Smooth Sections of Asteroid Itokawa (APOD 22 Apr 2007)

[astrofs]

Doesn't this look like two separate pieces of rock that have gently collided. The loose dust would be dislodged toward the point of impact and deposited there. Low gravity suggests quite a gently impact and the theory of "Pile of Rubble" for the Asteroids.

[craterchains]

That is a distinck possibility, for some.

[astrofs]

There are quite a few peanut shaped asteroids (NEAR for example), so this might be a more common process than believed. The lack of cratering could indicate the age of collision, and also support the "pile of rubble" theory, as the collision could have wiped out existing craters if the bodies were loose aggrigates. You have to assume there were craters, otherwise you are looking at the only body discovered so far in the Solar System to escape the cratering process.

[craterchains]

Pardon the "pun", but it just doesn't seem to be possible concidering the almost null gravity of the object. There are a few (very few) possible craters showing in the picture though. http://antwrp.gsfc.nasa.gov/apod/ap070422.html

[iamlucky13]

I love the fact that they used the term "Brazil nut effect" in a science-related context.

Does anybody know how fast this asteroid is spinning compared to its gravitational limit? The thought occurred to me if it is a loose conglomeration then over long periods of time, perturbations that cause this Brazil nut effect to sift smaller particles downward, such as passing near a planet, should also cause the two lobes to collapse into a more uniform ball. That suggests to me with three theories:

1.) It is the result of a very recent merger.

2.) While the outside may be rubble, the inside may be more solid, perhaps even two rounder asteroids pulled together, with a coating of debris.

3.) It is spinning at a high enough rate for centrifugal momentum to maintain the lobes.


Also, the caption states that Hayabusa probe did collect a sample, but last I heard (a couple months ago, compared to a 2005 source in the caption), no one is sure yet whether it actually was able to. Additionally, it has had some thruster issues and might not make it back to earth with its hoped-for cargo. It would be a pity. JAXA has had a run of hard luck recently.

[AZJames]

If, indeed, this asteroid may someday impact the Earth (as postulated in the APOD commentary) then we definitely have our work cut out for us in deflecting its orbit. These Earth-crossing "rubble piles" present an insuperable problem at our current level of technology to deflect them while maintaining their cohesion.

I hope someone comes up with a bright idea.

[NoelC]

If, indeed, this asteroid may someday impact the Earth (as postulated in the APOD commentary)

This kind of talk makes me wonder...

I have sky charting software (Cartes du Ciel) that will show me the positions of things within very high accuracy. For example, at any given time it will show me the exact positions of the planets and even all the satellites of a planet (e.g., Jupiter or Saturn), and it will match exactly with photographs taken at the exact time entered into the program. It's clear that someone has measured their orbits with high precision, and that the future positions can be simulated with some accuracy.

Also, consider the probes we've sent out through the Solar System... They find planets and satellites as planned with incredible precision.

Given that software can preduct orbital mechanics and have them match observed reality extraordinarily well, is it not possible to say with some certainty if and when a known asteroid will collide with Earth?

Or are we simply struggling with the level of accuracy of the orbital measurements?

Is there an ongoing program, e.g., in NASA, to apply ever better measurements of known objects to simulations of the future? Surely there must be.

-Noel

[iamlucky13]

Darn it...I just had a long post commenting on your thoughts, NoelC, and I got a 404 error when I clicked submit. Forgot to copy it to the clipboard, too.

Basically I was talking about gravitational perturbations, keyholes and other sources of long term uncertainty in predictions.

There is an asteroid discovered in during a close pass in 2004 that for a while was thought to have as high as a 2% chance (unprecedented in the NEO program) of hitting earth in 2029. Further observations refined the orbit and allayed that fear. It will pass within the orbit of a geosynchronous satellite, but miss. However, there is still a chance, currently only estimated at 1 in 12 million, that it will pass through a gravitational keyhole that will cause it to hit in 2036.
http://en.wikipedia.org/wiki/99942_Apophis

I think this page is a good illustration of the keyhole:
http://neo.jpl.nasa.gov/news/news149.html

I also ran the impact through the University of Arizona's Impact Effects Calculator, with some estimate numbers. The results were significantly worse than the Tunguska event in Siberia, but not cataclysmic. It would dig a 3+ mile crater if it hit land. There would be a 6.9 earthquake. From 20 km away the shock wave would topple most trees and buildings, and ejecta 10 feet in diameter would rain down, covering the ground several feet deep on average. Fun stuff

[NoelC]

Ah, so it seems the accuracy of the measurements of speed and position (of the asteroid and assumedly of the other solar system objects as well) are what limit scientists from determining the precise position. Slight misalignments during close approaches can cause radically different trajectories. This implies that after 2029 we should have a very good idea of where the asteroid is going next.

-Noel

[iamlucky13]

Right. In fact, I'm guessing as it approaches in 2029 there will be plenty of astronomers taking sightings to improve it's trajectory, and we'll actually have a really good idea before it reaches earth how close it will pass in subsequent years, especially 2036.

There is an additional source of prediction error, and that is unaccounted factors like minor gravitational perturbations. For example, this asteroid crosses the earth's orbit twice a year, but I'll bet they only factor in the earth's gravity if it's within a certain distance, and the moon's gravity for even closer approaches. Maybe they consider Jupiter's gravity even though it's a long ways away because it's big, but what about the dwarf planet/asteroid Ceres? Also, how about the solar wind? Most of these are small enough you can ignore them for any reasonable time period, but given long enough they add up.

A better studied example is Mars' moon Phobos. For years it was always creeping a just little bit ahead of where they thought it should be in its orbit. Then finally someone came up with tidal forces as the source of the error. When they did the math, they found this explained the error almost perfectly.

[craterchains]

Personaly I doubt that Phobos is a good example as it is also losing altitude and spiraling into the planet. Many scientists have stated that it lacks the mass that it should have if it were solid. All most as if it were hollow, or has alot of voides in it.

As iamlucky13 points out, many factors have to be taken into concideration when trying to determin where it is going, and where it came from.

[FieryIce]

A better studied example is Mars' moon Phobos. For years it was always creeping a just little bit ahead of where they thought it should be in its orbit. Then finally someone came up with tidal forces as the source of the error. When they did the math, they found this explained the error almost perfectly.

Iamlucky, you didn't finish the explaination. You left out the main points about Phobos.
Quoted from another thread:

Try looking at Mars moon Phobos. Decades ago scientists were reporting Phobos is/was so unusual it could only be explained if considered to be an artificial construct. This theory was substantiated, consider:

The First Mars Express Science Conference had four presentations specifically about the research done concerning Phobos. If you examine these presentations, which are in PDF format, you will see it stated that Phobos over the last observed 6 years has an “increased secular rate … MER Rovers see 11-12 km orbital advance … HRSC/SRC [ESA Mars Express] see 11-12 km orbital advance”, Thomas C. Duxbury et. al., JPL California Institute of Technology, 11_Duxbury.pdf.

“Phobos ahead of its predicted orbital position by approx. 1 radius, Bell Duxbury et al., Nature”… “Phobos estimated to be off its normal (JPL ephemeris) orbit by 6s (approx. 12 km) along-track; across-track position errors <1 km”, J. Oberst et al., and the HRSC Co-Investigation Team, 12_Phobos_Oberst.pdf.

In the PDF presentation by John Murray et al., the images of Phobos specifically the leading edge of Phobos does not show the leading edge crater chains to be larger than the trailing edge crater chains so their theory that Phobos flew through Mars debris or flew through ejecta debris is not valid or was not validated. But they did achieve to acquire some better imaging of the leading edge of Phobos.

What you might find even more interesting is the last presentation PDF by Severine Perrier et al., SPICAM Team on the Mars Express. They worked on the UV absorption or reflectance of Phobos and Deimos, the albedo of those two moons. What they found was a repetitive reading in the 220 um, “significant absorption feature around 220 um, similar to interstellar extinction feature … could be caused by the presence on Phobos of organic material … not compatible with the UV silicate signature (around 260 um) … similar to the extinction feature observed in the Interstellar Medium of 217.5 um” To quote them even more “Nature of ISM absorbing material? Possible organic material”.

The First Mars Express Science Conference Presentations, http://sci.esa.int/science-e/www/object ... ctid=36537

The Mars Express (JPL) MRSC/SRC investigative teams conclusioned that Phobos is out of predicted position but amazingly Phobos must have some organic material.

[iamlucky13]

The main point I wanted to bring up with regards to Phobos for the purposes of this thread was simply that its orbit didn't match the old predictions because they didn't account for what turned out to be a significant factor.

As we discussed back when that thread was active, tidal forces or a hollow body experiencing atmospheric drag could both explain the discrepancy, but I don't think either of us convinced the other of their conclusion.

[NoelC]

Hm, with the computing power available to us today I'd be kind of surprised if the model were oversimplified. That is unless the model code itself hasn't been updated since a time when we didn't have so many compute cycles available...

And of course mass estimates must have some level of error in them as well, though it must be pretty small if predictions years in advance can be made already.

One could envision a digital orbital model of the solar system that both tracks ever increasing numbers of objects, and refines their mass estimates iteratively as more observations are entered over a longer period of time, ultimately for the purpose of making predictions. That would actually be a pretty cool project to work on. Coupled with improved observational capability (e.g., more space-based telescopes, more deep space probes, etc.), one might imagine knowing where everything consequential is in the not too distant future.

I wonder if some kind of "galactic tidal influence" might be important for refining the model after that. Or the pressure (bow shock) from moving through the interstellar medium.

Or the influences of man... If we "slingshot" enough probes around Venus, will we change its orbit?

Does solar activity - e.g., coronal mass ejection and the solar wind - have an effect? A bit tough to predict that...

Sorry, I guess I just got into a free association type of mood.

-Noel

[FieryIce]

a hollow body experiencing atmospheric drag could both explain the discrepancy

The accretion disk theory does not account for hollow bodies, maybe some caverning but not hollow; nor Uranus. So whatever happened to Uranus?

[iamlucky13]

I understand that. I only mentioned the hollow body idea because I know what you're getting at.

[SittingDownMan]

If, indeed, this asteroid may someday impact the Earth (as postulated in the APOD commentary) then we definitely have our work cut out for us in deflecting its orbit. These Earth-crossing "rubble piles" present an insuperable problem at our current level of technology to deflect them while maintaining their cohesion.

I hope someone comes up with a bright idea.

Superglue. Scads and scads and buckets of it. With cats-eye reflectors,
and Scotch-Light paint embedded in it. Also ribbons of that stuff
reflective armbands are made of. Miles of them.

Not only would that hold it together, so it would be unlikely to do a
string of pearls, like SL9, it would also allow Sol to accelerate it
better. It might miss, instead of impacting. I've always thought this
was a far better, cleaner and cheaper choice than massively nuking a
falling rock. It has the added advantage of not turning said rock into a
radioactive shotgun blast wider than countries.
If we can land on Eros, we can land buckets of goop *anywhere*. Given
enough advance notice. All it takes is the will, and some cash.
We've already done all the engineering. The rest is just deciding
whether saving the planet is worth a year's load of football games.
Those who prefer the sport... no, play nice. Even they deserve not to
have large rocks fall on them from orbit.

[NoelC]

Good ideas, but...

Uh oh, anything that's proactive instead of reactive is rather doomed in this world.

-Noel

[craterchains]

This is why we all know that so called "moderators" are just plain Oxen Shizer ! ! !

Prove you can moderate and remove these Oxen Shizer posts so the topic can continue to be discussed.

And, it may be a good idea to warn posters like these that their Oxen Shizer posts will get them banned from this forum. That is if the moderators had any balls here.

Norval