New mosaic map of Itokawa Options

[Phil Stooke]

Having a bit of time free I have embarked on a new global photomosaic map of asteroid 25143 Itokawa. Follow its construction here as I go. I'm hoping it won't take more than 4 to 6 weeks as other duties call. The mosaic will eventually go into PDS.

This follows the work I did on a map made from rendered images derived from Bob Gaskell's shape model. That had to be the first step because the control I'm using is derived from published lat-long grids superimposed on his rendered images. Now each individual image will be reprojected to fit that map. The large local relief will make it impossible to make all seams invisible, however.

First step: the north polar area. The outer edge is at 40 N, with 90 N at the middle and 0 longitude at the top.

Phil

[elakdawalla]

Yaaaay Phil! I can't wait to see this come together. After I assembled Chuck Clark's cut-and-assemble model, I tried to identify the named features on it but made almost no headway at all; it was too hard to figure out what was being named on the photo map, even using the stuff from the USGS nomenclature page and map. I hope it'll be easier to figure things out with your maps. The large smooth area on this image is Sagamihara regio, right?

[Phil Stooke]

Yes, it's Sagamihara.

Phil

[Phil Stooke]

... and the south pole. Each of these polar maps is a mosaic of four images. There might be some improvements later. Getting the opposite sides to match well is not easy, but this is a start.

Phil

[elakdawalla]

OK, so that one shows MUSES-C regio. There should also be a crater named Gando at -70, 205, but I see several vaguely circular outlines that might or might not be identified as crater rims, and I don't even know if they should look circular on this map...

[Phil Stooke]

They should look circular on that map! But not on this one: here's the current version of the cylindrical global mosaic with the new poles added. I'll deal with trying to figure out nomenclature when it's all finished (if you can wait that long, Emily!)

Phil

[elakdawalla]

Sorry, I'll be patient I've just had this danged Itokawa model sitting on my desk since I tried to assemble it, and when I couldn't use it to find all the named places, I got kinda frustrated. Carry on with your work, I'll wait till you're done!

[Phil Stooke]

Next step in the mosaic. I have added a section around the 90 degrees west longitude region, a mosaic of three images. The edges of it are a mess, but will be improved as the mapped area is extended. Edges are always a mess in this process.

Phil

[Juramike]

Thanks, Phil! It's really neat seeing the step-by-step evolution of mapping this asteroid!

[chuckclark]

After I assembled Chuck Clark's cut-and-assemble model, I tried to identify the named features on it but made almost no headway at all; it was too hard to figure out what was being named on the photo map, even using the stuff from the USGS nomenclature and map.

Emily, is the lack of lat long lines on the pictures the root of your problem?
I've got lat longs drawn on my plastic model, so -- as I'll be popping Phil's new mosaic onto the foldable map -- I should be able to locate all those features at the same time.
Didn't know you've had trouble; speak up next time.
Let me tell ya, drawing the lat longs onto the plastic model was a J O B! Things get verry complicated around the neck and chin. But now, it's fairly routine to locate a feature on the plastic model and then find it on a map, cylindrical or other-style.

One question -- what happened to Woomera Regio? Did that become Arcoona Regio?

Phil, if it's not too much trouble when you finish, please post (or send me directly) a larger-size file. Otherwise I'll again pixellate in those areas where your image greatly enlarges when it transforms to my constant scale natural boundary format -- the chin and neck particularly.

[Phil Stooke]

Will do!

Phil

[The Singing Badg...]

What would be the surface area of Itokawa? I'm just wondering how much real estate we're looking at here. Would it be the size of Wembley Stadium, or more like central London?

[djellison]

http://en.wikipedia.org/wiki/25143_Itokawa

Dimensions 535 × 294 × 209 m

Very roughly - call it a 300m sphere, Surface area, very roughly, about a quarter of a million square metres

[Eluchil]

Very roughly - call it a 300m sphere, Surface area, very roughly, about a quarter of a million square metres

So probably a bit over 3 Wembly's then. Assuming my back of the envelope calculation of the latter's area at nearly 80,000 m² is correct (based on a reported circumference of 1 km).

[The Singing Badg...]

Thank you!

So you could probably stroll around it an hour or so (under Earth gravity!). Interesting.

[Phil Stooke]

Yes, you could walk (float) around the blasted think a lot faster than you can map it! 3 days working on one image...

Phil

[chuckclark]

Itokawa on Wembley, at least from my point of view, looks like this:
An outline of the solid body is at upper right; the other shape, of course, is the asteroid's unfolded surface, using a finely branched system of ridges as the map boundary.

Attached thumbnail(s)

 

[djellison]

Personally, I think the addition of an asteroid is a drastic improvement.

[Phil Stooke]

Here's an update to the Itokawa mosaic. I have added several images to the area on and north of the equator and around the 180 longitude region (middle of this map). The southern edge of that region will be next. Slow going, but it will gradually fill in. There will still be some further improvements to parts already done.

Phil

[chuckclark]

Wow! That is a fine piece of work, Phil.

But, to digress, I'm finding a few discrepancies in the plastic model that JAXA made for me, and the location of various features (three prominent rocks, so not very many places) in your earlier map. One reason is that had to draw lat/longs on the model by hand and eye, so my constant-scale natural boundary map, we should expect, is not perfectly aligned with the lat/longs of features on the cylindrical map.
But the curious thing is that the discrepancy is an almost perfect 10 degrees.
I'll post a map later with the misalignments called out, but is it possible that there might be some projection anomalies, let's call them, in your initial projection?

[Phil Stooke]

Yes, let's have a look at the discrepancies. The relief distortions on Itokawa are more extreme than almost anywhere else. There might be problems at any stage in the development of this map from Bob Gaskell's shape through the alignment of the grid and on to the reprojection and mosaicking itself. So let me see what the problems are, and maybe I can sort them out. I still have improvements to make to my new mosaic, which might possibly correct the problems you're talking about.

Phil

[chuckclark]

Yaaaay Phil! I can't wait to see this come together. After I assembled Chuck Clark's cut-and-assemble model, I tried to identify the named features on it but made almost no headway at all; it was too hard to figure out what was being named on the photo map, even using the stuff from the USGS nomenclature page and map. I hope it'll be easier to figure things out with your maps. The large smooth area on this image is Sagamihara regio, right?

Here is Phil's first cylindrical map with the USGS features named (craters are marked with a triangle; regios are just generally labeled for the moment because drawing their boundaries is iffy from the pictures.

But there appears to be a discrepancy in the nomenclature lat/longs for Miyabaru. USGS lists it at -40;244, which puts it in the southern hemisphere, and roughly along the short axis. But by the picture Emily links to (and also the 2009 Icarus article Figure 4) Miyabaru is definitely on the so-called head, and in the northern hemisphere. So on the map I've placed it at a depression at roughly +10 lat; 13 long.

Phil, I'll post the rock location discrepancies here shortly. Patience.

Oh, and there's more, now that I double check the regio lat/longs list. I placed these based on the pics, not the lat/longs in USGS. Arcoona is way off. It's the tail end of the otter (and I have a plastic model, so easy to locate it by eye); it can't possibly be where USGS says it is (+28; 202).
The listing for LINEAR regio is at best at the extreme southern edge based on the pics.
The listing for Ohsumi regio is at best at the extreme northwestern edge based on the pics.
The listing for Yoshinobu regio appears to be way way off. By the pics, Yoshinobu is the humpback on the neck, i.e. northern hemisphere around the zero longitude. USGS's point is on the belly.
The listing for Uchinoura regio synchronizes with the pics.
MUSES-C and Sagamihara are so extensive the listed centerpoints are not much help in defining the regions.

I wonder if I'm misreading or misunderstanding the USGS nomenclature chart, but then, the small features (craters) all plot out on target with my plastic model and Phil's map.

So, Emily, perhaps it's no wonder you couldn't make much headway.

Attached thumbnail(s)

 

[elakdawalla]

Thanks for labeling those, Chuck, and I feel much better!

[chuckclark]

happy to be of help.

[chuckclark]

Oh, by the way, here's how Itokawa scales onto The National Mall.
A float around the asteroid the equivalent of, let's say, an half-day tour of the various Smithsonians;
Itokawa's long dimension a loose fit betwixt the Lincoln and Second World War memorials.

Attached thumbnail(s)

 

[chuckclark]

Here is the (old) cylindrical map showing regio boundaries.

Arcoona Regio shows both the outline from Emily's link (shown in solid line), and the outline from Icarus 2009 (shown dashed), which is bit larger.

Neither from the pics nor the link could I find complete boundaries for Sagamihara Regio or MUSES-C Regio; solid line shows the boundary from the link, dashed line shows my guess at closure.

Attached thumbnail(s)

 

[Phil Stooke]

After a year-long hiatus I have returned to the Itokawa mosaic. I have finished two of the three equatorial sections, leaving the hardest part until the last - the head of our cute little otter asteroid. Hardest because the distortions will be most extreme in this area. Here is what I have so far, reduced scale and heavily compressed. The final product will eventually end up in the PDS Small Bodies Node.

Phil




PS one area here looks a bit sketchy - just under the middle of the image. It was never seen well, always on the terminator and/or near the limb. Best I can do right now.

[chuckclark]

[quote name='Phil Stooke' date='Sep 2 2011, 01:25 PM' post='178269']
After a year-long hiatus


Go Phil!

[Phil Stooke]

Current version of the mosaic - the worst remaining gap is at left and right edges south of the equator, but a few other issues remain as well.

Phil

[Phil Stooke]

The global photomosaic map of Itokawa is almost finished. It looks like this now:





Just a few cosmetic improvements still to do... but they will have to wait as I must return to Mars.

Phil

[Phil Stooke]

The mosaic map of Itokawa will be available from PDS later this summer.

Meanwhile, I have been experimenting with some new map projections for Itokawa and other elongated objects. This is a Morphographic Equidistant (that's like an azimuthal equidistant, except it uses the local radius everywhere in the equations, instead of a constant radius) version of the Itokawa mosaic projected onto an ellipse. The ellipse was originally scaled for Ida, not Itokawa, but it gives a pretty good interim result. Versions with grids will follow later.

Phil

[chuckclark]

. . . new map projections for Itokawa and other elongated objects. This is a Morphographic Equidistant (that's like an azimuthal equidistant, except it uses the local radius everywhere in the equations, instead of a constant radius) version of the Itokawa mosaic projected onto an ellipse.

So is each individual ellipse a map of Itokawa's complete surface? Or does it take two of these ellipses to make one complete world map? Four?

Will be easy to tell when you plop on the grids, but for those of us who can't wait . . .

[jasedm]

Very nice Phil!
Itokawa is a bewildering little world - often makes me wonder how many different combinations of rock/ice/gravity/collisional history are possible. Seems every new celestial body we see is subtly different.
It's an amazing solar system in which we live.

[Explorer1]

The early solar system was like a blizzard of rock and dust; little wonder none of these snowflakes are identical!

[Phil Stooke]

"So is each individual ellipse a map of Itokawa's complete surface? Or does it take two of these ellipses to make one complete world map? Four?"

Each of these maps is of a 'hemisphere'. They are labelled north and south, or centered on longitudes 90 and 270 (with 0 degrees at one end). So although it might look like the common Mollweide projection (which maps 360 degrees of longitude into an ellipse) it is not. Two of these maps cover the whole body, and I'm mapping it here in two different ways with the poles or the equator at the middle.

Phil

[chuckclark]

Each of these maps is of a 'hemisphere' . . . Two of these maps cover the whole body, and I'm mapping it here in two different ways with the poles or the equator at the middle.

Okay. But, sorry to be dense, which ones together? The two polar ellipses combine to make one complete map of Itokawa, the poles in the middle of each respective ellipse, and the two "other" ellipses combining to make another complete map of Itokawa, the equator running along each ellipse's long axis?

[Phil Stooke]

That's exactly right, Chuck.

Phil

[chuckclark]

That's exactly right, Chuck.
Phil

Good. Thank you. Seeing no gap between the two pairs was confusing me. My architectural eyes were trying to imagine four orthographic (boxlike) views.

Now, (Sorry not to have put the whole idea in one post), it looks like the contact spot of two (paired) ellipses is a point common to both hemispheres.
Can you nudge the two ellipses together, creating a little overlap, a shared, central region? Seems like this might work for a distance of, say, the middle third. If not the middle half.

Not that I don't like them this way!
They're fun to cut out and fold together into elliptical Itokawa "coins."

[Phil Stooke]

"it looks like the contact spot of two (paired) ellipses is a point common to both hemispheres."


That's true of the top two, which align perfectly at the equator. Those two could be cut out and rolled around their perimeters to make a common point anywhere you liked. It's not true of the two equatorial views (as I have aligned them) - they are both north-up so the south pole of one touches the north pole of the other. But you can cut them out on a print or digitally and move them into any position you like where their edges would align at a common point. As for the overlap question, it would work for a very narrow central vertical strip but the projection distorts the surface away from there.

Phil

[JohnVV]

---edit---

[Phil Stooke]

Maybe for Itokawa it needs to be a brick-shaped map, a cuboid rather than a cube...

Phil

[Phil Stooke]

My photomosaic map of Itokawa is now available at the PDS Small Bodies Node (along with a shaded relief map of comet Wild-2, and all the previous maps as well)

I have not yet got around to adding the grids to the elliptical maps above - I need to make some adjustments and I have not found the time yet.

Phil

http://sbn.psi.edu/pds/asteroid/MULTI_SA_M.../aamapdesc.html

[Phil Stooke]

Resurrecting an old thread here to post what I said I would post ages ago. This is the Itokawa mosaic projected into a triaxial (best fit) ellipsoid, mapped in the Morphographic (modified azimuthal) equidistant projection, with added grid lines. Low res version for now, but a better version will follow in PDS.

Phil

[Phil Stooke]

And... for comparison, though it doesn't really belong here, the same for Eros.

Phil

[Phil Stooke]

Another asteroid map comparison - no, it doesn't really belong here, but there's nowhere else right now and it does follow on from the last two posts here.This is 243 Ida, imaged by Galileo, mapped onto an ellipsoid which has been only roughly scaled to approximate Ida. This is a demonstration project rather than a highly accurate map, but it does illustrate what can be done with very elongated objects now.

Phil

[Phil Stooke]

Hot off the press, an experimental map of the northern hemisphere of Comet Borrelly - as with the other maps above, this isn't Itokawa, but it shows the same technique. This will be in my LPSC poster next year.

Phil

[Phil Stooke]

I'll put this here even though it's not Itokawa because a series of posts started out with Itokawa and then illustrated maps of other elongated objects. This is the nucleus of Comet Hartley 2 in the same projection as the preceding maps, except that Hartley 2 is rotating about its long axis, not its short axis. Peter Thomas and colleagues have a paper in Icarus describing its rotation and shape, including maps which form the basis for the new mapping done here.

Phil