examines where on the surface ice could remain stable over the life time of the solar system, rather than boiling away more quickly. If Ceres is acting like a comet, it must have ice patches that can survive for a long time before being heated by the sun as it moves into a warmer part of its orbit.

Titus found that ice could only be stable in regions above 40 degrees latitude. But the plumes spotted by Herschel seemed to come from nearer the equator, which implies they can't be comet-like. "The water ice is just not stable at the latitudes that the plumes are supposedly coming from," Titus says.

Although, that doesn't mean that their current models are necessarily right, which seems to be the point all of the researchers are making. They don't have enough data about Ceres to say definitively that it can or can't be cryovolcanism, or that it can or can't be outgassing, or that the interior of Ceres can or can't be warmer than expected due to radioactive decay.

They simply need more data, which will come over the next several months. Until then, then can make semi-educated guesses based on the current models of the make-up of Ceres (models that could be wrong), AND they can also keep open minded to other possibilities that go against those current models, knowing full well that the models might be wrong.

Heck, at this point I suppose the "it has something do do with intelligent aliens" hypothesis could still be on that table, but that would be even more against the odds than the odds that you broke down for cryovolcanism.

Both the main explanations for the bright spots on Ceres, cryovolcanism, and exposed surface ice, appear to have serious flaws. An interesting one that applies to both, is that the temperature of the bright spots was found to be the same as that of their darker surroundings. This result apparently came a surprise to NASA. Light colored areas, because they absorb less, and reflect more light, should be cooler than darker ones. Some new explanation may become necessary.
How is it that we are supposed to estimate the odds of finding signs of an extraterrestrial presence in our solar system? We know far less about the true distribution of intelligent life in the galaxy than we do about Ceres. For all we know, every solar system may contain signs of either intelligent habitation or visits by extraterrestrials.

a reply to: Ross 54

Some new explanation may become necessary.

The way it looks now, its not "may", but "must".

We cannot solve our problems with the same thinking we used when we created them.

Albert Einstein

www.brainyquote.com...

As just about everyone can agree upon is, I'm no Astrophysicist. But in saying that it would also be true that I have studied the subject for a considerable time.

The above quote in this particular case is a door opening statement, or to some here at this web site, and invitation to exit the box. And in this case, to me, Albert is telling us the answers are not going to be found in standard models of Astrophysics.

What I fear the most is that the Astrophysics community will shy away from what is being documented, and they will do this out of fear. A fear of facing a dilemma of ignorance, because what they see does not fit into the accepted model of planet formation. The thinking that created this model, will not answer the question as to what the light is, or isn't.

I am quite certain that aliens are not involved with the light, except to maybe try and conceal its reality. Other than that, I feel the light is absolutely, normal.

For those that are interested in the alternative explanation feel free to U2U me for the details.

According to the published schedule, Dawn should be making images of Ceres today. Past experience suggests that we might get to see this on about the 15th or 16th. Further images are planned for the 14th. These will probably be released around the 19th or 20th. Because of uncertainties about the rotational period of Ceres, the bright spots may, or may not be visible in these images. It will be interesting to see which is the case.

originally posted by: raikata
Cmooooonnnn....
*Please be aliens, please be aliens*

Be careful what you wish for.

originally posted by: Ross 54
According to the published schedule, Dawn should be making images of Ceres today. Past experience suggests that we might get to see this on about the 15th or 16th. Further images are planned for the 14th. These will probably be released around the 19th or 20th. Because of uncertainties about the rotational period of Ceres, the bright spots may, or may not be visible in these images. It will be interesting to see which is the case.

Since the reaction wheels have failed last year, the ability to orient the craft so the antenna is pointing back toward Earth has been compromised, and their high-bandwidth communication opportunities are limited. Dawn may have been already pre-programmed to take the images (programmed the last time the up-link antenna orientation was correct), but the ability to transmit those images back may need to wait until it moves itself into a better position.

The reaction wheels were used to turn the craft without using thrusters. If the reaction wheels were working, the craft could be turned more easily without the use of the attitude control thrusters and without using up the very limited supply of hydrazine fuel. Unlike the main electric ion engines, the attitude control thrusters use chemical fuel -- hydrazine. Therefore, if they want to conserve the hydrazine fuel, they need to wait for the craft's orbit to naturally put the up-link antenna in the correct orientation.

I'm not sure if that is the only factor holding up the release of images, but that is at least one factor.

originally posted by: All Seeing Eye
a reply to: Ross 54

Some new explanation may become necessary.

The way it looks now, its not "may", but "must".

We cannot solve our problems with the same thinking we used when we created them.

Albert Einstein

www.brainyquote.com...

As just about everyone can agree upon is, I'm no Astrophysicist. But in saying that it would also be true that I have studied the subject for a considerable time.

The above quote in this particular case is a door opening statement, or to some here at this web site, and invitation to exit the box. And in this case, to me, Albert is telling us the answers are not going to be found in standard models of Astrophysics.

What I fear the most is that the Astrophysics community will shy away from what is being documented, and they will do this out of fear. A fear of facing a dilemma of ignorance, because what they see does not fit into the accepted model of planet formation. The thinking that created this model, will not answer the question as to what the light is, or isn't.

But that's not how it works.

If something challenges an accepted model (for instance the plethora of "Hot Jupiters" found orbiting very close to other stars), then we find better models. That's how science works.

We're not rooted to dogma nor "stuck on stupid".

When something doesn't fit an accepted model we like it because that's the surprise of investigation. If all we found was what we expected then science would be a very boring field.