Asteroid 25143 Itokawa.

3488 · Apr 20, 2007

Interesting article. Think it proves that asteroid 25143 Itokawa is a rubble pile held together by gravity. ============================================================================== Like a jiggled jar of mixed nuts, shaking on the near-Earth asteroid Itokawa is sorting loose rock particles on its surface by size, causing the smallest grains to sink into depressions, a new study suggests. Researchers analyzed images of a mix of boulders and gravel, called regolith, covering the surface of Itokawa. The images, taken by the Japanese Hayabusa spacecraft in 2005, revealed that some areas were coated with fine particles and appeared smooth, while others regions looked bumpy, as if the asteroid suffered an intense case of acne. In a study detailed in the April 20 issue of ScienceExpress, an online publication of the journal Science, researchers suggest the regolith’s patchy distribution is the result of shaking, which causes the finest and lightest materials to accumulate in dips on the asteroid’s surface, where the local gravity is lowest. “It’s sort of like if you poured water over Itokawa, all the water would tend to pool in these [low] regions,” said study team member Daniel Scheeres of the University of Michigan. “The water would flow downhill until it couldn’t go downhill anymore.” A shaky asteroid The new findings suggest seismic activity of some kind is occurring on Itokawa, a small asteroid only 1,600 feet (500 meters) in diameter. “Even though it’s this tiny little guy, it is in some sense geologically active,” Scheeres told SPACE.com. “Things are happening on the surface. Stuff moves from one point to the other.” The regolith distribution suggests Itokawa has been shaken up in the past, but what might have rattled it is still an open question. One hypothesis is that smaller asteroids occasionally strike Itokawa and shake the space rock up. Because of its diminutiv <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 20, 2007

A close-up of regolith on Itokawa's surface. Visible are piles of gravel with crater-like depressions and smooth areas where debris has drained into a areas of low local gravity. Credit: Univ Tokyo/JAXA. Full resolution image is here. Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 20, 2007

Image of the near-Earth asteroid 25143 Itokawa. The boulder-free areas appear relatively smooth and are filled with small, uniformly sized particles. Credit: Univ Tokyo/JAXA Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 20, 2007

Images of 25143 Itokawa, through a complete rotation. Univ Tokyo/JAXA. Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 20, 2007

Sorry what an imbecile I am. Just realized, this thread should be in SS&A, not ATA. Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

MeteorWayne · Apr 20, 2007

I agree, we'll ask a Mod to move it. {shouting} Hey Mod, can you move it? {/shouting}(I'll request in Suggestions and announcements if you haven't yet) <img src="/images/icons/smile.gif" /> I still recall the stunned look on my face when the images of Itokawa came in. I'm still amazed at what we learn with each asteroid, comet, planet, and moon we visit. Thanx, Andrew! <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

yevaud · Apr 20, 2007

Moving it now. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

michaelmozina · Apr 20, 2007

It's always very impressive to me when scientists can do things like put a spacecraft next to a speeding asteroid and get up close and personal with it. That is really impressive to me. I'm not very surprised at the fact it's a "rock in space". That always seemed to be the most likely scenario to me. It's not going to go over very well with the dirty snowball crowd however. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

MeteorWayne · Apr 20, 2007

Hey wait a minute, the dirty snowball referred to comets not asteroids. Asteroids are rocky, that's a given, although it's not a sharp divide between them. Clearly there is a continuum. And we have not examined enough comets to eliminate dirty snowballs, or icy dustballs from the realm of "normal" <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

Swampcat · Apr 20, 2007

Fascinating images. It makes you wonder what it would be like to walk around on that thing. Or hop, or whatever <img src="/images/icons/smile.gif" />. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

3488 · Apr 23, 2007

Hi all, Thank you Yevaud for moving this thread & MeteorWayne for his always helpful input. I was just plain tired, stupid & not feeling too good at the end of last week. Whilst I am a lot better these days, my condition does still give me some grief!!! Anyway, The surface gravity of 25143 Itokawa is less then 100,000 th of that of Earth. Even a light 'hop' would exceed escape velocity. Hayabusa, could not 'orbit' 25143 Itokawa (as NEAR Shoemaker could do with 433 Eros), but remain in Heliocentric orbit in formation with 25143 Itokawa, using onboard thusters to alter position & even land (more like a docking, than landing). From a navigational view point, this must have been a nightmare!!!! I am surprised that this object exists at all!!!! I cannot help but think, that there must be a solid nucleus somewhere inside this silicate rich rubble pile. Shame the images at the beginning have no scale bar present. Can not tell how large the rock fragments are. I guess they are only pebble sized, so the area imaged is probably less then one square metre, but would be good to have it confirmed. Quite like the view below too. Credit: Univ Tokyo/JAXA Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 23, 2007

How about this huge boulder postioned on the limb of 25143 Itokawa? Perhaps a small moon that once accompanied this tiny asteroid???? Credit: Univ Tokyo/JAXA Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

silylene old · Apr 23, 2007

There was an issue of Science dedicated to this asteroid about 18 months ago. A fantastic issue. Interestingly, if you map the gravitational field of the asteroid onto its complex shape, things get very weird. At the "head" and at the "butt", the gravtiational field is higher. The ground slope at specific points on the upper neck under the "chin" gets very severe (60 degrees). This means that a an object dropped at certain points of high field curvature on the upper neck falls upwards towards the head, rather than downwards to the body. Strange! Boulders on the this portion of the neck are attracted upwards to the head. An interesting discussion from this excellent article in Science: <blockquote>In reply to:<hr />Landslide-like deposits at the base of the head are observed (10), and this region has slopes in excess of 35° (Fig. 2B). On Itokawa, most angular grain materials have an angle of repose on the order of 32° to 35°, and slope angles in excess of this height cannot be maintained unless there is cohesion. The observation of the candidate landslide, and the fact that the steep slopes on the head measure up to near 50°, may suggest that at least this region resulted from an angular rubble pile that collapsed. Itokawa looks to be composed of two parts, the head and the body. There are plausible origin scenarios to produce such a bifurcated configuration. The first scenario is the contacted bodies hypothesis: Originally the head and body could have formed separately and later come into contact at a slow relative speed, and, almost retaining the original shape of both bodies but with some mass movement, the present shape of Itokawa was formed. Between the head and body, a depressed neck zone is observed, and in this region there is a high-slope region (expressed as yel</blockquote> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

3488 · Apr 23, 2007

Hi silylene, Thank you very much. It figures that this would be the case. If 25143 Itokawa was two seprate bodies that merged, the central 'masses' of both would remain intact. I wonder how strong the 'neck' is? Not very I would imagine. If material continues to migrate from the 'neck' towards the ends, then perhaps 25143 Itokawa will become a binary object again in the far future. Once again, thank you & am always happy to be put right (as in the case of canine vision). I always like your posts, even though many, if not most are way above my head!!!! Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

oscar1 · Apr 23, 2007

Very nice images Andrew, thanks. When I look at them though, I get the urge to grab hold of my potato peeler. <img src="/images/icons/wink.gif" />

silylene old · Apr 23, 2007

Once again, thank you & am always happy to be put right Actually you had it exactly right. That huge boulder on the asteroid's butt was stuck exactly where it should be, in an area of high gravitational field. Maybe the huge boudler was a little moonlet originally - I thought your idea was reasonable. You had a very interesting observation, and that's what motivated my post. If you can, try to read some of the articles from the June 2006 Science on Itokawa - I think they can be found online. It was a great issue! I found many of the articles to be quite readable even though I lack in depth training in the fields (I am neither a geologist or an astronomer, rather I am a chemist). <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

MeteorWayne · Apr 23, 2007

It was the 2 June 2005 issue of Science, sitting right here in the "Asteroid" pile next to my computer. I'm glad you brought up the subject Andrew, that issue has now, defying gravity, moved away from the center of the earth's gravitational field to the top of the pile. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

brellis · Apr 23, 2007

hi MW that issue has now, defying gravity, moved away from the center of the earth's gravitational field to the top of the pile Sacrilege! When the Vatican finds out about this -- wait, erm <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

MeteorWayne · Apr 23, 2007

Hmmmm, I guess APOD reads SDC!! Andrew, you are inspiring <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

3488 · Apr 24, 2007

Hi MeteorWayne, I was not aware of that. Thank you. 25143 Itokawa despite its small size is turning out to be an interesting little world!!! Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

3488 · Apr 26, 2007

Hayabusa has begun the trip home, hopefully with at least a few samples of 25143 Itokawa on board. I have put an update here. Andrew Brown. <div class="Discussion_UserSignature"> "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". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

JonClarke · Apr 26, 2007

And we have not examined enough comets to eliminate dirty snowballs, or icy dustballs from the realm of "normal" Sorry Wayne. Normal comets are dirty snowballs to icy dirt balls. Denying this fact (validated by decades of spectroscopic observations and a dozen space missions) is like denying the Mars is made of rock. Jon <div class="Discussion_UserSignature"> 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 Arthur Clarke </div>

MeteorWayne · Apr 26, 2007

Jon that's actually what I was saying, though not very well. I was reponding to a previous comment that one side was upset with recent observations. In fact the data does indicate that there is a continuum from rock to ice and all mixtures in between. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

centsworth_II · Apr 26, 2007

"Normal comets are dirty snowballs to icy dirt balls." Are you talking about a continuum from dirty snowballs to icy dirtballs here, or did you mean 'comets are dirty snowballs as opposed to icy dirt balls? Are there really two distict populations of objects or does the relative amount of ice to rock/dust go from 1:0 to 0:1 with no gaps? <div class="Discussion_UserSignature"> </div>

MeteorWayne · Apr 26, 2007

I would say the data shows a continuum from pure rock asteroids, to nearly pure ice comets, with no gaps, though there may be ratios that are more common. We just truely don't have enough samples from each population (Main belt asteroids, NEO's, Centaurs, KBO's SDO's, Short Period, Halley class, Intermediate, and long period comets from the Oort cloud, which may have come from different origin points in th solar system, etc, etc, etc) to be sure whether certain ratios are more common than others. Remember, too, that any icy comet, after many perihelia (inside 2 AU) will become depleted in ices, hence there is a movement toward the rockier composition....but the process proceeds very slowly, since most ice in comets is shielded from the sun by overlying material. I know you asked Jon, but that's my up to the day analysis of what we've learned. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

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