Thanks Bruce!

Thus, the ice crust is roughly 50 kilometers thick.

Er - I feel I'm being awfully picky but kg != weight. Pounds are a measure of weight (ie a force) so yes it would be about 4000 pounds on Ceres but its mass would still be ~60,000 kg.

Pedantic...

~600,000N - Newtons if we are talking mass

The full "Nature" paper is now available at http://oposite.stsci.edu/pubinfo/pr/2005/27/pdf.pdf . (That double "pdf" at the end is no mistake.)

It turns out I made a dumb mistake by assuming that the "25% ice" figure was a reference to Ceres' volume, rather than its mass. Since ice is much lower density than rock, if that figure is for ice then the water-ice mantle on Ceres would have a bigger volume and thus be thicker than I had calculated. Sure enough:

"Assuming the densest core materials and the nominal mean density of 2,077 kgm23, ice mantles are 110–124km thick and constitute 24–26% of the body mass. The lighter core material requires a mantle thickness of 66 km and a 16% ice mass."

Thanks for the link and info, Bruce!

From reading, it almost sounds like Ceres is in its own class of 'roid, since it's the only one truly "relaxed". It's interesting that they expect the denser materials to have sunk to the core, and yet Ceres still maintains a spectral class of "C". Is there perhaps a layer of dusty "regolith" that is leftover from ice-sublimation that maybe lends it this spectral class, despite the fact that it is likely a "differentiated CM-chondrite"?

I had never even considered 'roids as the first stepping stone for a permanent human science base, but Ceres might make excellent sense. A 9 hour rotation period is a little funky, but maybe Ceresians would enjoy a nice after-lunch siesta every 18h "day" (if it's acceptable to call 2-full rotations a "day").

Perhaps most exciting in terms of human exploration potential is from the Nature letter: "Even the minimum mantle thickness is greater than the likely
excavation depths of craters a few hundred km across." So even if the crust is a nasty jumble of pebbles n' dust, a large crater would provide easy access to the water-rich mantle. A nice RTG rover could maybe scratch the bottom of the crater rim and begin melting a hole through the dirty-ice and begin excavating a nice cavern. Spray the walls with ice to make it air-tight, insulate with foam, pressurize and presto! Instant-igloo!

Before I rush out in my covered wagon to stake my claim in the land-rush:

1. is solar-power economically viable from Ceres? How much panels would be needed to crank out the equivelent of the ISS? (ISS = 110kW using 2,500 square metres of solar-panels).

2. is the low gravity a problem for long-term residents? would a gravity-centerfuge be required to keep folks healthy enough for return to earth?

3. is nitrogen available anywhere near the belt?

4. what would be the raison d'etree for a Ceres Base? Watching 'roids? Fuel-depot for outer-solar-system missions?

5. how hard would it be to move nearby small 'roids into orbit for material's processing?

Exciting stuff to dream about!

Not only are pounds and kilograms measures for the same thing (the newton correction is right), but the original point is using the right measure for what it is supposed to show - how hard something would be to support on Ceres under its gravity. So there is nothing to be picky about here....

Future generations who spend their whole lives on worlds like Ceres will probably have no issues with a 9-hour day whatsoever, having never been on Earth. Of course the colonies may be set up inside these rocks, so daylight can be an entirely artificial and controlled affair.

And we are assuming that future space colonists will be humans and not AI machines, who likely would have no concerns about day-night awake-sleep cycles.

Ceres is at ~ 2.77 AU on average, solar panels in orbit around Ceres would produce about 18% of the power of an equivalent array in Earth orbit. On the surface that would be reduced by a further 50 to 75% depending on whether they were Sun tracking or not.

The numbers you quote for ISS are interesting - the Solar constant in Earth orbit (the amount of radiation incident per m^2) is 1.37 kW. Most Solar panels in orbit are >16% efficient on average (the MER type are very good at ~26%) which means that the ISS panels are only generating 40% of their capacity even after accounting for a 12 hour night cycle. I assume this is due to layout and mechanical difficulties keeping them perfectly normal to the sun.

Asteroid or miniplanet? Cornell astronomer finds Ceres appears to have shape and interior similar to terrestrial planets

http://www.news.cornell.edu/stories/Sept05/Ceres.to.html

Sept. 15, 2005

By Thomas Oberst
cunews@cornell.edu


ITHACA, N.Y. -- When is a space rock more than just a space rock?

Ceres 1 was already holding the title of the solar system's largest asteroid. Now new observations show the space rock may be more worthy of the appellation "miniplanet."

On Sept. 7 NASA released photographs of Ceres that show the rock is a smooth ellipsoid, or oblong sphere, with an average diameter of approximately 590 miles -- about the size of Texas. A scientific paper on the findings, by a group led by Peter C. Thomas, senior research associate at Cornell University's Center for Radiophysics and Space Research, appeared in the Sept. 9 issue of the journal Nature.

Co-author Joel Parker, an astronomer at the Southwest Research Institute in Boulder, Colo., used the Hubble Space Telescope's Advanced Camera for Surveys to snap 267 images of Ceres on Dec. 28, 2003, during a nine-hour period -- one Ceres "day."

I would think it would be more natural to push 3 hours longer to a 27 hour day rather than compress by 6 hours to an 18 hour day. So maybe it would be like:

[ dark ][light ][ dark ][light ][ dark ][ light]
---- )( morning )(nap)( - evening - )( sleeptime

This gives you around 9 hours of sleeptime each 'night' with another 2-3 hour midday
nap. That leaves 15-16 hours of uptime split into a morning and evening period.

There have been studies putting people into such an environment: here, for instance, is a report from a 28-hour day study. The circadian rhythm doesn't stretch so far -- it ends up cycling around 24 hours 11 minutes -- but apparantly people function without major problems on such a cycle.

If Ceres has much in the way of axial tilt, then that might also cause the length of day to vary...

The new "Nature" article confirms that its obliquity (axial tilt relative to its orbital plane) is only about 3 degrees. But this dosn't make much difference in any case -- for any future inhabitants of Ceres, after all, are going to spend most of the time UNDERGROUND, where they will be perfectly free to stick to the old 24-hour circadian cycle. Ditto for the Moon. (Any surface work teams will, of course, have to consider whether the Sun is shining on the surface at the moment or not.)

A more serious obstacle: Ceres' very low gravity will leave its inhabitants susceptible to the same harmful health effects that weightlessness does. But then, the same thing is true of dwellers on the Moon, and maybe even on Mars. As Poul Anderson points out, regular hours-long exercise sessions on a centrifuge will be an annoying necessity of life elsewhere in the Solar System.

The problem is, we don't have any real data on how much gravity the human body needs to stay healthy, and for how many hours in a day it needs that gravity.

Some astronauts who suffered mild SAS symptoms on their way out to the Moon felt much better after landing on the Moon. It only took 1/6G for them to feel completely normal and comfortable.

While that's anecdotal information at best, there is still, as of right now, *zero* research data on micro-gravity deterioration effects at 1/6G, or 1/3G, or even 1/20G.

And physiology, like most things in the real world, doesn't follow nice, clean curves. A body can take some conditions a fairly wide degree out of "normal" for quite some time without showing any real degradation. But change the degree just slightly, or change another parameter in addition, and the body hits a "trigger" and starts reacting in ways that are ultimately destructive (loss of bone mass and minerals, etc.).

It's possible that 1/6G might be more than enough gravity for the body to retain normal bone density levels indefinitely. Maybe, though less likely, 1/20G will be enough to do the trick.

It seems to me the *only* way to get this data is by flying spacecraft (in LEO, for ease of the commute) which can be spun at different rates to create different gravity levels (via momentum / centripetal force). Heck you could create different levels at different distances from the rotational center.

Then put people aboard those spacecraft for three months, then six months, then nine months, then a year... do direct observational science on physiological reactions to spending extended periods at whatever gravity strength you want to create.

It wouldn't be all that hard to put together -- just build a central control bus and attach two TransHabs to it. Balance the weight in the TransHabs properly, set the whole thing spinning on the ends of a truss. Put solar panels near the center of the control bus, and keep your consumables down at the ends of the Habs. Cheap (relatively speaking), easy (relatively speaking) little station, which can support (with refurbishment/resupply) a crew of 3 to 6 for up to a year.

Run it for a year at a 1/3G speed, then for a year at 1/6G speed, and then for a year at 1/20G speed. Test crews in all three modes. Get your baseline data.

THEN start planning what kind of spacecraft you need for really long journeys.

-the other Doug

If the idea of using people is deemed somehow unfeasible, rabbits or rats or even monkeys could always be used, too.

It is a good idea - someone will do it eventually. If not NASA or ESA or whoever, then a corporation who wants to see just what their space miners can handle..

I vaguely remember reading a paper once in which the size distribution of main belt asteroids was studied. The number of asteroids with radii of 1 km, 10 km, 100 km and all the radii in between was graphed as a function of radius.

The curve fitted to this graph predicted that the largest asteroid should have a radius considerably smaller than Ceres' (but still larger than Pallas or Vesta). The authors took this as an indication that Ceres might have experienced a small amount of runaway accretion late in its formation. Thus it could really be considered as a "mini-planet", distinct from the other asteroids, but not in the class of the major planets.

Wish I could remember where this came from.

Well, probably not. It is generally thought that the Galileans formed in Jovian orbit.

Vesta, of course, may turn out to be a piece of an embryonic planet destroyed in an impact. If so, it might provide us a great window on a planetary interior.

I'm still trying to decide if I need to stake out my claim...

1. While the low gravity well sure simplifies landing and takeoff, doesn't it also mean there is a correspondingly high cost for being captured in orbit? Most mars probes save gobs of fuel by aerobraking, but for wimpy Ceres, how much fuel would be burned to allow for a fast-route Hoffman xfer?

1-A. Could a Mars flyby be used to slow-down (instead of speed up) the wagon? Even if possible, is it stupid because you're only ~25% of the distance, so instead Mars should be used to gain velocity instead of loose it?

1-B. Assuming sufficient electrical power, could water and carbon in the dust grains be used to manufacture rocket fuel? What would be the fuel of choice?

2. What are some reasons to send people to Ceres? Would it make sense to park space-telescopes on either pole as a huge inferometer, with astronauts required to install and commission them? Are the organic compounds worth the risk of sending people to collect the samples? Would it make sense to setup Ceres as a communication hub between earth-mars so we don't have those crappy opposition blackouts?

Marz:

1. No, it'd be pointless, not least because Mars might be in entirely the wrong place - and Hohmann transfers are, er, the slow jobs. That's the point of them...

1-B. There's fuel, and there's oxidiser - anything that burns is fuel, anything that oxidises is, er, well, oxidiser. The big hope would be water ice, which breaks down into both very nicely - but look at the in-situ fuel generation on Mars discussions for a whole range of alternative, lower energy, chemistries.

2. George O Smith's 'Venus Equilateral' described such a system, but really, it's hardly an economic solution. As for the astronomy, why bother with an asteroid?

In short, Ceres may well be a world in it's own right, with it's own imperatives. Personally, I can hardly wait - if Earth is to Mars as Mars is to Ceres, then it will shed so much light on the other Terrestrial planets (oops!).

Bob Shaw

http://www.swri.org/press/2005/Images/ceres_movie.html

I was looking at the above animated Gifs of Ceres rotation and I think I see a hint of a Massive crater right in the middle of the little body.

Does anyone else see it?

I see something that looks like it. But it may be an illusion. Better imagery will tell.

I noted in the "Dawn" thread the excellent Keck photos of Ceres taken in 2003 ( http://www.cfht.hawaii.edu/Instruments/Ima...pueo-nui-ss.pdf , pg. 13), which clearly show what looks like a big dark circular patch with a big lighter-colored patch smack in its middle (feature "B"). When these were shown at the 2003 DPS meeting, that feature's continued existence as Ceres rotated -- and its resemblance to a dark crater with a big light central peak region, like Tsiolkovsky on the Moon's farside -- was much clearer than in the published photos, for some reason.

Apparently that light-colored central patch is the same as the (relatively) bright spot in the Hubble photos, where they massively cranked up the contrast (the "light spot" is actually only about 5% higher albedo than its surroundings, and so the Keck photos showed it much more realistically).

Heres another map. Forgot where I found this.

Things like this really make me mad...Here is space.com's map of Ceres...

http://www.space.com/reference/debris/maps.html



Clearly a bunch of cloned crap from Gaileo's images of Gaspra, a world not even on a similar scale. And no disclaimer....

How sad.

What's even worse is that they put it under the heading of "space debris".

I realize that there is room for argument over definitions, but I do not think that anybody can look at Ceres and call it "debris".

You mean like this?

Link

James

Yeah. Cool stuff. If I had an infinite amount of money, well, I'd fund everything, but this would be one of the first.