DAWN mission to orbit 1 Ceres & 4 Vesta.

[h2ouniverse]

For Xenon?<br /><br />To make it less costly, they would need to increase significantly the market size, so that the companies who extract Xenon gas (from atmosphere) invest into more efficient processes.<br /><br />What I can tell you is that for a satellite few years ago with plasmic prop the gas needed for on-ground testing was recycled. Actually we RENTED it (can you imagine, renting a gas???). And had a purity requirement akin to the "leave it as clean as you had it" clause when renting an apartment...

 

[h2ouniverse]

When I said ground testing I did not mean thrust! Once plasma-ized it is no longer recoverable in a practical way.<br />

 

[h2ouniverse]

Hi all,<br /><br />Ceres polar "caps" should be of interest as their temperature is always very cold, far lower than 170K max, with very low water ice sublimation. Thanks to the low tilt of Ceres spin axis vs its orbital plane. <br /><br />Does anybody know whether Dawn's orbit is going to be polar (heliosynchronous e.g.?) or equatorial? Will it get close views of the poles?<br /><br />Regards.

 

[MeteorWayne]

A JPL feature creates a bump...<br /><br />IT Came From Vesta<br />October 29, 2007 <br /><br />Their infiltration began - like so many other infiltrations - with a tell-tale contrail of smoke and flame creating a supersonic slash across the afternoon sky. But this time they would not go unnoticed. This time, two Australian station workers, just going about their job, opening a gate to a boundary fence, witnessed their arrival. The eyewitnesses later said they observed a "fireball with sparks coming off," streaking from the south to the north, make its descent into a hummock of spinifex grass. It would be another 10 years before they told their story. A decade before the world realized -- the Eucrites had arrived. <br /><br />"Most people do not realize there are eucrites all are over the planet," said Dr. Christopher Russell of UCLA. "How they get here is something of a mystery but we believe they came from Vesta." <br /><br /><br />Full feature story <br /><br />Oct 18 first images from Dawn's Framing Camera <br /><br />1395 days to Vesta!!<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[3488]

Thank you very, very much MeteorWayne.<br /><br />The first images from DAWN in space. A very important milestone has been passed.<br /><br />I have downloaded those images. True it is a star field in Cancer, just north of<br />Praesaepe / M44, but it matters not.<br /><br />The Framing Camera WORKS. <img src="/images/icons/laugh.gif" /><br /><br />Great stuff.<br /><br />The article about the Eucrites is very interesting indeed.<br /><br />Thank you again MeteorWayne.<br /><br />One of the missions I helped to fight to approve & save is working very well. <img src="/images/icons/laugh.gif" /><br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[3488]

Hi Joel, <br /><br />AFAIK, the orbit wil be polar & heliosynchronous<br />passing over the 2 AM & 2 PM zones.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[h2ouniverse]

Thanx.<br />Means it should have a clear view of the polar areas.<br />(Great!)

 

[3488]

Hi Joel,<br /><br />The orbits around both 4 Vesta & 1 Ceres, have beed designed to get the best possible coverage<br />of both objects. <br /><br />The 2 AM & 2 PM heliosynchronous angle, will enble good IR readings of both bodies at the<br />coldest time in the morning & the 'warmth' of the afternoon Sun.<br /><br />I am not too sure if the shape of the orbits will change. AFAIK, the orbits will start higher up<br />(to enable mapping & geomorphological studies), <br />but DAWN will slowly descend, enabling high resoluton imaging, etc, before heading off again.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[comga]

"The 2 AM & 2 PM heliosynchronous angle, will enble good IR readings of both bodies at the coldest time in the morning & the 'warmth' of the afternoon Sun. "<br /><br />One slight quibble: Because solar flux comes in from essentially one direction, but heat radiates over the whole sky, and while 2PM is the warmest meridian, 2AM is not really the coldest. That is closer to 6AM. However, 2AM is cold enough, and you can't choose them independently.<br /><br />(Arguing with an engineer is like wrestling a pig in mud. After a while, you sense that he is enjoying it.)<br /><br />Please tell, though, how does the team know enough about the oblateness and mass distribution of Ceres and Vesta to choose an orbit that is sun synchronous? Will they do this by trial and error? Can they derive it by telescopic observations? And can they really do this at their initial orbital altitude? On Earth I thought that there was only so high a satellite could go and still get the orbit torque to stay sun-synchronous.

 

[alokmohan]

I have lost track.Where is DAWN now?

 

[MeteorWayne]

Dawn is still on the way to the Mars gravity assist in February 2009.<br /><br /> here's a map of the trajectory <br /><br />Dawn Mission Timeline<br /> <br />Launch September 27, 2007 <br />Mars gravity assist February 2009 <br />Vesta arrival August 2011 <br />Vesta departure May 2012 <br />Ceres arrival February 2015 <br />End of primary mission July 2015 <br /><br />MW<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[3488]

Hi Comga,<br /><br />It is at the moment largely guesswork. 1 Ceres is 975 KM wide across the equator, <br />but is 909 KM through the poles.<br /><br />Of course mass distribution is at present a wild guess, but the axis appears stable & the <br />oblateness, is constant with a differentiated body.<br /><br />4 Vesta, is known to have a giant south polar crater & is home to one of the tallest known <br />mountains in the solar system, right at the south pole. The rotation also appears stable.<br /><br />What would help, would be the discovery of any moons & tracking them would be of immense help,<br />but so far, neither 1 Ceres or 4 Vesta appear to have any.<br /><br />Of course, to coldest point is usually at dawn, so my error there, but DAWN cannot jump<br />timezones, so it looks like the 2:00 AM & 2:00 PM meridians are the best option.<br /><br />There are to be further obs with HST & I am sure with AO @ the Keck, etc, prior to DAWN<br />arrival.<br /><br />Hi MeteorWayne.<br /><br />The Mars encounter, will be a great workout for the instruments. There is still no 'Where is DAWN' <br />part on the website.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[3488]

Hi Joel,<br /><br />IIRC DAWN has no radar. Also I think the best hope is outgassing, exposed ice in impact craters,<br />cryovolcanoes if they exist, etc.<br /><br />DAWN is equiped with the VIR (Visible & InfraRed Spectrometer) & this <br />instrument is EXTREMELY sensitive), if water is present on 1 Ceres (which I think it is at the polar <br />regions, not equator, far too 'warm' @ minus 34 C max).<br /><br />DAWN is to image 4 Vesta in seven colours & 1 Ceres in three (do not know why, this is so. <br />If I had my way, both would be imaged in seven colours), & both will be surveyed in the full <br />IR range in the VIR.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[h2ouniverse]

in reply to<br />-------<br />if water is present on 1 Ceres (which I think it is at the polar regions, not equator, far too 'warm' @ minus 34 C max). <br />-------<br /><br />Hi Andrew,<br /><br />Well, Mars is even warmer... And yet there is still this possibility for this ice (or tuff?) seriously envisaged at Mars equator. So why not in non-polar parts of Ceres? under some mineral layer, with the same arguments as the ones arisen in the Mars Ice thread. On Ceres there might have been some upwelling of convective ice or water relatively recently.<br /><br />Regards.

 

[JonClarke]

We know there are hydrated minerals on Ceres from spectroscopy. Dawn should provide good global maps of the distributin of these. There may be ices in shaded spots but I suspect that Ceres is too close to the Sun to have significant percentage of ice in its crust. of course if the ice is bruied by dust we may not be able to tell if it is there, unless there are vets or similar, hiting at their presence, or perhaps exposures in the walls of fresh craters.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[3488]

Hi Jon,<br /><br />Thank you very much. I did think that hydrated minerals were already confirmed. <br /><br />I agree, the smoking gun, so to speak, will be vents & / or exposed crater walls, etc, just<br />like those on the Saturn moon Phoebe.<br /><br />Exposed ice on wall of giant northern depression, Jason on the Saturn moon Phoebe.<br /><br />13 Kilometre wide crater on Saturn moon Phoebe. Exposed ice is clearly visible as bright<br />patches. Blow up of crater floor showing ice boulders & more bright patches.<br /><br />Perhaps DAWN will show similar on 1 Ceres??<br /><br />IMO, there will be cliffs & rifting, as the ice mantle froze & expanded, under an already <br />brittle crust.<br /><br />I do not think that 1 Ceres will be a bore, for a single minute, neither 4 Vesta for that matter. <br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[JonClarke]

Hi Andrew<br /><br />That's the sort of thing to look for. But... Saturn is ~10AU and well and truly beyond the snow line (~4 AU). Ceres is only 3 AU and gets 33% more solar radiation than the maximum compatible with extensive exposed ice. It also gets 11 times the solar radiation of Saturn. So unless there are areas of permanent shadow (and I don't think dawn can see into Shadowed areas), we are not going to see exposed ice on Ceres unless it is very fresh.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

Hi Jon and Andrew,<br /><br />Thanks for the answer.<br />Indeed the equator and most of Ceres surface is beneath the frost line. But the polar axis is pretty well perpendicular to the orbital plane. So the polar "caps" (beyond about 80° latitude) have always max diurnal temperature below 170K (whatever the season is). So in some way the caps should be beyond the line... <br /><br />Regards.

 

[JonClarke]

That's an interesting possibility I hadn't thought of. <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

I hope it will be so.<br />A reservation however: they do not detect water ice at the spectro from Earth. But can they really detect the signature of ice if it is at the limb (where the caps should lie when viewed from Earth)?

 

[JonClarke]

I guess it would depnd on the resolution of the instrument. maybe Keck can resolve on this scale.<br /><br />BTW, where did you get the 170K figure from? <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[h2ouniverse]

170K is what I get at 75° latitude (for a horizontal surface!), with the thermo-optical coefs alpha/epsilon(*) that allow for having 239K radiative equilibrium temperature at noon at the equator when Ceres is at its perihelion. Assuming a 5° polar axis tilt angle, this would mean that any horizontal surface beyond 75+5=80° latitude can never see equilibrium temperatures higher than 170K.<br /><br />As far as frost line in vacuum is considered, I have in mind 170K as a reasonable value. If I understand well, the sublimation kinetic is low enough at 170K to consider ice "stable" in vacuum. I would assume this depends on gravity on second order (ability to retain a surface pressure not too null). <br />At 4AU, that should be 197K for alpha/epsilon of 1.<br />What is the value you would consider?<br /><br />Regards.<br /><br />(*) conservative, as presence of H2O ice would sharply increase the albedo, hence decrease the alpha/epsilon.

 

[h2ouniverse]

Hi Andrew,<br /><br />Bad news, the differentiation of Ceres is not that established...

 

[JonClarke]

I'd be surprised if it's not. Vesta is smaller (even allowing for impact modification) but is differentiated. Ceres is also spherical, indicating isostatic equilibrium, which implies differentiation as well.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[MeteorWayne]

It's pretty round to have not redistributed it's interior.<br /><br />It makes you kind of wonder what kind of world Vesta came from. Was it similar to Ceres in the past? Was it impacted hard enough to drive away the volitiles yet leave a rocky/iron core? How <img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /><br /><br />This is a great mission that will teach us so much <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>